Spikes and Surges

moonloopsun said:

Hi guys.
i hope that someone can help us.
We moced to a new flat and installed an audio system in a room where we have 4 Shutters that are driven by a Shelly 2.5 relay.
the problem is that when the relays are starting or stopping the engine the turntable‘s preamp is picking a spike pop noise and amplify it.
we tried everything from the audio system‘s side (electric filters, surge suppressors, different cables...),
On the relay side the only thing we tried is to to wrap the cables with Ferrite clips.
we don’t know if the spike sound is created by the relay itself or the Shutters engine.
but we can’t use our sound system because those amplified pop sounds can destroy the speakers.
wirth to mention that in this room there is also a motorized beamer screen running by a different type of relay and it creates the same problem..
is there anyone that could possibly help us to understand what we have to do?

thanks a lot for your time.

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Pommie said:

If the interference isn't getting into the input cables and is being amplified, could it be via the power supply? What happens if you power the amp via an extension from another room?

Mike.

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KeepItSimpleStupid said:

The motor MAY be a PSC motor that uses a capacitor. You end up with 3 wires with a common, a CW and CCW directions It might be useful if you can find a wiring diagram. You connect c to either the CW or CCW sides.

You likely have a large antenna. So, when the motor turns on, you get a nice little short briefly at the other end.

What I was really suggesting to do is to:

Shield the wires from the Shelly to the motor and if there is a capacitor, move it closer to the relay.

Try this for fun. If you know the approximate path of the wiring, temporarily put a sheet or sheets of grounded aluminum foil along the path, Just see if it gets better. It's not foolproff, but the radiation could be to a nearby power line as well. In that case, try powering the stereo from an extension cord to another circuit. There might be a change. I am in no way suggesting the problem will go away.

I'm just using this https://www.hurst-motors.com/lyg42geared.html as a wiring diagram. An AC synchoous motor is essentiall constant speed because speed is related to frequency, so as long as the motor has enough torque, speed will be constant.

There are X and Y capacitors or safety capacitors e.g. https://www.digikey.com/en/product-highlight/k/kemet/emi-suppression-capacitors and thats what you need for a snubber. Also Metal oxide resistors.

They should go across the contacts of your relay. Would need some info about the motor to try to size a value.
A ZNR would probably also help.

Another idea that MAY work is to use a delay on make relay and a delay on break relay. Unfortunately, these are usually just control relays and would need another one to handle the current. You can apply power through a metal oxide resistor for a short time and teh short that resistor out. The resistor would burn out if left in the circuit for a long time.

The coolpart about metal oxide resistors is that they pretty much break in half when they are overloaded.

I would suspect that the delay on make would only help the ON spikes and not the OFF ones.

The voltage across an inductor v = is L di/dt. So, when the motor is turned off, di/dt is esentially any you get a nice big voltage spike/

So, shorting out the motor when it's turned off, reduces the voltage. Having that short closer to the motor reduces the antenna length.

di/dt happens when the motor turns on too.

You have a big antenna.

So, the supression has to be close to the contacts AND close to the motor. Close to the contacts should dampen turn on spike. Close to the motor, turn off spikes.

The snubber also "protects" the relay contacts.

At work we had a 1000 W arc lamp that required a 40 kV pulse to start the lamp. Normal power was 22V at 40A or so. there were two 5' cables going to the lamp housing. Whenever we started the lamp the 8" floppy drive would move. We just didn;t start the lamp with the floppy drive running. Moving the ignitor inside the lamp housing fixed the problem. The OEM redesigned the ignitor module.

I don't think it would work, but you could interrupt the pre-amp signal with an optofet or short it for a short time when the motors turn off.
Like I said. Not a good idea.

As you no doubt found out, "Throwing money at the problem" doesn't work either.

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moonloopsun said:

Hi

mike. When i plug the whole audio system to another room it helps a lot!
Any guesses?

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KeepItSimpleStupid said:

In that case, try powering the stereo from an extension cord to another circuit. There might be a change. I am in no way suggesting the problem will go away.

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Pommie said:

What happens if you power the amp via an extension from another room?

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KeepItSimpleStupid said:

Snubber design: https://sciencing.com/design-rc-snubber-12030206.html and https://daycounter.com/Calculators/Snubbers/Snubber-Design-Calculator.phtml

Capacitors: https://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=x1+y1+capacitors Note the X1 and Y1 and the voltage rating. https://www.hunker.com/13408990/differences-in-x1-x2-y1-and-y2-capacitors You want an X class.

Metal oxide resistors: https://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=metal+oxide+resistors
These can work too: https://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=non+inductive+resistors

The snubber will go across the relay contacts.

ZNR's Search for ZNR's at RS-oniine. You probably want 240V operating. The ZNR across the line in and motor so you would end up with three.

Do, I think it will work 100%? No. Help? yes.

Wires that parallel each other pick up interference by capacitance, Wires that cross don;t so much.

A note on shielded cables: https://www.mouser.com/pdfdocs/alphawire-Understanding-Shielded-Cable.pdf

So, really and short lengths and metal conduit combined with a snubber have the best chance of fixing it.

Power conditioning: I can tell you that these https://www.powervar.com/products/power-conditioners/ground-guard-power-conditioners or similar
combined with https://www.tripplite.com/isobar-8-outlet-surge-protector-12-ft-cord-3840-joules~ISOBAR8ULTRA The connected equipment warranty in the US is hard to beat. We used the warranty once for the ISOBAR in an ISOBAR only surpressed system. The suppressor was covered in black soot. Then someone decided to replace them with plastic supressors from APC.

I took a failed one apart and got really angry, The plastic was compromised and the "protection" if it fails "protects: the surge supressor and not the equipment.

The Triplite and Powervar (Then known as OneAC) made a fantastic power conditioner. I used the combination at work in the 1980's for eventually three critical data acquisition systems where a complete loss of power was OK.

One particular Macintosh computer was in service for 17 years, The SCSI hard drive had no issues. The floppy drive died (mechanical) and the computer accumulated dust, With the computer prior failures were fans due to dust, power supply and 8" floppy drives.

For the most part, the power conditioner is an isolation transformer that re-references the neutral/ground connection of the secondary.
The order probably doesn't matter much. What the transformer does is it attenuates greatly any high frequency spikes because they won;t pass from the primary to the secondary. You also get a clean ground.

Renting a power line disturbance monitor might help. https://www.dranetz.com/dranetz-hdpq-family-of-power-quality-analyzers/

So, I think it's EMI radiated into the power line, so you can prevent it from getting there or prevent or reduce it from getting into the audio system.

Snubbing, shielding, surge suppressing and making the distance between the switch and the motor should be primary objectives.
The re-referenced isolation transformer is another way.

The powering of the stereo from another circuit is going to reduce the capacitive coupling. Powering the motors form another circuits should do the same thing.

In some respects, it more like an EMP event. https://en.wikipedia.org/wiki/Electromagnetic_pulse

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1. Verify that the electrical switch is in the “Off” position and connected to a power source.
   
   Measure the voltage across the switch by placing the voltmeter probes across the input and output terminals of the switch. Turn the switch to the “On” position and read the value on the voltmeter. This is the voltage across the switch. Write that down