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Home > Archive > Alternative Power sources > August 2005 > charge controller for 24VDC generator?
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charge controller for 24VDC generator?
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| Robert Morein 2005-08-25, 4:21 pm |
| I want to use a 24VDC NATO field generator to charge a battery bank that's
also connected to a Xantrex SW4024+.
The idea is that when grid power is not present, the generator will charge
the battery bank at the same time the Xantrex is drawing on them.
The Xantrex is capable of drawing 200 amps continuous, 350 amps surge.
The generator can supply up to about 70 amps at 28 VDC, adustable 27-31.
As the Xantrex draws down the battery bank, the current demand to the
generator will increase, until the breaker trips. It would be good to have a
charge controller in between the generator and battery bank that limits
current to less than the genny capacity.
Investigation of DC charge controllers, and a discussion with a guy at
Morningstar, suggest that there is no DC charge controller that also has a
current limiting function. This is because the common use of these products
is in conjunction with solar sources that are intrinsically current limited.
There are some MPPT controllers that limit current. However, there is no
advice available with respect to use with generators. Among the concerns
are:
1. Brush noise might spook the MPPT algorithm.
2. Interaction between the MPPT algorithm and generator load regulation.
Suggestions?
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| RF Dude 2005-08-25, 11:21 pm |
| I think the answer will be in your generator regulator. If this circuit is
accessible, you will likely be able to control your exciter current (a few
amps) which in turn will control the generator output (lots of amps).
However, to limit current will require you to regulate down to a much lower
voltage (perhaps down to 20.0V) than the float voltage (~27.0V). The idea
is to let the battery pick up the excess current while the generator remains
within its capabilities.
Some DC generators control their output by varying the speed of the engine.
Good luck.
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| Robert Morein 2005-08-26, 12:21 am |
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"RF Dude" <post@thisnewsgroup.com> wrote in message
news:g9uPe.1439$Rc.435233@news20.bellglobal.com...
> I think the answer will be in your generator regulator. If this circuit
is
> accessible, you will likely be able to control your exciter current (a few
> amps) which in turn will control the generator output (lots of amps).
> However, to limit current will require you to regulate down to a much
lower
> voltage (perhaps down to 20.0V) than the float voltage (~27.0V). The idea
> is to let the battery pick up the excess current while the generator
remains
> within its capabilities.
>
> Some DC generators control their output by varying the speed of the
engine.
>
Not this one. It is a diesel with a mechanical governor.
>
Your solution is what I'm stuck with, which is to manually regulate the
generator, using the voltage pot. However, this just postpones the problem
to the point where the battery bank runs down. At the point where the
battery bank discharges to the set voltage, the generator current will
suddenly zoom upwards. The real solution would be an automatic current
regulator.
20 volts is not a good idea, since that corresponds to a dead battery. The
purpose of this genny is to keep it charged.
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Robert Morein wrote:
> I want to use a 24VDC NATO field generator to charge a battery bank that's
> also connected to a Xantrex SW4024+.
>
> The idea is that when grid power is not present, the generator will charge
> the battery bank at the same time the Xantrex is drawing on them.
Yeah, I've heard of people doing that ;-).
> The Xantrex is capable of drawing 200 amps continuous, 350 amps surge.
> The generator can supply up to about 70 amps at 28 VDC, adustable 27-31.
Yep. Personally, I'd like to see you draw 200 amps continuous out of
that 4024. That's a whole lot of juice. Likely, you've got a 250 amp
breaker in your DC disconnect. She'd pop under a continuous load like
that I'd bet, after a few hours, not to mention that the inverter would
probably melt. Yeah, yeah, I know, not on paper. But ten years as a
millwright in a chemical plant, building MCC rooms, trust me, keep a
handful of spare fuses around if you're going to draw down on it like
that.
> As the Xantrex draws down the battery bank, the current demand to the
> generator will increase, until the breaker trips. It would be good to have a
> charge controller in between the generator and battery bank that limits
> current to less than the genny capacity.
If it was one of my clients with this problem, I'd say two things:
1) you're using too much electricity.
2) get a bigger battery bank.
Myself, I don't see anything wrong with running the DC generator, set
for, say, 29 volts DC, and just letting it do what it does. I would
imagine that once the battery voltage hit 29 volts, it'd just be
spinning its wheels. Can't see how that would hurt, seeing is that's
what it was designed to do...
DJ
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| Robert Morein 2005-08-26, 1:21 pm |
|
"DJ" <dj_macintyre@hotmail.com> wrote in message
news:1125070408.870118.157520@g47g2000cwa.googlegroups.com...
>
> Robert Morein wrote:
that's[color=darkred]
charge[color=darkred]
>
> Yeah, I've heard of people doing that ;-).
>
>
> Yep. Personally, I'd like to see you draw 200 amps continuous out of
> that 4024. That's a whole lot of juice. Likely, you've got a 250 amp
> breaker in your DC disconnect.
