PRAM Battery 'relocator' prototype

[3pcedev]

Hi all,

I've managed to be quite lucky over the years in that I haven't had a PRAM battery leak inside my Macintosh computers. Despite this it has always been in the back of my mind as I have had several PC motherboards which have been damaged or destroyed due to leaky batteries.

Like most people I don't always get to regularly maintain my fleet of vintage computers, hence I thought it would be good to relocate the battery away from the logic board. This isn't a new idea and usually involves soldering flying leads to the battery socket and then taping the battery to some location inside the case. I was about to do the same but I didn't like the idea of ruining the originality of the boards, plus I thought I might have to go back to the 'battery on the board' at some point.

The result is the following 'PRAM relocator'. The battery is replaced by a 3d printed battery substitute (ABS plastic) with copper contacts on each end. Flying leads are then attached to the contacts which are connected to a CR2032 button cell holder. The CR2032 holder is a common PC board mounted unit, so I have also 3d printed a 'cap' which goes over the pins on the base. This keeps the wiring tidy and also gives a nice flat surface to attach some tape/velcro.

I went with a CR2032 as they are a) cheap and plentiful, b) not as leak prone as the lithium thionyl chloride batteries and c) compact. Since they only have about 1/4 to 1/3rd the capacity of a regular PRAM battery they won't last as long, but in my estimate it should last about 3yrs. The best part about the design is that it is not locked into using the CR2032 - I can just as easily install a 1/2AA battery holder and use a regular PRAM battery.

I have now installed these into two Macintosh Classics and a Quadra 605. Both are working great so far!

The main reason for posting is not just to share my idea but to gauge if there is any interest for making a limited run of them. They are printed and hand assembled by myself so don't expect a concourse fit and finish; but they do the job quite well. I would be able to offer a few different options - for example CR2032 holder, 1/2AA holder, no holder (i.e. solder it up yourself), different lead lengths etc. Total cost would be about $10USD plus postage to wherever you live.

Pictures are below - let me know if you have any suggestions or comments etc.

 

[glitch]

In the past, I used a piece of wood dowel with tacks in the ends. Works great, low tech, doesn't cost much. If you use brass tacks you can even solder the wires on.

 

[Chuck(G)]

I tried a CR2032 on a Mac Performa and found that it didn't really work. The standard PRAM battery is 3.6V, whereas a CR2032 is 3.0. I couldn't get the Performa to power on with the 2032.

 

[3pcedev]

I tried a CR2032 on a Mac Performa and found that it didn't really work. The standard PRAM battery is 3.6V, whereas a CR2032 is 3.0. I couldn't get the Performa to power on with the 2032.

Yeah I'm actually surprised it worked with my Classic/Quadra @3V. I actually bought a heap of 1/2AA holders just in case it didn't work. IIRC my cousin had a performa which was a really tricky unit; I remember something along the lines of if the PRAM battery was even slightly flat it wouldn't power up.

In reality a fully charged 2032 is about 3.3V - so maybe I am just living on the edge at the moment.

Time will tell as to how long it holds up though.....

 

[RWallmow]

I've had a CR2032 in my SE/30 for a few years now, but those aren't as demanding as some Macs, it's pretty much just keeping the clock set. I too mounted it remotely, but I just soldered some wire to the underside of the board at the battery holder location and ran it up near the hard drive, still have to take the back off, but I don't need to pull the board out to access it.

 

[Al Kossow]

The standard PRAM battery is 3.6V

You should also measure the current draw. I would think a 2032 would go flat pretty quickly, especially in any Mac that uses the 68HC05 for that function.
Battery life improved a lot when we switched to a lower power part.

Also, the Mac 3.6v batteries are Lithium. PCs used NiCds which leak.

 

[glitch]

Also, the Mac 3.6v batteries are Lithium. PCs used NiCds which leak.

Mac batteries will leak too, just cleaned up a SE/30 motherboard with damage from a leaking lithium cell. As 3pcedev said, they're lithium thionyl chloride, which does use a non-solid electrolyte. They are *much* less likely to ruin a board than a NiCd barrel battery. They're also available in hermetically sealed packages that will definitely not leak on your boards. These are common on some of the industrial stuff I work on, especially VersaLogic boards:

They're expensive (I think I usually pay around $15/ea qty 1) but don't leak, even in some of the harsh environments that industrial embedded stuff faces.

 

[Chuck(G)]

I don't do much Mac work, but I'm a bit curious what the high-end tolerance for the PRAM supply is. I wouldn't mind using 3 x AA external alkaline cells, for example. They'll last a good long time and can be removed if long-term storage is anticipated.

Anyone know for certain?

 

[njroadfan]

Folks with ROM 01 Apple IIgs machines, which came with a soldered on 3.6v cell, just clip the battery off and use a 3xAA holder with leads. The higher voltage doesn't seem to be a problem, otherwise one could use rechargeable batteries which have a lower rated voltage.

 

[RWallmow]

Folks with ROM 01 Apple IIgs machines, which came with a soldered on 3.6v cell, just clip the battery off and use a 3xAA holder with leads. The higher voltage doesn't seem to be a problem, otherwise one could use rechargeable batteries which have a lower rated voltage.

I did a 2xAA holder in mine and it's been coping with the lower voltage just fine for years now. MOST clock chips have a fairly wide voltage range they will run on. My IIgs had 1V reading on the cell when I picked it up, and it was STILL keeping time/settings.

Some of the Mac's are less tolerant though, they are doing more than just clock/settings with that battery, some use it to provide power-on signal to the rest of the machine, those would be the one's where I would be more concerned with voltages.

 

[Unknown_K]

I think all 3 of my IIgs systems still have the original battery connected and working so it is not used for more then keeping time when they are not plugged into main power. Other macs actually use the battery to start the system up so they use quite a bit of power for an instant and a coin battery is not going to provide that. Mac II's are the worst as the battery that is used to jump start the system always goes bad before the other one.

 

[njroadfan]

Yeah, somehow the Varta cell in my ROM 01 IIgs is still keeping time and holding the PRAM settings for nearly 30 years! Macs can be a pain with the batteries going flat. Who thought it was a great idea to require the battery to boot the machine up, particularly the ones that don't have soft power like the PM6100. You have to "double tap" the power switch on one of those to get them to boot with a flat/missing battery.