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Dc coil Contactor

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New Member
Hi .. i am new in this forum, I hope can find some answers.

I hit a road block to think of away to solve a current issue.

I doing a project call change over supply of 48VDC from 2 different supply. by using a DC coil Contactor.

When this contactor engage with battery power it will instantaneous active and deactive. But when using a rectifier or voltage regulator the are some delay on deactivation process when switch off the power

I know the reason why. Rectifier and the DC voltage regulator discharge the load more slower compare with battery because of the built in capacitor and that's why make the deactivation process have at a second delay..

The issue now, how to can I get instantaneous deactivation by using rectifier and DC voltage regulator?

I try using Resistor to bring down the DC coil voltage but does not help much. I try with additional relay.. is bit faster but is the resuit i need.

I am out of idea. i do hope someone can share some idea. :rolleyes:


Well-Known Member
Most Helpful Member
If you are using a rectifier, filter cap, and regulator to feed the Relay coil, you must be trying to detect the presence or absence of an AC voltage to run your 48V load on battery or not?

Why not just use an AC line-powered relay ?
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New Member
The system for AC coil already exist .. but the system have to involve an Dc- Ac Inverter and is big...they only Supply me 48Vdc load, so AC is impossible to get because of the distance.

The entire system is actually for DC system which means there 2 Dc supply, primary and secondary and only have one output. This contactor act as a switching device from primary to secondary when there is an error on primary supply. That's why the swictching time must be instantaneous so there is no down time at all when the process of switching happen. The dc coil now is getting the supply from primary as well.

This process is a sucess when using an Ac Coil relay... but now I try to reduce the size of this system by using Dc coil so i can take away the inverter.

Is there any way that I can cut off the DC supply straight away when there is a primary failure.


Most Helpful Member
Why is the system not using diodes to block one supply from back feeding to the other?
Why relay isolation?

Got a schematic to better illustrate what your working with?


Well-Known Member
Not clear on your exact requirements but sounds like you have two D.C. supplies going to a remote location which contains the relay. The secondary supply that runs the relay also supplies power to other circuitry.

You can put in a voltage supervisor that drives an N-ch MOSFET in the negative side of relay coil. When voltage of primary supply drops, say to 46 vdc, the supervisor circuit immediately open the N-ch MOSFET controlling the relay. Make sure you have a shunt back EMF damper diode across the coil.

There are several voltage supervisor IC's on the market or you can design your own circuit to drive the MOSFET.
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