The DC disconnect is 400 amps, Xantrex specifies dual 4/0 power leads.
She'd pop under a continuous load like
> that I'd bet, after a few hours, not to mention that the inverter would
> probably melt.
I go by the Xantrex time/load curves. 8500 watts for 5 seconds, with a
smooth time derating curve leading to automatic shutdown if the continuous
load exceeds 4000 watts.
Yeah, yeah, I know, not on paper. But ten years as a
> millwright in a chemical plant, building MCC rooms, trust me, keep a
> handful of spare fuses around if you're going to draw down on it like
> that.
>
have a[color=darkred]
>
> If it was one of my clients with this problem, I'd say two things:
> 1) you're using too much electricity.
> 2) get a bigger battery bank.
>
It's already 36 kwh.
> Myself, I don't see anything wrong with running the DC generator, set
> for, say, 29 volts DC, and just letting it do what it does. I would
> imagine that once the battery voltage hit 29 volts, it'd just be
> spinning its wheels. Can't see how that would hurt, seeing is that's
> what it was designed to do...
>
If this was a flooded electrolyte battery bank, you'd be right. However, it
is a Hawker AGM Powersafe. They claim a 20 year lifetime, but regardless of
whether that's realistic, they have an extremely stringent charging
requirement: constant voltage only, which means that bulk=float, to within a
temperature compensated 0.1 volts of center value. Provided that is met, the
battery will efficiently recombine the electrolyzed water. The current setup
does this.I can't set the generator point above the float value, or the
battery will rapidly lose water.
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Robert Morein wrote:
> The DC disconnect is 400 amps, Xantrex specifies dual 4/0 power leads.
That's usually what I use in any case, and never smaller than 2/0,
yeah.
> It's already 36 kwh.
Ok, so you have a 36kwh battery bank? 36 useable, or 36 total? Even
actual, that should be a dozen or more useable. Just how long are you
planning on having the power be out, exactly?
DJ
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| Robert Morein 2005-08-27, 8:22 pm |
|
"DJ" <dj_macintyre@hotmail.com> wrote in message
news:1125071608.931824.275500@g43g2000cwa.googlegroups.com...
>
> Robert Morein wrote:
>
>
> That's usually what I use in any case, and never smaller than 2/0,
> yeah.
>
>
> Ok, so you have a 36kwh battery bank? 36 useable, or 36 total?
According to Hawker, 1200 discharge cycles to 80%, which means 28 kwh. Of
course, they were surplus batteries, so we could probably take at least 20%
off the service figure.
> Even actual, that should be a dozen or more useable. Just how long are you
> planning on having the power be out, exactly?
>
I may have more of a survivalist mentality than most people on this group,
who generate power for practical, everyday reasons. The area I live in is
served by the largest grid in the U.S., the PJM Interconnect, which dates
back to 1927: http://americanhistory.si.edu/power...it/gallry26.htm
and
http://www.pjm.com/index.jsp
In my entire lifetime, I have never experienced a regional power failure,
although some areas 30 miles to the south have had ice storms that caused a
one week loss of service. The Ohio failure of 8/14/03 represents a newly
recognized instability of this grid that caused some customers in the upper
midwest to lose power for 28 days. It did not reach my area, but it came
within 70 miles.
At the time the Twin Towers came down, I lived 99 miles away. Do you
remember the shock and horror of that day, when the U.S. was under attack? I
can understand if most people prefer to forget. I wonder how many Americans
actually followed the recommendations of the DHS for personal preparedness?
For me, it was a watershed. Even though I'm a liberal, I looked at what the
Mormons advise their people to do. I decided to continue my daily life
(except that I no longer commute into NYC during the rush hour!), but I
would try to prepare for a worst case autonomous existence. Electricity is
just one part of the equation.
In response to your question, "how long are you planning on having the power
be out, exactly?", I'm preparing for the unthinkable. Estimates do not work
very well for such things.
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| Loren Amelang 2005-08-27, 8:22 pm |
| On Thu, 25 Aug 2005 14:28:00 -0400, "Robert Morein"
<nowhere@nowhere.com> wrote:
>I want to use a 24VDC NATO field generator to charge a battery bank that's
>also connected to a Xantrex SW4024+.
>
>The idea is that when grid power is not present, the generator will charge
>the battery bank at the same time the Xantrex is drawing on them.
I use a Delco alternator on a Honda engine to do the same with my
original Trace SW4024.
>The generator can supply up to about 70 amps at 28 VDC, adustable 27-31.
Mine maxes out at around 40 A, and just has a manual rheostat for
field adjustment. I typically crank it up to maximum possible output,
and it has handled that for over ten years now.
>As the Xantrex draws down the battery bank, the current demand to the
>generator will increase, until the breaker trips.
