3.6v Phone battery hacked as PRAM battery ?

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MacTrash_1's picture
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Joined: Dec 20 2003
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Has anyone ever tried to use a 3.6v ni-cad battery from a cordless phone as a PRAM battery ? I made my own 4.5v battery for my PPC 5500 out of a 9volt battery(1/2 of the cells) and it works great. My 3.6v phone battery looks about the same and has wires already ! Will it work as a PRAM battery in my G3 ? ?Any thoughts ?

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Krow,

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Joined: Dec 19 2003
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i dont see why it shouldnt ..

i dont see why it shouldnt ...

TOM

G4from128k's picture
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Joined: Dec 20 2003
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Yes, the battery will work.

Yes, the battery will work. But it won't work for more than a few months (unless your "G3" is a powerbook). Most rechargeable batteries (NiCad, NiMH, and Lead-Acid) tend to self-discharge -- they lose a significant fraction of their charge every month even if unused. Its not a problem if you don't mind yanking your homemade PRAM battery every few months for a recharge in the old phone. If your G3 is a powerbook, then I believe it has an internal recharger (most powerbooks use rechargeable PRAM batteries).

If you are feeling adventurous (and know enough about circuits), you could rig a charger using a couple of diodes and resistor that connects the + side of the battery to the +5V of the PSU and recharges the battery. The diodes would help drop the +5 to +3.6, and keep the battery from trying to power the computer when the PSU is off. A resistor (I'm thinking maybe 3 to 30 kOhms depending on the battery size) would regulate the recharge current. But before rigging up a recharger like this, you might need to do a little circuit sleuthing to make sure that cross connecting a low-current low-coltage shunt between the +5 and the battery won't cause major death and distruction. After rigging it, I'd watch the current in the recharge line and the voltage across the battery to ensure that is stays within reasonable limits. Also, NEVER NEVER NEVER attempt to recharge a regular PRAM battery as it will most likely burst and ooze nasty battery guts inside your Mac.

YMMV, "Ideas may appear smarter than they actually are." & Don't blame me if you fry your PSU, logic board or embed flaming battery-bits in the ceiling of your room.

MacTrash_1's picture
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Joined: Dec 20 2003
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Now that you mention it, the

Now that you mention it, the phone does need a constant recharging for the battery to stay fresh. Duh, I didn't think of that.
But I do have a extra phone base with the re-charger in it......
I'll check the output of the charger.

Maybe I'll try it on one of my extra Macs, or better yet a Umax c500.

Krow,

My Apple art at:
http://krowmagnum.4mg.com/index.html

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jt
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Joined: Dec 20 2003
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Search the REAL 'fitter site . . .

. . . for topics started by Trash80toG-4 and you'll see my notion to do exactly the same thing, but more importanty, there's infoposted there by hackmaster bob about how to do the trickle charge circuit you need and another source to compare your bat prices. Try the term "alltex" and you might turn it up quickly.

jt

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applemachome's picture
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Joined: Dec 20 2003
Posts: 132
blown up batteries....

Actually, I dont think batteries will blow up, they just start oozing stuff. You can charge regular batteries for a while, but when they start to get real hot take em out, ive had the experience and it works fine once or twice for about a 10 minute charge.

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