Checking batts; individual cell voltage

[Xtreme Cartz]

Here is a diagram of my battery pack and the individual cell readings. I'm not sure why the first cell of every battery was lower than the rest. Also, almost every time I would go back and check a cell, the reading would be different +/- 0.1 volts. Did I do this right?

[Nate]

Batteries do strange things like this; I can't explain it but know it happens. This is why regular balance charges are important.

[Xtreme Cartz]

Nate, I forgot to measure the last cell to the negative terminal and then add it to the first.

How do you do a balance charge? If I diciphered the Chinese symbols correctly, there is a switch on my charger for normal or balance charging mode.

[Nate]

Hey Xtreme, you raised a few questions from folks asking how you measured individual cell voltage. I don't know how you did this and assumed you used the SG + 84 calculation.

The best way to balance charge is to hold the cells at 2.5V and 5 amps or less for batteries 50 lbs or heavier. If batteries get warm reduce current, I don't know if your charger has this feature.

[Xtreme Cartz]

I measured the individual cell voltage with a digital voltmeter and 2 metal coat hanger extensions attached to the meter's test leads. Well, thats the way I planned on doing it but I couldn't get a reliable connection. I ended up just dipping the test leads and cleaned them off afterwards with a baking soda mixture.

I went back and added the first and last voltages. Here's the corrected numbers. Do they look within reason? All of the cells are within 0.1 volts of each other except for the battery with the 2.52 and 2.08 cells.



I also worked on changing around the rear battery box so that the batteries could be cleaned easier. I hadn't washed them since ever and there was some acid build up.

[Nate]

2.08 and 2.52 are a little further apart than I would want to see. I wouldn't totally believe the way you checked them but a balance charge would not hurt. You may have done a great job of measuring the cells but it is just a little unconventional. Excellent work from that perspective!

[dereckbc]

Forget the voltage, check specific gravity and compensate for the temp. It will tell you a lot more than the voltage will.

[Xtreme Cartz]

I'll have to get a new hydrometer. Mine leaks and the spacing between the numbers seem to far apart for an accurate comparison.
I have actually never used a hydrometer before except for my failed attempt with the leaky one. When it spewed acid out the side onto my hand I gave up and grabbed the voltmeter. With the hydrometer, do you measure each cell and they should all be the same?

Here's my cheapo hydrometer. Do they come any better than this or should I dig mine back out of the trash can? Also, since it's not digital are we just looking for approximately close numbers?

[pggroves]

I use a refractometer but most don't/won't have access to one nor want to spend that much but IMO it is the best.



A good temperature correcting glass hydrometer should be ~$10 at about any auto parts store.