Hodgdon Extreme Posted May 2, 2023 Report Share Posted May 2, 2023 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. dx4picco 1 Quote Link to comment Share on other sites More sharing options...
koracing Posted May 2, 2023 Report Share Posted May 2, 2023 Your diagram shows Aux12 as being the output from the ecu for the relay? Aux12 can't PWM - so is that correct? Quote Link to comment Share on other sites More sharing options...
Hodgdon Extreme Posted May 2, 2023 Author Report Share Posted May 2, 2023 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 Quote Link to comment Share on other sites More sharing options...
Adamw Posted May 3, 2023 Report Share Posted May 3, 2023 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. Admiral Akhtar 1 Quote Link to comment Share on other sites More sharing options...
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