Voltage from PSU decreasing as more load is added?

Cheers for the help all - I guess the PSU dying was the likely cause here (hopefully nothing I did 😁)
 
I'd say at least 3 years now? Potentially older as we had a break between doing Christmas lights recently...
 
Here is a link to its datasheet.

SE-600-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com

This particular supply happens to be one that shuts down on overload and over-voltage and needs re-powered to recover. Meanwell's datasheet doesn't show the remote sense terminals. The sense terminals are on a small header off to the side of the V+/V- terminals. The datasheet is also rather vague about how to connect the remote sense terminals. Which unsurprisingly is nothing very unusual as I have a Meanwell HRP-300 with remote sense and its datasheet is not very clear either.

Remote sense terminals used improperly can easily lead to supply damage but if these have not been used or anything connected to them that likely is not the situation here. However, if the voltage adjust potentiometer has been moved, there is the possibility that upon power on the supply may be going over voltage and promptly shutting back down. According to the datasheet such a scenario is not supposed to happen, but it would be something to check presently.
Be that as it may, the SE-600-XX supply should function properly without anything connected to the remote sense terminals. Some supplys require sense terminals to be connected either to local sense terminals or the appropiate V+/V- terminals. The HRP supply I have doesn't require that and I suspect the SE supply does not either.

Other than that, perhaps an internal fuse. At this point however, whatever testing is done I'd suggest nothing hanging off the output terminals.
 
Check also you don't have a short somewhere in your strings
 
aplant92 said:
Ah that's good to know! Thanks for looking into it - I was trying a few more things this morning and now the PSU seems completely dead...wondering if that's perhaps not entirely expected given the way it was behaving beforehand.

Seems I'm in the market for a new PSU!
Click to expand...
The fact that your voltage was dropping and then the whole unit died the next day tells me that there was some kind of overload. Every power supply has its limits and they should never be exceeded as this is a major fire hazard.
You should open the unit and see if the circuitry shows any spots where it has become very hot. Usually the overheated components will leave a dark brown discolouration on the circuit board.
There's also a very distinctive burning smell emitted by fried electronics. If you can smell that, it means something inside the PSU has started to burn due to an excessive buildup of heat which is usually only caused by an overloaded circuit.
In extreme cases, you may see smoke, hear zapping sounds or have a breaker trip depending on how severe the fault is.
If this happens, I'd recommend unplugging the PSU, cutting the supply cord and discarding the faulty unit, ideally by taking it to an E-Waste recycling centre instead of throwing it in the bin as E-Waste is banned from landfill in most states.
Hopefully this helps out with what may have happened. This info is from my electrical knowledge that I've gained through personal experience and online sources.
 
Lots of SMPS units simply die from running hot and slowly cooking the capacitors. Sometimes you'll see diodes go shorted or resistors go high in value. Most modern, good quality SMPS handle overloads pretty well, shutting down to save themselves.
 
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