I have a computer with three power inputs: "-48vdc", "return", and "chassis ground".
The 48vdc power supply which I got with it (and which the former owner said he used with it) has three wires coming out, two from positive and one from negative.
So what goes where?
i think "chassis ground" would probably be the negitive ... that leaves the other two as positive ...
Yeah, but I'd think "return" would be, too, and I really don't want to wire this up wrong...
I'm going to differ here. The computer is expecting one negative (-48VDC) and two relatively positive (the return and case ground) inputs. The grounds are positive in a relative sense, positive with respect to the -48 VDC that the supply puts out. Thus, the negative output of the supply (-48) goes to the negative input of the computer and the two positives are the return and case ground. You can probably tell which is which by looking inside the supply - case ground will clip to the case and return will go straight into the board in the supply.
Do be careful, though, that you have the right supply (you probably do given that the former owner used it). That "48 VDC" power supply must be a -48 VDC, not a +48VDC supply.
I finally got in touch with the previous owner and you're entirely right. Thanks!
What kind of comptuer is this? It sounds very unusual, maybe an old cp/m machine perhaps? Inquiring minds want to know.
i would expect to see a page on AF about it very soon
I'd be willing to bet a plug nickel it's something rack mounted, possibly quite recent. That 48V+/- power supply arrangement isn't uncommon.
(Cisco and Sun sell networking equipment and servers with the same power requirements.)