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Home > Archive > Electrical Engineering > April 2006 > Adding voltmeter to car
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| Author |
Adding voltmeter to car
|
|
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| I am in the UK and have a 1.3 litre Mazda which is over 10 years
old.
I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".
Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and how
it is charging?
Can I permanently connect my cheap handheld digital voltmeter to
the car battery. I would then mount the meter permanently on the
dashboard.
Is there a real danger that the meter will get damaged by various
current or voltage surges? Is it good enough protection to have a
quick blow fuse in line with the test lead going to the positive
terminal?
Thanks
--
The voltmeter web pages include:
http://www.carbuyingtips.com/jumpstart.htm
http://www.repairfaq.org/ELE/F_Car_Battery.html
http://www.inct.net/~autotips/batterm.htm
| |
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"Andy" <nomail@nomail.com> wrote in message
news:Xns97A4E3D492A8F74C1H4@127.0.0.1...
> I am in the UK and have a 1.3 litre Mazda which is over 10 years
> old.
>
> I have been reading a few web pages which made reference to the
> reader's car which "may have a dashmoard voltmeter".
>
> Is a voltmeter actually all that useful to see tjings like what
> the condition the battery is in and how the battery copes and how
> it is charging?
Auto voltmeter - also known as the "somebody stole your battery" gauge.
Because other than a missing battery, it basically tells you, too late, what
you already know - weak lights, poor start, bad battery, etc.
An in-dash ammeter, on the other hand, tells you before you are stranded if
you are charging or discharging the battery and how much is going in or
out, and the amps are if steady or fluctuating , all of which can be used as
an indicator for the condition of the alternator and battery, the
connections, and switch-off draining.
Don't waste your time putting in a voltmeter.
>
> Can I permanently connect my cheap handheld digital voltmeter to
> the car battery. I would then mount the meter permanently on the
> dashboard.
>
> Is there a real danger that the meter will get damaged by various
> current or voltage surges? Is it good enough protection to have a
> quick blow fuse in line with the test lead going to the positive
> terminal?
>
> Thanks
>
>
>
> --
>
> The voltmeter web pages include:
> http://www.carbuyingtips.com/jumpstart.htm
> http://www.repairfaq.org/ELE/F_Car_Battery.html
> http://www.inct.net/~autotips/batterm.htm
| |
|
| Andy wrote:
> I am in the UK and have a 1.3 litre Mazda which is over 10 years
> old.
>
> I have been reading a few web pages which made reference to the
> reader's car which "may have a dashmoard voltmeter".
>
> Is a voltmeter actually all that useful to see tjings like what
> the condition the battery is in and how the battery copes and how
> it is charging?
>
> Can I permanently connect my cheap handheld digital voltmeter to
> the car battery. I would then mount the meter permanently on the
> dashboard.
>
> Is there a real danger that the meter will get damaged by various
> current or voltage surges? Is it good enough protection to have a
> quick blow fuse in line with the test lead going to the positive
> terminal?
>
> Thanks
>
>
>
Don't bother with a voltmeter. A far better investment is a set of
jumper cables.
Chuck
| |
| SQLit 2006-04-13, 10:21 pm |
|
"Andy" <nomail@nomail.com> wrote in message
news:Xns97A4E3D492A8F74C1H4@127.0.0.1...
> I am in the UK and have a 1.3 litre Mazda which is over 10 years
> old.
>
> I have been reading a few web pages which made reference to the
> reader's car which "may have a dashmoard voltmeter".
>
> Is a voltmeter actually all that useful to see tjings like what
> the condition the battery is in and how the battery copes and how
> it is charging?
>
> Can I permanently connect my cheap handheld digital voltmeter to
> the car battery. I would then mount the meter permanently on the
> dashboard.
>
> Is there a real danger that the meter will get damaged by various
> current or voltage surges? Is it good enough protection to have a
> quick blow fuse in line with the test lead going to the positive
> terminal?
>
> Thanks
>
>
>
> --
>
> The voltmeter web pages include:
> http://www.carbuyingtips.com/jumpstart.htm
> http://www.repairfaq.org/ELE/F_Car_Battery.html
> http://www.inct.net/~autotips/batterm.htm
volt meters have nothing to do with the status of the battery. sure they
will show the amount of voltage produced. most are highly in accurate.
talk to a good mechanic
| |
| Gary Schafer 2006-04-13, 11:21 pm |
| On Thu, 13 Apr 2006 22:23:47 +0100, Andy <nomail@nomail.com> wrote:
>I am in the UK and have a 1.3 litre Mazda which is over 10 years
>old.
>
>I have been reading a few web pages which made reference to the
>reader's car which "may have a dashmoard voltmeter".
>
>Is a voltmeter actually all that useful to see tjings like what
>the condition the battery is in and how the battery copes and how
>it is charging?
>
>Can I permanently connect my cheap handheld digital voltmeter to
>the car battery. I would then mount the meter permanently on the
>dashboard.
>
>Is there a real danger that the meter will get damaged by various
>current or voltage surges? Is it good enough protection to have a
>quick blow fuse in line with the test lead going to the positive
>terminal?
>
>Thanks
If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter. A voltmeter will tell you much more
about the battery and the charging system than an ammeter.
A properly running alternator should raise the battery voltage to
around 14 to 14.2 volts. Some cars may run as high as 14.4 volts. Any
higher and you can suspect a problem with the regulator.
If the voltage fails to come up this high you can suspect a problem in
the alternator, shorted diode etc.
A voltmeter can also tell you if the alternator is capable of putting
out enough current. As you turn more things on, lights,
air-conditioning etc. the alternator should be capable of maintaining
the voltage at the 14 volt range. If the voltage drops well below that
range you can look for problems.
After the car has been shut down for a period of time you can read the
battery voltage to tell you the approximate charge on the battery by
the resting voltage.
You can also watch how far the voltage drops when turning on
headlights etc. with the engine not running. If the voltage drops way
off you may have a battery that is developing a high resistance,
battery is dying.
You can also watch how far the voltage drops when starting the car.
This is another indication of battery condition.
None of these things can be done with an ammeter.
An ammeter will only tell you if the battery is being charged or
discharged at a particular time. If the battery has a high resistance
or is fully charged you can not tell the difference with an ammeter.
About the only thing an ammeter is good for is to let you know that
the battery is not being discharged while the car is running.
The voltmeter should be connected directly to the battery terminals
with its own leads for the above indications to be meaningful. Put a
small fuse in the hot lead right at the battery to protect the wires.
Regards
Gary
| |
|
|
"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com...
> On Thu, 13 Apr 2006 22:23:47 +0100, Andy <nomail@nomail.com> wrote:
>
>
> If I had only one instrument to connect to the car to watch the
> battery it would be a voltmeter. A voltmeter will tell you much more
> about the battery and the charging system than an ammeter.
