Exploding PRAM batteries...

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volvo242gt's picture
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Joined: Nov 9 2004
Posts: 25

On the 68kmla forums, there is a thread about exploding Maxell PRAM batteries. Well, it can happen to other brands as well. Was dealing with an SE/30 that wouldn't boot, instead showing garbage on the screen. Finally, after three tries, I shut it down, and opened the case. Noticed the usual crud from a leaking capacitor on the underside of the board. Flipped the board over and was greeted with this:

Please, do yourselves a favor, and replace the batteries if they're 10 years old or older, or if you don't know when you last replaced it Even if it works at the moment.

-J

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2407
Re: Exploding PRAM batteries...

Hello volvo242gt,
the advice is really good..... just to explain additionaly the technical background:
after the litium battery has dropped down below so called "low discharge" and if the electrolytic capacitor started leaking in the capacitors a shortcut is caused and positiv electricity passes the shortcut up to the negativ pol of the battery and this results with a leaking/exploding battery...... this happens each time when the negativ pol of the battery gets in contact with a electrical load that is more positiv than at the plus pol.... and because the plus pol of the battery is blocked by a Diode which disables electricity to flow towards the plus pol that condition is fullfilled.... the Diode only permits electricity to flow from battery to mainboard but not vice versa ( in that direction the diode blocks ... )....
sincerely speedyG

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volvo242gt's picture
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Joined: Nov 9 2004
Posts: 25
Re: Exploding PRAM batteries...

Interesting... Makes sense.

-J

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current: //e, IIgs, ///, Mac Plus 4/0, SE 4/230, IIsi 17/250, IIci 4/500, IIfx 32/1G, Centris 650 48/1.2G/CD, B&W G3 upgraded to G4 proc 2G/30G/DVD-RW, G4 DA 1G/80G/DVD-RW.