Gday Guys,
I am upgrading the electronics for a new cycle hydrogen engine we are building. We have had the engine running to about 3000 rpm and it works fine. We have found however that the MOSFETS we have been using (IRF 540N) are not handling the load to drive the fuel injectors at full fuel. I am installing better heat sinks and I was hoping someone could advise a more suitable choice of MOSFET. The circuits are 12v, the fuel injectors are 2.6ohms, the frequency varies from 5 Hz to 50Hz and the duty cycle varies up to 65%.
Thank you for your time
Brendan 
Hi Brendan,
Sounds interesting! What in the circuit is driving the MOSTFETS high/low (a microcontroller pin, or something else)?
Thank you for your reply Graham
The MOSFETS are driven by an Arduino micro controller sending 5v high/low signals to optocouplers that engage the gate.
There range of parameters we measure off the engine is growing but at this stage we only use the engine speed in our algorithms. The value of the rev limiter is determined by a voltage read through a manually adjusted potentiometer.
Right now we are trialling the MOSFETS using a simple simulator program (a modified BLINK program) just to see if we can control the temperature before we put the circuit back to work.
Any feedback would be most welcome
Thank you
Brendan
Nice to hear. And how are they wired-up to drive the MOSFET on/off (perhaps a screenshot of the circuit, or a quick sketch)?
I’m just making sure the MOSFET gates are being pulled up/down as fast as possible before going into some recommendations 
I am sorry for the poor quality of the drawing. I hope you can make sense of it.
As you will see there are two separate circuits, Engine and Control if you like.
EARTH = earth on engine for 12v battery
GROUND = ground on micro controller using separate battery attached via USB
And Graham the wave forms on the oscilloscope on both sides of the 4N25 optocoupler are nice and square. So as far as I am aware the gate switching speed is fast. Today I wired in two MOSFETs in parallel. It has made a considerable improvement and may do the job for the oxygen injectors. However if there was a more robust MOSFET it would be good to use them for the hydrogen injectors at least, as they are on for twice as long.
Looking forward to your reply
Thank you
Brendan
This page has a list of replacement FETs for the irf540n:
https://www.el-component.com/mosfets/irf540n
For example, the irf8010 is rated as follows:
Charactiristics IRF8010 MOSFET transistor
- Type: n-channel
- Drain-to-Source Breakdown Voltage: 100 V
- Gate-to-Source Voltage, max: ± 20 V
- Drain-Source On-State Resistance, max: 15.000 Ohm
- Continuous Drain Current: 80 A
- Total Gate Charge: 81 nC
- Power Dissipation: 260 W
- Package: TO-220AB
Alternatively, try some of the big electronics supplier such as Digikey, and try putting in the requirements in the component selector. Perhaps specifying automotive grade components.
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Thank you Robin,
I see the 8010 you referenced dissipates twice the power of the 540N we have been using. I will do a trial today with two 540’s in parallel and if they can’t handle the simulated full fuel load I’ll source the 8010’s.
Thank you again and have a great day
Brendan
