Relay voltage spikes

[(*steve*)]

No I don't! Do you mean something like the attached picture?

Yes, he does. You need one (almost without exception).

 

[Harald Kapp]

A reverse diode is always a good idea, if only to protect the control circuit for the relay.

Powering on the 45W AC appliance (which is actually a fan) while the relay is already activated. Result: no click

Probably because the fan has an integrated filter to suppress the power-on surge, which may be bypassed if the fan is already in the on position and mains is switched by the relay.

Your observations make it rather obvious that the problem is not on the coil side of the relay, but on the contact side. I recommend you use a mains filter in the power supply to the fan, even better one filter in each of the supplies of the speakers and the fan.

 

[cvicente]

Ok...

So, just to make it clear (for me), the diode implementation is as I've referred in my last post, correct?

Probably because the fan has an integrated filter to suppress the power-on surge

Couldn't I implement one, or does it have to be dimensioned depending on the AC appliance I'm connecting to the relay?

Carlos

 

[KrisBlueNZ]

Yes, connect the diode as in the diagram in post #20.

The diode's current rating needs to be at least as high as the maximum relay coil voltage. Typically people use 1N400x diodes, though the 1N914 / 1N4148 is suitable for small relays.

Edit: I meant the diode's current rating needs to be at least as high as the maximum relay coil CURRENT.

Also, the diode's reverse voltage rating needs to be at least as high as the voltage applied to the coil. Generally both voltage and current ratings should be at least 50% higher than those minimums.

 

[cvicente]

Yes, connect the diode as in the diagram in post #20.

Thank you Kris!

Thank you all for the help provided. I'll probably still investigate how could I implement some kind of power surge protection.

The idea is to plug-in any AC appliance up-to 16A (@230VAC), so I would be more confortable knowing that my circuit would be already prepared to deal with surges generated from whatever AC appliance is connected to the relay.

Carlos

 

[Harald Kapp]

You can use a socket with integrated mains filter like this one or one of those.

Or use a filter module like one of these and integrate it into your circuit.

 

[cvicente]

Thank you Harald,

But I was actually thinking on giving it a shot with varistors. I still have a lot of study to do on the matter, but as far as I understood, that's pretty much the way to go:

Varistor and a fuse when overheating becomes a problem.

Or am I waaaayy of?

Carlos

 

[Harald Kapp]

A varistor will limit voltage spikes. At this point we do not know whether it is spikes that cause the "click". It can also be a sudden drop in voltage due to the inrush current of the load. In fact, I think this is far more likely. In this case a varistor is of no use. You need something to filter out the harmonics that are caused by the voltage sag.

 

[cvicente]

It can also be a sudden drop in voltage due to the inrush current of the load. In fact

Oh... I didn't think of that... but we're talking about 45W@230VAC, so if my calculations are correct that means that it will draw a max of 200mA. Would that be enought to lower the voltage that much to be the cause of the "click"?

And, since we're at it, how can I know for sure what's really happening (I'm not doubting you, just wondering, how such a thing can be investigated)?

Carlos

 

[Harald Kapp]

That's 200 mA in steady state. At turn-on, the motor is not yet rotating. A motor in standstill cannot generate a counter EMF. It look like a very small resistor to the power supply at that moment (use your Ohmmeter to verify). Therefore a comparatively huge inrush current will flow.

 

[cvicente]

It look like a very small resistor to the power supply at that moment (use your Ohmmeter to verify)

Do you mean measuring the resistance of the fan? If that's the case, won't I have to get the fan motor uncovered?

Carlos

 

[Harald Kapp]

You don't have to.
Disconnect the fan from mains.
Put the switch in the ON position.
Measure the resistance across the pins of te mains plug.

This way you measure the resistance as seen by themains outlet.

 

[cvicente]

Yeah... I end by doing exactly that, although I just wasn't sure if that would be the way to go!

The result: 571 ohm.

 

[cvicente]

Ok, so... In the middle of all this great advises (thank you all, once again, for all your patience) I've just realized something that incredibly I just noticed this night.

So... don't you hate me for this... but... I just realized that the power cord, which is powering up my circuit and the fan itself is already connected to a power strip with surge protection... so... I guess what Harald said in a past post:

It can also be a sudden drop in voltage due to the inrush current of the load. In fact, I think this is far more likely

Makes even more sense now, right?

 

[CDRIVE]

Having the amp and the fan sharing the same power strip isn't helping eliminate your problem. It's more likely exacerbating it.

Chris