[Hella SSR Relay fuel pump control issue.]

2 hours ago, Stevieturbo said:

The Crydom DC-series SSR's work fine, I've been running my 450's off one all last year with no problems. But yes you do need a flyback diode at the pumps. ( 2x450's off one 60A ) I've a 3rd in tank pump if need be and a 100A relay sitting if and when I do need to use it

And in no way whatsoever is the little Hella relay suitable for such a purpose, even from the standpoint of coping with the current of such a pump, nevermind trying to pwm it too.

 

Haltech offer this drawing and is how I use mine with Syvecs. Although a high frequency would probably be better with a proper controller, it does seem SSR's dont really enjoy being pushed in this way. I found mine happy around 200Hz.

https://www.haltech.com/wp-content/uploads/2017/10/SSR_Power_SW_Web.pdf

 

I do use one of the Hella SSR relays for my water injection though.

I'm glad to someone else has blazed this path! I'm very new to all of this and the learning curve has been steep. That 1k pull-up resistor is interesting. I've never seen it used for PWM on anything else, but I bet it makes for a much cleaner signal coming from the ECU...

How big of flyback are you using? I know when it's going to a solenoid, it's supposed to be rated for the amperage that it takes to operate the solenoid. But that's not really feasible with pumps drawing 20+ amps and fans drawing 40+ amps...

[Hella SSR Relay fuel pump control issue.]

Any time you're running an inductive load it's a good idea to use a flyback diode. It'll even help normal relays last longer by saving the contacts from extra arc burn. I'm wondering if anybody has tried these Crydom SSR's? They have a huge current capacity, accept PWM, they isolate the ECU from any noise from the load with a optocoupler, and you can pick up a heat sync for cheap on amazon. I ordered two 60a (overkill, but they were unused old stock for 40% off) ones off eBay and am going to test them with a fuel pump and cooling fan with PWM from the ECU. But I will definitely be using some big diodes to protect them. They even have a wiring diagram showing how to wire the diode for an inductive load. I'm still waiting on delivery but I'll try and report back when I see how they work.