Potted Lisa Batteries?

[CelGen]

I know the purpose of the four cells in the Lisa originally were to keep the settings intact and the date/time correct when power was cut....if for about half a day...but lets say someone is a nitpick and wants the machine complete.

We already know very well that when the batteries go bad they leak. New cells won't be any more of an exception, however what if we pot them? I usually see this done to electronics and batteries when they are going to be used in rough environments or "disposable" products but the major advantage is that while it does keep moisture and dirt out it keeps the contents of a leaking cell in. It's also really easy to do yourself. Make a small box using card paper, place the batteries inside, leave the battery leads sticking out and fill the box with cheap dollar store epoxy.

Has anyone considered this before?

 

[Floofies]

That would certainly contain a leak... unless pressure built up past the epoxy's structural limits. If that happens, you'd essentially be creating a bomb, depending on the type of battery, especially if the epoxy became somewhat brittle. Very specific combinations of materials are used to safely pot batteries commercially, so I'd go with whatever mix they're using. Definitely stay away from "cheap dollar store epoxy".

Thinking about the chemistry of a battery, though, maybe you could also encase it in some sort of fire-neutralizing agent before potting it?

 

[CelGen]

The odds of a chinese Ni-Cd or Ni-MH cell with tabs being that big of a fire hazard after they fail is so minimal I wouldn't even consider that an issue. You make it sound like a leaking AA becomes a bomb in a confined space. Worst case scenario is the pressure on the block causes it to split after what I can only assume is YEARS of leaking.

 

[Floofies]

I swear that every time I read what people write on this forum (with great authority nonetheless), I get dumber.

Floofies, no- just no. There is no risk. This is not a giant gel cell, this is not a LiPo pack.

Is every dallas RTC with a potted battery (they use normal epoxy resin) an explosion risk too? I'm sure you know better than their engineers...

NiCd and NiMh don't vent.

 Hence the line "depending on the type of battery".

 

[snuci]

I have an Amiga 3000T that I replaced the motherboard soldered battery with a coin cell battery.  I soldered a couple of wires on the motherboard and extended the wires to a safe distance.  I then used a coin cell holder and put this in a bag.  It hangs in place so it's nowhere near the motherboard.  It allows you to easily replace the battery or take it out, if you wish.  In other computers, I bought those little plastic boxes that take AAA or AA cells and soldered the wires that protrude from these to the motherboard battery contacts.  Again, this is some ways from the motherboard so if the batteries corrode, it will corrode the contacts in the plastic box and not touch the motherboard.  Here's some pics: http://vintagecomputer.ca/?computers=commodore-amiga-3000t

These options will give you a safe working battery that you can remove when not in use for periods of time with the safety of being safely away from the motherboard in case the batteries do corrode.  I've done this with Dallas RTC chips also (scraping away the plastic until you get to the contacts and cut the existing battery leads).

 

[CelGen]

The issue is that on the Lisa the PCB's all sit above the backplane which itself is a pluggable part of the card cage. There is no place to position the battery where it is easily accessible and doesn't need to be disconnected every time you pull the boards out...OR when the package itself finally fails (you will never get a perfect seal around the wires that exit the block) it won't drip down on something critical.

A potted block is way more practical and elegant. Hell, experiment with the mold and see if you can imprint an Apple logo on the top.

 

[lisa2]

I know the purpose of the four cells in the Lisa originally were to keep the settings intact and the date/time correct when power was cut....if for about half a day...but lets say someone is a nitpick and wants the machine complete.

We already know very well that when the batteries go bad they leak. New cells won't be any more of an exception, however what if we pot them? I usually see this done to electronics and batteries when they are going to be used in rough environments or "disposable" products but the major advantage is that while it does keep moisture and dirt out it keeps the contents of a leaking cell in. It's also really easy to do yourself. Make a small box using card paper, place the batteries inside, leave the battery leads sticking out and fill the box with cheap dollar store epoxy.

Has anyone considered this before?

This makes no sense to me.  If someone was a "nickpick", they would want the batteries to look apple OEM, and they would most certainly not want card paper box full of "cheap dollar store epoxy".   The Lisa batteries function is of very limited use, so worthless in-fact that apple removed them from the design for the second revision of the IO board.

The best thing for a "nickpick" would to have empty battery shells that "look" correct, but serve no electrical function and can not leak damaging the boards.

 

[CelGen]

I dunno. Lets just say a guy didn't like always having to reset the date and time every time he plugged it in.

 

[lisa2]

The Lisa batteries will only retain the time & date for a few hours at most, and the hardware and software only support a 16 year range of starting in the 1980's or 1990's.  

Why would it matter if you had to reset the clock if it's always over 20 years slow?

Even if she did support the current year, what good would it be to turn her off at night, remove the mains power, and then power back up the next day and still have to reset the clock because the battery was only good for a few hours and died over night?  

 

[CelGen]

You are most negative people I've dealt with for a while. I make a proposal, specify a design and purpose and no matter what alternative I brainstorm you shoot it down with "you don't need it anymore".

I'll keep working on this on my own time but no photos and if you want to know how I did it, forget it. You can figure it out.

 

[CC_333]

I think you're idea is fine.

And besides, with newer batteries, it could probably last a bit longer, couldn't it?

c

 

[Floofies]

I actually like your idea, sorry if it came off as negativity.

 

[BadGoldEagle]

I'm actually looking for a Lisa.

And if I get a 2/5 (the one with the hidious battery pack) I would totally remove it and replace it with a potted battery pack! I'm interested.

What are the original battery's specs? I know someone who could make a battery pack if needed.