Mean Well RT-85A making high pitched noise

[rcboosted]

So I picked up a mean well RT-85A power supply per suggestions from retroRBG. First one would pulse on and off at 1hz, 2nd one turns on, but has a high pitched whine. Come to think of it, the 1st one had the whine during the pulses too. Has anyone noticed this? It's annoying enough that if I can't get rid of the whine, I'll probably get rid of the power supply. It's bad enough first one is DOA, but 2nd one is whining like no tomorrow.

Using a wooden stick as a stethoscope, I found C7 and C29 capacitors are the ones whining. They're on either side of the 2 huge caps in the back of the power supply. Is this another bad unit or this is just how they are? Is there anything I can do about it?

 

[nem]

You do have a load on it, right? If there's not enough load on the rails, it can whine.

 

[rcboosted]

Thank you for the reply. I was hesitant to put a load on it, but I just tested with my load tester. At 0.3A 5V, it stops whining, or 0.2 12V. As soon as load stops, it whines like you said. It's both good and bad news. Maybe I'll put a load resistor on it to keep it from whining when it's on but not in use.

 

[rolins]

Yea you can damage a switching power supply if doesn't have a proper load, especially if you leave it on for several minutes like that. The datasheet on Meanwell RT-85A recommends that CH1 (5V) should have a load > 20% of its rated current which is 8A. So try a 2A load resistor.

 

[rcboosted]

Yea you can damage a switching power supply if doesn't have a proper load, especially if you leave it on for several minutes like that. The datasheet on Meanwell RT-85A recommends that CH1 (5V) should have a load > 20% of its rated current which is 8A. So try a 2A load resistor.

Wow 2A load is needed? I don't think the OSSC or MV1B would even draw that much while in use. I've got a 24V mean well I used for charging batteries, it has been sitting idle with no load for months. You think it can be damaged this way?

 

[rolins]

20% of 8A is actually 1.6A. I just rounded up to 2A.
I personally don't leave my power supplies idle without a proper load. It might still work as-is but you can reduce its lifespan or permanently damage it for sure if you continue to do that.
I don't know what the current draw on a OSSC is but a MV1B should draw more than an 1A. Think that's safe.

 

[rcboosted]

20% of 8A is actually 1.6A. I just rounded up to 2A.
I personally don't leave my power supplies idle without a proper load. It might still work as-is but you can reduce its lifespan or permanently damage it for sure if you continue to do that.
I don't know what the current draw on a OSSC is but a MV1B should draw more than an 1A. Think that's safe.

I use old laptop supplies as well, and I usually don't turned them off or unplugged them when not in use. But I will take your advise, either load it up, or don't leave it on. The first 1 is definitely DOA though, as soon as power was applied without load, it clicked on and off, so that one wasn't even on for long. I just tested it again with a load and it still clicks on and off. Thanks for the advise.