Use MS to control Electric Water Pump.

[Crazy2287]

I was asked a question in regards to water pump control, and it got me thinking.

I am helping a friend run MSnS-E for spark only. Crby 6 cylinder. he is useing a Davies Craig electric water pump.
Not using the mega squirts fast idle control so looking closely at it im thinking i should be able to use it instead, to feed the waterpump motor. All the controls are there, frequency, high and low temp setpoints and dutycycle at setpoints.
The main problem is the PWM duty cycle reduces with engine temperature. So the motor would slow down with engine temp.
From what i understand i should be able to use a circuit such as this to invert the signal so when engine is hot and PWM output duty is 0% corrected PWM and voltage will be 12v 100% duty:


Would replace the 39ohm collector resistor with a 1-2k and delete the flyback schottky diode.

Problem is it's not been done as far as i can tell. looked in all my channels and couldn't find anyone who had done this before.

some input would be grouce

[Paul_VR6]

Got any specs on that pump? I would be surprised if the IRLZ44 can drive a ~7a inductive load.

[SymTech Laboratories]

Got any specs on that pump? I would be surprised if the IRLZ44 can drive a ~7a inductive load.

The IRLZ44N should be able to sink quite a bit of current (Id is 44A) as long the gate drive is strong enough and the device is attached to a suitable heat sink.

[Crazy2287]

So you think the idea is viable then? Pump is dc 12v up to 12 amps. I was not useng the fet Showen the one I have is only 15 amps. Illalso have to put some sort of failsafe in for the stall voltage.

[SymTech Laboratories]

So you think the idea is viable then? Pump is dc 12v up to 12 amps. I was not useng the fet Showen the one I have is only 15 amps. Illalso have to put some sort of failsafe in for the stall voltage.

Sure, you could do something like this and use the FIDLE circuit as the inverter. This circuit will clamp the current to ~14A, just like the fuel injector drivers.

water_pump.png

[Crazy2287]

Love the current clamp, very clever. Ill come up with something to clamp the min duty to keep the pump above 6 volts and get you to look over it. Its alwas good to get others to see flaws in your plans before you build them.

[Paul_VR6]

The biggest problem is the startup current. I use 6x steady state as an estimate. If its a 12a motor it might not be enough

[SymTech Laboratories]

The biggest problem is the startup current. I use 6x steady state as an estimate. If its a 12a motor it might not be enough

Six times the operating current is probably estimating a little on the high side for a DC motor, but the inrush current is certainly something to keep in mind.

[Paul_VR6]

Rule of thumb I learned many moons ago but has never been wrong om the side of part damage. Do the math if you really want to get it right!

[SymTech Laboratories]

Rule of thumb I learned many moons ago but has never been wrong om the side of part damage. Do the math if you really want to get it right!

Absolutely, overestimation is often safest! The IRLZ44N should do the trick in this case, but there are beefier MOSFET's if not, or even inrush limiting thermistors. Crazy 2287, do you know the DC resistance of the pump? Davies, Craig seems to only list the "maximum current" for their pumps, which implies the stall/inrush current (for a DC motor, at least).

[racingmini_mtl]

However, if the goal is to use the MS board and the DB37, I would not want to drive anything that will require a beefier MOSFET than an IRLZ44N (or even come close to maxing out its capability).

Jean

[SymTech Laboratories]

We wouldn't recommend installing this circuit inside the MegaSquirt ECU. You would need to use at least two DB37 pins to be able to safely handle the operating current.

[Crazy2287]

The idea is to have the inverter amplifier external in its own zippy box. The fidel wire goe into the bo. Box connects to waterpump. Job done.
Do not know startup currentbut the units supplied controller has smallwires. About 18 awg. No relays so max current wouldent be more then 15 amps.

[SymTech Laboratories]

The idea is to have the inverter amplifier external in its own zippy box. The fidel wire goe into the bo. Box connects to waterpump. Job done.
Do not know startup currentbut the units supplied controller has smallwires. About 18 awg. No relays so max current wouldent be more then 15 amps.

It sounds like you have it all figured out. Please let us know how it turns out!

[dll67]

So how did it turn out? I'm looking to do the same thing with a meziere water pump