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Old February 7th, 2018, 07:33 AM   #1
lesmar96
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running an AC coil on DC

Would like your input........

I am not sure I know all how a shunt trip breaker works, but the ones I am used to you use a control voltage signal to trip the breaker.

I have a customer ( and I don't have all the details) that has a tripping coil rated for 125VAC. Now he needs it to run on 125VDC for whatever reason. Is it possible to run a coil like that on either AC or DC? What will happen?
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Old February 7th, 2018, 07:51 AM   #2
lfe
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Coil impedance increases with frequency, higher the frequency lower the current and with DC the impedance is minimal.

If you run with 125 VDC probably it will burn in a matter of seconds , don't try it.

The coil should be changed for other rated for 125 VDC

Last edited by lfe; February 7th, 2018 at 07:59 AM.
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Old February 7th, 2018, 08:51 AM   #3
JesperMP
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There are coils that are rated for both AC and DC, but unless actually labelled for DC or AC/DC - replace the coil.
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Old February 7th, 2018, 03:09 PM   #4
T Gibbs
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You could always set a relay with a DC coil and run AC through the contacts to the shunt trip coil.
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Old February 8th, 2018, 10:34 AM   #5
lesmar96
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My customer came up with the idea to run a bridge rectifier in reverse to run this coil. I don't think there is any way this will work. A recitifer cuts the sine wave, right? to take the hz out of it? Running it in reverse, there is no way that it will be able to build a sine wave? He is sure that he has done this before, and it worked, but I don't see how.

Any thoughts?
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Old February 8th, 2018, 10:39 AM   #6
dogleg43
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Quote:
Originally Posted by lfe View Post
Coil impedance increases with frequency, higher the frequency lower the current and with DC the impedance is minimal.

If you run with 125 VDC probably it will burn in a matter of seconds , don't try it.

The coil should be changed for other rated for 125 VDC
Agree with the above response.
I saw a customer hook up several 24VAC rated relay coils to 24VDC and they all got hot very quickly.
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Old February 8th, 2018, 11:26 AM   #7
Dirt
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Quote:
Originally Posted by lesmar96 View Post
My customer came up with the idea to run a bridge rectifier in reverse to run this coil. I don't think there is any way this will work. A recitifer cuts the sine wave, right? to take the hz out of it? Running it in reverse, there is no way that it will be able to build a sine wave? He is sure that he has done this before, and it worked, but I don't see how.

Any thoughts?
Is he joking?

Yeah it's diodes cutting the sine wave, in reverse the dc would see either a "brick wall" or a short circuit.

An inverter would do the trick, but that sounds more expensive/complicated than just getting the correct relay?

Last edited by Dirt; February 8th, 2018 at 11:29 AM.
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Old February 8th, 2018, 11:56 AM   #8
Mickey
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Talking

Quote:
Originally Posted by Dirt View Post
Is he joking?

Yeah it's diodes cutting the sine wave, in reverse the dc would see either a "brick wall" or a short circuit.

An inverter would do the trick, but that sounds more expensive/complicated than just getting the correct relay?

This thread should clear the above up. A long read but funny. I miss those old threads.

http://www.plctalk.net/qanda/showthr...light=thing+dc
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Old February 8th, 2018, 01:00 PM   #9
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Quote:
Originally Posted by Mickey View Post
This thread should clear the above up. A long read but funny. I miss those old threads.

http://www.plctalk.net/qanda/showthr...light=thing+dc
What I took away from that thread was:

You see, this forum is kinda like talking to my wife. You ask her one question, and you get a whole boat load of something else.


*
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Old February 8th, 2018, 07:52 PM   #10
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Quote:
Originally Posted by Mickey View Post
This thread should clear the above up. A long read but funny. I miss those old threads.

http://www.plctalk.net/qanda/showthr...light=thing+dc
Lol, thanks for wasting 20 minutes of my life. It was haliarious. Unfortunately, I think I actually agree with the a$$hat
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Old February 9th, 2018, 04:57 PM   #11
NetNathan
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The are 2 types of trip units.... "Shunt Trip" and "Undervoltage Trip".
A "Shunt Trip" device trips on voltage applied.
An "Undervoltage Trip" device trips on loss of voltage.

These can be ordered at different voltage levels.
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Old February 17th, 2018, 09:25 PM   #12
DickDV
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I don't mean to suggest this as any kind of practical solution but I believe you will find that an AC rated coil in a relay will operate successfully at a much lower DC voltage. You can play around with one in the lab and I believe that if you start very low with the DC and come up slowly, you will reach a voltage where the coil will attract the armature and not overheat.

This is not to recommend doing this. It might do if your life was at risk and you were stranded on a remote island with nothing but variable DC power but few other places.

If you disassemble an AC relay coil, you will find that it is simply a coil of wire (just like the DC version) but with a bronze shading ring around the nose of the magnetic core.

Without the shading ring, you would have a 60hz buzzer much like a motor starter with an AC coil and a broken shading ring. You have to replace the coil to get the starter to stop chattering but really, all you need to replace is the broken shading ring (comes with the new coil).

Of course, the AC coil is wound with different inductance and wire turns if the voltage was to be the same AC for DC in addition to the shading ring.
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Old February 18th, 2018, 02:36 AM   #13
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Not reliable - been there - done that! Works sometimes and not other times.
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