6 Jun
2009
6 Jun
'09
12:08 p.m.
On 6 Jun 2009 at 18:17, Tony Duell wrote:
Yes, fuses are very useful for protecting things like transformers and
wiring harnesses. On the other hand, expensive power semiconductors are
useful for protecting fuses ;-)
Reminds me of the time smoke poured out of a 3rd
party (Plessey IIRC)
Unibus expanison box. It was clearly coming from the PSU area and I
thought I could see something glowing orange inside. Turns out (after
takign the PSU apart) that a bridge recifier had shorted and the
orange glow was the wires linking that to the transformer -- all the
insulation had burnt off and they were more than red hot. Replaced the
rectifier and thw wires, no problems...
That UPS I wrote about a couple of days ago turned out to have a
similar problem that should have resulted in magic smoke, but a
thoughtful engineer saved me from that. The charging circuit is pretty crude by modern
standards--an LM317K
TO3 regulator on a large (4"x6") heatsink with a 50W zener and a
What's tyhe 50W zener for, given you have a regualtor chip?
thermostatic switch. It could probably benefit with
some upgrading
to a "smarter" circuit.
This UPS has been in continuous service since 1989.
Well, if it's been working for 20 years with no problems, I am not sure any
'upgrade' is going to be that beneficial :-)
-tony