SPD3303C Siglent Power supply tripping the circuit breaker when switching ON

Thread Starter

jacopo1919

Joined Apr 12, 2020
115
Hello, I have a SPD3303C Siglent linear regulated power supply which has quite a big toroidal transformer included.

This unit behave unexpectedly and I need to understand the reason because it is quite an issue for me.

About 40% of the times that I switch the unit ON, this trips the 16A circuit breaker.
I have read that could be a too high inrush of current but I sincerely believe that this should have been limited somehow from the designer.
This is quite a cheap PSU but I don't think is so cheap that it's a designer would intentionally omit some components.
Therefore I suspect that the unit might be faulty.

Demonstration video here.

Does anyone have experience with it? Do you think this is normal or could you suggest some tests before sending back the unit?

I also have read that someone has ''fixed'' this by connecting a light bulb in line with it but obviously i wouldn't call it ''fixing''; that's more a turnaround
Thanks
 

LowQCab

Joined Nov 6, 2012
4,290
This is 100% normal operation for a large Toroidal-Transformer,
they are very efficient, sometimes too efficient.

A Light-Bulb, with an SSR to bypass it, is a legitimate solution.

And yes, the designer would leave this out if he thought he could get away with it.
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Thread Starter

jacopo1919

Joined Apr 12, 2020
115
Is this is 100% normal, You mean that 100% of the buyers have the same problem and use a lightbulb to solve this issue? And that this would be true also for many buyers of various other models of large Toroidal-Trasformer's PSU?
When you say legitimate solution,is this to be intended as an '' if it works, it works'' solution?

Do you know about alternatives?
Thanks
 

LowQCab

Joined Nov 6, 2012
4,290
You may have a exceptionally sensitive Circuit-Breaker, or one that is worn-out.
( Circuit-Breakers DO wear-out or become weak ).

I'm just stating that this is a very common problem, which can be fixed.

Yes, there are many alternative schemes for limiting Inrush-Current.
How much money do You have to work with ?
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Lundwall_Paul

Joined Oct 18, 2011
236
Looks like your whole bench is shutting down. redistributing the bench load to more then a single breaker may just fix that. Have you tried to repeat that with other bench items off?
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
115
@LowQCab your last question makes me think that if I don't choose the cheap solution, the alternative is gonna be very expensive :)
But If you can suggest alternatives that don't involve a lightbulb constantly ON, I would be curious to read!

I found Inrush current limiter devices like this, and this is already quite pricier then a lightbulb + SSR. Also pricier then what I intended to spend.
I will first try to change circuit breaker, as @nsaspook advised.
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
115
Looks like your whole bench is shutting down. redistributing the bench load to more then a single breaker may just fix that. Have you tried to repeat that with other bench items off?
In the video I posted, there is only 1 Imac and a monitor active. All the rest is off. I did notice that when the computer is ON, the circuit breaker trips more often.. Said that, I'm not sure the Imac has a very high current drawing
 

MisterBill2

Joined Jan 23, 2018
19,374
What is missing is the claimed current draw of the power supply, and the actual load draw through the circuit breaker prior to switching on the power supply. AND has the circuit breaker carry-capacity been verified? There does exist a cheap, simple, and commonly used scheme that I have seen many times on high voltage power supplies. That arrangement provides a resistor in series with the load transformer, with a second switch across the resistor. so the resistor is in series with the load when it is switched on, and then a second or two later the switch across the resistor is closed, after the inrush has subsided. It may even be possible to implement that functionality in a three position mains switch for the supply. The series resistor should be just a few ohms, perhaps ten, or maybe only five, and rated for several watts.
 

LowQCab

Joined Nov 6, 2012
4,290
A Light-Bulb type Inrush-Current-Limiter only illuminates the Bulb for less than half a Second
before the Light-Bulb is completely bypassed by an SSR.
The Light-Bulb may not ever reach full intensity,
it's just being used as a temporary, high-power, Resistance-Element.

If You want to tinker-around inside your Power-Supply,
this setup can be ridiculously simple,
( of course this depends upon the particular construction methods, and types of Circuitry used ).

The goal is closing a Relay, or SSR, to bypass the Light-Bulb,
at the point when the Bulk-Storage-Capacitors are almost completely charged to full-Voltage.

And, of course, there's also the option of just never turning off the Power-Supply,
or, switching-Off all the Circuitry that follows the Bulk-Storage-Capacitors internally.
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