[vcf-midatlantic] A little electronics hack

David Gesswein djg at pdp8online.com
Mon Sep 30 08:43:25 EDT 2019


> >> It's called a 'crowbar' circuit.  Prevents things from burning up.
> 

What I normally called a crowbar circuit is the overvoltage protection
where it intentionally shorts the output of the power supply. This sounds
more like over current protection.

> What are common reasons why those stop working? Neville and I didn't see
> any obvious signs of damage to it.
> 
Either component value shift or failed component. You indicated that it is
driving the motors better than it ever has. It may also be your motors
are a heavier load than it was intended to drive.

If you're interested in investigating further if you point us to schematics
we can give suggestions.


> On Sun, Sep 29, 2019, 1:56 PM Mike Loewen <mloewen at cpumagic.scol.pa.us>
> wrote:
> 
> > On Sun, 29 Sep 2019, Evan Koblentz via vcf-midatlantic wrote:
> >
> > > Neville noticed something that I wouldn't have. The circuitry contains a
> > > safety mechanism to shut off all power if the current jumps too high,
> > such
> > > as a kid inserting a paper clip. There's probably a technical name for
> > that
> > > but I do not know it. Anyway, for unknown reasons this circuit was
> > kicking
> > > in! He jumped it with an equal-length wire. :)
> >
> >     It's called a 'crowbar' circuit.  Prevents things from burning up.
> >
> >
> > Mike Loewen                             mloewen at cpumagic.scol.pa.us
> > Old Technology                          http://q7.neurotica.com/Oldtech/
> >


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