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I need someone to ID a doohickey.

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That looks like it should do the trick for you.

Cheers  :beer:



What is the output from your Batt. Charger ?

IF that cap. is across the input AND you charger is not a smoothed DC, it will be having a desparately hard time, and will fail catastrophically.

You need a Low ESR cap across the input, if this is the case. One about 1000uF per Amp of output is about right. Maybe a bit more.

A lot of older types of Batt. Charger were 'Rectified AC' output. Not a smoothed DC.

Ther's some stuff on Wiki  .. Look for low esr, dissipation factor, tan d.

Did it on an electronics forum months ago, either enquirer sorted his problem or he gave up. Heard no more.  :D 

Just a thought ..

Dave BC

The reversing switch is downstream of the board, rather than between the power supply and the board? These electrolytic capacitors are polarised, and don't like being subjected to reverse voltage. A salvaged one should be perfectly OK, if it's 47uF, with a voltage rating of at least 35V. One with a bigger voltage rating would be fine, if it will physically fit. Make sure there are no bits of foil etc left from the old one, ready to cause a short-circuit.

I speak as one who once accidentally reversed the polarity on a 4" diameter, 470 MILLIfarad one in the kitchen  :zap:  :bang: . It took hours to clean up the mess, and there were consequential losses - dinner for two, to stop the  :hammer: over what she had carefully prepared and left simmering on the stove.


That's what I was just going to say. I've bought what looks a very similar PWM board from ebay to control an electric locomotive. I noticed that they do ones with reverse built it, but I thougt, why do I need that, I will just revers polarity after the output of the circuit board. As Andy said, electrolytic capacitors are polarised so you have to keep your input as intended and when you solder it back on, make sure it's the right way around!

They sound pretty dangerous in that size Andy! I remember when we were at school purposely connecting little ones the wrong way around to get them to :zap: and get the puff of white powder ... no idea what it was!


I think the DP switch must be after the PSU.

I doubt if the chip would work at all on reverse polarity, he does say it worked for a bit.

Dave BC


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