Power supply kept blowing the circuit

**Bob Willson** · 19th March 2012, 05:48 PM

As some of you may remember, I bought an extra Antek power supply to go with my existing power supply that I already had, to upgrade my system to supply sufficient power for the upgraded motors that I got from Ausxmods

This seemed to work fine for a while and then started to blow the breakers every time I turned on the machine. Actually, it wasn't every time, more like every other time. Anyway, I had a circuit that I only ever used for my air compressor, because it is a 15 amp circuit, so I decided to chuck another point on that circuit so that I could use the extra power. So I then plugged it all into that circuit and the breaker started to blow every time I turned the machine on instead of almost every time. Most frustrating.

I thought that I must have a short somewhere, so I disconnected all the steppers, it still blew. all the other bits and bobs (shut up Rod), and still it blew. Faulty PSU? I then tried each PSU separately and they worked OK. The house lights flickered a little when I turned the PSUs on, but they booted up fine.

This is when I found that you cannot get 29 amps of machinery out of a 10 amp circuit. Well, not for very long anyway.

I also at this time found that the fans from computer power supplies last only a few seconds when run on 70 volts instead of 12 volts.

. Luckily, I had spares.

I was getting quite frustrated by this stage, so I returned to basics and had a look at the wiring schematic for the PSUs.

The smaller PSU requires 13 amps in total (11 amps at 70 volts, 5 volts at 1 amp and 12 volts at 1 amp) and the larger one uses 16 amps in total (14 amps at 70 volts and 1 amp for each of 5 volts and 12 volts).

I had not remembered that amps are a an absolute measurement and that just because it is only drawing the voltage at 70, 12 or 5 volts, this does not change the actual amperes drawn in any way.

When the power is first turned on is the time of maximum power draw as the copper wires and the capacitors fill up with electricity. As soon as they are full of it, everything evens out and the requirements become a little less stringent.

Disregarding the absurdity of the last paragraph, I have found that I need to use two separate circuits to get enough power to the motors. One of 15 amps for the larger PSU and one of 10 amps for the smaller one. It is all still right on the edge.

**petersemple** · 19th March 2012, 05:59 PM

I am not a sparky. I have done quite a bit with electronics though, and i believe your 3rd last paragraph is wrong. What matters is power (VA). Your smaller PSu needs to provide 787W. This means that if it was completely lossless, it would draw around 3.5 at 240V. Of course, your PSU is going to incurr losses, but I doubt if it needs to draw 13A at 240V to provide those outputs you quote. Similar for the larger one. You are right that you can get an inrush current when the power is forst turned on, and power supplies with large transformers will sometimes have slow blow fuses to cope with that. I have not heard of slow blow in switchmode supplies though (although I have certainly not of everything that is out there.

**Bob Willson** · 19th March 2012, 06:52 PM

Hi Peter

The PSUs are torroidal PSUs. Maybe this makes a difference. I don't know.

Here are links to the PSUs.

Smaller one

Larger one

The fact remains that when I plug them both in to the same 10 amp OR 15 amp outlet they blow the circuit breaker. Maybe there is something wrong with both of them or maybe it is the house wiring which was recently all replaced after the floods.

**SawDustSniffer** · 19th March 2012, 06:52 PM

RCD on those breakers ?, RCD"S hate in rush currents
what about 2 switches , turn the big PSU on first , then 5 seconds later turn on the small PSU

Originally Posted by Bob Willson

This is when I found that you cannot get 29 amps of machinery out of a 10 amp circuit. Well, not for very long anyway.

I also at this time found that the fans from computer power supplies last only a few seconds when run on 70 volts instead of 12 volts.

. Luckily, I had spares.

.

i recommend that you dont remove the RCD's
get 3 circuit 's ?

**Bob Willson** · 19th March 2012, 07:18 PM

Hi Ken

It could well be the RCDs as I didn't have them before I got new wiring and it didn't blow prior to that.

It seems to be OK with two separate circuits that I can switch in independently of one another. Why do you say three circuits? I can't even think how to do that because the 12v and 5v are incorporated on the same toroid.

**SawDustSniffer** · 19th March 2012, 11:06 PM

3 circuits ??? 1 for large PSU , 1 for small PSU & PC, 1 for spindle ??
"line filters " would be good on the spindle and large PSU they clean up the interference you might get between components ( and stop SWMBO going on about the TV braking up when the spindle is running )
3 ten amp circuits , all on separate switches

RCD's monitor the AMPs going out , and coming back , if there is a difference in the two (by 50milliamps) the RCD shuts off the power
RCD's hate large capacitive loads (huge capacitors ), or large inductive loads ( huge coils of copper)

**petersemple** · 19th March 2012, 11:25 PM

OK, Toroids are the major ones for inrush current. Any audio amp with a toroid in it will have slo-blo fuses for exactly that reason.

**Bob Willson** · 20th March 2012, 09:56 AM

Originally Posted by SawDustSniffer

3 circuits ??? 1 for large PSU , 1 for small PSU & PC, 1 for spindle ??

3 ten amp circuits , all on separate switches

Well I suppose that I almost have that.
1 circuit of 15 amps for the big PSU and a second circuit of 10 amps for the smaller PSU. This second circuit goes to a 4 way outlet with individual outlet switches and then I can switch on the PSU and the VFD separately from there.

Maybe I should try plugging this 4 way outlet into the 15 amp socket and see what happens if I turn everything on/off one at a time from there.

**Bob Willson** · 20th March 2012, 09:59 AM

Originally Posted by petersemple

OK, Toroids are the major ones for inrush current. Any audio amp with a toroid in it will have slo-blo fuses for exactly that reason.

Good to know this Peter. It certainly explains why I have got problems now that I didn't have before.

Thanks

**RayG** · 20th March 2012, 03:34 PM

Hi Bob,

At a guess, I'd say that it's the initial charging of the caps in the power supply that is tripping your RCD.

What happens is that the RCD measures the imbalance between the active and neutral, and while the capacitors are charging the imbalance is sufficient to trip the RCD.

One possible fix is to have a resistor between the bridge and the capacitors that get's switched out with a relay when the voltage across the caps rises sufficiently. This used to be normal practice on big linear power supplies.

The other and probably more preferable solution is to see if you can get your electrician to put in some less sensitive RCD's.

Regards
Ray

**Bob Willson** · 6th May 2012, 02:38 PM

It would appear that the inrush current tripping the circuit breakers was what was doing it.
I split the circuit and put everything in a metal box. I also went with a separate 5v supply for the BOB.
Now when I turn on the power I allow about 5 seconds between the various switch turn ons and I have not blown a circuit since.

Thread: Power supply kept blowing the circuit

Thread Tools

Search Thread

Power supply kept blowing the circuit

Similar Threads

Advice needed -Carbatec AW106PT blowing circuit breaker

Question about amp power supply...

power supply

Tags for this Thread

Posting Permissions