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Starnge interference

Starnge interference

Starnge interference

May I begin with an apology for hand-drawing the attached circuits, I am no wiz at drawing tools.

I am facing a very strange (interference) case that has kept me busy for three days trying all I can think of with no use,

My problem in short:

I have two circuits as shown (1/2), when I operate circuit 2 with a switch coming out of the PSU to activate the 3 relays, they work fine and my circuit is OK and I get my LED lights on. HOWEVER, circuit 1 which is about 50-100cm away is affected (!). Two monitors connected to two of the PCs in circuit 1 "wobble" when the relays of circuit 2 are powered! Further more, I have some USB devices connected to each PC thru powered hubs and only the USBs connected to PC2 disconnect and connect upon powering the relays of circuit 2! To add to the mystery (I think it is), If I disconnect the 220V side on the relays and just power the relays, the monitors do not wobble but the USBs still get disconnected and connected. Last but not least, the monitors wobble when I power the relays but the USBs connect/disconnect when I turn off relays!

I cannot find any logical explanation to this!

I tried to distance the R1-R3 relays to as far as 150cm from the other circuit! I tried to wrap the 3 relays with foil paper to prevent or reduce the magnetic field (if any), BUT no use!

If I operate one relay at a time, the monitors wobble much less and the USBs do not disconnect. Two or three relays then I get larger wobble on the monitors and USBs connecting/disconnecting.

Anyone has an idea what could be the case?

I will try to supply the two circuits with a different phase each (I have 3-phase power).

I would really appreciate your help.


RE: Starnge interference

Changing the mains to two different phases did not make a difference.

RE: Starnge interference

Update 2:
The wires from the UPS's are running in the same conduit. Would drawing from one line cause interference on the other? BUT still even without power on the relay , powering it with the 12V causes interference on the monitors and loss of USB on the other circuit

RE: Starnge interference

Voltage drop.
Both AC relays and transformers have inrush currents several times normal running current. The inrush current of either the relays, the LED transformers or both is probably causing a voltage dip which is responsible for your issues. The inrush may be exceeding the rating of the UPS.

"Why not the best?"
Jimmy Carter

RE: Starnge interference

Hmmm, my UPS's are 6000W each!

What u say is absolutely correct, but the issue I have is even without the 220V side on the relay (no load on the circuits) and only the 12V operating the relay itself, I still get effects on one monitor (minor) and the USBs, all on a completely separate circuit.

The main issue is that I have two UPS's connected to two separate phases each feeding a separate circuit altogether, yet I get an effect on one circuit from the other independent one and only when powering the relays!

I have now changed my "mechanical/magnetic" relay to a Solid State one and it seems to have eliminated the problem! I am testing and praying that this was the issue. I cannot detect any wobbling in the monitors, any fluctuations in electricity or any disconnects in the USB devices.

Could it be that the magnetic relays causes such high interference that affect independent circuits a meter away! No electric devices are that sensitive, at least not computer monitors or USB devices on different circuit!

To be accurate, circuit 1 is feeding a flight simulator cockpit with several powered hubs and many electronic modules and tens of criss-crossing wires and USB wires connected to 3 PCs! A mess! (I wanted to attach a photo of the mess but I am really ashamed of it!)

Nevertheless, the whole cockpit is on one circuit and the second circuit I have been trying to use just to control some room lights.

I am not seeking to just resolve the issue, I want to understand what was (and is) going on (the engineer in me!)! I could simply not use the relay and turn the lights on/off by hand and i do not have a problem smile

Thank u for ur feedback.

RE: Starnge interference

I noticed that the mechanical relays had no surge suppression on the coil, diode or mov. This could be the reason that going to solid state relays solved the USB reset problem.

RE: Starnge interference

Can you please tell me some more about the use of surge suppression, diode or mov?
What is an mov?
How do I use these items?
What sizes?

RE: Starnge interference

OK I have done some quick reading and selecting these suppressor methods will be a hassle for me!
I am not electrically savvy and i would rather buy me some ready solution. What relays do you recommend to pass 220V up to 1500W (7Amp) and operated with 12VDC that will not produce electric noise or spikes?

RE: Starnge interference

Are your UPSs 6000W or 6000WH (watt-hour)? Big difference.

Verify your chassis ground connections. I expect one or more circuits is not grounded properly and may be getting a return path through the USB cables.


RE: Starnge interference

I know the UPS's are 6000VA. Did not know there is a difference between W and WH! W and VA I know that much smile

Chassis ground are all OK everywhere. I do not know how one can get return through USB cables! USB cables and devices are not grounded. I have diodes on the USB cables to prevent power flowing from the powered hubs to the PC.

When I changed to a Solid State relay, the problems went away! It must have been very large spikes or surges by the EMR on cutoff, which was the case I observed with USB's dropping the connection, they did when I turned the relays OFF.

It still bothers me to know that EMRs were causing surges in one circuit that was affecting a separate circuit on a different phase source, it just does not make any sense! And what is worse, this even happened when there was no load on the AC side of the relay, just 12VDC turning the relay ON/OFF!

Do you have an advise on a no-surge (protected) relay I can use in my setup?

RE: Starnge interference

One of the biggest problems with USB is the fact that they ARE grounded. Which makes them capable of bringing nasty noise and transients back from the connected devices(your UPS) to the computer.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Starnge interference

OK, i did not know that! So what can I do to prevent the interference and noise from affecting my USBs and my circuits in general?

RE: Starnge interference

You may have two problems.

1) If these are CRT monitors the wobble could be magnetic field issues from the relay coils and armatures.

2) The USB stuff is most likely ground issues as suggested above.

Check out this search.

SeaLevel Systems makes good products, but there are lots out there.

Hopefully your different systems have their wiring physically separated and same goes with any low voltage wiring.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Starnge interference

I think the problem came from 220V/12V converter and not grid voltage dip or relay issues.
I think these converters are SMPS and loop control have instability at some load step value, so power stage became a "good" high frequency / large bandwidth source that pass signal by air and interact with USB signal (data/clock) and video signal. With static relay step load is not enough to have same loop oscilation.
Change these converters.

RE: Starnge interference

But operating the mechanical relay (powered from a computer power supply (220/12/5/3.3v) without any load (no converters) connected, still produced interruptions to the monitor and to the USBs on the other completely separate electricity circuit!
I did change the relays from mechanical to solid state and that did the trick!
I still have no scientific explanation to this!
An EMR operating on 12v with no load voltage (current) woukd affect a completely separate circuit a meter away, affecting power to monitors and interrupting USB signlals! Those EMRs must have been producing a massive EM field! But havibg so many electronic modules and devices around that did not get effected make me completely baffled!
I am very curious as to what happened!

RE: Starnge interference

In computer power supply main loop is on 5V, much less "priority" is on 12V output and depending of IC controller and implementation may have same oscilations at some load on 12V and no load on 5V (not a normal operating mode for a computer power supply).
For testing replace computer power supply (and converters) with a battery.

RE: Starnge interference

Good info, I had no idea that PSUs prioritized their outputs. I will have to find a battery and try it sometime, but for now the SS relay solved the problem (so far). It must have been the connect/disconnect current (Inrush or whatever it is called) which I think is not there with SSRs?

RE: Starnge interference

SSRs have much low command current than relays and relays are an inductive load. These differences may be enough to lead power supply internal loop in an instability mode.
Battery test will show if my opinion it's correct.

RE: Starnge interference

It will take me some time but I will try to test with battery, I will report back here when I have something. Thank you for your advice and help.

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