Controling fuel pump with inj1 output

[bojane-1]

The vehicle have two wahlbros fuel pumps 255 lph. Have a small battery and no charging, so therefore thinking of pwm-driving one of the pumps with the inj1 output. The current-draw from the pump is approximately 10 A at 100% dutycycle. Will there be any problems doing this ?

/ Anders

[sedd]

Even if you could run it thru the MS3, it might be safer to run those amps thru a separate relay. Just use the MS3 for turning a separate relay on and off. Run the higher amps thru the relay contacts. The alternative is to potentially damage the MS3 with much higher costs to repair.

In previous response, I was thinking only of on and off control, two equally matched pumps in parallel. PMW would not be the way to go. I should have been more clear on my thoughts.

Isnt there a way to program a simple on and off signal from the MS system that has some deadband around the trigger point, so the relay doesn't chatter? Once you turn on the second pump you should have double the capacity.

[dontz125]

Running something PWM using a relay is somewhat problematic - the relay mechanism tends not to last very long. Since you're asking about this in the MS3 section, I assume you are using an MS3, and can use the Generic PWM outputs. If you don't have a MS3X board, you might consider a good-quality FET on the proto area; the in and out lines should be direct to the DB37 pins, or add a heavier connector through the end plate on the opposite side of the DB37.

To actually answer your question - without changing the code, I don't believe you can use the INJ1 driver for this.

[SymTech Laboratories]

You can use the INJ1 driver as a generic PWM output with MS3, but you obviously have to use the MS3X injector outputs for your fuel injectors. INJ1 can physically handle the current, and you can configure it to output a 11.1-78Hz PWM signal based on MAP vs. RPM.

Nothing on the MS3X board can handle this amount of current, and you should be cautious about building your own circuit in the proto area (sorry dontz125) as whatever MOSFET you choose will probably dissipate a lot of heat (conduction losses are least 6W at 10A with an Rds-on of 60mohm).

[dontz125]

Ok, I'll eat my words for the proto area (shoulda gone with my first thought of remote mount), but I just re-read the MS3 manual, and it lists 6 PWM ports, and INJ1 isn't one of them. What am I missing?

[SymTech Laboratories]

There are six dedicated PWM outputs, but you can use unused injector drivers (on the main board or MS3X), JS11, the LED's, the IAC pins, or the FIDLE pin as generic PWM outputs too.

[prof315]

I've successfully used INJ1 to provide PWM control on a water/meth pump without any problems. However, it never ran for longer than 30 seconds continuously but I think you'd be ok.

[jsmcortina]

The software can do it. The challenge is ensuring you dissipate the heat and have a suitable current path.

inj1 as pwm A

Screenshot-Generic PWM A.png (43.75 KiB) Viewed 580 times

James

[bojane-1]

Ok then it should work. Will only use the pump for a couple of seconds at a time.

Thank you
/Anders

[ahpu99]

Depending on your ultimate purpose, this isn't a great way to control a the fuel pump. The frequencies provided aren't great for driving motors and the pump won't start to spin until you get over 80% duty cycle or so and it can overcome the static pressure. If you simply want a staged pump start only, use 0s below & 100s at and above your set point.

[SymTech Laboratories]

Depending on your ultimate purpose, this isn't a great way to control a the fuel pump. The frequencies provided aren't great for driving motors and the pump won't start to spin until you get over 80% duty cycle or so and it can overcome the static pressure. If you simply want a staged pump start only, use 0s below & 100s at and above your set point.

For on/off control, he might as well use a programmable output.

[bojane-1]

But I have red in other treads, that you can control the fuel-pressure with pwm output, fuel-pressure sensor and a pid controller

[dontz125]

For a SINGLE pump, yes, but you're trying to pwm against the full-pressure output of another pump. Your secondary pump will NOT be happy.

[bojane-1]

Very Interesting I will do a test where I measure the flow after the pressure regulator, then increasing the pwm% until the flow starts to increase. From that point the second pump must have passed the static pressure.

/Anders

[bojane-1]

Well have done the test. The static pressure is achived when pwm exceeds 60-70 percent. Problem is that I fried the output after a few seconds So I will drive with relay and a on off control.

[jsmcortina]

You could still your the table-based "PWM" output in on/off mode to allow a blend of rpm/load to switch the pump on/off if desired. i.e. low loads at high rpms don't need the pump, but when planting the throttle at low revs it might be a good idea to enable the pump ready for a WOT sweep.

James

[frank_ster]

what pump did you burn out the driver with ?

i want to run a gas turbine engine and regulate it with variable speed pump I was planning on using a warbro 255. the injection pressure of this thing is around 20 psi to run. and then raise with engine load. but i could use inj1 and inj2 together to doubble the current load ability.

[bojane-1]

It was a walbro 255 I was trying to drive. I'm guessing it's not the current that killed the output, but high voltage spikes when chopping the motor on and off , the 3 ads channels on ms3x also died at the same time.....

[dontz125]

It could be flyback spikes depending on what FET you used to drive this, but the ones on the MS3X should be fairly rugged.

Thoughts for the crowd - any motor starting or held at low speed will draw a LOT more current than one spinning at full speed. Could this be the cause of the burn-out?

Bojane-1 - what about running both pumps PWM together? What about running a second regulator in line with the second pump, outlet in parallel to the main regulator at the rail? This way the secondary pump isn't fighting the back-pressure of the primary.

[bojane-1]

This was a "quick fix" to make the battery last longer. The ordinary pump was off when I tried pwm the second pump. The pressure on the regulator was 3 bar.

Now I have the pump connected to a relay instead. And ms3x injector output to control the relay. On/off of course.