Solid State Main/Aux Relay

[Bitsyncmaster]

I now have the three relays that are needed to run the engine solid State. I may also do the Aux Relay since it is the same as the Main but I think I will stop there and move on to something new.

Here is the design of the Main. A little overkill using three FETs but I still get no heat at all even without heat sinks.

[rhd_delorean]

This is an interesting update, might try to do a few myself.

Is there any disadvantage for using such relays?

[DMCMW Dave]

What's the forward valtage drop through the FETs?

[Bitsyncmaster]

I have had these FET relays and my solid state RPM relay in my car since.
Have not had any problems.

The voltage drop through a FET is computed by ohms law since the FET is just a swiched resistor. Most FETs are fully turned on with 10 volts on the gate to source. The data sheet then specifies the resistance at this point.

Ohms law.....E=IxR....or volts equal amps times resistance.

The IRF2204 specifies a typ. 3.0 mOhm.
10 amps = 0.03 volts
30 amps = 0.09 volts

Now you can compute the heat that needs to be disipated by the FET.

P=ExI....or power equals voltage times amps.

@10 amps = 0.3 watts
@30 amps = 2.7 watts

Now you see why I used three FETs for these high current relays. It's not the voltage drop but the reduction in heat....so I don't need heat sinks. Three FETs now give me 1.0 mOhm. so power disipation @ 30 amps drops to 0.9 watts.

I'm now running out of things to do to my D and I plan to replace my FANZILLA with a solid state unit next.

[bmdmc]

Oh no, I have a better project for you, check your PM.