Electrical Engineering - SEEMS like a simple enough part to find (NOT!)

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SEEMS like a simple enough part to find (NOT!)

george

2005-08-25, 7:21 pm

Would anyone happen to know a source (for 1, not a thousand) for a 31 ohm
(or close) 5W resistor of the thru-hole variety? It is as near as I can
tell what the trickle charge resistor used to be in my Porter Cable 8501
battery charger (an oldie). (I may be overestimating what was used on the
5W part of the spec...it only LOOKS like about 2W (which might explain its
toasty brown color) but I think 5W is closer to what it should have been.)

TIA,
George

gfretwell@aol.com

2005-08-26, 1:21 am

On Thu, 25 Aug 2005 17:47:11 -0400, "george" <nowhere@newsonly.com>
wrote:

>Would anyone happen to know a source (for 1, not a thousand) for a 31 ohm
>(or close) 5W resistor of the thru-hole variety? It is as near as I can
>tell what the trickle charge resistor used to be in my Porter Cable 8501
>battery charger (an oldie). (I may be overestimating what was used on the
>5W part of the spec...it only LOOKS like about 2W (which might explain its
>toasty brown color) but I think 5W is closer to what it should have been.)

Remember all those resistor ladder puzzles you did in elecrtronics
101. Dust off that skill and build a resistor with the values you can
find. Three 100 ohm rersistors in parallel will get you close. If you
started with 6, and checked them I bet the tolerance would let you get
very close.

ehsjr

2005-08-26, 1:21 am

george wrote:
> Would anyone happen to know a source (for 1, not a thousand) for a 31 ohm
> (or close) 5W resistor of the thru-hole variety? It is as near as I can
> tell what the trickle charge resistor used to be in my Porter Cable 8501
> battery charger (an oldie). (I may be overestimating what was used on the
> 5W part of the spec...it only LOOKS like about 2W (which might explain its
> toasty brown color) but I think 5W is closer to what it should have been.)
>
> TIA,
> George
>
>

For odd values, you can use series and/or parallel resistors.
For example:
You could parallel 2 62 ohm 5 watt resistors - part 62W-5-ND
from digikey if you have the space. Or, if 30 ohms is close
enough, you could use part # 25J30R-ND. If you must have
31 ohms, you could add a 1 ohm 1 watt # ALSR1J-1.0-ND
resistor in series.
Another combination: 82 ohms 3 watts # 23J82R-ND in
parallel with 50 ohms 3 watts # 23J50R-ND would give
you 31.06 ohms at a bit under 5 watts.

How sure are you of the 31 ohms? Hard to figure out
why a trickle charger would need such an odd size -
only 1 ohm from a standard 30 ohm value.

Ed

TimPerry

2005-08-26, 12:21 pm

"george" <nowhere@newsonly.com> wrote in message
news:C%qPe.2388$Yh6.646@fe04.lga...
> Would anyone happen to know a source (for 1, not a thousand) for a 31 ohm
> (or close) 5W resistor of the thru-hole variety? It is as near as I can
> tell what the trickle charge resistor used to be in my Porter Cable 8501
> battery charger (an oldie). (I may be overestimating what was used on the
> 5W part of the spec...it only LOOKS like about 2W (which might explain its
> toasty brown color) but I think 5W is closer to what it should have been.)
>
> TIA,
> George
>
>

in a pinch try a light bulb. an auto tail light or brake light can come in
handy. correctly sized, if the lamp glows brightly if the battery is
shorted.

just add more in series or parallel to adjust the desired charge rate.

george

2005-08-26, 2:21 pm

<gfretwell@aol.com> wrote in message
news:lp2tg1h7rjid8easluc894t0vrf650qnv2@4ax.com...
> On Thu, 25 Aug 2005 17:47:11 -0400, "george" <nowhere@newsonly.com>
> wrote:
>
>
>
> Remember all those resistor ladder puzzles you did in elecrtronics
> 101. Dust off that skill and build a resistor with the values you can
> find. Three 100 ohm rersistors in parallel will get you close. If you
> started with 6, and checked them I bet the tolerance would let you get
> very close.

Hmmm, guess I wasn't clear enough on this... It's not that I forgot how to
figure out how to make what I want with 1,000 resistors that are 1/8W and
around 1k ohms in value. The problem, as I see it, is that I'd like to have
it
still mountable to the printed circuit board, fit inside the case, and keep
costs
reasonable by buying a reasonable number of resistors (preferably one,
though
two is okay, and three is about my limit (I still have to be able to close
up the
case and keep everything out of the way of all the case screws)). There
also
isn't anything sacred about 31 ohms...30, 33, 27, 36 are all fine, I just
stated
what is in there (I think...it IS hard to read and you can't measure a
burned-out
resistor).

The big problem that I'm encountering is:
1) almost everywhere, all I find in through-hole resistors are 1/8W and 1/4W
(once in awhile I'll even find 1/2W, but even 10 resistors in parallel isn't
a very
attractive proposition)
2) the higher wattage resistors that I find all seem to be wirewound (even
one
would be too big to fit inside the charger case)
3) I DID find some current sensing resistors (power handling is fine, the
problem
is they are values like 0.1 ohm...310 resistors in series doesn't seem like
a practical
solution)
4) resistors like this USED to be common (they were never common where I
live
now)...I thought someone might be aware of a stash somewhere...

Thanks in advance everyone,
George

BFoelsch

2005-08-27, 8:21 pm

"george" <nowhere@newsonly.com> wrote in message
news:C%qPe.2388$Yh6.646@fe04.lga...
> Would anyone happen to know a source (for 1, not a thousand) for a 31 ohm
> (or close) 5W resistor of the thru-hole variety? It is as near as I can
> tell what the trickle charge resistor used to be in my Porter Cable 8501
> battery charger (an oldie). (I may be overestimating what was used on the
> 5W part of the spec...it only LOOKS like about 2W (which might explain its
> toasty brown color) but I think 5W is closer to what it should have been.)
>
> TIA,
> George
>

NTE 5W033

I am sure any nmber of places carry them, but www.cablesandconnectors.com
has them at 2 for 1.39, no minimum order.

george

2005-08-29, 1:21 am

"BFoelsch" <BFoelsch@comcast.ditch.this.net> wrote in message
news:ie2dnXqC6Puj543eRVn-2g@giganews.com...
>
> "george" <nowhere@newsonly.com> wrote in message
> news:C%qPe.2388$Yh6.646@fe04.lga...
>
> NTE 5W033
>
> I am sure any nmber of places carry them, but www.cablesandconnectors.com
> has them at 2 for 1.39, no minimum order.
>
>

Thanks. I wasn't aware of this source...+ it looks like they have some
other stuff I
can use for other projects, too.

George

Michael A. Terrell

2005-08-30, 12:21 pm

george wrote:
>
> "BFoelsch" <BFoelsch@comcast.ditch.this.net> wrote in message
> news:ie2dnXqC6Puj543eRVn-2g@giganews.com...
>
> Thanks. I wasn't aware of this source...+ it looks like they have some
> other stuff I
> can use for other projects, too.
>
> George

<http://www.nteinc.com/NET_St_lst/Disty.html> list every NTE
distributor.

<http://dilp.netcomponents.com/nteinc.html> lets you search all their
distributors inventory at once.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

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