Testing PSU "unloaded"

chewie303 · 22 November 2014, 22:05

Not being an expert in electrical engineering I tested the voltages of the pins of my PSU directly with a multimeter....

In hindsight (and after doing some research) I see that this was not a good idea as it is testing in an "unloaded" state

What's the chances I've damaged my PSU?

Cheers

prowler · 22 November 2014, 22:33

Quote:

Originally Posted by chewie303

What's the chances I've damaged my PSU?

None whatsoever, unless you shorted anything with your probes while testing.

chewie303 · 22 November 2014, 23:18

I.e. connecting the ground pin and and a voltage pin with the metal of the same probe? No didn't do that..

Cheers!

Hewitson · 23 November 2014, 05:45

Quote:

Originally Posted by prowler

None whatsoever, unless you shorted anything with your probes while testing.

Actually, if it was a switcher, it could have suffered some damage from being run without a load.

chewie303 · 23 November 2014, 10:18

Quote:

Originally Posted by Hewitson

Actually, if it was a switcher, it could have suffered some damage from being run without a load.

It's a standard lightweight A600 supply, part no 391029-02. I tested the pins in turn, one probe always on ground, the other on each other pin in turn.....?

Shadowfire · 23 November 2014, 16:38

In the early days of switched PSU design, it was in fact entirely possible to damage the PSU by running it without a load.

This hasn't been the case for decades for anything that isn't designed in China. The zero-load case will be accommodated by something in the design.

chewie303 · 23 November 2014, 17:28

Thanks for the info

It seems to be working OK, only had the probes on each pin for less than 10 seconds each.... A valuable lesson learned anyway, will use a car bulb as load in future as per info from other threads on the same topic, as I understand now that you won't actually get an accurate read without some load.

daxb · 23 November 2014, 18:22

While measuring the multimeter is the consumer and if the load is enough for the PSU all should be ok. If this is wrong, please correct me.

chewie303 · 23 November 2014, 22:18

Quote:

Originally Posted by daxb

While measuring the multimeter is the consumer and if the load is enough for the PSU all should be ok. If this is wrong, please correct me.

Good info on this thread:-
http://eab.abime.net/showthread.php?p=748490

Hewitson · 24 November 2014, 07:53

Quote:

Originally Posted by daxb

While measuring the multimeter is the consumer and if the load is enough for the PSU all should be ok. If this is wrong, please correct me.

A multimeter has a huge resistance (usually 10 Megaohms). If it had a low enough resistance to act as a load then the measurements would be inaccurate.

Daedalus · 24 November 2014, 16:25

I'm sure your PSU is fine. When the PSU can be disconnected from its load by the customer (as is the case with the 500, 600 & 1200), it would be crazy to use a design that could be damaged by turning it on without the computer attached! I'm sure Commodore (or their supplier) incorporated some sort of protection into their switching PSUs or there wouldn't be so many of them still around today.

22 November 2014, 22:05	#1
chewie303 Registered User Join Date: Nov 2014 Location: Glasgow Posts: 15	Testing PSU "unloaded" Not being an expert in electrical engineering I tested the voltages of the pins of my PSU directly with a multimeter.... In hindsight (and after doing some research) I see that this was not a good idea as it is testing in an "unloaded" state What's the chances I've damaged my PSU? Cheers

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22 November 2014, 23:18	#3
chewie303 Registered User Join Date: Nov 2014 Location: Glasgow Posts: 15	I.e. connecting the ground pin and and a voltage pin with the metal of the same probe? No didn't do that.. Cheers!

23 November 2014, 16:38	#6
Shadowfire Registered User Join Date: Aug 2001 Location: Connecticut USA Posts: 617	In the early days of switched PSU design, it was in fact entirely possible to damage the PSU by running it without a load. This hasn't been the case for decades for anything that isn't designed in China. The zero-load case will be accommodated by something in the design.

23 November 2014, 17:28	#7
chewie303 Registered User Join Date: Nov 2014 Location: Glasgow Posts: 15	Thanks for the info It seems to be working OK, only had the probes on each pin for less than 10 seconds each.... A valuable lesson learned anyway, will use a car bulb as load in future as per info from other threads on the same topic, as I understand now that you won't actually get an accurate read without some load.

23 November 2014, 18:22	#8
daxb Registered User Join Date: Oct 2009 Location: Germany Posts: 3,307	While measuring the multimeter is the consumer and if the load is enough for the PSU all should be ok. If this is wrong, please correct me.

24 November 2014, 16:25	#11
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,374	I'm sure your PSU is fine. When the PSU can be disconnected from its load by the customer (as is the case with the 500, 600 & 1200), it would be crazy to use a design that could be damaged by turning it on without the computer attached! I'm sure Commodore (or their supplier) incorporated some sort of protection into their switching PSUs or there wouldn't be so many of them still around today.

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