Never seen that. What happens here is that if my usage is getting
ahead of the generator output, the battery voltage declines. The
generator would be happy to pump its output into a 12 V load, and just
keeps pumping out current - actually a bit more as the load voltage
decreases. There is a fuse in the line, but it is only for
short-circuit protection, sized to handle the maximum the generator
can provide.
Presumably the low voltage cutout on the inverter would eventually be
triggered, but I've never pushed the situation to that point.
>It would be good to have a
>charge controller in between the generator and battery bank that limits
>current to less than the genny capacity.
Are you saying your generator is capable of blowing its own output
breaker while operating into a normal load? I would expect the
generator was built to cope with any load that might be connected to
it, hopefully by being internally regulated (or capable of running
flat-out, like mine) rather than brute-force limited by the output
breaker.
For clarity of thought, leave the inverter out of the system. If you
connect the generator to a big empty battery bank, will it blow its
output breaker trying to put out more current than the nameplate
specifies?
Loren
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| Robert Morein 2005-08-27, 8:22 pm |
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"Loren Amelang" <loren@pacific.net> wrote in message
news:gtoug1dmksf111upls4kpsft0cqnecs6al@4ax.com...
> On Thu, 25 Aug 2005 14:28:00 -0400, "Robert Morein"
> <nowhere@nowhere.com> wrote:
>
that's[color=darkred]
charge[color=darkred]
>
> I use a Delco alternator on a Honda engine to do the same with my
> original Trace SW4024.
>
>
> Mine maxes out at around 40 A, and just has a manual rheostat for
> field adjustment. I typically crank it up to maximum possible output,
> and it has handled that for over ten years now.
>
>
> Never seen that. What happens here is that if my usage is getting
> ahead of the generator output, the battery voltage declines. The
> generator would be happy to pump its output into a 12 V load, and just
> keeps pumping out current - actually a bit more as the load voltage
> decreases. There is a fuse in the line, but it is only for
> short-circuit protection, sized to handle the maximum the generator
> can provide.
>
> Presumably the low voltage cutout on the inverter would eventually be
> triggered, but I've never pushed the situation to that point.
>
>
> Are you saying your generator is capable of blowing its own output
> breaker while operating into a normal load? I would expect the
> generator was built to cope with any load that might be connected to
> it, hopefully by being internally regulated (or capable of running
> flat-out, like mine) rather than brute-force limited by the output
> breaker.
>
> For clarity of thought, leave the inverter out of the system. If you
> connect the generator to a big empty battery bank, will it blow its
> output breaker trying to put out more current than the nameplate
> specifies?
>
> Loren
I believe that is the case. It has no current limiting. It does have voltage
regulation.
The AGM batteries are part of the cause of the problem, because they accept
extremely high charging currents. In autombiles that have been retrofitted
with AGM batteries, if the battery is discharged, it must be charged before
the car is run, because it presents a near dead short to the alternator.
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| RF Dude 2005-08-27, 8:22 pm |
| You haven't provided any details about your generator. Most important is
the exciter current required for maximum generator output. There must be
some sort of automatic voltage regulation and you adjust the voltage with
the external pot. What you want is constant voltage up to a set maximum
current at which point it becomes constant current regulation. Depending on
your generator exciter current, if you have some electronics experience, you
obtain a 5-pin voltage regulator and set it up to control the exciter
current. The generator output would be fed back to the sense lead on the
regulator. Usually you can add a potentiometer and resistor, per regulator
data sheet, to define the maximum current output of the regulator. In this
way, your exciter current ( and voltage) remain regulated until the maximum
current is reached. If more power is demanded, the voltage starts to fall.
This is why I suggested that the regulator must take the generator voltage
down to 20V in case you find yourself having to charge a dead battery.
There might be a few minor issues with this approach, but it would be cheap
and rather simple to implement.
Good Luck.
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| Robert Morein 2005-08-27, 8:22 pm |
|
"RF Dude" <post@thisnewsgroup.com> wrote in message
news:%LRPe.3210$Rc.610465@news20.bellglobal.com...
> You haven't provided any details about your generator. Most important is
> the exciter current required for maximum generator output. There must be
> some sort of automatic voltage regulation and you adjust the voltage with
> the external pot. What you want is constant voltage up to a set maximum
> current at which point it becomes constant current regulation. Depending
on
> your generator exciter current, if you have some electronics experience,
you
> obtain a 5-pin voltage regulator and set it up to control the exciter
> current. The generator output would be fed back to the sense lead on the
> regulator. Usually you can add a potentiometer and resistor, per
regulator
> data sheet, to define the maximum current output of the regulator. In
this
> way, your exciter current ( and voltage) remain regulated until the
maximum
> current is reached. If more power is demanded, the voltage starts to
fall.
> This is why I suggested that the regulator must take the generator voltage
> down to 20V in case you find yourself having to charge a dead battery.
>
> There might be a few minor issues with this approach, but it would be
cheap
> and rather simple to implement.
>
> Good Luck.
>
Good idea. I'll take a look at it.
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