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Unread 28-03-2002, 15:04
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Joe Johnson Joe Johnson is offline
Engineer at Medrobotics
AKA: Dr. Joe
FRC #0088 (TJ2)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1996
Location: Raynham, MA
Posts: 2,648
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Test your batteries

We have just gone through a serious set of tests of all batteries in our stock.

There is a very wide range of performance.

Basically, we bought high wattage Ohmite 1 ohm resistors, banked them in parrallel to give us either .2 ohm or .1 ohm resistors. We plugged in our batteries and then checked the voltage every 30 seconds until the battery voltage went below 8.0V.

This allowed us to rate our batteries as red, yellow, or green.

For us, in order for a battery to be green it had to last over 4 minutes with the .1 ohm resistor. We found that for a battery to be green, .2 ohms required 11 or more minutes to drain it to 8.0V. We stopped doing the .2 ohm test after a while because there it didn't seem to give us any more information than the .1 ohm test (good batteries on one test were good batteries on the other test) and because it took longer to do the test.

Surprisingly, there was very little variation amoung green batteries or best green battery was 300 seconds our worst green battery was 270 seconds.

So, either a battery was good or it was not. It was also surprising how poorly age predicted whether a battery would be green or yellow or red. We had some almost new batteries that were red. We had some batteries from 1999 that were as good as any green battery we have.

I urge everyone to test their batteries. You may be surprised at what you find out.

Joe J.

Last edited by Joe Johnson : 28-03-2002 at 15:08.