Restoring G1 Drive Batterys

[bwilson4web]

Originally Posted by ChapmanF

...
Looking through your picture sequence again, I saw the disappointing result with the heat-sealed stainless tee nut, and wondered whether, as another maintenance-friendly modification idea, it might be worth testing whether you can just drill a hole in the top and tap it, and just directly insert a screw (either stainless or nylon, both easy to get in the hardware store) with a sealing washer. The plastic top looks thick enough ...

It measures 2 mm., pretty thin. However, you're thinking the right way.

Now I've been looking at the 'safety vent' and believe it to be 'too tight.' I would be more interested in a reworked safety vent and that provides a lot more material to work with. But this is tricky stuff.

Bob Wilson

[ChapmanF]

Originally Posted by bwilson4web

I've been looking at the 'safety vent' and believe it to be 'too tight.'

By too tight, do you mean it relieves at too high a pressure? (Out of curiosity, what do the normal range of pressures and the valve's relief pressure seem to be? I've been at a loss to estimate what the pressure must have reached in the overcharged battery you pictured - is that torn steel I see in the lower right corner?)

An M3x0.35 tap (it seems only right to use metrics ) could cut ~5 full threads in 2mm of material, if the material is plastic enough to cleanly cut a thread that fine - I'm not sure what the pullout force would be, but the screw would present only about 7 mm^2 of area to the pressure.

-Chap

[bwilson4web]

Originally Posted by ChapmanF

By too tight, do you mean it relieves at too high a pressure? (Out of curiosity, what do the normal range of pressures and the valve's relief pressure seem to be?

I've pulled a vacuum of 25-28" and it didn't open up. I plan to test it with high pressure but I need to rig up a pressure fitting.

Originally Posted by ChapmanF

... I've been at a loss to estimate what the pressure must have reached in the overcharged battery you pictured - is that torn steel I see in the lower right corner?)

Yes and fairly recent. I've included the photo to try an impress on folks we are playing with powerful forces. I am not one to try and scare folks but make them seriously consider the importance of the right tool for the right job.

Originally Posted by ChapmanF

... An M3x0.35 tap (it seems only right to use metrics ) could cut ~5 full threads in 2mm of material, if the material is plastic enough to cleanly cut a thread that fine - I'm not sure what the pullout force would be, but the screw would present only about 7 mm^2 of area to the pressure.

The problem is threaded hole cut in a flat surface that goes under pressure would tend to 'bow out' and thus increase the diameter of the hole under strain. The stress looks more like a blow-out plug.

One thought is to fabricate a small cylinder with a center, threaded hole. One end of the cylinder would expand in a cone into a thin disk. These cylinders could be rapidly spun and inserted into a beveled hole and friction heating weld the disk to the battery top. When the disk reaches the top of the battery it would brake to a stop and the weld is complete.

The advantage of this approach is a through weld and a threaded cylinder that the pressure would 'force closed.' As the pressure increased the cylinder would more tightly grip the threaded fastener. But this leaves the problem of leakage around the terminals.

My thinking is I need pressure testing not only of the relief valve but also of the terminals at higher temperatures, 40-50C. The pressure relief valve set point needs to be less than the terminal leakage pressure so the KOH solution won't bubble out and eat the copper bus terminals. This is not a trivial problem.

Bob Wilson

ps. The temperature probe hole would be an ideal, threaded cylinder but it is located in the wrong location, a center cell.