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Thread: Using NiMH in devices designed for NiCd?

  1. #1

    Default Using NiMH in devices designed for NiCd?

    Good afternoon all,

    I'm playing with a pile of "vintage" (read: old and cheap) test equipment that I got a while back trying to see what works and what doesn't. Specifically a Simpson 460 bench VOM, a BK Precision 820 capacitance meter, and a Fluke something or other bench VOM. All use NiCD C or D cells and I was told they won't work properly on AC without the cells installed. Sure enough the Simpson was acting weird but I stole the NiMHs out of the Mag-Lite that sits by the front door (it has some old Maha Imedion AAs in it with D cell adapters) and it settled right down.

    Now it looks like I can find NiCD D cells (Amazon sells Tenergy made ones) but my AAs in adapters actually have more capacity (5000 for the NiCd, let's say at 2100mAh three AAs would be 6300, or a purpose made D cell NiMH is 10,000 these days). I CAN'T seem to find C size NiCd cells with button tops at all.

    Is it really bad to use NiMH instead? I'm sure when the meters are plugged in it just floats the cells at 5.something volts/4 cells. I'm well stocked on NiMH.

    Unfortunately, only the Simpson came with cells in it and they were well and truly toast. Had to do the Deoxit treatment on the battery holder.

    Thanks for any advice.

  2. #2

    Default Re: Using NiMH in devices designed for NiCd?

    Quote Originally Posted by N8N View Post
    Good afternoon all,

    I'm playing with a pile of "vintage" (read: old and cheap) test equipment that I got a while back trying to see what works and what doesn't. Specifically a Simpson 460 bench VOM, a BK Precision 820 capacitance meter, and a Fluke something or other bench VOM. All use NiCD C or D cells and I was told they won't work properly on AC without the cells installed. Sure enough the Simpson was acting weird but I stole the NiMHs out of the Mag-Lite that sits by the front door (it has some old Maha Imedion AAs in it with D cell adapters) and it settled right down.

    Now it looks like I can find NiCD D cells (Amazon sells Tenergy made ones) but my AAs in adapters actually have more capacity (5000 for the NiCd, let's say at 2100mAh three AAs would be 6300, or a purpose made D cell NiMH is 10,000 these days). I CAN'T seem to find C size NiCd cells with button tops at all.

    Is it really bad to use NiMH instead? I'm sure when the meters are plugged in it just floats the cells at 5.something volts/4 cells. I'm well stocked on NiMH.

    Unfortunately, only the Simpson came with cells in it and they were well and truly toast. Had to do the Deoxit treatment on the battery holder.

    Thanks for any advice.
    As far as I know, in every application where NiCd cells are used, NiMH cells are an equivalent modern replacement. Old nicads were problematic as they aged, which is why NiMH became so popular. They also, as you observed, have a higher capacity.

  3. #3

    Default Re: Using NiMH in devices designed for NiCd?

    Nimh can replace Nicd in all but a few instances such as trickle charging and very hi current draw devices.
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  4. #4
    Flashaholic* fivemega's Avatar
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    Default Re: Using NiMH in devices designed for NiCd?

    Other problem is:
    1- Charger of NiCad is normally charging at 1/10 C for 14~16 hours (after complete discharge) and user must stop overcharging.
    NiMH of similar size, has much higher capacity so charging at same rate will not fully recharge the cells at 14~16 hours.
    2- NiMH cells unlike NiCad don't like overcharge so better use smart charger. I am not saying that NiCads like to be overcharged but they are more robust against overcharge.

  5. #5
    Flashaholic* turbodog's Avatar
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    Default Re: Using NiMH in devices designed for NiCd?

    You should be fine. Just make sure the cells don't get above slightly warm if your devices charge them during usage.
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