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gmamo

PIC NICAD / NIMH Capacitance meter

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HI ..

Anyone has built a cell matching instrument using PICs ( as not to use many discretes ) ???? There are a couple of schematics on the net, but all use a lot of components, and you'll have to build many copies of these circuits to arrive anywhere with a couple of 10-20 cell packs to be matched.

A PIC or a PC can be used to time a discharge to an adjustable cutoff point and give capacity or time taken to discharge. However, it needs to have a high discharge capacity ...5-20 Amps to be realistic.

HELP !!!!

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You bring up a question that I have asked before, but never really got an answer.

What is the best way to put a load on a circuit?

For instance, I see people adding a couple of resistors to their voltmeters and say that's the equivalent of having a 350ma load while testing their batteries at the field. I haven't tried it as such, but somehow I don't think a couple of resistors are actually draining 350ma from the batteries.

I just bought a Hobbico (or something similar) voltmeter for the field. I use to bring my Multi-Meter with me, but I'm tired of moving it back and forth from the flight box to the shop table etc. It supposedly has adjustments on it for 3 loads 250ma, 350ma and 500ma or something similar.

Another reason why I ordered it (besides it being on sale and cheap) was that I wanted to see how they did that.

I guess I should also open up my battery recycler and take a look in there how they actually drain the batteries.

But if someone has the answer and saves me from opening up yet somethinf else in this house, that would be great. No "extra parts" lying around afterwards that way.

Regards,

Mike

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There are a couple of schematics on the net, but all use a lot of components...

Can you post a link to these projects?

What is the best way to put a load on a circuit?

The little handheld ESV meters just use resistors. The high-end battery cyclers use a transistor based load configured for constant current operation.

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Here's some links that I remember :

1) http://www.yoredale.uklinux.net/electronic...electronics.htm

2) http://www.uoguelph.ca/~antoon/gadgets/disch.htm ... taken from the site :

http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm

3) http://www.geocities.com/SiliconValley/Gar...schematics.html

but the link doesn't seem to work anymore :(

Thanks MR. RC_Cam... The best way to drain ( controllably high currents is to use banks of transistors as a constant current load.. or else some Switching Power Mosfets.

It is important that we measure a cingle cell capacity in this application. Therefore if we do not want to have a very long process... and to use realistically high currents, we must discharge at 20 Amps for the Sub C Cells That means 1.2V * 20A = 24 Watts of dissipation... Not unbearable :)

George

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My Webpage

Transisitors are a great way to do a load bank. I created one that I vary with a pot or can be controlled using a dac. Handles 5 amps with a heat sink easily, rated for much more, but you need to be able to dissapate the heat.

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