AA NiMH cells...

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LinkOfHyrule
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AA NiMH cells...

Alright, here's the deal:

I decided to start on a little project (by started I mean I have a motor and sprocket and decided to use them). I've decided to use everyday AA NiMH cells.

Yes, I'm aware that they are a little small and therefore not generally well suited for this type of application. But, they are cheap and, more importantly, thin. I'll let you guess why that's important until it's done ;). Actually, I would have gone with AAA if it wouldn't be hell to wire them up (not to mention they would cost way more per watt hour).

The problem is this: I'm having serious problems choosing a brand. There's like a google (excuse the pun) of them! I have no idea which ones are of sufficient quality. The only ones I've ever used personally are Duracell and Energizer. I can't really attest to the quality of those since I've never tested them in a particularly scientific manner. All I've used them for is my MP3 player (AAA) and my Wii and Gamecube remotes (AA). Those are very low drain anyway.

The cheapest I can seem to find are from All-Battery. They say they're 2600 mAh but I know they're really about 1500 mAh. I've also heard Ansmann batteries are supposed to be good, but they're more expensive.

I'm hunting for pretty much anything in the 2000 to 2700 mAh range.

Oh, also I'm gonna need, like, 200 of them :).

HCT
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Re: AA NiMH cells...

I also been using AA cells for the past couple years , the Sanyo Ni-MH 2500 .Purchased several hundreds and found them to be within 2200 to 2500 mah at almost the 1C rate (2000 mah)discharge .
They also have the lowest internal impedance 16 millions to 30 milliohns , the other brand are all over the range from 900 mah to 1800mah and with ridiculous impedance 40 milliohms and up to over 100 milliohms .
Assuming that you are looking to drawn any power out of the pack ,I highly recommend that you focus on low Impedance as well as high capacity .I will alway take low impedance over high capacity .
What good is high capacity cells if you cannot take it quickly ,and if you push them ,it just dissipated power in the cell.
The Sanyo are not the lowest price cells ,but very cost effective.
No I am not affiliated in any way with Sanyo , just a 63 years guy that has been working with batteries for over 45 years.Be glad to answer any question .

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

LinkOfHyrule
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Re: AA NiMH cells...

Yeah, I knew about the impedance thing, forgot to mention it. D'oh! Thanks for reminding me.

Where did you get yours from? I'm not particularly concerned about the cost (to a point), but I don't want to spend more than I have to (who does?).

I have to ask, though: How are you charging them? Are you just charging the individual parallel packs as if they were one battery? I heard that was a problem because of the negative delta at the end of their charge cycle. Overcharges the good batteries or something. String charging (eek! balancing hell!)?

As it was, my intention was to have them wired up 20 in series and around 10 in parallel (haven't decided on an exact number) in connection to the motor. For charging I was going to hook them all up to a mezzanine connector and charge them individually with a bunch of those everyday smart chargers you can find all over the place. You know, the ones that charge 8-10 batteries at once? I went with this because there is NO WAY I'm putting a BMS in a 200+ cell pack, and this would solve most of the balancing problems.

Any thoughts?

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

HCT
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Re: AA NiMH cells...

What power level are you trying to obtain and what voltage ?
WOuld not recommend either charging or dischargin cells is parallel , especialy the Ni-Mh . as far as charging goes , they do not like to be slow charged . best C/2 or even C rate , with careful review of voltage and temperature rise of each cells.
If you are serious about building a high power level pack using AA then you must have a BMS for all the cells .
It is the only way to get the reliability .not cheap , but cheaper on the long run than replacing cells or whole batteries pack .

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

LinkOfHyrule
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Re: AA NiMH cells...

Trying to run a Kollmorgen (24V 400W).

It would seem you found a way to make me put a BMS on the thing...

This is becoming a PITA. The things I'll do to have a cool-looking pack. Oh, well. Good thing I'm so patient. Guess I'll have to do some research on balacing chips and the like. Unless someone can tell me where to get such a monster of a balancer. Anyone able to give me some leads on some good electronics?

Nice to hear they like to be fast charged. More convenient for me.

Anyway, care to explain exactly why they don't like to be discharged in parallel? Don't be afraid to get technical :).

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

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