Can a NiMH pack be used in place of NiCAD ?

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videobruce

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I have a Tempo (not the radio name) SLM (Signal Level Meter) that is around 8 years old. It has a 2300aH NiCAD 8 C cell battery pack. I want to replace it with a 5000aH NiMH pack;
http://www.onlybatterypacks.com/showitem.asp?ItemID=11073.10

Is there a problem with the different type of cells and/or the higher current capacity?

One battery outlet said a NiCAD charge circuit uses a pulsed output and a NiMH does not.
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zz0468

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I've used NiMH batteries with niCad with no ill effect. The different battery chemistry creates slightly different charge characteristics, and slightly different voltages when fully charged, but generally, you can use them interchangeably. There ARE chargers optimized for NiMH batteries, but they usually take advantage of battery characteristics to sense when the battery is fully charged, so they switch from a fast charge to a trickle charge automatically.

If you're trickle charging them, you can use the same charger, but you have to increase the time to allow for the higher capacity. If you're fast charging them, you need to be aware of the time required to bring them to a full charge, since an automatic NiCad charger isn't going to be aware of the NiMH batteries needs.
 

videobruce

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The charging is done inside the meter. The specs say 8 hours recharge time. I understand the longer charging times, but I'm concerned about higher current capacity on the charger.

What's this about 'pulsed' charging NiCADS vs MiMH?
 

zz0468

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The pulsed chargers are used for NiMH, and that's for sensing when the battery is fully charged.
 

zz0468

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Yeah, there are some pulsed chargers for nicads. I suppose whether it's needed or not could be one of those endless debates. I think you're concern is going to needlessly over complicate the issue. Just figure out what charge rate your batteries want, and provide it. Neither NiMH batteries nor NiCad batteries have overly complicated charge requirements.

They both like to charge at c/10 (one tenth the capacity), they both like to be discharged to about 1 volt per cell. You can use your existing charger, you'll just need to charge for more than 8 hours if the batteries are of a higher capacity. Rapid charging gets a bit more complicated and risky, but an 8 hour charger is not a rapid charger.

You're doubling the recommended battery capacity. Try doubling the charge time with the existing charger and see how it works for you.
 

slicerwizard

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The charging is done inside the meter. The specs say 8 hours recharge time. I understand the longer charging times, but I'm concerned about higher current capacity on the charger.
It's a non-issue. Just charge them longer if you actually run them all the way down.


What's this about 'pulsed' charging NiCADS vs MiMH?
Another non-issue. NiCd and NiMH couldn't care less if their charging current is pulsed or not.
 
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