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What is wrong with this circuit?

Question asked by Anup pr in #Electronics on Aug 19, 2019
Anup pr
Anup pr · Aug 19, 2019
Rank E1 - BEGINNER

I'm trying to build an electromechanical relay with an electronic circuit used to trigger the relay coil to turn it on. Well my circuit has a MOSFET which is AURIF2807 and an OPTOCOUPLER which can be used to turn on the EMR coil. well the rated voltage for the coil is 48VDC @ 48A but the relay works good with 48VDC @ 2A, when rated current 48A is applied to it. It burns up the EMR. One of the problems that Ive noticed is even after the EMR is turned off the MOSFET still conducts (Gate conducts). Please help me with your views on what went wrong with this circuit and how can I fix this. Appreciate your help thank you!ce9r-emr.jpg 

Posted in: #Electronics
Ramani Aswath
Ramani Aswath · Aug 19, 2019
Rank A1 - PRO

Something doesn’t gel. An EMR rated  48 V and 48 A? That’s nearly 2.5 KW. What sort of relay guzzles that much power? Assuming that it does then the turn on current cannot be as low as    2 A.

If all that’s wanted is a opto-coupled relay switch, why not use an SCR to switch the coil? The circuit can be far simpler.

It is possible that you have some other constraints. I have used such opto-coupled relay circuits for various purposes. Very trivial circuits. Never gave any trouble even after years of service.

Anup pr
Anup pr · Aug 19, 2019
Rank E1 - BEGINNER

@Ramani Aswath Thank you so much for your reply sir! will look into SCR.  

Anup pr
Anup pr · Aug 19, 2019
Rank E1 - BEGINNER

UPDATE: My bad the load is 48VDC @ 20A and so is the rated specs for the EMR. Well the 48VDC @ 20A passes through the contacts. So the contacts has to carry 20A but it fails to do so either it burns up or even after EMR is off the gate still conducts and contacts weld together. don't know if I have to change the circuit completely? Appreciate your help!

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