[sdiy] Cheetah MS800 replacing NiCd Varta Mempac

Tom Wiltshire tom at electricdruid.net
Thu Jun 3 17:25:23 CEST 2021


On the Polysixes I’ve worked on, I always replaced the NiCd with a coincell battery holder. The diode that provides charging just gets removed.

Then you can just stick a new watch battery in it every five/ten/whatever years.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 3 Jun 2021, at 15:29, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> Hi all,
> 
> I'm currently servicing a Cheetah MS800 digital wavetable synth and want to change the old NiCd Varta Mempac to a brand new NiMH Varta Mempac before putting it up for sale.
> 
> The old blue NiCd battery hasn't started to leak yet, and is still holding it's charge but I know that old NiCd Mempacs are regarded as a ticking time-bomb in equipment of this age (>.<)  I wouldn't feel comfortable selling it without addressing this issue first.
> 
> The existing 100mA 3.6V NiCd trickle charges from the 5V supply rail through a 1k resistor when the unit is powered up.  Should I be looking at changing this trickle charge current when changing the battery type to the 150mA 3.6V NiMH replacement?
> 
> I did a search online and found very little solid information about this. Everything from "The NiMH Mempacs are a drop in replacement" to "you need to decrease the trickle charge current because NiMH is less tolerant of being overcharged"  The trickle charge current already seems low to me.
> 
> I would be interested to hear your thoughts!
> 
> -Richie, 
> 
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