Steve N. wrote:
Mike,
I'm confused. The "crowbar" I am familiar with is an over voltage
protection device. If the supply output voltage goes up too high, it
triggers, turns on providing a very lo resistance load and effectively
shorting the output. Thus it initiates the over current protection device,
whatever that is.

If I read this correctly, it appears you are PLACING a short on the supply
and testing the over current protector...

It sounds like "Crowbar" is also used for an over- current protector...

I always thought the term came from using a real 1 inch diameter steel
crowbar (the tipe used in Christmas Story to open the crate containing the
leg lamp) to short the output of a power supply as a really good way to get
to zero volts in a hurry - but only in principle, of course.

73, Steve, K9DCI

You're on the money as to what gets done to save the IOT. It's a lot
more expensive than the entire power supply, and so the PS gets to
suck it up between the time the hydrogen thyratron (or ignitron or
whatever) turns on and the time the overcurrent limiter or magnetic-
controlled breaker on the PS input decides to Turn Things Off Right
Damnit _Now_.

You're also on the money about crowbars being used as overcurrent
protection as well as overvoltage protection.

My experience with crowbars involves both the voltage-foldback flavor
and the current-foldback flavor. Sometimes you'll be running something
at constant current and want to limit the voltage across it; for that,
you fold the curent back to keep from exceeding the max voltage.
Sometimes you'll be running something at constant voltage and want
to limit the current through it; for that, you fold the voltage back
to keep from exceeding the max current. In the extreme case, you cut
the voltage across, or current through, a device off by putting a
short across the PS output. We had some lab PSes at the NASA Manned
Spacecraft Center with adjustable voltage _and_ current limits,
though none with high-capacity crowbars involving ignitrons, hydrogen
thyratrons, and such (to me) exotic devices. But both voltage and
current limits came in very handy.

--
Mike Andrews, W5EGO

Tired old sysadmin