EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: rthorntn on February 15, 2023, 04:48:05 am
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Hi all,
I have a Meanwell RT-125A here, it's never been used, I connected it up with no load and I get a flashing green light, I think this PSU needs some amps on the 5V so this may be the problem.
But it got me checking things, so I bust out my U1272A put it on Ω and hit Shift, if I put one probe on common and the other on +5V I get a tiny beep and the display reads 45, it happens to a lesser extent on -5V but the display quickly goes to 0.
I read that this could just be "Most linear supplies will show a short for a few seconds until the caps charge up from the probe's bias current. That is normal" [gearspace.com] but now I'm worried and I didn't think this Meanwell was linear (although I think I can see a transformer inside there)?
Thanks.
Richard
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Unless it shows a dead short, a continuity reading on the output of a power supply is meaningless. (You'd be checking it when it's unplugged/off)
Better to put some sort of a small resistive load on it, power it on, and measure the voltage across the load. Aim for a current draw of around 10% of it's rated output for a quick test. (not super critical)
Doesn't look like that power supply has a minimum load requirement according to this datasheet. (https://www.mouser.ca/datasheet/2/260/RT_125_SPEC-1292053.pdf)
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I put my re:load on it, set to 2A and it worked fine!
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I have a Meanwell RT-125A here, it's never been used, I connected it up with no load and I get a flashing green light, I think this PSU needs some amps on the 5V so this may be the problem.
According to the datasheet, there is a minimum load requirement of 15% of the rated output current for CH1 (5V @ 12A) which translates to:
15% of 12A = 1.8A. 2A > 1.8A.
I think that the reason the LED flashes is because of the minimum duty cycle capability of the PWM controller; I don't think it's low enough to regulate without a load connected to the output.