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I have a bunch of adjustable DC power supplies which I need to adjust to 5 VDC output, but I suspect that when I just test it with multimeter it won't show correct voltage. Would would be a simple way to test it under load? Put some kind of resistor between power supply output and multimeter?
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I have a bunch of adjustable DC power supplies which I need to adjust to 5 VDC output, but I suspect that when I just test it with multimeter it won't show correct voltage. Would would be a simple way to test it under load? Put some kind of resistor between power supply output and multimeter?

If it's regulated supply (aka. switching) then it shouldn't make any difference.

PS: You could always try one and see ... that's how we learn! smiley

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I have a bunch of adjustable DC power supplies which I need to adjust to 5 VDC output, but I suspect that when I just test it with multimeter it won't show correct voltage. Would would be a simple way to test it under load? Put some kind of resistor between power supply output and multimeter?

 Measuring the power supply under a 'dummy load' is a good idea. It doesn't have to draw the maximum current rating of the supply to still be a valid test. What type of load is best/easiest to use depends on the maximum current rating of the supply. Be sure if you do use a fixed resistor that it's wattage rating is well above the wattage it will consume.

Lefty
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I have a bunch of 10W 5 and 10 ohm cement resistors for this purpose.
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Put some kind of resistor between power supply output and multimeter?

That sounds like you're thinking in series?- I think parallel is the correct way, ie the load is across the power supply and you in turn measure the voltage across the connections. I'm no expert, but that makes more sense to me....
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Put some kind of resistor between power supply output and multimeter?

That sounds like you're thinking in series?- I think parallel is the correct way, ie the load is across the power supply and you in turn measure the voltage across the connections. I'm no expert, but that makes more sense to me....

Yes one measures voltage in parallel with the power supply output terminals and one measures current in series with the load.

Lefty
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Yes one measures voltage in parallel with the power supply output terminals and one measures current in series with the load.

I'm bored so I drew a pic of that  smiley-cool


* VA.jpg (9.61 KB, 454x272 - viewed 19 times.)
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Yes one measures voltage in parallel with the power supply output terminals and one measures current in series with the load.

I'm bored so I drew a pic of that  smiley-cool
Thank you, that's actually what I was looking for! smiley
If it's regulated supply (aka. switching) then it shouldn't make any difference.

PS: You could always try one and see ... that's how we learn! smiley

Yes it's switching DC to DC based on LM2596. I'm getting different output voltage depending on the input voltage (i.e. at 5 V in I'm getting 4.8V, and at 12 V I could be getting 5.5V). I read it it could be because I'm measuring without a load, thus my original question smiley
Not sure what you mean by "try one and see".
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That's common with switching supplies.  They often have good regulation under various loads, but under no-load conditions, they'll be a bit unpredictable.  The output filter (converts pulses into smooth DC voltage) needs a resistive element to complete the filter.  It shouldn't take much to start coming together.
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I often use simple car lamps as test loads since you can then see the actual load in operation.
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That's common with switching supplies.  They often have good regulation under various loads, but under no-load conditions, they'll be a bit unpredictable.  The output filter (converts pulses into smooth DC voltage) needs a resistive element to complete the filter.  It shouldn't take much to start coming together.
Thanks! I measured it under load (actually wired to finished project), and it's strange but I'm not getting above 4.5V output when I'm using 5V input supply. No matter how far I adjusted it. Is it expected?  It's rated for 4-35V, but maybe I'm hoping for too much here smiley It has no problem giving 5V out with 6VDC and higher supply...
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Thanks! I measured it under load (actually wired to finished project), and it's strange but I'm not getting above 4.5V output when I'm using 5V input supply. No matter how far I adjusted it. Is it expected?  It's rated for 4-35V, but maybe I'm hoping for too much here smiley It has no problem giving 5V out with 6VDC and higher supply...

So it's a voltage booster...?

If you want good answers you could start out by saying what you're doing/using. So far everybody has assumed a switch-mode power supply with an adjustment screw.

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For some reason I thought it was a booster, I guess not..
Here it is:
http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/370772814758
I use it to power my custom ATMega644P board that also has RTC, WaveShield and 32x16 LED matrix display...
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For some reason I thought it was a booster, I guess not..

"Buck" means it can only reduce the voltage.

I'm not getting above 4.5V output when I'm using 5V input supply

Problem solved...

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For some reason I thought it was a booster, I guess not..
Here it is:
http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/370772814758
I use it to power my custom ATMega644P board that also has RTC, WaveShield and 32x16 LED matrix display...

Your hint should have been the "Step Down" in the product title.

Lefty
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