>
> A properly running alternator should raise the battery voltage to
> around 14 to 14.2 volts. Some cars may run as high as 14.4 volts. Any
> higher and you can suspect a problem with the regulator.
> If the voltage fails to come up this high you can suspect a problem in
> the alternator, shorted diode etc.n
or more usually, the connections on the dash. (like my three cars).
>
> A voltmeter can also tell you if the alternator is capable of putting
> out enough current.
Just kind turning on the fan and watching the lights dim, but the voltmeter
is not nearly as accurate.
As you turn more things on, lights,
> air-conditioning etc. the alternator should be capable of maintaining
> the voltage at the 14 volt range.
granted, the voltmeter tells you that the computer says to raise the field -
but it does not say if anything is being generated and/or sent to the
battery.
- kind of like my jeep did two weeks back, where the voltmeter said all
was ok - and the battery had just enough to turn it over twice.
And next time it didn't start with 12 volts shown, so after it was running
after a jump (voltmeter had said zero) - voltmeter went to 14.4 and then
went down to 13.5 after driving. But the ammeter said it was sending 10
amps into a battery. At the shop, the disconnected battery had all of 11
volts and wouldn't take a charge. Voltmeter was reading alternator output
voltage, not energy going into the battery. The battery had the capacity of
a AAA, and tyhe voltmeter said 12 volts.
If the voltage drops well below that
> range you can look for problems.
>
Just like a low battery does - turn the key and get a click, but the
voltmeter is not as accurate
> After the car has been shut down for a period of time you can read the
> battery voltage to tell you the approximate charge on the battery by
> the resting voltage.
>
> You can also watch how far the voltage drops when turning on
> headlights etc. with the engine not running. If the voltage drops way
> off you may have a battery that is developing a high resistance,
> battery is dying.
Of course, turning the key after that test also tells you you need a tow and
a battery.
An indication which helps a lot when you are driving - that is also
indicated by the car not starting.
>
> You can also watch how far the voltage drops when starting the car.
> This is another indication of battery condition.
>
> None of these things can be done with an ammeter.
And nor does one want to - and unlike voltmeters that tell you voltage level
rather than energy transfer, ammeters only check the battery input and
output running and motor off, and the charging circuit, the starting
circuit, alternator output, and cable/connection/belt condition running. You
know, the energy the vehicle actually uses.
> An ammeter will only tell you if the battery is being charged or
> discharged at a particular time. If the battery has a high resistance
> or is fully charged you can not tell the difference with an ammeter.
>
Sorry, yes you can. Same symptoms as with the voltmeter.
You know, there's a reason so many expereinced people in
alt.engineering.elect jumped on the thread to roundly condemn voltmeters as
next to worthless-
(BTW, the reason ammeters were removed was to save weight to get fleet
mileage up - an ammeter takes a ballast resistor and heavy cables and
connectors. A voltmeter takes an inch of circuitboard foil. And, anything a
voltmeter does is also sensed by the diagnostics and flagged, on my
vehicles)
> About the only thing an ammeter is good for is to let you know that
> the battery is not being discharged while the car is running.
>
> The voltmeter should be connected directly to the battery terminals
> with its own leads for the above indications to be meaningful. Put a
> small fuse in the hot lead right at the battery to protect the wires.
>
> Regards
> Gary
>
| |
| Rheilly Phoull 2006-04-14, 7:21 am |
| hob wrote:[color=darkred]
> "Gary Schafer" <gaschafer@comcast.net> wrote in message
> news:gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com...
>
> or more usually, the connections on the dash. (like my three cars).
>
>
> Just kind turning on the fan and watching the lights dim, but the
> voltmeter is not nearly as accurate.
>
> As you turn more things on, lights,
>
> granted, the voltmeter tells you that the computer says to raise the
> field - but it does not say if anything is being generated and/or
> sent to the battery.
> - kind of like my jeep did two weeks back, where the voltmeter said
> all was ok - and the battery had just enough to turn it over twice.
> And next time it didn't start with 12 volts shown, so after it was
> running after a jump (voltmeter had said zero) - voltmeter went to
> 14.4 and then went down to 13.5 after driving. But the ammeter said
> it was sending 10 amps into a battery. At the shop, the disconnected
> battery had all of 11 volts and wouldn't take a charge. Voltmeter
> was reading alternator output voltage, not energy going into the
> battery. The battery had the capacity of a AAA, and tyhe voltmeter
> said 12 volts.
>
> If the voltage drops well below that
>
> Just like a low battery does - turn the key and get a click, but the
> voltmeter is not as accurate
>
>
> Of course, turning the key after that test also tells you you need a
> tow and a battery.
> An indication which helps a lot when you are driving - that is also
> indicated by the car not starting.
>
>
> And nor does one want to - and unlike voltmeters that tell you
> voltage level rather than energy transfer, ammeters only check the
> battery input and output running and motor off, and the charging
> circuit, the starting circuit, alternator output, and
> cable/connection/belt condition running. You know, the energy the
> vehicle actually uses.
>
> Sorry, yes you can. Same symptoms as with the voltmeter.
>
> You know, there's a reason so many expereinced people in
> alt.engineering.elect jumped on the thread to roundly condemn
> voltmeters as next to worthless-
>
> (BTW, the reason ammeters were removed was to save weight to get fleet
> mileage up - an ammeter takes a ballast resistor and heavy cables and
> connectors. A voltmeter takes an inch of circuitboard foil. And,
> anything a voltmeter does is also sensed by the diagnostics and
> flagged, on my vehicles)
>
So says Hob
I reckon both have uses and the interpretation is only a problem to the
inexperienced.
Each to their own IMHO :-) I like both but if had to choose would go the
voltmeter.
--
Regards ......... Rheilly Phoull
| |
|
| In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
says...
> If I had only one instrument to connect to the car to watch the
> battery it would be a voltmeter.
Spot the pillock who knows fuck all about car electrics.
> A voltmeter will tell you much more
> about the battery and the charging system than an ammeter.
No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.
Think I'm wrong? Why are batteries tested with a drop meter?
--
Conor,
Same shit, different day.
| |
|
| In article <443f6aaa$0$32103$5a62ac22@per-qv1-newsreader-
01.iinet.net.au>, Rheilly Phoull says...
> Each to their own IMHO :-) I like both but if had to choose would go the
> voltmeter.
>
<walks away shaking head>
OK then....
--
Conor,
Same shit, different day.
| |
|
| hob wrote:
> "Gary Schafer" <gaschafer@comcast.net> wrote in message
> news:gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com...
>
>
>
> or more usually, the connections on the dash. (like my three cars).
>
>
>
>
> Just kind turning on the fan and watching the lights dim, but the voltmeter
> is not nearly as accurate.
If you were to log voltage over time it would tell you a whole lot more
than current.
