hbj@uafhcx.uucp (Bernard Johnson) (07/15/90)
I recently bought a NCR PC-6 power supply to power some hobby projects. When I received the supply, I measured the outputs. The +12V line measured +4.95V and the +5V line measured +4.8V. I have been told that the +12V line will not be +12V until a load is connected to the supply. I was told that the scheme was somewhat like the IBM 'goodline', whatever that is. If this is so, what is reason for this and what kind of load should be connected? Posting is fine but I would prefer email. If there is enough interest I will summarize. Bernard Johnson hbj@uafhcx.uark.edu
v105l4lg@ubvmsd.cc.buffalo.edu (collie) (07/16/90)
In article <4924@uafhp.uark.edu>, hbj@uafhcx.uucp (Bernard Johnson) writes... > >I recently bought a NCR PC-6 power supply to power some hobby projects. When I >received the supply, I measured the outputs. The +12V line measured +4.95V >and the +5V line measured +4.8V. I have been told that the +12V line will not >be +12V until a load is connected to the supply. I was told that the scheme >was somewhat like the IBM 'goodline', whatever that is. If this is so, what is >reason for this and what kind of load should be connected? >Posting is fine but I would prefer email. If there is enough interest I will >summarize. *************** I don't know about that NCR PC-6 supply,but I do know that the IBM power supply gives the expected voltage without a load being apply,if my memory serves me right.So in that case,I would assume that maybe something is wrong with that NCR job you have. ******************************************************************************* collie ******************************************************************************* x Under durest !!
larry@kitty.UUCP (Larry Lippman) (07/16/90)
> >I recently bought NCR PC-6 power supply to power some hobby projects. When I > >received the supply, I measured the outputs. The +12V line measured +4.95V > >and +5V line measured +4.8V. I have been told that the +12V line will not > >be +12V until a load is connected to the supply. I was told that the scheme > >was somewhat like the IBM 'goodline', whatever that is. > > I don't know about that NCR PC-6 supply,but I do know that the IBM > power supply gives the expected voltage without a load being apply,if my > memory serves me right.So in that case,I would assume that maybe something > is wrong with that NCR job you have. I have no specific knowledge of the NCR PC-6 power supply, but I would like to point out something that I have seen on other computer power supplies which *could* be your problem. Some well-designed power supplies provide an external sense lead which is connected to a terminal on the PC-board backplane. This will automatically compensate for any IR drop between the supply and the backplane. If your power supply has a multi-pin connector whose pin functions are not explicitly labeled or otherwise known, it may be that one or more pins are for sense purposes. Failing to connect a voltage sense lead to the power output lead will result in an incorrect voltage with lack of regulation (usually, but not always a *lower* voltage). Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry
geoff@actrix.co.nz (Geoff McCaughan) (07/17/90)
In article <4924@uafhp.uark.edu> hbj@uafhcx.uucp (Bernard Johnson) writes: > >I recently bought a NCR PC-6 power supply to power some hobby projects. When I >received the supply, I measured the outputs. The +12V line measured +4.95V >and the +5V line measured +4.8V. I have been told that the +12V line will not >be +12V until a load is connected to the supply. I was told that the scheme Sounds like you have a normal SwitchMode PSU. Normally these need a minimum load in order for the regulation circuitry to operate, many have overload and underload protection. I once had an SMPSU (from an I*M peecee as it happens) I was using to power a Hard Disk. It would spin the drive up, but once the initial load dropped off it would underload and switch itself off. Adding another drive fixed that problem. -- ------------------------------------------------------------------------------- Geoff McCaughan Email: geoff@actrix.co.nz Phone: +64 3 539545 or 852101 Amiga/Hardware/Unix/Quantum Mechanics Hacker Phax : +64 3 539567 "Anarchy: Think of it as evolution in action." ^ NEW ZEALAND!
rpw3@rigden.wpd.sgi.com (Rob Warnock) (07/18/90)
In article <3852@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: +--------------- | Some well-designed power supplies provide an external sense lead | which is connected to a terminal on the PC-board backplane. This will | automatically compensate for any IR drop between the supply and the | backplane. If your power supply has a multi-pin connector whose pin | functions are not explicitly labeled or otherwise known, it may be that | one or more pins are for sense purposes. | | Failing to connect a voltage sense lead to the power output lead | will result in an incorrect voltage with lack of regulation (usually, but | not always a *lower* voltage). +--------------- And even *more*-well-designed supplies contain internal resistors between the sense leads and the outputs to keep the output from wandering far afield if the sense leads get disconnected. The internal resistor is usually a lot larger than the resistance of the sense wire but small enough to give good regulation if the sense wire is broken/missing. (A typical value is ~20 ohm.) -Rob ----- Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311
karn@envy.bellcore.com (Phil R. Karn) (08/01/90)
In article <4924@uafhp.uark.edu>, hbj@uafhcx.uucp (Bernard Johnson) writes: > I have been told that the +12V line will not > be +12V until a load is connected to the supply. Some multi-voltage switching supplies regulate only the 5V output. If there is no 5V load, the switcher will cut back to a very low duty cycle, and this may not be enough to sustain the 12V output (especially if there is a load there). Try putting a load on the 5V output and see if that affects the 12V output. Phil