Hello,
I use 220-690VAC contactor to switch 30A 220VAC load.
I give 24VDC voltage to auxiliary contact of contactor from my 24Vdc vehicle power supply.
But when I energised auxiliary contact , 24Vdc is rising to around 65V in 50 nanoseconds(I mean spikes ) as shown the picture below.
At the same time there are some pcbs that are fed from 24Vdc vehicle power supply and I measured the voltage spike from one of pcbs 24VDC supply connection.
What kind of proteciton should I use?
Does a schottky diode be useful?

 

What is your aux contact operating in to?
You may be either seeing contact bounce or is the contact switching an inductive load of any kind?
A schotky diode is recommended for inductive loads.
Max.

 

What is your aux contact operating in to?
You may be either seeing contact bounce or is the contact switching an inductive load of any kind?
A schotky diode is recommended for inductive loads.
Max.

I can see these spikes even when the load is not connected,normally I use resistive load.
Operating range of aux contact in my system is 24Vdc and other pcbs take supply voltage same source.
And also I measured ground signal when the auv contacts are energized and I saw 8VDC .

 

And also I measured ground signal when the auv contacts are energized and I saw 8VDC

8VDC with respect to what reference point?

 

8VDC with respect to what reference point?

The referance point was one of pcbs ground connection but all of them(grounds) connected to each other.
And there was a spike(about 8V) on ground signal too.

 

So are you measuring this spike with the relay contacts connected to the load it will drive?
If so then a TVS or a zener diode should work to clip the spike.
Also a large (1-10μF) capacitor from the relay output to circuit ground should also work.

 

So are you measuring this spike with the relay contacts connected to the load it will drive?
If so then a TVS or a zener diode should work to clip the spike.
Also a large (1-10μF) capacitor from the relay output to circuit ground should also work.

here is my system simply:

 

No BEMF diode across the relay coil!!
No Wonder!
Max.

 

No BEMF diode across the relay coil!!
No Wonder!
Max.

so it is a quite normal situation without a diode, isn't it?
I've tried TVS diode but It didnt work.
Maybe TVS diode that I used was slow for nanoseconds.

 

Use Schottky or even a 1n2007 and test again.
Max.

 

Use Schottky or even a 1n2007 and test again.
Max.

thanks

 

Hi again,
I used 1N4007 diode and tried again.
But there is still spike and it is causing the other boards shut down because of the mil std 1275 circuit on my boards.
I've tried many diodes such as SMCJ30, 1N4148..
None of them worked.

 

Please show your new schematics- how the diode is connected?

 

Here is my diode connection simply.

 

Is the diode connected physically close to the coil ? Or on long lead
run to coil. The fact there was no change makes one wonder if your
screen shot is looking at the right terminal on the contactor, I see no charac-
teristic ringing....is that because there is a snubber across coil ?

Regards, Dana.

 

The diode is connected so close to the coil of contactor.
There is not a snubber circuit,only a diode.Only the load is connected the contacts of the contantor.
I've shared signals of spike point with diode and without diode connection.

 

You said earlier you've tried this with the load disconnected and still saw the noise. Did you mean the 24V auxiliary contact load, or the 30A 220VAC load?

I'm wondering if arcing in the main contacts due to making/breaking a 30A load isn't radiating noise into the auxiliary wiring. All of this stuff is way over my head, but I've seen some things I thought were amazing when it comes to the power and insidious effects of relay arc noise radiation.

If you haven't already tried it, can you disconnect the 30A load and see if the noise goes away?

 

RC snubber across the contact.
Max.

 

1) You said earlier you've tried this with the load disconnected and still saw the noise.(YES)
2) Did you mean the 24V auxiliary contact load, or the 30A 220VAC load? The load is 30A 220VAC.
3) I'm wondering if arcing in the main contacts due to making/breaking a 30A load isn't radiating noise into the auxiliary wiring.
Both main contacts(220VAC) and coil(24Vdc) of the contactor switching are causing spike.I've tried them separately.
I removed 24VDC coil connections and swicthed contacts manually and I measured main 24Vdc busbar,there was still spike.

 

1) You said earlier you've tried this with the load disconnected and still saw the noise.(YES)
2) Did you mean the 24V auxiliary contact load, or the 30A 220VAC load? The load is 30A 220VAC.
3) I'm wondering if arcing in the main contacts due to making/breaking a 30A load isn't radiating noise into the auxiliary wiring.
Both main contacts(220VAC) and coil(24Vdc) of the contactor switching are causing spike.I've tried them separately.
I removed 24VDC coil connections and swicthed contacts manually and I measured main 24Vdc busbar,there was still spike.

Ok, so you've tried:

• manually activating the relay with the coil disconnected, presumably with the high voltage load connected
• Switching the relay with the normal 24V coil operation, but with no high voltage load connection

What about trying it with no load on the 24V auxiliary contact side?

I'm inclined to agree with Max's suggestion, both because it sounds logical and because I trust his judgement in these matters. Nevertheless, I'm curious to identify the source, if possible. It has to be coming from something.