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Electromagnet circuit

Bruce Baker

New Member
Ron,
I have been working on the circuit that we talked about before with the help of a novice relative when I have the time. Putting in a crude diagram of what I have hooked up (reminding you I am not an electronics person) but the electromagnets are staying on all the time. I tested DC at the MOSFET gate and got .002 volts while the AC tested there was .010 volts. I also cut wire to reed switch to make sure the cause wasn't there but coils remained in on position. I ordered FQP30N06L-ND mosfet which is an N channel.

Bruce
 

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audioguru

Well-Known Member
Most Helpful Member
The datasheet of your Mosfet shows that it needs a gate-source voltage of 10V to fully turn on, some conduct the tiny threshold current when the gate-source voltage is 4V and yours is 5V. Use a "logic level" Mosfet.
Your circuit is missing a very important diode parallel with the coil to squash its high voltage flyback each time it is turned off.

Yours is turned on all the time maybe because it has bees zapped by static electricity or because you have the source and drain pins swapped causing it to be a turned on diode.
 

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