Paul
I'm always a little wary of this scheme since using it myself a while ago
and not getting the results I expected. I would call it a limiter not a
crowbar.
I'm guessing these supplies have a relatively high (compared to conventional
linear regulator) output resistance and when I've done this with other
supplies it doesn't actually blow the fuse. I'm sure it would still protect
your rig, but simply act as a peak limiter using the fuse and holder and
output resistance to pull the output below the clamping level. Don't know
what fuse you are using: say it's an ordinary "fast" blow 20A, then you will
need >40A for 30s to blow it by which time the transient has long gone. The
clamping voltage also depends on the current drawn and could be as high as
21.2V according to the spec. I would have to draw a load line to find out
how that would perform with the supply but that would be only static
conditions.
David
G3UNA
I'm a bit leery of the over-voltage protection circuits built into these
small supplies. I added a Vishay 1.5KE15A 15-volt transient suppressor,
reverse-based across the DC output (Mouser P/N 625-1.5KE15A). The diode
is in parallel with the DC output terminals but a series fuse is inserted
just ahead of the diode. This is essentially a zener crowbar device that
upon reaching 15 VDC will conduct and blow the DC fuse before any damage
is done to the rig (or one hopes!)
>
Paul, W9AC
.
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