Mod 4AA NiMH charger for 3AA?

[walkabout]

Hi all, need your wisdom. Couldn't find this with Search.

I use a lot of headlights with 3AA NiMHs.

I'd like to modify one of my 12VDC NiMH chargers (charges 2AA or 4AA) to charge 3AA.

This will let me burn up a bunch of old Energizer 2500s that will take a charge but self-discharge in a couple of days. Might as well get my money's worth.

I'm thinking about soldering a high-wattage resistor across the fourth battery slot to complete the circuit and perhaps slow down the charge cycle a little.

Will this work? Is there anything that will come back to bite me? Thoughts and recommendations appreciated.

Thanks!

 

[Mr Happy]

This isn't something that's going to work. It's best to get a charger with four independent charging slots. All your batteries will be better for it even when charged in sets of 2 or 4.

 

[TakeTheActive]

...Couldn't find this with Search...

...I'd like to modify one of my 12VDC NiMH chargers (charges 2AA or 4AA) to charge 3AA...

...I'm thinking about soldering a high-wattage resistor across the fourth battery slot to complete the circuit and perhaps slow down the charge cycle a little.

Will this work?

Please read this thread from ~10 days ago: will this hurt charger or battery?

 

[walkabout]

Okay, thanks, it was a long shot. Doesn't really solve the problem, but seriously I do appreciate the feedback.

Again, I'm restricted to 12VDC in this situation, and I want to use up the old Energizer 2500s I have kicking around. Otherwise they go in the recycle bin. (If you look at threads about 4 years back, you'll get the full comment on these junkers.)

I'll stick with the duct-tape solution I'm using already: keeping the highest-self-discharge cell as the "dummy" in the 4-cell charger.

Thanks anyway.

 

[45/70]

Yeah, not a good idea. Most chargers that require cells to be charged in pairs (1 channel 2x cells, or 2 channel, 2x cells + 2x cells), are series chargers. If you simply short (or resistor) out one slot, the charger will try to charge the remaining cell of the pair to 2.8 Volts or so. Even if the charger is smart, or semi smart, it'll be looking for a ~2.8 Volt delta V instead of a ~1.4 Volt delta V, for example.

Dave

 

[qwertyydude]

Maybe it's better to then just use 2 sets of 3 lsd cells. That way when you kill one set you put in the other set. When you kill both sets you charge 4 of them up to full then charge the remaining two.

 

[Marduke]

Plenty of 4-channel smart chargers will work on 12VDC power supplies.

A better idea of your needs would help recommendations.

 

[walkabout]

After doing further reading on this site, I purchased a Duracell Mobile Charger CEF23DX4N (includes 12VDC adapter). Seemed at bit pricey at $30 CAD, but if it's kind to my batteries it will pay for itself.

I had no idea it was an individual channel charger. I would have bought one years ago. Why the heck don't they say that on the packaging?

Thanks CPFers for the replies and information.

 

[Marduke]

It doesn't spell it out because the average consumer has no idea what independant channels means or why it is important. Too many technical details will make a consumer avoid a product.

You can however infer it's independant channel by looking at the detailed specs on the back, or the seperate datasheet online.

 

[walkabout]

I see your point. Note that the packaging on this side of the border has no tech specs whatsoever.

I'm not convinced that saying "Charges 1, 2, 3, or 4 cells" and "protects batteries from overcharging" is too technical at all. It justifies spending the extra money.

Anyway, I hope this charger works out. It's ticking away right now, feeding off my 12VDC PV panel/battery setup. If all goes well, I may need a spare for the cabin.

 

[Hondo]

Good choice. Glad you were able to still find one, they have been discontinued.

 

[walkabout]

If they're discontinued, I'd better pick up a spare right away.

Completed my first charge cycle. Looks very good. Batteries barely warm at the end. Unlike the other chargers I have.

 

[TakeTheActive]

...I'll stick with the duct-tape solution I'm using already: keeping the highest-self-discharge cell as the "dummy" in the 4-cell charger...

Were you ever discharging this cell in one of your devices?

If not, then you're (possibly / probably) overcharging the daylights out of this cell.

SERIES chargers work best with closely-matched cells. Otherwise, with 2 cells per channel as an example, one cell gets overcharged and/or one cell gets undercharged.

 

[TakeTheActive]

After doing further reading on this site, I purchased a Duracell Mobile Charger CEF23DX4N (includes 12VDC adapter)...

Same decision as generallobster, the OP of the thread that I referred you to. :thumbsup: Based on the positive comments I've read here (and the good price AND the fact that it's been discontinued), I bought 2 for myself. It should serve you well.

...Seemed at bit pricey at $30 CAD, but if it's kind to my batteries it will pay for itself...

One of the CPF members recently posted a 'good price' (~$16 US) at Drugstore.Com when using a FatWallet code. Do a SEARCH. Does Drugstore.Com ship to Canada?

...I had no idea it was an individual channel charger. I would have bought one years ago...

Probably the ad writers didn't think it was as important as the info they did include. AND, on my version (also CEF23DX4N), everything is written twice - once in English and once in French.

...Why the heck don't they say that on the packaging?

I've been gathering info on chargers that I see positive feedback on in: TTA's NiMH/NiCD Battery Charger Specifications Thread.

 

[walkabout]

Were you ever discharging this cell in one of your devices?

If not, then you're (possibly / probably) overcharging the daylights out of this cell.

Two of the eight cells I bought 4? years ago developed a very rapid self-discharge all on their own. Though it could be argued that the junk charger they shipped with was to blame; seems likely. Anyway, they drop a substantial amount of their charge in 24-36 hours, so they became the "dummy/toaster" in my junk charger. I wasn't discharging the other three cells past 1.2 volts, so it probably wasn't much of an issue.

But yeah, I get your point. Water under the bridge, and lessons learned.

EDIT:
I've charged half my fleet with the Duracell unit, and I think it's going to suit me fine. I'll search around for a super deal on a spare, but in my experience when shipping etc. is tacked on it's rarely a deal. I'll grab one locally tonight (and keep the receipt just in case I'm lucky).

 

[Hondo]

Also, some of the best closeout deals on the Mobile charger are the "short" kit with only the charger and two LSD AA's. You got the deluxe one with the DC 12V adapter and I assume two AAA's as well. I paid $25 + tax for my full kit.

 

[walkabout]

Thanks, Hondo. Makes me feel better. Yes, mine had the extra AAAs and the cig. lighter plug. So with the 5% difference in our currencies (plus exchange fees), I'm paying nearly the same.

I generally buy for the long term, so I don't mind paying for quality up front. (I'm the guy who buys clearance business laptops instead of the latest bells-and-whistles consumer POS. Why? Five years later, the biz unit is still cranking and the consumer thing is at the recyclers.)

Thanks again, CPFers. This site is a great resource.