> -----Original Message----- > From: Robert Jarratt [mailto:robert.jarr...@ntlworld.com] > Sent: 19 December 2015 09:56 > To: 'General Discussion: On-Topic and Off-Topic Posts' > Cc: 'cct...@classiccmp.org' > Subject: RE: VAX 4000-500 PSU Overload? > > A bench test of the PSU with a small dummy load saw the PSU appear to > work fine. It might help to load it more to see if it still operates correctly > under load. The specs for the PSU are: > > > 22 amperes at +12.1 Vdc > 60 amperes at +5 Vdc > 7 amperes at +3.4 Vdc > 4 amperes at -12.1 Vdc > > Has anyone got any suggestions for how to create a higher load in a fairly > simple manner? It would take a lot of resistors or vehicle light bulbs to create > some of those loads, and something heftier than a breadboard to connect > them together. > > Thanks >
Actually, I may have just narrowed it down a bit. I connected a 12V DC bulb to the -12 output, in parallel to a 15R resistor, and the PSU shuts down immediately. The 12V bulb has a 21W rating. If my calculations are correct, that means the bulb draws 1.75A. The 15R resistor would draw 0.8A. So a total of 2.5A, which is well under the spec of 4A, but causes the PSU to shutdown. Using the 5W filament of the bulb does not cause the PSU to shut down. Is there a flaw in my calculations, or am I really not overloading the -12V supply? Just to recap I had a 15R resistor and a 12V DC 21W bulb in parallel, on the -12V output. Looks like I have an avenue to explore. Thanks Rob
