Pwm 12volt square wave

[matthunter1448]

Just wondering how to get this, my new fuel pump(fuel lab) uses pwm just has to be a 12 volt square wave

[nathaninwa]

Can you use a solid state relay? I'm using a pwm output to a ssr to control a cooling fan

[matthunter1448]

Don't need to I can connect the signal wire direct to the fuel pump that's how it's designed

[matthunter1448]

Here's the instructions

[nathaninwa]

Ahhh. I think I get it. You need a pwm signal that is 12v positive instead of ground switching like it is now Hmmmmm. Wonder if you'd have to use a low amp ssr to create this?

[matthunter1448]

Not sure I'm sure somebody here knows

[matthunter1448]

Hard-line mentioned this in about another thread I just want to be sure it's right

The range of duty cycle that the FPDM recognizes is 10% (pump speed of 20%) to 50% (Pump Speed of 100%) If it sees a pwm value of less than 10%, it will assume a fault and run the pump at full speed, and if it sees a PWM Value of around 75%, it recognizes that as the fuel pump shutdown command that the factory ECU would send. It wants the PWM signal to be a 12 volt square wave, so you'd set the fuel pump output to inverted and use a 330 ohm to 1K ohm resistor as pullup to 12 volt. Works like a charm for me. I run mine in closed loop mode, and have a 5 bar fuel pressure sensor that is of a differential pressure type (fuel pressure is referenced to manifold pressure, not atmospheric.

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[nathaninwa]

Gotcha. Read the little ? Mark on the fuel pump page for polarity. Doing what you quoted should just right

[matthunter1448]

But which resistor? that's a range he gave, I just want to wire it right the first time

[billr]

Well, I read that posted wiring scheme different, so I went to the Fuelab site and looked at the full instruction set. That confirmed my belief that this pump does not want a 12V signal to its control terminal. Rather, it wants a grounding driver (has a built-in "pull-up) and can work with 0-5V. There is no mention of input current, so I can't tell if it is truly a "logic-level" input. Note that the pump instructions distinctly show that input being either open or pulled to ground for 2-speed control. They say <1/4V is "low speed" and >2.5V is "high speed", with any PWM between those giving an in-between speed.

I am not trying to be argumentative, and surely could be wrong, but felt I had to raise a flag. I don't want to see you going off in the weeds. Anybody else care to confirm or refute my dissenting opinion?

[hardline]

My post was for driving a Ford FPDM. If you aren't running one of those, my info does not apply

[juansh2385]

first you need to know the draw current. if is less than 500ma just use one of the stepper iac out. if it use more current that what the stepper can supply use the standar pwm circuit in the manual and add a 1k pull up to 12v.


Juan.