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Author Topic: Periodically Tripping breaker when turning on machine...  (Read 1326 times)

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Periodically Tripping breaker when turning on machine...
« on: April 28, 2016, 12:07:39 PM »
I am having a problem that I have no clue how to troubleshoot. 1 out of 5 times when I flip the switch to turn on my machine the 20A breaker trips. The only load on that circuit is my PC (already running when I turn on the machine). I am running a Toroid PS-8N56R power supply which is 800w. My first guess is that the culprate is startup surge considering it is sporatic and only at start-up and if there was a short of some kind it would trip all the time but it does not make sense that an 800w power supply would trip a 20A breaker (the PC power supply is 350w).

Any thoughts on how to confirm I do not have a more serious issue and what kind of options do I have to resolve this?

Thanks,
Matt
Re: Periodically Tripping breaker when turning on machine...
« Reply #1 on: April 28, 2016, 04:39:43 PM »
The power supply is the problem. Until the capacitors in the power supply charge they are a short circuit which is tripping the breaker. Typically this type of power supply have a current limiting resistor attached to the capacitors to prevent this. Switching power supplies don't have this problem.
Re: Periodically Tripping breaker when turning on machine...
« Reply #2 on: April 28, 2016, 04:51:29 PM »
geh7552 thank you for answering this question (and my other questions too)... should I add a current limiting resistor? What you say makes perfect sense because now that I think about it the only times it has happened is on cold starts. If I shut it off and then back on it doesn't trip the breaker.. The question I guess then is how do I prevent this since the MFG did not seem to put the current limiting resistor on the capacitors

Thanks.
Re: Periodically Tripping breaker when turning on machine...
« Reply #3 on: April 28, 2016, 10:01:32 PM »
Sizing is a little complex and depends on the size of the capacitor (uF) and the DC voltage at the capacitors. If the power supply isn't powered the capacitors slowly discharge until they are at zero volts. Options:

1) Contact the power supply mfg and see what they recommend.
2) Add a line reactor (a coil choke) to the AC line side of the power supply.
3) Use a switching type power supply.
4) Leave the power supply energized.
(No subject)
« Reply #4 on: May 01, 2016, 05:09:47 PM »
Another option is adding a PTC (aka a polyfuse) between the xfmr secondary and the capacitors to limit inrush. Hard to say how practical that would be w/o knowing the particulars of the power supply.

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Offline Davek0974

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Re: Periodically Tripping breaker when turning on machine...
« Reply #5 on: May 02, 2016, 03:25:02 AM »
One other option is an old-fashioned soft-start button in the primary side  - a power resistor of a couple of ohms and a push button wired so that the resistor is in in circuit only when button pressed. It limits the current until the caps have charged sufficiently to stop the inrush.

You press the button, switch on, wait 1-2 seconds then release the button, this can all be automated but depends how complex you want to get, used to be used in valve amplifiers.
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Offline Hood

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Re: Periodically Tripping breaker when turning on machine...
« Reply #6 on: May 02, 2016, 03:31:23 AM »
What about getting a D type circuit breaker?
Hood