> As you turn more things on, lights,
>
>
>
> granted, the voltmeter tells you that the computer says to raise the field -
Computer? ignition simply being ON energises the armature field. I've
not seen any computer input needed here?
> but it does not say if anything is being generated and/or sent to the
> battery.
Wrong! It shows exactly this. A car battery will not rest at 14v.
therefore if your measuring 14v @ battery you know without any question
what so ever that the battery is being charged.
> - kind of like my jeep did two weeks back, where the voltmeter said all
> was ok - and the battery had just enough to turn it over twice.
High internal resistance, you'll again see this by cranking the engine
and the battery voltage will fall extremely low, again an ammeter will
not be able to show this.
> And next time it didn't start with 12 volts shown, so after it was running
> after a jump (voltmeter had said zero) - voltmeter went to 14.4 and then
> went down to 13.5 after driving. But the ammeter said it was sending 10
> amps into a battery. At the shop, the disconnected battery had all of 11
> volts and wouldn't take a charge.
Again what you have said shows a tired and worn battery
(cracked/sulphated cells) and can be easily demonstrated with a load
(cranking) and a voltmeter.
> Voltmeter was reading alternator output
> voltage, not energy going into the battery. The battery had the capacity of
> a AAA, and tyhe voltmeter said 12 volts.
Your completely reading this wrong. The fact that the voltmeter was
working and correctly showed your system voltage showed you immediately
where the problem was (battery) Process of elimination. You see the
symptoms - battery voltage is ok, charge voltage is ok, yet not enough
current to crank = dead battery!
> If the voltage drops well below that
>
>
>
> Just like a low battery does - turn the key and get a click, but the
> voltmeter is not as accurate
Yes it is!
>
>
> Of course, turning the key after that test also tells you you need a tow and
> a battery.
> An indication which helps a lot when you are driving - that is also
> indicated by the car not starting.
>
If you do this test and then you are unable to start, like Gary said the
battery is dying. Clearly if you felt this was such a risk you would not
make this test unless you had another way to start the car. There are
thousands of cars on the road with batteries that have nearly no reserve
capacity, you need surprisingly little to be able to start a car, but
you only really notice after you have left your lights on for a few mins
only to discover you cannot start again!
>
>
>
> And nor does one want to - and unlike voltmeters that tell you voltage level
> rather than energy transfer, ammeters only check the battery input and
> output running and motor off, and the charging circuit, the starting
> circuit, alternator output, and cable/connection/belt condition running. You
> know, the energy the vehicle actually uses.
No offence I think your blinded by your own ignorance. Everything you
say there can be shown better with a volt meter. You say that an ammeter
shows the "cable/connection/belt condition running" ok so what exactly
should the current be when its all correct? I can tell you a voltage
that I know would be right but since once the car has started and the
battery has regained its lost charge (not long under usual conditions)
how an ammeter between the battery and anything else would show nothing
useful at all, apart from a varying and often small charge. (which again
can be shown much better with a voltmeter showing around 14v)
Lets assume you connect it in series with the alternator. An instant
disadvantage is the fact that you now have introduced more resistance to
the circuit, so you slightly loose efficiency (fact of physics and is
how all ammeter works) You could be running in daylight conditions
lights off and little load, you could be running at night in the rain
lights on heaters on fans on etc etc and again you see load. Great. So
are you actually going to be able to see what current is right or wrong
as fast as I can read a voltmeter and go PROBLEM or not?!
>
> Sorry, yes you can. Same symptoms as with the voltmeter.
Nope not so. A battery with high internal resistance with an ammeter all
you would see is a charged battery, that assumption made by the fact
that there will be little charge current.
> You know, there's a reason so many expereinced people in
> alt.engineering.elect jumped on the thread to roundly condemn voltmeters as
> next to worthless-
Using other peoples posts to back up your own is pretty pointless.
> (BTW, the reason ammeters were removed was to save weight to get fleet
> mileage up - an ammeter takes a ballast resistor and heavy cables and
> connectors. A voltmeter takes an inch of circuitboard foil. And, anything a
> voltmeter does is also sensed by the diagnostics and flagged, on my
> vehicles)
The main reason they were removed as they are not needed as people
wouldn't know what's right or wrong, and alternators have simply removed
the need. Where as voltage meters are much more common, because that
actually shows you something useful.
Further if current meters are such a good way of knowing the status of
charge of a battery or condition of a system then intelligent battery
chargers would measure and monitor battery charge by current - which
they don't. Virtually every type of charger stops when a certain voltage
is met, and has no concern with current other than the fact to limit it
to prevent damage to cells.
| |
| Chris Whelan 2006-04-14, 9:21 am |
| Ed wrote:
[...]
> Computer? ignition simply being ON energises the armature field. I've
> not seen any computer input needed here?
Then, with the greatest of respect, you don't know much about how a modern
car's charging system works.....
Chris
--
Remove prejudice to reply.
| |
|
| Conor wrote:
> In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
> says...
>
>
>
>
> Spot the pillock who knows fuck all about car electrics.
>
>
>
>
> No it won't. A completely fucked battery can show >12v but still not be
> able to provide enough current to turn an engine over.
>
> Think I'm wrong? Why are batteries tested with a drop meter?
Oh well done, but if the car starts fine an ammeter is no help to show
the condition of a charge system.
| |
| Chris Whelan 2006-04-14, 10:21 am |
| Ed wrote:
[...]
> What?
>
> Ok so you have a car come in with a charging problem.
>
> Do you:
>
> 1, pick up your ammeter and proceed to test with this.
>
> or
>
> 2, pick up a volt meter and proceed to test with this.
Yes, but there is a huge difference between testing for a fault in a
workshop, and providing something meaningful for the driver to use to
monitor the health of his vehicle.
IME, even a red "No charge" light is too much for some drivers to
comprehend...:-)
Chris
--
Remove prejudice to reply.
| |
| Michael A. Terrell 2006-04-14, 10:21 am |
| Ed wrote:
>
> Conor wrote:
>
> Oh well done, but if the car starts fine an ammeter is no help to show
> the condition of a charge system.
Sure it is. If the battery isn't taking a proper charge it will show
up in the first couple seconds after the engine starts. There should be
a high charging current as soon as the alternator comes up to full
speed, then drop back to nominal as soon as the battery returns to fully
charged. I've had fairly new batteries be almost fully discharged, but
I managed to jump start the vehicle and drive for an hour to work as it
fully recharges the battery and slowly drops back to nominal while the
battery terminal's voltage doesn't change more than a few millivolts.
After all, a car alternator is a constant voltage charger.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Gary Schafer 2006-04-14, 1:21 pm |
| On Fri, 14 Apr 2006 12:15:42 +0100, Conor <conor.turton@gmail.com>
wrote:
>In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
>says...
>
>
>Spot the pillock who knows fuck all about car electrics.
