Charley,
Welcome to the forum. Under normal circumstances etiquette would require you to start another thread for your question. But I see you have just joined and this is your first post.
Charley Higgins said:
We have a feeder breaker with 125VDC control that has a history of burning up closing coils.
You say this is a closing coil. Does it need to stay energised or the breaker will drop out?
Charley Higgins said:
the breakers are old some of the coils that have been purchased and used were marked AC with no other additional information.
When I read this it sounds like you have the wrong coils for the application. If this antique gear and all that is available anymore is the AC coils, then perhaps this approach will work.
Many large DC powered contactor coils use a resistor in series with the coil to limit the continuous current. But they also use a contact to short across the resistor when the coil is first energised. This way the coil has the power to "seal" in but is current limited during "run". Most DC powered coils use a "late breaking" aux contact for this purpose. If you don't have one of these available, then perhaps a DC powered "delay on make" relay will work for you.
As far as the amount of resistance to use, I'm afraid it's experimentation time. How large and heavy is the coil? Do you have any simular sized and or weighted coils that are AC powered on site? If you do then see if you can get
Edit: This test is for the 120v AC powered simular sized coil.
1. Ohm reading.
2. Amp reading using Ron Beaufort's test with the armature not sealed. Don't do this for very long!
3. Amp reading with the armature sealed.
This will give you a starting point for the amount of resistance needed. The size and weight of the coil determine the amount of energy it can dissapate before burnout occurs. Of course the final determination would be: Will the coil remain sealed with the resistance in line?
The wattage can be figured by Ohm's law