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Proximity of AC coil to snubber network

J

Jon Danniken

Jan 1, 1970
0
I have a contactor with an AC coil, controlled by a small SPDT relay, and I
have the need for a snubber to reduce kickback when the relay opens.

It would greatly simplify things if I were able to mount the snubber network
on the board with the relay, which is a few feet from the AC coil on the
contactor.

I do realize that having the snubber network seperated from the AC coil by a
few feet is going to have the wires acting as little antennae, but for the
purposes of protecting the contacts on the little relay, will it be fine?

Thanks,

Jon
 
J

Jamie

Jan 1, 1970
0
Jon said:
I have a contactor with an AC coil, controlled by a small SPDT relay, and I
have the need for a snubber to reduce kickback when the relay opens.

It would greatly simplify things if I were able to mount the snubber network
on the board with the relay, which is a few feet from the AC coil on the
contactor.

I do realize that having the snubber network seperated from the AC coil by a
few feet is going to have the wires acting as little antennae, but for the
purposes of protecting the contacts on the little relay, will it be fine?

Thanks,

Jon
That snubber will do it's job fine there. If you're worried about noise
then use a twisted pair to drive the coil. If the snubber is properly
sized, it should do well in reducing RF radiation. Some use a shielded
pair with the shield connected only at the driver end to ground.


Jamie
 
J

Jon Danniken

Jan 1, 1970
0
Jamie said:
That snubber will do it's job fine there. If you're worried about
noise then use a twisted pair to drive the coil. If the snubber is
properly sized, it should do well in reducing RF radiation. Some use
a shielded pair with the shield connected only at the driver end to
ground.

Nice, thanks Jamie. I hadn't thought about using twisted or coax, but
that's a perfect idea to reduce any emissions that might want to propagate.

Jon
 
L

legg

Jan 1, 1970
0
It doesn't much matter where you put the snubber. From an EMI
standpoint, close to the relay coils is probably a little better than
near the coil.

John

Actually, it will be most effective at the breaking-contact location.

RL
 
J

Jon Danniken

Jan 1, 1970
0
legg said:
John Larkin wrote:

It doesn't much matter where you put the snubber. From an EMI

Actually, it will be most effective at the breaking-contact location.

Cool, even better! Now that I think about it, that would explain why
snubbers get mounted on silicon power devices instead of the transformers
which they control.

Jon
 
J

Jamie

Jan 1, 1970
0
John said:
All shields should be grounded at both ends, if not more often!

John
Oh really. Think about that for a moment.

Jamie
 
J

Jamie

Jan 1, 1970
0
John said:
On Mon, 31 Jan 2011 03:20:53 -0600,



Let'em happen, and deal with them. That's a lot better than having
tens of volts of common-mode RF and spikes at the ungrounded end.

John
Really,, You've never heard of shielded grounds?

Jamie
 
R

Rich Grise

Jan 1, 1970
0
John said:
Really,, You've never heard of shielded grounds?

No. What's a shielded ground?[/QUOTE]

I've heard of grounded shields. ;-)

Cheers!
Rich
 
Huh, most pro audio systems use balanced signals and are immune to
ground loops.

That's not true. Of the major pro audio intercom standards, one of three is
balanced. Even with the one that is, there is no guarantee that there isn't
several volts between systems.
The best way to keep RF out, is to ground the shields to the chassis
at both ends. The balanced audio is not bothered by the resulting
ground loops.

But things can sure get hot!
 
J

Jamie

Jan 1, 1970
0
Rich said:
I've heard of grounded shields. ;-)

Cheers!
Rich
I find it hard to believe to that none has ever used coax or the
like cable as a ground leg.

The end that is attached to the ground source has both the shield
and center conductor combined. On the other end for the device that
wants the ground with out the noise with it, you use only the center
conductor and tape off the shield as close to the device as possible.

In the past, I've used RG8/213 type cable from a good out side ground
source, and led them up to the entrances of the shack/house with a metal
plate that had a coax female connector on it where we would attach this
coax. On the inside, you simply use the center conductor only..

This same is done noisy environments to reduce noise from traveling
along the ground legs and along the shielded signal wires.


Jamie
 
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