Homebrew PRAM Batteries

[Compgeke]

In a similar way, I've just straight up soldered CR2032 holders in place of the originals. Both Keystone #1058 and unknown SMT 2032 holders from Excess Solutions fit fine with the tabs directly over the original through holes. Flood through holes, glue holder in place, heat tabs. Works great. 

 

[Scott Squires]

I designed this thing a couple years ago and was intending to sell them. I ordered 300 custom cable assemblies for it. It's designed so that the original mainboard can be preserved without modifiction, while re-locating the battery somewhere else (I was thinking outside the case). I never settled on a mounting / enclosure mechanism for the battery board. It uses two 3032s and a voltage regulator with very low quiescent current to provide 3.6v.

 

[Hopfenholz]

Some ingenious solutions in this thread

 

[mdeverhart]

I’d originally posted this on another duo thread, but figured it would be better off here
—

Duo PRAM battery fabrication:

I ordered 2x of these from Amazon. They’re 3V lithium rechargeables, with solder tabs to make the job a little easier, and hopefully keep too much heat from the soldering iron from reaching the cells.

https://www.amazon.com/dp/B07W4NWHJ8/

The first image shows the battery I took out of the machine. The red wire is connected to the positive (+) terminal of the top battery, the white wire is connected to the negative (-) terminal of the top battery and the (+) terminal of the bottom battery, and the black wire is connected to the (-) terminal of the bottom battery. I desoldered the wiring harness to reuse for the new battery.

I bent the solder tabs on the new batteries to put the stack together. The (+) terminal of the top battery got bent all the way over, and the (-) terminal got bent flat so that it (just barely) protruded out the side. The (+) terminal on the bottom battery got bent flat to make a long tongue, and the (-) terminal on the bottom battery got bent all the way over. Then, I soldered the (-) terminal on the top battery to the (+) terminal on the bottom battery, and finally resoldered all of the wires, with the white wire connected to the middle “tongue” and the red and black wires connected to their respective terminals. Some heat shrink tubing and Kapton tape finished it off.

Try not to hold the iron on the tabs too long as you’re soldering to them - you want as little heat as possible to get into the cells. Mine is working, but I suspect I was a little slow and may have shortened their life expectancy - but it’s hard to tell.

 

[Andrew]

Hello all,

Do you believe it is ok to use a normal AA battery in the macintosh plus? I heard and verified that it works, even though the factory one is 4,5V.

Do you think there is a downside, other that longevity?

Thanks

 

[TimHD]

I designed this thing a couple years ago and was intending to sell them. I ordered 300 custom cable assemblies for it. It's designed so that the original mainboard can be preserved without modifiction, while re-locating the battery somewhere else (I was thinking outside the case). I never settled on a mounting / enclosure mechanism for the battery board. It uses two 3032s and a voltage regulator with very low quiescent current to provide 3.6v.

View attachment 30842

Are you still progressing with this? I’d certainly be interested in a few of these for my various macs.

 

[Scott Squires]

Are you still progressing with this? I’d certainly be interested in a few of these for my various macs.

Not really. I still don't have a (semi-universal, not involving adhesive) method for attaching the battery outside the case. It could be a free-hanging box I guess, but that's awkward. I'm open to ideas.

 

[ymk]

I wouldn't use a 3xAAA holder with alkalines, though maybe with Eneloops. I've seen far too many alkalines explode, well before their printed expiration date. Some in circuit, some just sitting there in the package. Sometimes I'm around to hear the bang.

For my 1/2AA machines, I replace with a Tadiran and stick a date label on the back of the case.