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View Full Version : OT: Replacing ni-cad cells with ni-mh



Dan Craig
08-31-2006, 01:42 PM
OT, except that the cordless is in the shop...

I have a proprietary cordless for the phone system, which has a ni-cad rechargable battery pack. It has poor talk and standby time.

Can I replace the cells with ni-mh cells or will I run into trouble with the charging circuit?

The ni-cad pack is rated approx. 3.6v 600mAH. My thought was to use 3 AA sized ni-mh cells with a higher mAH value.

can i do this without starting a fire or exploding the cells? Am I barking up the wrong tree?

ptjw7uk
08-31-2006, 01:48 PM
You can use them as long as you recharge them out of the device - as NiMh generate a lot of heat when they charge!!

Peter

Evan
08-31-2006, 02:04 PM
You probably just need a new nicad pack. Look for one with a higher amp hour capacity if possible. Rechargeable batteries don't age gracefully.

Alguy
08-31-2006, 03:04 PM
I did that some 6 years ago for my cordless phone, ni cads were shot so i made my battery pack from 3 nimh, no nimh battery packs were availble when i did it, they lasted till about month ago then i replaced them with an off the shelf pack, i had no problems with mine , but you might want to watch the heat first couple charging cycles, also i noticed mine got better talk and standby time after several charge cycles, my phone is an off the shelf uniden
allen

Dan Craig
08-31-2006, 05:03 PM
Ok, well this looks somewhat promising.

Regarding replacing the battery pack - I just did. This one is only a few weeks old - and while it lasts for a half day if I'm not talking on it - I'd like it to last on standby for most of the day at least and give me more predictable low power indication before the handset turns off.

I'm not sure that a ni-mh pack is made for this phone since the manufacturer discontinued it a while ago due to poor battery and reception - it's a nortel cordless which works with the rest of the phone system. And since the shop is about 5000' sq of mostly open space my reception is good enough. It saves me from running from the farthest corner from any phone every time.

I may see what i can find this weekend and I'll report back with my findings.

Thanks for the responses thus far.

Magicniner
08-31-2006, 08:06 PM
I've replaced pairs of NiCads in my DECT phones with NiMh and had 'em running for a year so far, charging in standard cradles,
Nick.

BillH
08-31-2006, 08:12 PM
Nimhs should have a more sensitive auto peak detecting charging circuit as the fall off is less noticiable than nicad. Nimhs put out less amps than Nicads, because of a slightly higher internal resistance but usually have more capacity.
I hate batteries.

Benta
09-01-2006, 05:07 AM
This just goes to show..... I learned my lesson some years back:

When buying cordless phones or stuff like that, ALWAYS CHECK THE ACCU TYPE!
I ONLY buy equipment that will take standard AA or AAA size cells. The proprietary battery packs cost a fortune when they need to be replaced. And in a pinch, I can put in normal dry batteries until I get round to buying new accus.

Regards,

Benta.

Evan
09-01-2006, 08:58 AM
:D ACCU=accumulator=battery

Magic9r
09-01-2006, 03:25 PM
And there I was thinking a battery was a set or group of accumulators:p

Dan Craig
09-01-2006, 03:39 PM
Yeah, my siemens cordless at home takes a standard AA size ni-mh. Nice and easy to replace when they finally wear out. Which I think I've only done 3 times over the last 7 years.

Evan
09-01-2006, 03:57 PM
The term accumulator isn't used at all in North America anymore to refer to a battery or a single cell. It has vanished from the vocabulary. They are all called batteries regardless of type.

Here it is taken to mean a pressure accumulator in a hydraulic system or the math register in a CPU.