>
>
>No it won't. A completely fucked battery can show >12v but still not be
>able to provide enough current to turn an engine over.
>
>Think I'm wrong? Why are batteries tested with a drop meter?
Actually if a battery only shows "12 volts" it is near dead!
If you will take note, when a battery is tested with a "drop meter" it
actually has a voltmeter in the instrument! Simple ones have ONLY a
voltmeter! More sophisticated ones have a voltmeter and an ammeter.
The idea of the test is to see how well the VOLTAGE holds up on the
battery with a given load placed on it. With the simple testers it is
a given amount of resistance placed on the battery for a certain
length of time while monitoring the battery voltage.
If the resting voltage of lthe battery, no load, shows 12.6 to 12.8
volts that is an indication of a fully charged battery. If that vltage
drops significantly with the load test then the battery probably has a
high internal resistance. If the resting voltage is near 12 volts the
battery is in need of charging.
With the better units which contain an adjustable load, ammeter and
voltmeter the load is adjusted to see how much current the battery can
supply before the voltage drops to a certain level. Without knowing
the voltage the rest of the test is pretty much meaningless.
If you read my first post again, carefully, you will see where I
explain (with the engine off) how to watch the voltmeter in the car
while turning on accessory items and watching how far the voltage
drops to give you an indication of battery health. Also how much the
voltage drops when starting.
This does essentially the test that is done with a load tester.
One important point about use of the voltmeter, it needs to come
directly from the battery terminals and not be connected into wiring
that also serves other things like lights etc. Otherwise you will not
get a true reading of battery voltage when turning those other things
on as it will also read the voltage drop in the wiring and not the
true battery voltage.
Also note that some factory installed voltmeters are wired as noted
above and some are also very poor quality meters.
You can have all the instruments you can manage to gather but if you
don't know how to interpret them they do little good.
Regards
Gary
| |
| Douglas Payne 2006-04-14, 1:21 pm |
| Ed wrote:
>
> What?
>
> Ok so you have a car come in with a charging problem.
>
> Do you:
>
> 1, pick up your ammeter and proceed to test with this.
>
> or
>
> 2, pick up a volt meter and proceed to test with this.
3, get all in a huffy and go and post rude words on some newsgroups.
(c:
--
Douglas
| |
| Douglas Payne 2006-04-14, 2:21 pm |
| Conor wrote:
> In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
> says...
>
>
>
>
> Spot the pillock who knows fuck all about car electrics.
>
>
>
>
> No it won't. A completely fucked battery can show >12v but still not be
> able to provide enough current to turn an engine over.
>
> Think I'm wrong? Why are batteries tested with a drop meter?
Is a drop meter like a voltmeter for measuring voltage drop?
--
Douglas
| |
|
| "Ed" <ed@NOSPAMmicra.org.uk> wrote in message
news:VUL%f.677$nh5.581@newsfe7-win.ntli.net...
> hob wrote:
voltmeter[color=darkred]
>
> If you were to log voltage over time it would tell you a whole lot more
> than current.
>
field -[color=darkred]
>
> Computer? ignition simply being ON energises the armature field. I've
> not seen any computer input needed here?
The computer controls the field of the alternaotr - think "voltage
regulator"
>
>
> Wrong! It shows exactly this.
Sorry -WADR - wrong -- since a voltmeter only directly measures potential,
it CANNOT directly measure flow. And energy flow is what fills the battery,
not electrical potential.
14 volts on the line means 14 volts at the alternator, not amps flowing
into the battery or flowing out of the alternator.
>A car battery will not rest at 14v.
> therefore if your measuring 14v @ battery you know without any question
> what so ever that the battery is being charged.
>
all[color=darkred]
>
> High internal resistance, you'll again see this by cranking the engine
> and the battery voltage will fall extremely low, again an ammeter will
> not be able to show this.
>
Hmm.. think of it this way..
crank the engine and watch the battery voltage fall extremely low and then
I can tell that I have a battery problem - a reason to have a voltmeter?
Hint - _I_ do not need a voltmeter to tell me my battery is bad when I can
also hear my starter drop off after a second or two of cranking.
"rrr..rr..rrr....." "look, my voltmeter is dropping fast"
"rr........rr..............rr.........
.......r.....................................". (It's not the voltmeter that
says my battery is dead.)
That is why the voltmeter is refered to as a "battery is missing" gauge.
It tells you there is a problem nearly always AFTER it is fairly obvious
there is a problem.
An ammeter,on the other hand, spikes and drops back after start, telling you
the alternator is outputting, the regulator is responding, and the battery
is accepting. The level of flow tells you the cable condition. The best
part is that unlike a voltmeter, it tells you before the battery is missing.
running[color=darkred]
11[color=darkred]
>
> Again what you have said shows a tired and worn battery
> (cracked/sulphated cells) and can be easily demonstrated with a load
> (cranking) and a voltmeter.
Or rather than use a voltmeter and runa test, perhaps just use an ammeter
while driving?
(BTW, the battery in my example was less than 18 months old, and bad.)
>
of[color=darkred]
>
> Your completely reading this wrong. The fact that the voltmeter was
> working and correctly showed your system voltage showed you immediately
> where the problem was (battery) Process of elimination. You see the
> symptoms - battery voltage is ok, charge voltage is ok, yet not enough
> current to crank = dead battery!
>
Or bad cable, security system lockout, or faulty starter relay, all of which
give the same symptoms -- and all only after I am dead in the water..
I put my DC power-ammeter on the battery cable of the running vehicle and
saw under 10 amps feeding the just-jumped 18 month old dead battery - THAT
was my definitive on the problem. The ammeter on a running vehicle said
bad, the voltmeter on the running vehicle said good.
If I had had an ammeter on the dash as we used to have or as I have in
my RV instead of a "battery missing" gauge I would have been in for a
charging system check well before I needed a jump.
>
> Yes it is!
>
both tell you it is dead - how can one be more accurate? - it is dead, not
slightly dead.
and[color=darkred]
> If you do this test and then you are unable to start, like Gary said the
> battery is dying. Clearly if you felt this was such a risk you would not
> make this test unless you had another way to start the car. There are
> thousands of cars on the road with batteries that have nearly no reserve
> capacity, you need surprisingly little to be able to start a car, but
> you only really notice after you have left your lights on for a few mins
> only to discover you cannot start again!
level[color=darkred]
You[color=darkred]
>
> No offence I think your blinded by your own ignorance.
No offense taken, but you should know that besides having hobbied for 40
years in racing and auto restoration, and having worked on everything from
V-12 Ferarris to flathead Fords, Austins to 300Zs; having worked hands on
from 120,000 volts at 60 amps to 1 volt analogs; repaired and certified test
equipment from scopes to rf meters; as one who consulted on those
early/mid-eighties-vehicle analog computers post 80s; and as a PE, degreed
in electrical and mechanical, I do have some hands-on as well as theoretical
knowledge of measuring and automotive circuits.
