VAX 4000-500 PSU Overload?

[Dave Wade]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Robert
> Jarratt
> Sent: 19 December 2015 17:20
> To: 'General Discussion: On-Topic and Off-Topic Posts'
> <cctalk at classiccmp.org>
> Subject: RE: VAX 4000-500 PSU Overload?
> 
> 
> 
> > -----Original Message-----
> > From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Mouse
> > Sent: 19 December 2015 16:09
> > To: cctalk at classiccmp.org
> > Subject: Re: VAX 4000-500 PSU Overload?
> >
> > > But getting something in series to measure load is going to be
> > > really awkward, [...]
> >
> > As in, you don't have any such thing to put in series, or you don't
> > see a
> good
> > way to get it in series?  I've got a couple of 0R1 resistors which
> > work
> nicely for
> > that in conjunction with a voltmeter that can handle millivolt
> measurements;
> > you might be able to get something similar.  Mine are 10W, and, while
> > they are designed for bolting to a heatsink, they can probably handle
> > at least
> 2 or 3
> > watts, which means some 5-6 amps, in free air.  (Though that then
> > drops about half a volt, which can be a problem when you can't put it
> > on the
> input
> > side of the
> > regulation.)
> >
> 
> I think the suggestion was to put an ammeter between the PSU and the
> backplane. That would be awkward to make all the connections with the PSU
> out of the machine. Also difficult is to make a dummy load for a bench
test
> that draws enough current to test that it can sustain its rated output at
full
> load (or some decent proportion of full load at any rate).
> 
> Regards
> 
> Rob

Rob,

Seeing as it already seems to have over current sensing, I guess it has some
small resistors in there so perhaps it is possible to measure the current. I
notices one looks like this:-

http://uk.farnell.com/welwyn/oar1-r020fi/resistor-1-0r020/dp/1200359

Dave