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[dpbarry]

As you can probably read from a previous post, from experience, I treat all electrics with the respect it deserves so, when in doubt, ask!!

When a 7.2V NImh Battery is fully charged, what should (would) the voltage read? 8.4V?? (ish) (1.4v per cell charged x 6 (number of cells in pack).

I know some voltage will drop of down towards 1.3v per cell which gives around 7.8V but I can never get the hang of measuring volatges to check if a pack has been fully charged.

Any help greatlt appreciated.

Declan

[OMK]

When a 7.2V NImh Battery is fully charged, what should (would) the voltage read? 8.4V?

Good question. But since all my Ni-Mhs are 4.8 volts (receiver) and 9.6 (motor) I don't think I'm qualified to answer.
However, if it's any help, Ive been using ni-cads for years, and - like you - I'm unsure of just what the voltage should be. There are too many conflicting reports. Some say to do such-and-such, while others will have you believe something totally different.
The ni-cads you see here are solely for use in a glider - not in a boat. Since the motor (Speed 600) is only running during the time to reach altitude, the batteries come back still with a near-full charge after approx. ten-minute flight time.
They're quite old now, but they still hold a good charge. I follow a couple simple rules...

1) Discharge the cells when not in use.
2) Do not discharge below 1.1 volts per-cell.

Since the charging rate/time varies from pack to pack, I'm still in the dark as to what the exact charging parameters should be. Instead, I let the peak detector work its magic (Pic #1).
Not much help, I'm afraid. But to answer one of your questions I charged a couple depleted packs, then let them rest for some 20 minutes while the voltages stabilised before taking a V. reading. One pack shows 8.375 volts; the other reads a tad under 8.22 volts. Like yours, they are rated at 7.2 volts. Current capacity is 1.8 amps.

A moot point since your question concerns Ni-MH cells.
Sorry I can't be more specific. Perhaps someone with more knowledge on the subject could throw some light this way?

[2772e]

Funny old thing that.

It appears that there is always someone out there that is having the same problem.

I was trying to measure a couple of 12 volt 12 amp batteries last night and they are showing 13.1 volts. As i am running a six and a 12 together that gives me about 19 volts?

How is that explained?
 ???

[Peterm]

The battery voltage will probably drop a bit when they are put under load.   The best way to check voltage is when the battery/ies are connected to the load, for example, a motor.   Pete

[dpbarry]

Emailed a lad in the know (Red's R/C Battery Clinic)

He said that 7.2 volts is 6 cells, the open circuit voltage just off charge should be around 8.4. After it rests for a few hours it will be about 7.8.

I explained that I charged my battery up and after a few days it was reading around 8.0v  I asked him if this constitutated a charged battery.

His reply was Yes, it is still charged, anything above 1.3 volts/cell is OK. The faster the voltage drops the more probable it is that the pack has deteriorated and self discharge is taking it down. Typical with packs as the age.

Does this help folk?

Declan

[John - ModelPower]

hi
battery voltage fully charged cells approx 1.38volts the higher the capacity the longer the run time i agree with last mail
    Cheers John modelpower.co.uk