And I should note that we need to keep in mind that an ammeter is just a
voltmeter measuring load across a fixed known resistance.
An in-dash voltmeter merely uses unknown loads to get qualitative
measurements of energy capacity and implied flow, while an ammeter gets
quantitative realtive measurents of amount and direction of energy flow at a
known common point, using a fixed resistance.
Everything you
> say there can be shown better with a volt meter. You say that an ammeter
> shows the "cable/connection/belt condition running" ok so what exactly
> should the current be when its all correct? I can tell you a voltage
> that I know would be right but since once the car has started and the
> battery has regained its lost charge (not long under usual conditions)
> how an ammeter between the battery and anything else would show nothing
> useful at all, apart from a varying and often small charge. (which again
> can be shown much better with a voltmeter showing around 14v)
>
> Lets assume you connect it in series with the alternator. An instant
> disadvantage is the fact that you now have introduced more resistance to
> the circuit, so you slightly loose efficiency (fact of physics and is
> how all ammeter works)
a .01 ohm shunt at 12 volts is far less a loss than the corrosion in the
battery cable terminals or lamp sockets. 1/8 watt loss is a red herring.
You could be running in daylight conditions
> lights off and little load, you could be running at night in the rain
> lights on heaters on fans on etc etc and again you see load. Great. So
> are you actually going to be able to see what current is right or wrong
> as fast as I can read a voltmeter and go PROBLEM or not?!
>
First - While voltmeter readers need to have the actual value of the
measurement to make a decision - ammeter readers only need direction and any
quantity to make a decision.
In other words, you are mistaken to believe I need a value to determine
the existance of a problem using an auto ammeter- the determinates for the
auto ammeter are "in or out", "quantity or no quantity", "large amount or
not". The specific value of flow is actually immaterial.
(and since the definitive amount of flow varies with environment and
accessories anyway, an exact amount is meaningless except to the few more
knowledgeable, and then in context.)
second - in your example, difference is -
1) I see no spike several seconds after start on an ammeter, that time just
after starting being the time when I and most people check all the gauges -
and I check the problem out before I am stuck somewhere -
- but with a voltmeter, with a good battery but alternator putting out 14
v and way-low current, it says 14 volts and my once good battery soon
becomes a 20 amp-hour-capacity-left no-reserve battery, and I am dead and
towed.
2) My ammeter says outflow five seconds after I start the car and it stays
there - time to get to garage -
same condition - my voltmeter says "OK" and I drain the battery as I drive
away on my sunny day, and after twenty miles heading to the woods the needle
is down enough to notice I have low voltage- and out twenty miles, I will
shut down on fault before I can get back to a garage.
>
> Nope not so. A battery with high internal resistance with an ammeter all
> you would see is a charged battery, that assumption made by the fact
> that there will be little charge current.
A battery with a high resistance will give you a running-vehicle voltmeter
reading of 14 volts (had it happen several times), while an ammeter will
give you no flow into the battery -
(there is always flow into the battery for 30 seconds after start)
as[color=darkred]
>
> Using other peoples posts to back up your own is pretty pointless.
>
anything a[color=darkred]
>
> The main reason they were removed as they are not needed as people
> wouldn't know what's right or wrong, and alternators have simply removed
> the need. Where as voltage meters are much more common, because that
> actually shows you something useful.
>
> Further if current meters are such a good way of knowing the status of
> charge of a battery or condition of a system then intelligent battery
> chargers would measure and monitor battery charge by current - which
> they don't. Virtually every type of charger stops when a certain voltage
> is met, and has no concern with current other than the fact to limit it
> to prevent damage to cells.
Totally different condition - the parameter in a vehicle is condition of the
charging and battery system and its controls in a two direction system-
the parameter in a battery charger is to control rate of charge and
prevent overcharge in a one direction system.
| |
|
|
"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com...
> On Fri, 14 Apr 2006 12:15:42 +0100, Conor <conor.turton@gmail.com>
> wrote:
>
>
>
> Actually if a battery only shows "12 volts" it is near dead!
Which makes a voltmeter next to worthless for determining the amount of
energy in a battery. 50 amp hours worth of charge on a sulphated battery
reads 12 volts, and 800 amp hours worth of charge reads 12 volts.
But one take a lot of current, and the other takes hardly any.
> If you will take note, when a battery is tested with a "drop meter" it
> actually has a voltmeter in the instrument! Simple ones have ONLY a
> voltmeter! More sophisticated ones have a voltmeter and an ammeter.
>
I think you are confused as to what an ammeter actually is... the drop test
uses an ammeter (a shunt and a voltmeter) to check battery condition.
An ammeter is just a voltmeter reading across a known resistance (i.e.,
voltage drop across a shunt carrying the current).
(And technically, all voltmeters use current passed through a known
resistance, the series resistor, to get a voltage indication. )
In the drop test, a known resistance is placed across the poles of the
battery, and in actuality, it is the voltage across that known resistance
that is measured to determine current flow.
In other words, and in comparison -
The "drop test" measures the amount of current drawn by the battery
through a known resistance (amps through the resistance), the amount of
current then indicated by the voltage across the known resistance. The meter
reads in volts, and the reading drops off as the current in the shunt drops
off.
An ammeter measures the amount of current drawn through a known resistance
(amps through resistance), the amount of current then indicated by the
voltage across the known resistance, The meter reads in amps, and the
reading drops off as the current in the shunt drops off (or increases as the
current increases)
In BOTH cases, a KNOWN resistance is used.
> The idea of the test is to see how well the VOLTAGE holds up on the
> battery with a given load placed on it. With the simple testers it is
> a given amount of resistance placed on the battery for a certain
> length of time while monitoring the battery voltage.
>
> If the resting voltage of lthe battery, no load, shows 12.6 to 12.8
> volts that is an indication of a fully charged battery. If that voltage
> drops significantly with the load test then the battery probably has a
> high internal resistance. If the resting voltage is near 12 volts the
> battery is in need of charging.
>
> With the better units which contain an adjustable load, ammeter and
> voltmeter the load is adjusted to see how much current the battery can
> supply before the voltage drops to a certain level. Without knowing
> the voltage the rest of the test is pretty much meaningless.
>
> If you read my first post again, carefully, you will see where I
> explain (with the engine off) how to watch the voltmeter in the car
> while turning on accessory items and watching how far the voltage
> drops to give you an indication of battery health. Also how much the
> voltage drops when starting.
> This does essentially the test that is done with a load tester.
>
> One important point about use of the voltmeter, it needs to come
> directly from the battery terminals and not be connected into wiring
> that also serves other things like lights etc. Otherwise you will not
> get a true reading of battery voltage when turning those other things
> on as it will also read the voltage drop in the wiring and not the
> true battery voltage.
