Here's a little bit more on recycling nicads at home in your spare time.
Whatever the percentage of flake KOH to distilled - or reverse osmosis filtered with a de-ionizing cartridge chaser - water, the goal is to reach a specific gravity of 1.19 to 1.22 at 60 deg. F. The higher s.g. is for very cold weather, the lower - normal - for greater cycle life. Patterson's article in HP #15 covers this and more.
Here are some nominal figures for S.G @ Deg. F:
1.182 90
1.185 80
1.187 70
1.190 60
1.192 50
About 0.01 of S.G decrease per 4 deg.F temp. increase. Another "Gotcha" is the state of charge and the electrolyte level in the cell; check out the HP article.
Chevron utility oil 22 can be hard to find in less than 55 gal. drum lots. Y'r local friendly distributor can tell you what they can come up with. The critical factor here is that the oil is what's called a "Wax Free" oil. The likeliest source I've found so far is an old fashioned (?) meat locker refrigeration plant, they use the wax free oil as lube for their compressors, and get their oil in five gallon pails, sometimes. Talk to the guy who maintains the machinery, may be willing to part with a gallon or so for $20; good to bring your own container. The "22" designation refers to the viscosity, and I wasn't able to find that, but did get a heavier viscosity of utility oil "68". It seems to be working. . . .
The oil layer should be 1/8 inch to 3/16 inch thick; about 4 millimeters.
On calibrating the hydrometer, I can't find my notes; they were just a bunch of arithmetic anyway, and if you google sodium chloride and specific gravity you should come up with the same stuff I did. Since I was aiming for 1.20 for my S.G. and the salt trick, as I vaguely remember gave me a figure of 1.2004 to calibrate to, it was a pretty good fit, but check it out for yourself.
Hope this helps, take care,
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