Button cell holder

[Theo Markettos]

I'm looking to replace some furry NiCd memory backup batteries with a silver oxide primary button cell and a diode. The silver oxide cells are designed for low drain applications and in 10 years time shouldn't die as messily as the NiCds do.

The NiCd cells are vertically PCB mounted, so I'd like to try to fit the buttons in their place. But I can't seem to find any button cell holders... there are plenty of lithium coin cell holders (eg CR1220, CR2032) but these are much too big for button cells like SR41, SR44 etc. I could possibly bodge one of these (pad it out somehow) but that won't be mechanically too stable. There are also clips which provide the positive electrode and are designed to hold a button cell to negative-electrode-sized pad on a PCB - but I don't have a PCB pad to attach one to.

So can anyone suggest any holders that I might use? Really all I need is a suitably bent piece of metal with an insulating gap between each side, but the problem is to get sufficient mechanical stability (so if it's dropped, the battery doesn't pop out). Anyone have any ideas of how I might do this?

Thanks Theo

[Tabby]

IIRC Rapid electronics has a range of button cell holders

NT

[Theo Markettos]

Forgot to mention that one type is horizontally mounted, and quite space-constrained (I have about 8-9mm diameter by 5mm height to play with, so I'm looking at something like an SR41 cell). It might be possible to make a land area for a negative electrode, but there's nothing to solder a positive electrode to that'll give mechanical stability.

Theo

[Frank Erskine]

Don't forget to ensure that the silver oxide cells aren't 'charged' like the NiCds.

[Theo Markettos]

Coin cell, but not button cell. This is the only button cell holder they do:

that needs a PCB land area to match it, which I don't have. I could make one out of copperclad, I suppose (I don't have etching facilities). Thickness and weight of the PCB might be an issue too. (Anyone sell very thin copperclad?)

Theo

[Theo Markettos]

Hence the diode :) If I select the right one I can also drop the voltage from 1.5V to 1.2V (though the chip being powered doesn't mind anyway). Theo

[Dave]

> and that needs a PCB land area to match it, which I don't have. I could

You can buy it as thin as tinfoil, but I can't help with sourcing it, sorry.

Dave

[Man at B&Q]

Buy a watch from the pound shop and butcher it for the battery holder. You even get a free battery :-)

MBQ

[Theo Markettos]

Hmm... not a bad idea. There's plenty of pound shop gadgets that use button cells.

And I get free electrolyte leakage all over my PCB in a few years too ;-)

Theo

[Dave Osborne]

[Terry Casey]

Use the clips you've already found. Drill two holes in the pcb either side of the negative land area (or remove copper from around the holes as needed) then solder a wire to the positive clip.

For the vertical holder, take a piece of insulating material (scrap pcb, Formica, etc..) and two clips. bore four holes - i.e.. two holes at right angles to the other two. Bastardise one clip as required for the negative terminal (cut off short support legs and some of the circular area for isolation from the positive) and fit the other as designed for the positive. Solder wires to the fixing tabs and connect as required.

If you have a suitable place on the pcb, mount it by soldering on of the long negative tabs in place of the original holder.

As you've got 30 clips to start with, it doesn't matter if you make a mess of it first time ...

[Theo Markettos]

Ouch. Not on an 8-layer laptop PCB! This one is really space-constrained, and mechanically very fragile (there's no other mounting than two small PCB traces for the original NiCd and possibly some glue, but I can't glue in the button cell). I'll have to think about it some more. Possibly a glued-in base+clip might work, if I can find something thin yet rigid (and non-metallic). Then copper screening tape for the connections.

That's roughly what I was thinking of (and those have a lot more space to play with).

I took a punt on a 'Signalex Personal Alarm' Poundland special, which takes three LR44s. But it turns out they're in a stack with AA-style springs at each end, so that doesn't help me. But I have some crummy LR44s now. Hope I have time to blink before they leak :)

Theo