PWM output

[congo]

An older post referred to using the IRF530 mosfet as a means to increase the amperage when switching larger loads, the response was to use an SSR. My expierience with this is that most puck style SSR I've tested are too slow and created excessive heat in the motor and poor control. Does anyone have any hardware suggestions for using the NANO PWM output to drive a 12VDC motor up to 7 amps?  

[support]

When you said the SSR is too slow

1) Are you using one with a DC output driver? The AC output type (TRIAC) will not work

2) What frequency are you driving the SSR? You need to check the maximum frequency that the SSR can handle without distorting the output waveform and keep your PWM frequency well below the maximum.

If you do not want to use off-the-shelf SSR you should still construct a circuit with an opto-isolator and a MOSFET output driver to drive your motor since the current is so high there are lots of inductive noise arising from switch the motor coil. Ensure that you have used a high speed snubber to bypass the inductive kick.  Use a separate power supply for the motor.

When a MOSFET drives 7A of current you have to mount it on a heat sink due to the power dissipated at the junction from the finite ON resistance on the solid state driver.

[congo]

The SSR is DC on the control and load side, so yes. The combination of 'On and Off' time capability limits the output carrier frequency to less than 1KHz, which when operating below 1KHz creates too much heat in the 3.5Amp motor I'm using, so I need to find a solution where I can run much higher frequency.

If there is more literature available detailing the MOSFET/opto-coupler circuit included in the manual I'd like to give that more testing. I tested that on the bench (only had IFR520 so used that) but I couldn't seem to see the PWM SIGNAL on the output side of the optocoupler and as soon as the IFR520 was connected it seemed to stay 'closed' and the motor just ran. I eliminated the optocoupler (downside is the motor circuit is 12VDC) but found the MOSFET output acted inversely to the Nano-10 PWM output. When the duty cycle increased the output through the IFR520 slowed the motor speed.

Either I'll need to figure out what's wrong with the breadboard level circuit or source an amplifier board that can take the PWM signal directly from the Nano-10 and drive the motor. Help with either of these would be appreciated.

[support]

Do remember that the IRF530 is N-channel MOSFET. You have to wire its Drain to the low side of the load, and the Source to the 0V of the load. The +12V is applied to the high side of the load.  

IRF520 is turned on by a positive gate voltage of >= 10V with respect to Source (S terminal). If your IRF520 is turned ON fully regardless of the PWM waveform you should use a multi-meter to check the voltage at the gate. If the voltage is low but the IRF520 is fully turned on it means that it could already have died and short circuited. Try changing the MOSFET.

IRF520 is a pretty old MOSFET. For high current application you can look for many new generation of MOSFET with very low RDS On and cost not much more.

E.g. STP160N3LL is N-channel MOSFET that can handle 120A of current continuously (with heat sinking, of course but the RDS is pretty low - 3.2m ohm @60A)