N cell Nicads

[Demetri]

Is it possible to charge Nicad N cell batteries in a charger meant for AA's, if I build a spacer? Safely? I've Googled for it, but keep coming up with references to people building their own charger. I'm having trouble getting led's to work(though I did finally figure it out, and am currently building LED auto bulbs to my specs), I don't want to tackle a charger. Thanks everyone.

Demetri

[Andrew]

First, ask yourself this, are n cells 1.2 volts?

If they are not the answer is very simple. NO.

If they are, depends on the charger. Nicads heat up when they are charged. This is usually the thing that tells the charger that the battery is charged. If your charger is like this, keep in mind that it might overcharge your battery. Some also detect end of charge by a slight voltage/current drop. This is very noticable on nicads, but a problem with nimh.

-Andrew

[Demetri]

Yes Andrew, the Nicad's are 1.2 volts, that did seem like a prerequisite. The charger has no sensors of any type, it's plug the batteries in and leave it until you think they're charged, then pull them out. Very simple. The Nicad's I am looking at are 150 mAH; I'm not sure what the rate of charge for my charger is, I'll check it with my multi meter later today. I haven't bought the Nicad's yet, no point in doing so if I can't charge them. They'll be used in an LED flashlight I bought, a Coast Cutlery V2 Powerchip. With new batteries, the light from this flashlight is easily in excess of most 2 or 3 D cell flashlights, and will blow a Mini Maglite out of the water quite easily. However, brightness does not come without a price, and the N cells do not last anywhere near the advertised 100 hour length. At 2 bucks per N cell, if I can't get rechargeables to work, then this flashlight will be going in the glove box and used only infrequently. I go through Maglite batteries almost every night, and bulbs every three or four nights, but at least they are rechargeable. Being able to get away from bulb changes would be great. Thank you all.

Demetri

P.S. I've talked to other people using this flashlight, they say 1.2 volts from the batteries instead of 1.5 won't make any difference, the regulator circuit takes care of it. Anyone know if these lights are Luxeon star or what?

[Andrew]

Well, I would say go for it.

The charge rate should be about c/10 which means that it might be a little to high for your batteries. Limit your current with a resistor. 1/8 or bigger watt resistor will be fine. good current limit assuming your current output is near 200ma, (assuming aa to c cells) put a 40-60 ohm resistor in series with your batteries. This gives a nice good trickle charge that wont overcharge your batteries.

Also, why not try a solar charger, they are really forgiving.

-Andrew

[Demetri]

Ooh, yeah, a solar charger........hmmmm. I hadn't thought of that. I really like that idea. Extremely elegant. A flashlight will do me no good in an extended blackout if I can't charge the batteries, nor have a source for new ones. I am definitely going to check into that. Thanks for the great info Andrew; sorry if I was a tad short with you in my reply.

Demetri

[Andrew]

Errr sure....

Were you being sarcastic?

Try the resistor idea, and let me know how it works.

-Andrew

[Demetri]

No, I wasn't being sarcastic. Just sounded that way to me when I re-read it after it had been posted. Oh well, if you don't have a problem with what I said, then I don't.

Demetri

[Andrew]

It's all good.

If you have a millammeter, you might try and hook it in series with the charger. Just keep the current under 100 ma. This is where solar cells are nice because if your batteries pull more than the panel can offer, the panel will simply drop in voltage. It's the ultimate in current controlled power.

-Andrew

[Demetri]

I found rechargeable N cells at Radio Shack, and adapters so that they can be charged in a AA charger. Five bucks each for the Nicads(I bought six), and three bucks for four adapters. I'm pleased.

Demetri

[jimu]

Demetri

Sure you can use an aa charger to charge N cells!.. N cells or just under the size of c cells, and I do it all the time..Most of the cheapo AA chargers are in the order of 50 ma  charge current, and will charge any 1.2 volt nicad, being it a AA, N, C, D etc.

Of course the larger the cell, the longer it may take.

I keep hearing references to these "Forgiving" solar chargers..Well, Im afraid that if I put my 300 watt PV system on a nicad (its a solar charger ;-> ), it would pop it in seconds..

 and to the reference of using resistors to limit current, this is not really a good idea, since once the voltage will continue to increase once the nicad ( or NiMh ) has reached it nominal charge voltage.

the easiest and simplist way to control the charge of a nicad is "voltage based" control, meaning that you would limit the voltage to the nicad at say 1.45 volts, and then the current would taper down to near nothing, and keep the nicad from overcharging.

"Current based" chargers I would shy away from, since they tend to keep the current constant, and allow the voltage to rise.

now, you really cant go wrong with with any charger that limits the current to about 50 ma., and can charge pretty much all day long.. I have built a few "smart" chargers that

fast charge at a hi ma rate, then taper down as it senses the voltage approaching nominal.

Some of the battery packs in my handheld ham eq. use a thermistor, that feedbacks temp data to the charger, and regulates the current based on the temp of the battery packs..

This is used in some of these "2 hour" quick chargers.

Anyway, have fun!

JimU

[Demetri]

Thanks Jim! My charger was pretty inexpensive, so I'll be I'm ok as far as charging current. I'll have to wait until I have a full load of batteries to charge before I measure current, as my charger won't charge any less than a full load. Thanks for the info!

Demetri