>
> Also note that some factory installed voltmeters are wired as noted
> above and some are also very poor quality meters.
>
All factory voltmeters that I know get their voltage from the circuit board
of the dash indicators.
> You can have all the instruments you can manage to gather but if you
> don't know how to interpret them they do little good.
>
> Regards
> Gary
>
| |
|
| In article <PKM%f.44330$g76.34878@newsfe2-gui.ntli.net>, Ed says...
> Conor wrote:
>
> What?
>
> Ok so you have a car come in with a charging problem.
>
> Do you:
>
> 1, pick up your ammeter and proceed to test with this.
>
> or
>
> 2, pick up a volt meter and proceed to test with this.
>
Does your voltmeter tell you the condition of the battery? No.
--
Conor,
Same shit, different day.
| |
|
| In article <fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com>, Gary Schafer
says...
>
> Actually if a battery only shows "12 volts" it is near dead!
>
Priceless....
--
Conor,
Same shit, different day.
| |
|
| In article <4aa0j6Frig3gU1@individual.net>, Douglas Payne says...
> Conor wrote:
>
> Is a drop meter like a voltmeter for measuring voltage drop?
>
It places an extremely high current drain on the battery.
--
Conor,
Same shit, different day.
| |
| Gary Schafer 2006-04-14, 10:21 pm |
| On Fri, 14 Apr 2006 13:12:08 -0500, "hob" <dehoberg@comcast.net>
wrote:
>
>"Gary Schafer" <gaschafer@comcast.net> wrote in message
>news:fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com...
>
>Which makes a voltmeter next to worthless for determining the amount of
>energy in a battery. 50 amp hours worth of charge on a sulphated battery
>reads 12 volts, and 800 amp hours worth of charge reads 12 volts.
> But one take a lot of current, and the other takes hardly any.
I see you like to pick things out of contexts to try and bolster your
point. If you read further about the point I make of loading the
battery, the voltmeter will easily tell you if you have a sulphated
battery. The ammeter willl not. The ammeter may tell you that there is
no or little charge going to the battery but you don't know if it is a
charging system problem, a battery problem or no problem at all.
>
>
>I think you are confused as to what an ammeter actually is... the drop test
>uses an ammeter (a shunt and a voltmeter) to check battery condition.
I am not sure exactly what you call a "drop test" on your side of the
pond. Over here we call it a "load test" and it is done with equipment
as I described. Maybe you don't understand how a load test works?
A simple tester has just a voltmeter, used as a voltmeter not as an
ammeter, and a fixed load resistor to see how long it takes for the
battery voltage to drop to a certian voltage when the load is applied.
The better units use both a voltmeter and ammeter along with an
adjustable load resistor to accomplish the test. Again, as I
described.
>
>An ammeter is just a voltmeter reading across a known resistance (i.e.,
>voltage drop across a shunt carrying the current).
We could also turn that around and say that "all voltmeters are just
ammeters with known series resistors" if we want to try and further
confuse the issue of whether we are measuring battery voltage or
current.
I am fully aware of how an ammeter and voltmeter work and how they are
used.
And technically, all ammeters are not necessarily voltmeters. As a
matter of fact most all of the older automotive ammeters were not
voltmeters inside them. They worked on the principle of directly
measuring the magnetic field produced by the wire passing through
them. No voltage drop across any resistance required.
>
>(And technically, all voltmeters use current passed through a known
>resistance, the series resistor, to get a voltage indication. )
>
>
> In the drop test, a known resistance is placed across the poles of the
>battery, and in actuality, it is the voltage across that known resistance
>that is measured to determine current flow.
>
>In other words, and in comparison -
>
> The "drop test" measures the amount of current drawn by the battery
>through a known resistance (amps through the resistance), the amount of
>current then indicated by the voltage across the known resistance. The meter
>reads in volts, and the reading drops off as the current in the shunt drops
>off.
Is "your" "drop test" measuring battery voltage or current supplied?
In other words, what is the meter calibrated in?
>
> An ammeter measures the amount of current drawn through a known resistance
>(amps through resistance), the amount of current then indicated by the
>voltage across the known resistance, The meter reads in amps, and the
>reading drops off as the current in the shunt drops off (or increases as the
>current increases)
>
>In BOTH cases, a KNOWN resistance is used.
>
>
>All factory voltmeters that I know get their voltage from the circuit board
>of the dash indicators.
>
>
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <Xns97A4E3D492A8F74C1H4@127.0.0.1>,
Andy <nomail@nomail.com> wrote:
> Can I permanently connect my cheap handheld digital voltmeter to
> the car battery. I would then mount the meter permanently on the
> dashboard.
You can get small LCD voltmeters from the likes of RS components. They
have approx a 16:9 aspect ratio and are about an inch wide. One hole
fixing. I've got one on my SDI. Only two wire connection. Only trouble is
no illumination - but you might find one that has now, I haven't looked
for a few years.
--
*Make it idiot-proof and someone will make a better idiot.
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <yICdnfkf1sLIVaPZ4p2dnA@comcast.com>,
hob <dehoberg@comcast.net> wrote:
> Auto voltmeter - also known as the "somebody stole your battery" gauge.
> Because other than a missing battery, it basically tells you, too late,
> what you already know - weak lights, poor start, bad battery, etc.
> An in-dash ammeter, on the other hand, tells you before you are stranded
> if you are charging or discharging the battery and how much is going in
> or out, and the amps are if steady or fluctuating , all of which can be
> used as an indicator for the condition of the alternator and battery,
> the connections, and switch-off draining.
> Don't waste your time putting in a voltmeter.
Err a voltmeter tells you the same things if you know how to read it. And
it will also tell you the condition of the battery when you switch on
which an ammeter can't.
--
*If a mute swears, does his mother wash his hands with soap?
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <MPG.1ea994bd86d1a81398c581@news.individual.net>,
Conor <conor.turton@gmail.com> wrote:
[color=darkred]
> Spot the pillock who knows fuck all about car electrics.
And I agree with him. ;-)
[color=darkred]
> No it won't. A completely fucked battery can show >12v but still not be
> able to provide enough current to turn an engine over.
Simply switch on the headlights with the engine not running. If the
battery has a high impedance cell the voltage will drop like a stone. An
ammeter won't show that.
> Think I'm wrong? Why are batteries tested with a drop meter?
As an instrument on the dash? Do tell. ;-)
--
*One of us is thinking about sex... OK, it's me.
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <443F9E39.486BB588@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
> After all, a car alternator is a constant voltage charger.
They're not unless using a SLA gel battery. As some off roaders may.
You'll see about 14.4 volts if the battery is low dropping back to 13.8
when it's charged. That's looking at a recent BMW with an accurate volt
meter.
--
*Some days you're the dog, some days the hydrant.
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com>,
Gary Schafer <gaschafer@comcast.net> wrote:
> Actually if a battery only shows "12 volts" it is near dead!
