Battery voltage question.

[Sully008]

Hello all,

If my Varta V80 is sitting @ 1.02v not connected or charged instead of 1.25v, does that mean it's done for? I've got 3 batteries here that seem to be no good anymore.

TIA,
Mike

[rewolf]

1.02V is a normal voltage for a discharged NiMH/NiCd. Even 0.9V is still ok.
1.25V is the average voltage during discharge.
NiMH full charge voltage (no load current) is about 1.35-1.4V, discharging below 1.0V should be avoided.

[Sully008]

Okay, so I should be able to attach a 3v source and recharge it back to 1.25v without any problems. What was happening was I'd hook up the batteries to my Synchronar and the display would show up and just drain. I started a thread in the Synchronar section about this. Thanks, rewolf!

Mike

1.02V is a normal voltage for a discharged NiMH/NiCd. Even 0.9V is still ok.
1.25V is the average voltage during discharge.
NiMH full charge voltage (no load current) is about 1.35-1.4V, discharging below 1.0V should be avoided.

[Synchroserious]

If you are only charging one 1.2 V cell you only need 1.5 volts.

Most distributors have them fully charged before shipping but not all.

[charger105]

Hi Mike.
Getting back to your original problem, are you saying that when you connect fresh batteries, the display lights up and stays lit until the batteries drain ?

Rgds,
Andrew.

[Sully008]

Hi Andrew,

No, what was happening was when I activated the time and held the switch, it was as if the SC wasn't charging the batteries, even under a bright lamp. The display would light up dim then fade away.

All seems to be better now. I used a pair of AAs to recharge the batteries that were only showing 1.0v and reconnected them to the module. I made sure the SC was outputting 3v. I just need to put the lexan case back together.

Hi Mike.
Getting back to your original problem, are you saying that when you connect fresh batteries, the display lights up and stays lit until the batteries drain ?

Rgds,
Andrew.

[rewolf]

Okay, so I should be able to attach a 3v source and recharge it back to 1.25v without any problems....

Yes, you can do that to charge 2 cells in series, but you need to limit the charging current.
A 22 Ohm resistor in series will limit the initial charging current to max 40mA @ 3.0V source. Current at end of charge (overcharge) will be 7mA. These are the maximum allowed currents according to the datasheet.

If you are only charging one 1.2 V cell you only need 1.5 volts.

Yes - but again you need a limiting resistor, about 10 Ohms.

Most distributors have them fully charged before shipping but not all.

NiMH cells have a rather high discharge rate. If they sit in the shelf for a few months, they lose a significant amount of charge. If they sit for a year, they will be almost fully discharged.
That's why manufacturers have invented "read to use" rechargeables like Eneloop, Infinium, etc.
If you have a distributor that charges the batteries before shipping to you: try to keep him! I've never seen one that does this. Mostly it's not even possible because the batteries are in a sealed package. I'd rather return batteries that arrive in an opened package.

[Sully008]

Okay, so I should be able to attach a 3v source and recharge it back to 1.25v without any problems....

Yes, you can do that to charge 2 cells in series, but you need to limit the charging current.
A 22 Ohm resistor in series will limit the initial charging current to max 40mA @ 3.0V source. Current at end of charge (overcharge) will be 7mA. These are the maximum allowed currents according to the datasheet.

Heh, I guess I should pay attention to the safety stuff more often. I'll put a resistor on my charger. I just touched the +ve to the +ve of the battery and the -ve to the -ve for about 3 secs, then checked the battery voltage with my multimeter.

If you are only charging one 1.2 V cell you only need 1.5 volts.

Yes - but again you need a limiting resistor, about 10 Ohms.

Most distributors have them fully charged before shipping but not all.

NiMH cells have a rather high discharge rate. If they sit in the shelf for a few months, they lose a significant amount of charge. If they sit for a year, they will be almost fully discharged.
That's why manufacturers have invented "read to use" rechargeables like Eneloop, Infinium, etc.
If you have a distributor that charges the batteries before shipping to you: try to keep him! I've never seen one that does this. Mostly it's not even possible because the batteries are in a sealed package. I'd rather return batteries that arrive in an opened package.

The V80s I purchased were from mouser.com and they came charged @1.25v already. They were "packaged" individually in little ziplock bags.