OWON SPE 6103 Blowing Fuses Roasted Diode

[clearchris]

Most bench power supplies have design shortcomings that can cause damage to themselves or the gear you are powering.
But I don't know your specific PSU. If you have the schematic, you can look for the protection parts, or if the marketing blurb says "it can charge batteries" then there is a chance it's OK.

Batteries
Most PSU's have a reverse-polarity diode which makes sparks or smokes and shorts, if you connect a battery backwards. Or it could be what happened to yours, rectifiers cooked beyond what the PSU could do to them.

I definitely didn't connect it backwards, 100% sure of that. I have color coded plugs on all my wires. Because I'd totally hook them up backwards otherwise.

The Backfeed problem
If the PSU is off, or set to a low output voltage, or there is a power outage - and you've connected a battery, the battery discharges back into the PSU and can damage semiconductors in it.
I think about half the bench PSU's I repair have no coverage for this. There are pics of one linear PSU that totally burned up and caught fire - because there is no fuse involved at all on the low voltage/battery side.
PSU designers only think current is coming out of the power supply, never back in.

Mine probably has no coverage for this, but I have turned if off before with the battery connected, I just haven't connected the battery with it turned off. Adding a fuse to the output would be pretty easy, would you suggest doing so? If so, both sides or just one?

The Turn Off
Set your PSU to a nice 5V say, then power it off (or a mains power failure happens) and the output voltage spikes way up, a blip that blows whatever you were powering.
This is due to the control logic power collapsing faster than the main filter cap, and a 20V blip is easily spit out there and quickly falls off to not make any smoke.
But next time you power up, surprise! your circuit is dead.

That's subtle.

So the one rule I follow is to have the PSU powered on, voltage and current set to near what the battery should get, and then connect the leads (not backwards).
I never leave the setup unattended, i.e. leave home and go shopping.

If you are really not sure, best is to add a series diode from the PSU output. This will prevent most of this drama but the voltage drop of the diode must be accounted for, which makes it kind of a hassle if you want exact charging voltage.

That does make it a hassle.

Thanks for the insight.

[RukyCon]

If you're still looking for a replacement part, the MUR3040CT, which can be bought on LCSC either in metal or plastic tabbed TO-220 packages seem to exceed the specs of the old diode in just about every way I can verify (recovery speed, current, voltage drop).