Not so. 11.5 should start the average car on an average day.
--
*Parenthetical remarks (however relevant) are (usually) unnecessary *
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Dave Plowman (News) 2006-04-22, 3:21 pm |
| In article <MPG.1eaa044421eea28098c58f@news.individual.net>,
Conor <conor.turton@gmail.com> wrote:
> Does your voltmeter tell you the condition of the battery? No.
Does your ammeter tell you the condition of the battery? Bigger no.
--
*They call it PMS because Mad Cow Disease was already taken.
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
|
| Dave Plowman (News) wrote:
> In article <443F9E39.486BB588@earthlink.net>,
> Michael A. Terrell <mike.terrell@earthlink.net> wrote:
>
>
>
> They're not unless using a SLA gel battery. As some off roaders may.
> You'll see about 14.4 volts if the battery is low dropping back to 13.8
> when it's charged. That's looking at a recent BMW with an accurate volt
> meter.
>
Dave, I think the voltages you reported are representative, but the
voltage doesn't drop because the battery is charged (I realize you
didn't say it did, but someone might think that is what you meant). Many
cars have temperature controllers built into the charging circuit that
drop the voltage as temperatures rise (i.e., when the car has been
driven a while). It's a way of discouraging over-charging, especially on
long summer trips.
Without temperature sensing circuitry, the alternator/regulator would
supply a constant charging voltage but due to voltage drops, the voltage
at the battery terminals would actually RISE from a lower voltage to the
regulated 14.4 volt level as the battery is charged. Just the opposite
of what you reported.
FWIW
Chuck
| |
|
| On Thu, 13 Apr 2006 22:17:49 +0000, chuck wrote:
> Andy wrote:
> Don't bother with a voltmeter. A far better investment is a set of
> jumper cables.
That's kinda like suggggesting one wear Depends instead of stopping at the
a rest area on the highway.
--
Keith
| |
| Steve Firth 2006-04-23, 9:21 am |
| Keith wrote:
[snip]
>
> That's kinda like suggggesting one wear Depends instead of stopping at the
> a rest area on the highway.
Can you say that again in English?
| |
| chuck 2006-04-23, 10:21 am |
| Keith wrote:
> On Thu, 13 Apr 2006 22:17:49 +0000, chuck wrote:
>
>
>
>
> That's kinda like suggggesting one wear Depends instead of stopping at the
> a rest area on the highway.
>
>
Nothing of the sort, really. If one is curious about battery charging
and discharging principles, then a voltmeter, ammeter, thermometer,
hydrometer, a lot of time, and a text book will prove rewarding.
But if the concern is to obtain early warning of an impending
battery/alternator/regulator/belt failure so as to avoid being caught on
the road without an electrical system, then most of us would benefit far
more from the jumper cable. ;-)
If the voltmeter would "prevent" such a breakdown by giving advance
warning of sufficiently high certainty to result in an immediate trip to
a competent repair technician, then it would be a good thing.
Unfortunately, even if the meter did so indicate, immediately and
unambiguously, one might be on the road far from any repair facilities
at the time of the indication, in which case jumper cables would be most
useful.
I wonder how many of us have looked at a voltmeter, concluded that
something was wrong, replaced the battery, and found that the world was
good again. Compare that number to those of us who, upon noticing a
strange reading of the meter, made a mental note to keep an eye on the
meter, and then eventually found ourselves with a dead battery. From the
postings, it seems not all of us would be able to interpret various
meter indications even if we had them before us.
Unlike the rest area "fix", a voltmeter will not "ward off" a leaking
battery failure. ;-)
Chuck
| |
| Gary Schafer 2006-04-23, 12:21 pm |
| On Sun, 23 Apr 2006 12:54:56 GMT, chuck <nospam@nospam.net> wrote:
>Keith wrote:
>
>Nothing of the sort, really. If one is curious about battery charging
>and discharging principles, then a voltmeter, ammeter, thermometer,
>hydrometer, a lot of time, and a text book will prove rewarding.
>
>But if the concern is to obtain early warning of an impending
>battery/alternator/regulator/belt failure so as to avoid being caught on
>the road without an electrical system, then most of us would benefit far
>more from the jumper cable. ;-)
>
>If the voltmeter would "prevent" such a breakdown by giving advance
>warning of sufficiently high certainty to result in an immediate trip to
>a competent repair technician, then it would be a good thing.
>Unfortunately, even if the meter did so indicate, immediately and
>unambiguously, one might be on the road far from any repair facilities
>at the time of the indication, in which case jumper cables would be most
>useful.
>
>I wonder how many of us have looked at a voltmeter, concluded that
>something was wrong, replaced the battery, and found that the world was
>good again. Compare that number to those of us who, upon noticing a
>strange reading of the meter, made a mental note to keep an eye on the
>meter, and then eventually found ourselves with a dead battery. From the
>postings, it seems not all of us would be able to interpret various
>meter indications even if we had them before us.
>
>Unlike the rest area "fix", a voltmeter will not "ward off" a leaking
>battery failure. ;-)
>
>Chuck
We might just as well throw out the fuel gauge then too. Just looking
at it will not keep us from running out of fuel. Might be better to
just carry a spare can of with us.
Like the voltmeter, if one doesn't know how to interpret the fuel
gauge properly it does no good to have it aboard. Admittedly the
voltmeter is a little more complicated to interpret than the fuel
gauge but it can also be a valuable instrument.
Regards
Gary
| |
| Gary Schafer 2006-04-23, 1:21 pm |
| On Sat, 22 Apr 2006 18:17:53 +0100, "Dave Plowman (News)"
<dave@davenoise.co.uk> wrote:
>In article <fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com>,
> Gary Schafer <gaschafer@comcast.net> wrote:
>
>Not so. 11.5 should start the average car on an average day.
A standard wet cell battery will exhibit approximately the following
voltages at various states of charge at 70 degrees F: Courtesy of
William Darden's Battery faqs.
100% 12.643
75% 12.443
50% 12.273
25% 12.053
0% 11.883
Maintenance free batteries will be approximately the following:
100% 12.793
75% 12.593
50% 12.393
25% 11.993
0% 11.793
Regards
Gary
| |
|
| Gary Schafer wrote:
> On Sun, 23 Apr 2006 12:54:56 GMT, chuck <nospam@nospam.net> wrote:
>
>
>
>
> We might just as well throw out the fuel gauge then too. Just looking
> at it will not keep us from running out of fuel. Might be better to
> just carry a spare can of with us.
>
> Like the voltmeter, if one doesn't know how to interpret the fuel
> gauge properly it does no good to have it aboard. Admittedly the
> voltmeter is a little more complicated to interpret than the fuel
> gauge but it can also be a valuable instrument.
