Dummy Load

[Shadow Lord]

A quick question: once you start a PSU using a dummy load will the PSU stay on if you disconnect the dummy load? I am wondering if there would be any point in putting a fuse inline in case of too much current draw. Thanks.

 

[Hugo Holden]

It might or it might not stay on.

With the current drain from the dummy load, this tends to store some energy in the the filter inductors and cause a small voltage drop from the smps transformer supplying it, even though the duty cycle of the drive voltage to the primary of the smps main transformer is increased to allow for that via negative feedback.

So what could happen, possibly, with the dummy load "suddenly disconnected" there could be a positive going voltage transient that might possibly shut down the supply (be detected as an over voltage error).

But it would depend on the design of the particular supply.

I would think though, once the supply was started and stable, if you removed the dummy load, say if it was in small increments, from a number of load resistors disconnected one by one, then probably you could get away with it and have the supply sitting there running with no load.

 

[whartung]

What do you use for a dummy load?

 

[Shadow Lord]

I would think though, once the supply was started and stable, if you removed the dummy load, say if it was in small increments, from a number of load resistors disconnected one by one, then probably you could get away with it and have the supply sitting there running with no load.

Well I was thinking more of taking the load off all at once (i.e. if a fuse blows and load is cut off). In my very scient... errr experiment with an n of 1 once the PSU was turned on disconnecting the load did not shut off the PSU. This is in a generic AT class PSU.

What do you use for a dummy load?

I am using a nonworking Seagate ST-225 but you could use anything you want. IBM used to specify a 50W 5ohm resistor for their dummy loads and other members on this board use automotive light bulbs.

 

[tipc]

Consumer power supplies are alleged to be more forgiving, but I was of the understanding that power supplies can be damaged w/o sufficient load. I for one am not going down that road.

 

[maxtherabbit]

Consumer power supplies are alleged to be more forgiving, but I was of the understanding that power supplies can be damaged w/o sufficient load. I for one am not going down that road.

they may not start or regulate properly, but I've never heard of one being actually damaged by a lack of load

 

[Agent Orange]

Save yourself some time without all the fuss and just grab an old mobo and an old HD or floppy and go from there.

 

[tipc]

that approach won't work for me as I want to test a replacement p/s I just received, one that's rated for 800 watts. Not looking to torture test it, but would like to run it for 24 hours drawing 400-600. The first one they sent was as dead as a door knob. These units are known for turning up dead. But allegedly are good runners if you can get them started ... so therefore, well not sure what I'm going to do just yet.

I'm planning a new build, one which might make this endeavor easier. The designated setup has 2 redundant 1600 watt supplies. Now I doubt I would even need half that, as I'm not building a server per se, But it's a hog. But I'm not ready to take the plunge just yet.

 

[Agent Orange]

Just curious as to why you insist on cut rate stuff when for a few more bucks you can get a good nights' sleep? I can understand that with peripherals it's more or less a crap shoot, but the P/S is the heart of the build.

 

[modem7]

What do you use for a dummy load?

I am using a nonworking Seagate ST-225 but you could use anything you want. IBM used to specify a 50W 5ohm resistor for their dummy loads and other members on this board use automotive light bulbs.

I have seen that '50W 5ohm resistor' specified at [here], but not specified elsewhere.

A 5Ω/50W resistor is going to be unsuitable for some power supplies. For example, putting one on the +12V line of the IBM 5150's stock power supply will result in 2.4 amps (12V ÷ 5Ω) being drawn. Per [here], 2.4 amps exceeds the rating of that power supply's +12V line.

There a 'quirky' power supplies such as the stock one fitted within an IBM 5155. See [here]. I doubt that a Seagate ST-225 alone will allow that supply to start.

 

[tipc]

Just curious as to why you insist on cut rate stuff when for a few more bucks you can get a good nights' sleep? I can understand that with peripherals it's more or less a crap shoot, but the P/S is the heart of the build.

I don't insist. All my other units are reputable brands. Nothing I'll be using this with is expensive whatsoever. No significant harm will occur. I have it in a box w/a 40$ motherboard and a celeron. So who cares. But I won't buy another Raidmax again. But I would have needed to spend nearly double for a reputable 800 watt supply for the record.

 

[Agent Orange]

I don't insist. All my other units are reputable brands. Nothing I'll be using this with is expensive whatsoever. No significant harm will occur. I have it in a box w/a 40$ motherboard and a celeron. So who cares. But I won't buy another Raidmax again. But I would have needed to spend nearly double for a reputable 800 watt supply for the record.

Okay. BTW - how are the kittens?

 

[tipc]

Kweeg, Deets, Zoe, and Nanna (sounds like Ghana not banana) are doing well. Their mom takes the liberty of cuffing them about the head and shoulders every chance she gets. She holds them in complete contempt, which is normal behavior once they've come of age. She's really harmless though. You wouldn't think so if you had seen her chase a 16 pound Norwegian Forest cat behind the sofa about 8 moons ago, him screaming for his life. He clears the block of every other cat that dared trod his territory. She just may have been an unknown back then. No more. Him and Heidi showed her they weren't to be trifled with. They reluctantly tolerate each other these days.