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SPD3303X Catastrophic Fault (Design Flaw?) - (Edit: Nope! User Error!)
Martin72:
Hi,
Exactly that, the output must be decoupled - the power supply unit does not expect any external voltage at its outputs.
Therefore, this is a :
--- Quote ---Catastrophic Fault
--- End quote ---
From the OP and no
--- Quote ---(Design Flaw?)
--- End quote ---
.
The outputs are presumably short-circuited so that voltage peaks are not passed on to any loads when they are switched on.
A certain cheap power supply unit at work did not have this feature a few years ago.
The result was that when it was switched on, the maximum voltage was briefly present before it went back to the set value.
And a circuit board full of ICs that were expecting 15V was only a complete failure.
zrq:
If I recall right, my HPAK 66332A/6632B have the same crowbar mechanism, and it makes them (although 2 quadrants capable) not really suitable as electronic loads.
RoGeorge:
--- Quote from: christopher.robot on December 20, 2023, 05:49:37 pm ---I was charging a large lithium ion battery (yes, through a BMS & active balancer) when we had a brownout in my building.
--- End quote ---
That's a thing you should never do with a power supply.
You must add a series diode when charging batteries.
For example, in the Rigol DP832 supply manual it is explicitly told NOT to charge batteries without a series diode. The series diode must be added to prevent the situations where the battery backfeed into the power supply output.
Many power supply also have an internal analog only "crowbar protection" for when somehow the output voltage becomes higher then the programmed voltage (to protect the load circuit against overvoltage, for example if the internal regulator fails, and start to deliver full voltage instead of programmed voltage). The crowbar will short-circuit the outputs if it sees more voltage than expected. Often it's triac meant in parallel with the output.
christopher.robot:
Still seems entirely preventable from a design standpoint, with this particular implementation.
That said, the general consensus is this was a setup failure - so I suppose I must concede.
Still, for the testing I was doing, adding a diode would have affected the logging, and an external fuse might not have prevented internal damage (though better than naught, I suppose).
I can add a diode and a downstream DAQ, but the latter seems much more convoluted and prone to error than anything introduced by a Schottky.
Maybe I'll build some kind mains-sensing interruptor between the mains and the PSU, so it stays off if the mains get sketchy (another thing that could probably be implemented in the original design).
Probably a lot of work for a one-off, but then again, so was the repair...
Thanks for the input everyone, (and my apologies to Siglent for the slander - [Fixed, edited the title]).
At least I learned something!
RoGeorge:
The good part when charging through a diode is that most often the charging current is constant, which means the voltage drop on the diode is also constant, so it can be only a subtract of constant 0.6V or so when logging, instead of an additional DAQ. That's what I usually do while logging a charging.
In case it's not constant current charging, then you can trace first the drop voltage of the diode against current, memorize the diode's I-V characteristic, then subtract the curve of the diode during charging.
For 3A or so power supply, the diodes must be quite beefy, and mounted on a radiator. I've uses a former CPU radiator, and two double diodes in parallel, such that I can connect 1 battery to 2 of the power supply channels at the same time, to double the charging current. The double diodes were recovered from a broken ATX power supply for PC.
Another thing you should have is a fusible right near the battery, because a big battery can easily heat a short circuit wire to red hot, which might start a fire. The short circuit might happen in ways you can not control or predict. For example, once a pigeon entered the room and managed to fly-bump erratically into almost everything around.
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