Solid state relay for fuel pump - how to

[Hodgdon Extreme]

I installed one of the big walbro pumps in my turbo IS300. It can draw 25 amps, so I chose to use a SSR so I can drive the pump only as hard as required to maintain sufficient fuel pressure. My intention was not to precisely control fuel pressure via PWM, so I have not implemented fancy duty cycle calibration maps/surfaces; just a simple 2D table of DC versus MGP so the pump increases DC as MGP increases.

Here is my system wiring diagram:

Basically I'm using the OEM relays to ultimately close a heavy duty 50A fuel pump "isolation" relay. This is because solid state relays leak current even when they're open - so the 50A relay removes power to the SSR when the key is off.

Note the fast acting flyback diode spliced across the pump power leads!

I mounted the SSR to a heat sink. I think it's overkill because it doesn't seem to get very warm.

I've got my PWM frequency set at 450Hz and it's been working great. 

I used a Crydom 100A solid state relay:

Be sure you get one designed specifically for direct current!

Here are some other potential choices for relays:

HELLA
PART NUMBER: 4RA-931-773-98 or 4RA 007 865-031

They're rated at 22A switching current which means they can handle more at 100% duty cycle. The big Walbros can draw about 25A - so I think this relay would do the job.

 

Part # 15620NOS

Rated at 20A switching and 40A continuous. I've read a bunch of good reviews about this unit.
 

Dorman 902-310 Engine Cooling Fan Relay Kit

Unsure on current rating, but fan motors draw a lot. Again, many good reviews on these.

[koracing]

Your diagram shows Aux12 as being the output from the ecu for the relay?  Aux12 can't PWM - so is that correct?

[Hodgdon Extreme]

9 minutes ago, koracing said:

Your diagram shows Aux12 as being the output from the ecu for the relay?  Aux12 can't PWM - so is that correct?

Nice catch!

It's wired to Aux 2, not Aux12

[Adamw]

A couple more relevant considerations:

• The Hella one doesnt like PWM'ing more than about 10A.
• The Crydom and other similar industrial ones need to be well overrated to give acceptable life, the 100A ones are usually ok, the 40A ones fail quick with just a basic pump.  They generally dont work much above 200Hz either so im surprised 450Hz is working for you.
• Fan controllers generally work ok but be aware there logic is generally designed to failsafe in the "100%" condition.  Whereas fuel pump controller's failsafe is 0%. 
• Be careful with slowing common aftermarket EFI pumps down too much that arent designed for variable speed control, many give extreme fuel pressure pulsations when the motor torque is reduced, I dont really know why but I assume the rotor speed must become unstable.  Most get pretty funky below around 45% DC.