PWMs

[rexmannb]

I have been trying to get this PWM working that I purchased on EBay (without any success). I think that the unit just does not work. The seller has not responded to messages so I am on my own. If my cell will draw over 50 amps but I only want it to draw 20 amps, do I need a 50+ amp PWM or can I use a 31 amp unit? I am very confident working with cars but not so much on the workings of electronics. How can I bench test this unit to see if it is working? There are 4 lugs, + power source, + to cell, - to cell, - battery. Any information would be appreciated. 

[Bob]

Well, its like this... if you plan to draw 20 amps you'ed best get a 30 amp PWM
if you want to draw 50 amps you probably better get a 65~70 amp PWM
if you want draw more amperage it better to go with a Higher capasity than you will need
other wise, if you hook a 30amp draw to a 30 amp PWM you'll fry it in short order
 about 20 amps is all I would draw on a 30 amp PWM....
chances are you've probably already fried the PWM by putting too much load on it without realizing it.
its quite typical for guys to make 150amp to 200amp Capability PWM's when only planning on running 100amps ... this gives you  some "margin for error"
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a 30 amp PWM won't run a 30 amp load... a 30 amp PWM will burn UP at 30 amps...
another words it will handle UP to 30 amps... but not any more ...without burning up
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You can probly post the Schmitac diagram or a drawing of it here and see if the guys can figure out how its supposed to be hooked up... We have some very smart guys on here and they can tell you that much...
but with the info you gave, there is not enough information to tell what it is that you have!
same goes for checking to see if its working or not... we need to see how the thing is arranged ... it should have came with a Schmatic diagram of its curcuitry,  with it you can trace the lines and tell what is what... well for the most part.
the number and make of the Mossfett in the PWM ( if it has one) is also needed so the operateing paramaters can be looked up in transister information catalogs to get a resistance readingbetween its pins to be able to tell if its burned up or not... or at least that kind of information HELPS anyway...
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I stopped working on electronics when My eyesight got to the point that I couldn't tell a diode from a resistor ! HAHAHAHHA
although I just bought myself some Magnifing reading glasses  and I am supprized at how good they work , it still leaves allot to be desired! HAHAHHAHA
...
Bob......