Do NiMH's require a deep discharge conditioning?

Do NiMH\'s require a deep discharge conditioning?

If they do is there a tell tale sign that suggest a conditioning is due?

Thanks,
Dave

Re: Do NiMH\'s require a deep discharge conditioning?

Dave.

NO! DO NOT DEEP DISCHARGE A NIMH!

Discharging below .8 or .9 volts per cell is a recipe for disaster and can ruin NiMH cells.

Every 6 months or so, you can charge up your pack, then discharge to end of cycle (.9 volts/cell), then charge it up again, and this is all the maintenance your NiMH batteries will need. Other than that keep them charged up and don't store them for more than 6 months without giving them another charge.

Also, there are break-in cycles for new battery packs, which usually goes like this: trickle charge at .1C for 14-16 hours; discharge at .5C; then trickle charge again, or fast charge at up to 1C, then discharge at 1C, then charge by any method. This will "format" the new cells and break them in.

Re: Do NiMH\'s require a deep discharge conditioning?

JS said:

NO! DO NOT DEEP DISCHARGE A NIMH!

So does this mean if I accidently leave a light Just one time on the batteries will be ruined? I've also read somewhere at CPF that it ok to deep discharge a NIMH every 2-3 months. Is it true that its ok to deep discharge a NICAD.

Thanks,
Steven

Re: Do NiMH\'s require a deep discharge conditionin

Just don't overdischarge nimhs.
Keep them topped off above 1 volt a piece.
Even nicads don't like a super deep discharge below .5 volts.
I had a regulated light murder a nicad D cell like that yesterday. /ubbthreads/images/graemlins/xyxgun.gif /ubbthreads/images/graemlins/str.gif

Re: Do NiMH\'s require a deep discharge conditioning?

[ QUOTE ]
STEVENT6 said:
JS said:

NO! DO NOT DEEP DISCHARGE A NIMH!

So does this mean if I accidently leave a light Just one time on the batteries will be ruined? I've also read somewhere at CPF that it ok to deep discharge a NIMH every 2-3 months. Is it true that its ok to deep discharge a NICAD.

Thanks,
Steven

[/ QUOTE ]

Steve,

Exactly. It's a real bummer, but if you leave your NiMH light on and forget it, you will most likely ruin the battery pack. I know. I've done it.

Re: Do NiMH\'s require a deep discharge conditioning?

Hello Dave,

This is a very interesting question.

I have been doing some reading up on NiMh batteries. It seems that (as Jim has mentioned) new cells seem to need about 3 or 4 cycles (from full charge down to 0.9 volts) before they reach their full capacity.

I have also read that smart chargers can have a problem detecting the delta v signal that they use to terminate the charge. This results in overcharging the cells. The general advice is to keep an eye on your batteries for the first few charge cycles. If they become hot, disconnect the charger and let them cool down.

Once the cells are "broken in," I have read varying discussions of how to keep them up. Some people say you are foolish to waste a cycle "re-forming" them, others suggest a discharge down to 0.9 volts every month. I like Jim's suggestion of a cycle every 6 months or so.

On the other hand, if you are regularly using your lights, this may not be a concern at all.

Tom

Re: Do NiMH\'s require a deep discharge conditioning?

Howdy Tom!

Thanks for the post. Nicely said.

I wanted to add to what I said earlier, and mention that the very first charge on a battery pack should be a NON-SMART slow charge--i.e. one that does NOT peak detect. According to what I've read, a peak charger will almost always terminate charge early on brand new cells because they are not all at the exact same state of charge. The break in .1C slow charge for 14-16 hours equalizes all the cells and ensures that they are all at the exact same state of charge.

Re: Do NiMH\'s require a deep discharge conditioning?

JS,

Thanks for your reply, been away from the computer for a few days. More confusion because I have an older set of 1600 NIMH batteries that I thought were deep discharged (a few times). But they still seem to have a lot of life in them. I have to assume they weren't really deep discharged or they can take some deep discharge abuse. When you said leave the light on and you ruin the cell did you mean ruined beyond any future worthwhile use?

Thanks

Steve

Re: Do NiMH\'s require a deep discharge conditioning?

I have a 'smart charger' that looks for the voltage depression that happens when charging an NiMH battery.. not just when it reaches a max voltage.. apparently NiMHs do two things when they reach max charge.. the voltage actually starts coming down and the temp rises.. a computer measureing those accurately can do a fine job of stopping the charge properly.

I have gotten a MEASURED 60+WH out of my 54.6WH battery and that's at approximately 10W draw... (nothing compared to the 200W+ that the drill pulls.. i'm still blown away by that.. like 13A through sub-c cells in series!).

When i use the batts in a drill.. when the voltage gets down to like 1.1V they have no gusto (can't turn the drill when it tries to demand 200W the batt says forget you).. when i use them in my light (more often).. i run them down 'til it turns off.. full drain usually.. down to 1V/cell.. maybe 1.07... 14V on 13Cells.. since i got like 99% of the use of the battery down to 1.1 it really made no sense to me to drain them to .9.. the voltage drops like a rock once below 1.1 (now this is in a case with 13 in series).. maybe it's a little different when using a few.

-awr