Variable DC Power Supply..... No Load?

[gaidin_]

Should a variable DC power supply ever be run with no load connected?

Just received a new power supply and plugged it up and turned it on to experiment with settings.... It blew up in less than 5 minutes with no loads connected. Bad supply or misuse?

Thanks,

[mariush]

Definitely bad power supply.

Open it up and post some pictures here if you can/want..

[AmmoJammo]

what's the supply? out of interest more than anything

[gaidin_]

Cap blew.....

[gaidin_]

Labeled Korad KD3005..... 30V 5A supply.

[AmmoJammo]

Did it just stop working? or did it goes snap, crackle, and pop?

[gaidin_]

Seems almost like what happened to David in Episode #315 just with smoke .

[gaidin_]

Oh I got a nice pop and a big puff of smoke.... Power immediately pulled.

[AG6QR]

A lab bench power supply that has adjustable voltage and current limits is normally happy to drive an open circuit, a dead short, or any resistive load anywhere in between.  Some can be intolerant if you apply a voltage to the output terminals via some external power source, but you weren't doing that.  And even if you were, that would be likely to fry a semiconductor, not a capacitor.

The only way I can think of misusing a supply that might cause the kind of damage you report is if you plug it in to the wrong voltage, like taking one which was designed for 120V AC mains input, and plugging it in to a 240V outlet.  There are switching supplies which are rather omnivorous regarding their input voltages and frequencies, but most linear bench supplies are designed to accept a specific voltage, and they might even be picky about frequency.

But my first guess would be that you got a bad supply.

[madires]

Seems to be the special Halloween edition :-) I'd return the PSU if it's a brand new one. If not it could be just that bad cap (high leakage current).

[gaidin_]

Thanks for the replies.... Just wanted to confirm my suspicions.

Of course here we are running on 110V but I did check that it was set to the right voltage section first thing before plugging it in.

Thanks,

[HackedFridgeMagnet]

No load instability? Maybe the design is very close to the edge.

[Whales]

Eek!  There is no good reason this thing should go like that.  Or at all -- AG6QR is right, you can short the outputs for all it matters and it will just current limit.

What is the history of the item like?  I'm assuming it's not new.  It might only need its PCBs cleaned and a fuse replaced, assuming nothing was damaged during the incident.  If you don't want to try and repair it, don't throw it away -- there are a lot of parts inside you can salvage, or at a later date you might decide you are in a better position to tackle fixing it. 

[gaidin_]

This was a brand new unit. Did not have it out of the box more than 10min before it blew. Going to return item for replacement or refund. Will see how it goes from there.

[AmmoJammo]

I've seen capacitors with their polarity label on wrong.... once... but if that was the case, trust me, the capacitor would have gone off with more of a bang!

[madires]

My guess is a degraded cap. I'd also assume that the cap's voltage rating is just a little bit above the max. voltage expected. The degraded cap got a very high leakage current at the max. voltage, becomes hot and goes bang.

[Whales]

This was a brand new unit. Did not have it out of the box more than 10min before it blew. Going to return item for replacement or refund. Will see how it goes from there.

Hope it goes well.  If you are in Australia, you can get a replacement/repair from EITHER the retailer or the manufacturer, at your own choice, if the item is sold to you faulty (as this one appears to be).

[tony3d]

I bought the next Korad up in the line from SRA Solder, and have ran it many times with no load, and never had an issue. If you bought it from SRA Solder you won't have any problem retuning it. Call, and ask to speak to Doug. They are excellent to deal with.

[gaidin_]

Was that the KA3005P tony3d?

[Eddie]

I can see from the picture that cap with all its internals where it should not be.

Looking again at the picture I see that the power supply is a linear type and these do not need a load on them to stop things going wrong, all the linear power supplies I have ever built have never needed a load on them.

Biggest linear power supply I built was a 50 Amp @ 13.8volts beast and that was built to run at 100% duty cycle as well, it was good for 90+ Amps for short durations until the regulator I had built failed (might get to and build a different regulator one day).

Cheers Eddie
vk6ya

[tony3d]

Was that the KA3005P tony3d?

No, The "d" without the serial port. I have had no problems, and have push 2amps through it for hours on end. This one

http://sra-solder.com/product.php/6946/1/korad_ka3005d_dc_precision_variable_dc_power_supply

My friend bought one as well, and both have been working perfect! Mine is very accurate on the readouts as well.

[Huluvu]

Seems to be the special Halloween edition :-) I'd return the PSU if it's a brand new one. If not it could be just that bad cap (high leakage current).

Especially if very cheap Chinese caps are used I would really not trust them ....
They tend to have too much Electrolyte (wet) that leads to very good ESR results in the  beginning of the life time and looks superb in the marketing...ähm sorry "Datasheet"
This high amount of electrolytic's will increase the pressure dramatically if you stress the caps during usage.
Second behavior will be that they have to reduce the process time (quality) to save money because most raw material used for caps are worldwide very similar in terms of price.