[SOLVED] Arduino Mega to 24VAC output

Projects General Guidance
1

I am replacing an old relay module controlled by Toshiba EX100 PLC with a Arduino Mega controlled system. I was able to easily use a Optocoupler (LTV-8X4) for the inputs to Arduino Mega. My problem is the 24VAC output.
I am using a bridge rectifier (RDBF310-13) as the switch to the motor contactors. The circuit is controlled by a N-Ch Mosfet (MCU80N03A) . The Mosfet gate is controlled by a Optocoupler (LTV-8X7) from a mega pin.
Every time I test the circuit, it either burns the Mosfet or Optocoupler. Can someone tell me what I am missing?

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2

That's clear :frowning:

A MOSFET deserves some gate voltage for turning on. If it only gets what the motor and rectifier leaves then it has sufficient voltage (5-10V) to kill at least the MOSFET if the current also is high enough.

You better use a relay or SSR or Triac or Thyristor+rectifier to control an AC motor, with an additional voltage to turn the Triac/Thyristor on.

3

If I remove the optocoupler, it works great. I was trying to buffer the mega with the optocoupler.

4

Because then the Arduino provides sufficient gate voltage to the MOSFET.

5

So, this should work without issues?

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6

Yes.

The pulldown resistor (R4?) should be connected to the output pin, not gate, to prevent a voltage divider.

Issues may arise from the lack of insulation between the motor and Arduino.

7

Use a relay......

8

Got it working correct after checking my math.

R48 was too high. Change it to 2200 and works fine.

Thanks everyone for the help/options.

9

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