CMOS batteries

[PhilipA]

A lighter note from me today. Franken-battery!


20130808_120934 by renault9gta, on Flickr

Took the battery apart in my Compaq Portable 386. These Eagle-Picher batteries are expensive! Bought a pair of 3.0V CR123A batteries for $3.75 off Amazon and hacked this together. Needed a bit of modification because the CR123A is a bit larger in diameter, and the "pip" is positive, not negative, like on the the original but the output is now behind the original protection resistor and diode.

NB the diode in the circuit is actually a transistor, hooked up to pass only as a single diod. I'm guessing that was cheaper than a bona-fide single-purpose diode.

--Phil

 

[PhilipA]

Now installed, buttoned up and remembering the time and hard drive settings.

No more booting up the setup floppy if I leave it switched off more than 3 minutes!

Powered off, 2.8V at the terminals. Seems happy enough with that.

--Phil

 

[Chuck(G)]

Diodes are very cheap--you can buy them by the 100 for a few dollars. If you want to realize a bit more voltage from that battery, you may want to try a Schottky rectifier (also not expensive).

 

[mdx]

I replace the original battery with an AA battery holder and a 3.6V 2400mAh TEKCELL Licium battery. To use the original wires, I decided to open up the little black box and by chance found the resistor and diode/transistor. Are they really necessary? Does the mainboard try to charge the battery otherwise?
Anyway, I kept those parts and things work fine for me now. Well, except for unrelated PSU trouble... (different thread)

 

[PhilipA]

I think there's the possibility of the motherboard charging the battery, hence the diode. Resistor is probably just in case of accidental short-circuit, that it won't discharge too quickly and cause the cell to heat up.

I figured that was good enough- it was done on a budget- two of those batteries for $3.75 and they're available at any store that sells guns and ammo. That's why it's not as tidy as it could be, but it's operational

--Phil