If yes, What would be the voltage and amperage for DC to operate the 120 VAC contactor? And, Can I connect two contactors in parallel, and actuate both using DC ? I need it for a project, where I can't use AC and have to work with existing 120VAC Contactors.

My project involves the use of limit switches, which is why I was using a dc power supply. And the output from the limit switches actuate the contactor that run lines to the AC motor. Is is safe to run AC through limit switches. The limit switches would be in close proximity with the user. If yes, then I do not need any conversion. And I can run the entire circuit on AC alone.

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    \$\begingroup\$ You don't double the current switching capacity by putting two in parallel, in case you were thinking of doing that. \$\endgroup\$ – Andrew Morton Sep 26 '17 at 15:04
  • \$\begingroup\$ Here is an application note that covers this very question. They appear to discourage it. \$\endgroup\$ – Spehro Pefhany Sep 26 '17 at 19:37
  • \$\begingroup\$ consider a starter solenoid \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 26 '17 at 20:39
  • \$\begingroup\$ Why can't you use AC or the proper solenoid. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 26 '17 at 20:45

DC can be used for AC contactor coils, but you will need to determine the voltage and current by testing. There is a good possibility that the voltage and current required to get the contactor to pull in may cause the contactor coil to overheat is maintained continuously. That will require an "economizer circuit" to reduce the current after the contactor has pulled in.

Some contactors have coils or core and coil assemblies that can be replaced with DC components. That would at least provide known coil characteristics. You may still need an economizer circuit.

If you can't use AC, what will the contactors be switching? AC contactors are very limited in their ability to switch DC current.

If you are asking about parallel coils, there is no problem with that, but each coil will need its own economizer circuit.

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  • \$\begingroup\$ Is there also a risk of the contactor armature sticking due to remnant magnetism with long-term DC magnetisation? \$\endgroup\$ – Transistor Sep 26 '17 at 16:18
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    \$\begingroup\$ It is likely that release would be slowed somewhat by the effect of the shading coil, but I wouldn't think that would be much different from connecting an inverse diode across the coil of a DC relay. I don't believe that remanent magnetism of the iron would be a big concern. Looking into that should be part of the task however. \$\endgroup\$ – Charles Cowie Sep 26 '17 at 16:54
  • \$\begingroup\$ Thanks. I asked because I'm aware that most DC relays have a little bump or 'bip' on the armature to maintain a very small air-gap to prevent magnetic latching. \$\endgroup\$ – Transistor Sep 26 '17 at 20:45

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