I am trying to design a circuit to control the starter motor of a RC aircraft engine.
It is a 30 cc two stroke gasoline engine and has an electric motor attached as onboard starter. The original control module states that it can withstand 100 Amperes. I do not know the exact current required but especially during startup it will be very high. The system will be supplied by a 3S LiPo battery (that means 11.1 - 12.4 V).
My first choice would be a relay. I would use an Attiny85 to control a transistor which in turn would control the relay. The Attiny85 would receive PWM signal from the receiver for the ON/OFF commands. This part of the circuit is very straightforward and does not need any discussion. But the power section has problems.
It was very difficult (actually impossible) to find a suitable relay which should work under 12V and be not too big and heavy. So I decided to look for a MOSFET solution. The logic level N channel MOSFET IRL540N seemed to be a good choice (continuus drain current of 20+ A and peak drain current of 110 A. With four paralleled MOSFETs those values would be 80 A and 440 A respectively). I planned to use two or four MOSFETs in parallel to handle the high current and decided to use PWM to limit the startup current surge which would otherwise destroy the MOSFETs.
My code was sending a PWM signal of 50 % duty cycle for the first two seconds and then switched over to full power. But unfortunately the MOSFETs produced a nice smoke and then the motor was switched ON continuosly (that means the MOSFETs vere burnt out.
Afterwards I found a suitable relay with a max. current of 30 A and used two parallel relays and the control module works flawlessly now.
But...
I really want to know whether it would be possible to design a MOSFET driver for this task. Attached you can see the circuit diagram.
I need to know how I can manage the startup of the motor without damaging the driver MOSFETs.
It is a 30 cc two stroke gasoline engine and has an electric motor attached as onboard starter. The original control module states that it can withstand 100 Amperes. I do not know the exact current required but especially during startup it will be very high. The system will be supplied by a 3S LiPo battery (that means 11.1 - 12.4 V).
My first choice would be a relay. I would use an Attiny85 to control a transistor which in turn would control the relay. The Attiny85 would receive PWM signal from the receiver for the ON/OFF commands. This part of the circuit is very straightforward and does not need any discussion. But the power section has problems.
It was very difficult (actually impossible) to find a suitable relay which should work under 12V and be not too big and heavy. So I decided to look for a MOSFET solution. The logic level N channel MOSFET IRL540N seemed to be a good choice (continuus drain current of 20+ A and peak drain current of 110 A. With four paralleled MOSFETs those values would be 80 A and 440 A respectively). I planned to use two or four MOSFETs in parallel to handle the high current and decided to use PWM to limit the startup current surge which would otherwise destroy the MOSFETs.
My code was sending a PWM signal of 50 % duty cycle for the first two seconds and then switched over to full power. But unfortunately the MOSFETs produced a nice smoke and then the motor was switched ON continuosly (that means the MOSFETs vere burnt out.
Afterwards I found a suitable relay with a max. current of 30 A and used two parallel relays and the control module works flawlessly now.
But...
I really want to know whether it would be possible to design a MOSFET driver for this task. Attached you can see the circuit diagram.
I need to know how I can manage the startup of the motor without damaging the driver MOSFETs.
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