Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again

Peter Coghlan cctalk at
Mon Oct 26 10:41:50 CDT 2015

> OK, so a couple years back, I wanted to have some chemistry fun with the kids.
> So, I got out the jump cables, clamped them onto some aluminum foil, stuffed
> the foil into test tubes, filled the tubes with water, inverted both of them
> in the same basin and sprinkled in a little salt, cranked up the car, and
> sure enough … bubbles started evolving off the foil and collecting in the
> test tubes. 
> Just as expected, one tube was filling with gas twice as fast as the other. 
> Just as expected, when we held that tube over a candle, it went “WHEEP” and
> got hot (the flame was barely visible). 
> Um… the OP had a 12V supply, right? How *do* you keep from electrolyzing
> your coolant in this apparatus.

Firstly, don't add salt.

Secondly, the low resistance dummy load is going to soak up almost all of the
current, leaving very little to go through the much higher resistance water
resulting in very little gas production.

If the minute amount of gas produced is still a problem, you could electrically
insulate the dummy load from the water.  However, this may also help to
thermally insulate from the water it which is not what you want.

> PS. this is a cool experiment but suitable cautions apply. The most subtle
> is: not too much salt, lest you start evolving chlorine gas instead of
> hydrogen. Flammable to explosive gasses, 12V sparks, etc. etc… be careful
> if you try to replicate this.

Also, beware of the danger of shorting the jump cables together, either
directly or via worn jewellery etc causing a large bang, melted terminals etc
and possible damage to kids, self and car.  Consider using something like a
current limited bench power supply instead.

Peter Coglan.

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