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Surge supressor unit for mini contactor

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Kal_B

Member
Hello guys,

I found into these units in a couple plugged into contactors in a couple of different control panels, different brands but basically surge suppressors plugged into 24VDC contactors. I read about them a bit and found that they're for DC coils only.

They're suppressing surge in the coil, how is the surge generated and why are they not used on every contactor?
Why are they made for AC coil contactors?


Thanks
Kal
 

crutschow

Well-Known Member
Most Helpful Member
They're suppressing surge in the coil, how is the surge generated and why are they not used on every contactor?
The "surge" is a transient voltage spike that is generated by the relay coil inductance.
When you try to suddenly stop the current in an inductor, it will keep flowing until the inductive energy due to the coil current (E = 1/2 LI²) is dissipated.
If the current has no place to go, it can generate very high voltages, possibly causing an arc, which can damage whatever is switching the coil current.
So a transient supressor is often used, which can be as simple as a simple diode across the coil (cathode to positive side) that provides a path for the transient current.
Some switching devices may have their own suppression circuits, or be robust enough to tolerate the spike without damage, so the relays don't require a suppression device across their coils.
Why are they made for AC coil contactors?
Why wouldn't they be?
AC coils also have turn-off spikes, depending upon where in the AC current waveform the turn-off occurs, but may require a different circuit since a simple diode will not work for AC.
 

JimB

Super Moderator
Most Helpful Member

Kal_B

Member
Thanks everyone.

crutschow, the question should've been : Why are the not made for AC coil contactors as I noticed in various product catalogs that they offer DC coil contactors with sruge suppressors,, but from your reply I'm sure they'e available.

I will have a closer look at the control panel where one is wired to find out why they only have one or two contactors with suppressors and not all of them.

Thanks
Kal
 

Kal_B

Member
Thanks again, your posts refreshed my memory and I think this is exactly what was suggested I use in this thread. I wasn't able to get that time to work so I'll try to use one a contactor with a surge suppressor and see what happens.

Cheers
Kal
 

crutschow

Well-Known Member
Most Helpful Member
Be sure that the MOSFET you use has a safe-area limit, as shown in its data sheet, that allows 10A @ 150V for a short period of time.
 

MaxHeadRoom78

Well-Known Member
I use Telemecanique DIN rail contactors and they supply all kinds of custom add-ons for their contactors. Including coil suppression for both AC and DC coils.
Including MOV, R/C and Diode types.
The symbol on the one in your OP shows a MOV type, so they should work on AC or DC..
Max.
 
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