>
> Regards
> Gary
Hello Gary,
Sorry, but I think the gas gauge analogy is pretty weak. Voltmeter
readings are much more difficult to interpret. Can you imagine a thread
like this one on interpreting gas gauge readings? ;-)
Many autos have been sold without voltmeters and many have been sold
without fuel gages (VW for many years). My car has both an idiot light
and a gauge for fuel (for volts as well, actually) but I pay much closer
attention to the fuel gauge idiot light.
Many automotive voltmeters lack sufficient precision to be useful (mine
has a number at each end of the scale and one in the middle, with the
needle width approximately equal to the difference between 50% and full
charge! When bored on long trips I tend to ponder whether the scale is
actually linear. I find this activity even more boring and quickly take
a renewed interest in traffic.).
I do think it is very difficult for a typical driver to extract more
useful information from a typical voltmeter than from an idiot light.
Chuck
| |
|
|
| Dave Plowman (News) 2006-04-23, 2:25 pm |
| In article <AOK2g.7634$Es3.6871@newsread3.news.atl.earthlink.net>,
chuck <nospam@nospam.net> wrote:
> But if the concern is to obtain early warning of an impending
> battery/alternator/regulator/belt failure so as to avoid being caught on
> the road without an electrical system, then most of us would benefit far
> more from the jumper cable. ;-)
What good is a jumper cable if your alternator/regulator/fanbelt has
failed on the road? You'd need a breakdown service to fix it and they all
carry starter batteries.
--
*Avoid clichés like the plague. (They're old hat.) *
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| PC Paul 2006-04-23, 2:25 pm |
| Dave Plowman (News) wrote:
> In article <AOK2g.7634$Es3.6871@newsread3.news.atl.earthlink.net>,
> chuck <nospam@nospam.net> wrote:
>
> What good is a jumper cable if your alternator/regulator/fanbelt has
> failed on the road? You'd need a breakdown service to fix it and they
> all carry starter batteries.
Once you've started with a jump either a battery OR an alternator+regulator
will get you home.
Unless you found out about the problem because it wasn't charging and now
it's run out...
| |
| Dave Plowman (News) 2006-04-23, 3:21 pm |
| In article <K8udnchHb8MpMtbZRVnygQ@brightview.com>,
PC Paul <me@home.com> wrote:
[color=darkred]
> Once you've started with a jump either a battery OR an
> alternator+regulator will get you home.
So you carry spares for these as well as jump leads?
> Unless you found out about the problem because it wasn't charging and
> now it's run out...
Yes. With no charge, jumping starting the car (because the battery is
flat) won't leave it running for long.
I do carry jump leads and a spare fan belt on the old car, though.
--
*It's o.k. to laugh during sexŒ.Œ.just don't point!
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Michael A. Terrell 2006-04-23, 3:21 pm |
| "Dave Plowman (News)" wrote:
>
> In article <K8udnchHb8MpMtbZRVnygQ@brightview.com>,
> PC Paul <me@home.com> wrote:
>
>
> So you carry spares for these as well as jump leads?
>
>
> Yes. With no charge, jumping starting the car (because the battery is
> flat) won't leave it running for long.
>
> I do carry jump leads and a spare fan belt on the old car, though.
>
> --
> *It's o.k. to laugh during sexŒ.Œ.just don't point!
>
> Dave Plowman dave@davenoise.co.uk London SW
> To e-mail, change noise into sound.
I used to have a spare alternator on my 1966 GTO. I blew the front
bearing out so often that I got the bracket for that Pontiac 389 CID
engine with an AC compressor, which required the Alternator to moved to
the other side of the engine. Over rev the alternator, stop, remove the
fan belt and plug from the bad alternator, plug it into the spare and
install the fan belt on that side. A one minute or less repair on the
side of the road. I also used #1 AWG welding cable on the main battery
to reduce the voltage drop.
On other vehicles I've had a dual charging system and a pair of the
biggest batteries that would fit under the hood. Need a jump? Flip a
switch to tie the two batteries together with a starter solenoid and
start the engine.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Michael A. Terrell 2006-04-23, 3:21 pm |
| Gary Schafer wrote:
>
> On Sat, 22 Apr 2006 18:17:53 +0100, "Dave Plowman (News)"
> <dave@davenoise.co.uk> wrote:
>
>
> A standard wet cell battery will exhibit approximately the following
> voltages at various states of charge at 70 degrees F: Courtesy of
> William Darden's Battery faqs.
>
> 100% 12.643
>
> 75% 12.443
>
> 50% 12.273
>
> 25% 12.053
>
> 0% 11.883
>
> Maintenance free batteries will be approximately the following:
>
> 100% 12.793
>
> 75% 12.593
>
> 50% 12.393
>
> 25% 11.993
>
> 0% 11.793
>
> Regards
> Gary
Is that a static voltage reading, or with the engine running and
charging the battery? Where is your voltmeter connected into the car's
wiring? How often is it 70 degrees F under your hood when you want to
check the voltage? Too many variables to get a useful answer with a
simple meter.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| PC Paul 2006-04-23, 3:21 pm |
| Dave Plowman (News) wrote:
> In article <K8udnchHb8MpMtbZRVnygQ@brightview.com>,
> PC Paul <me@home.com> wrote:
>
>
> So you carry spares for these as well as jump leads?
>
>
> Yes. With no charge, jumping starting the car (because the battery is
> flat) won't leave it running for long.
So how did I get 100 miles in a 3.0 Supra with *no battery at all* in it
then?
An alternator is quite capable of giving enough current to keep the systems
going. Probably not on full beam, heated windows etc., but for daytime
running it was fine.
Don't stall it though.
>
> I do carry jump leads and a spare fan belt on the old car, though.
| |
| Dave Plowman (News) 2006-04-23, 9:21 pm |
| In article <KNednaQs-JIXXtbZRVnyuQ@brightview.com>,
PC Paul <me@home.com> wrote:
[color=darkred]
> So how did I get 100 miles in a 3.0 Supra with *no battery at all* in it
> then?
The alternator was working. I was talking about when the charging system
or fan belt fails. Jump leads won't help you then.
> An alternator is quite capable of giving enough current to keep the
> systems going. Probably not on full beam, heated windows etc., but for
> daytime running it was fine.
The voltage from an unterminated alternator can go sky high and fry the
electronics. Not recommended.
> Don't stall it though.
--
*When you've seen one shopping centre you've seen a mall*
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
| |
| Gary Schafer 2006-04-23, 9:21 pm |
| On Sun, 23 Apr 2006 17:58:15 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:
>Gary Schafer wrote:
>
> Is that a static voltage reading, or with the engine running and
>charging the battery? Where is your voltmeter connected into the car's
>wiring? How often is it 70 degrees F under your hood when you want to
>check the voltage? Too many variables to get a useful answer with a
>simple meter.
http://www.batteryfaq.org/SoC.xls
Regards
Gary
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