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



"Mike Andrews" wrote in message
...
Hmmmm ...

Bobbie Barmore was discussing IOT power supplies and their crowbars on
the GowBugs list a few months back. Seems that the test to see if the
crowbar's good is pretty simple:

1) Turn everything off
2) Safety tag and padlock all the breakers and the START switch
3) Ground everything that even might think about biting
4) Put a piece of (?) 32-gauge wire between HV and ground.
5) Pull the shorting sticks, button everything up, unlock and
untag the breakers, untag the START switch
6) Make sure everyone's clear and safe
7) Push the START switch

The power supply's good for something like 700 mA at 35 KVDC, and it is
a _really_ bad idea to get across it if you might pass less than abount
700 mA. But the wire's good for more than 700 mA, and so will look like a
short to the PS.

If the wire melts, vaporizes, or explodes, then the crowbar circuit is
bad.
It should be unaffected by the test. Put 35 KV across a piece of 32ga wire
without blowing it up.

Hydrogen thyratrons to dump the power, and fast-acting circuit breakers to
Shut Things Down NOW, appear to be the way to protect the wire from the
PS.
Fascinating technology.

Homebrew _that_.

--
Mike Andrews, W5EGO

Tired old sysadmin