Frying bacon sound when shorting power supply?

[help_me_pick_username]

I bought a Gophert CPS3205 power supply. When I short the two output terminals, there is a frying bacon sound coming from the PSU. When I use the connection wires they provided, which were pretty crap since they have a pretty high resistance, the frying sound goes away completely. It's only when I use proper wires.

Since the PSU has current limiting, I was wondering if maybe this sound is happening because the PSU is delivering that current at a very low voltage (5A at only 0.3v when properly shorting(bacon sound), 5A at 6.5v with included low-quality wires(no bacon sound)). Also, the pitch and 'sizzling' of the bacon sound changes as I change the current limit. Could this be why? If so, why does the sound occur?

If not, what could be a likely cause of this sound? ...also, It's not bad to short the PSU, right? Since it has Short Circuit and Overcurrent Protection?

[xavier60]

One of my bench supplies makes a faint hissing or rattling sound under the same conditions because its SG3525 control IC isn't able to reduce the MOSFET's drive pulse width below a certain amount, so randomly skips pulses to get the average duty cycle low enough.
It's this random pulse skipping that causes audible noise from the magnetics.

[T3sl4co1l]

Just generally -- I wouldn't recommend operating at full load current at low voltages.  The switching losses in those stupid things can be fatal.  At low voltages, the switching duty cycle is very low, so that it's basically all switching, and the efficiency is atrocious.

Once had a one of those 100V 10A supplies nuke itself in this way.  They used 50A IGBTs for switching -- terribly oversized for the supply's ratings (overcompensating for their poor design, perhaps?), big gate capacitance.  Yet driven with mere 2SC1815s, far too weak.  Switching speed was about a microsecond...

If the circuit is actually well designed, it should be fine at all conditions.  And yeah, the hiss should just be the control loop struggling with timing limitations at this extreme operating condition -- that's not unusual and not necessarily fatal.  And if it's not well designed, it can possibly be improved, but that will require much inspection (and at which point, you might as well buy a good name brand..?).

Tim

[Zero999]

Yes, the control circuit is struggling with the extremely low duty cycle and high peak currents. The power supply is not designed to be continuously operated with the output shorted. The current limit is there to protect it from damage, rather than a normal operational mode.