nikg

I am charging some GP 3300 NIMH cells 6 at a time. One set of 6 has exhibited some weird behavior and made my charger false peak several times. These cells have already been through 3 cycles .5A charge/1A discharge.5A charge/1A discharge.5A charge/5A discharge. These cycles were donehe old fashioned way with a wal-wart to charge and automotive bulbs to discharge. I checked the actual current and voltage with my multimeter for these cycles.

After the three cycles I am charging at 1.6A for the 4th cycle on my Turbo 30. Many sets of cells have been fine as they charge up to about 8.0 volts rather quickly and then get up to about 8.40v after a few minutes and then very gradually climb from there over the next few hours until they peak.
This particular set of six cells rocketed up to about 9.8v within a few minutes and then topped out at 10.05v. They then hovered between 10.03 and 9.95v for a few minutes. I terminated the charge judging this voltage was way too high. At more mild current, such as .6A and below, they get up to about 8.7v within 5 to 10 minutes, but I still consider that high voltage at this charge current, so I terminated those charges as well.

Any ideas about what is going on? This seems like behavior more consistent with cells that have not been cycled in a while, but these just came off three nice easy cycles. I am slow charging them again to see if that has any effect. Should I focus on individual charging to see if there might be a few cells causing the problem?

Thanks

Flying Geezer

My Feedback: (14)

I don't know what kind of charger you are using, but you are probably reading the charging voltage. The higher the charge current, the higher the voltage required to push that current through the battery.

I would not be concerned with the voltage during charge. Make sure the cells don't get too hot. They will get quite warm near the end of the charge, just before peaking.

I charge a 6 cell 1700 mAh TX battery at 1A and the voltage exceeds 10V while charging, then settles to 8.4 after the charge is completed.

Voltage is not a concern with nickel batteries, just current. The opposite is true with lead acid and lithium.

Hope this helps,

nikg

Yes, I am reading the charging voltage, but I have seen a number of people giving advice such as not pushing NIMH's too high when charging ( I think the cutoff was like 1.7v per cell). It concerned me because none of my other packs, even my highest voltage ones, ramp up to such a high voltage. They usually top out at 8.8 to 9.1 volts at peak.

Anyway, I slow charged at 500mA for about four hours then completed the charge at 1.6A and everything went fine. No crazy jumps. I guess they may have just not been cycled enough yet.