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I have a custom made solenoid that is required to work at 60V to actuate with enough force.

I have tried two circuits shown in the figure below but both don't work. In the first circuit, the voltage across the coils is just 3V whereas in the second one, the voltage across the coil is zero although the opto isolator does work.

I can't figure out what is going wrong. I used IRFZ44N for mosfets at 30V source-drain voltage for testing.

enter image description here

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luiferns is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • \$\begingroup\$ What is the reasons for having two MOSFETs? You should do some research into switching a load as that has been asked many times before and also on this site. With the first circuit you're quite close, just remove Q1, short the points that used to be pin 1 and 3 of Q1. Do make sure Q2 is an N-channel MOSFET with 1 = drain, 2 = gate and 3 = source (IRFZ44N is an NMOSFET, so OK to use). \$\endgroup\$ – Bimpelrekkie Jan 10 at 10:13
  • \$\begingroup\$ Thanks a lot. That did work for the first circuit. The reason for the second mosfet was to prevent the capacitor from discharging through -ve terminal (which i would be using to store the charge instead of 60v supply). I guess its not needed anyway. I still dont get why the second one doesnt work. Seems so simple. \$\endgroup\$ – luiferns Jan 11 at 10:26
  • \$\begingroup\$ I still dont get why the second one doesnt work I do :-) Most optocouplers (or optoisolators) cannot conduct so much current through their output. Your EL817 can only support up to 50 mA. We generally only use the output of an optocoupler to control the gate or base of a much more powerful switching transistor. There are "solid state relays" that also use optical coupling and these are powerful enough to directly switch your current. But your EL817 isn't of that type. \$\endgroup\$ – Bimpelrekkie Jan 11 at 11:06
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For the first circuit remove the top mosfet and connect the diode and solenoid to the 60V supply. Make sure the MOSFET you use is fully saturated by the output voltage of the arduino, otherwise you'll find they die. You may also want to add more snubbing circuitry.

In the second circuit you've read the schematic wrongly, the component isn't a opto isolator, but an opto-isolated solid state relay.

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james is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • \$\begingroup\$ Thanks for the help. I got it working after @Bimpelrekkie commented. As for the opto part, the one is schematic is just for representation. the part i was using was EL817. Extremely sorry! \$\endgroup\$ – luiferns Jan 11 at 10:28

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