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Electric water pump PWM

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HI Guys

We are PWMing a Davies Craig water pump using a Motec M150. Would anyone know what Hz to operate the pump properly? Thanks Russell

I have used 250 hz for another brand electric water pump.

According to the Davies Craig website FAQ's:

When it comes to choosing a frequency, it really depends on your system, what it can handle and how you intend to wire it.

In general, low frequencies put less work on the control circuit but you sacrifice precise control at low speed and can also produce noise.

Higher frequencies give better control at low speed but can cause the control circuit to overheat and reduce life.

To choose the best frequency is really a trial and error process, once you have dialled in the frequency you control the speed on the pump by adjusting the duty cycle on the PWM signal.

**A reminder, we hold interntional patents for a Digital Controller that will manage the operation of the EWP® by varying the speed of the pump in response to the coolant temperature.

for what its worth i use 150Hz. i have heard of people using 50hz with success too.

hope you have more luck, i run mine at 5% Duty cycle and still cant get the engine up to temp on the road. once above 60kph my water temps drop to 60'c.

my duty cycle is 5% until 85's then from 85-92 its linear to 10%. then its linear to 100% between 92-100'c

looking into bypass thermostats, as on track the cooling system is adequate.

The best systems retain a bypass thermostat with the electric pump. 60 deg Probably doesn't matter unless you need to pass emissions testing or cruise economy rather than specific output if your primary goal.

yeah issues is remote bypass thermostats are bulky and expensive, im looking at machining one but i still worry about the restriction the thermostat will add and the effects on the EWP.

sorry to thread hijack.

I think part of your no temp problem is that a 0% duty cycle is on full and a 100% duty cycle is off. Try your test function and set the duty cycle to 0% and then 100%. Should be definitive.

ITs haltech software so its not inverse like you have shown.

thank you but

Joshua are you using a booster pump in your bypass pipe. If not what's stoping coolant going the wrong direction down the bypass pipe to your ect sensor.


no bypass lines at this stage, was looking at adding a -10 bypass if adding a thermostat to assist getting coolant temps up on the road.

adding small bypass pump that feeds through the turbo maybe an alternative to the thermostat and assist in getting coolant up to temp.

The stock system has a bypass system as the thermostat is on the inlet side of the coolant system. I take it you have the pump in the bottom hose.

The std pump setup sucks from the bottom hose so it takes a small amount of hot water from the outlet side to flow over that thermostat.

Don't run a thermostat even with drilled holes as your pushing cold water from the radiator straight over the thermostat closing it when it should be open. The temp it's reading now is not correct. Hence why you only need a small amount of duty cycle.

You need to stop the water flow going backwards down the factory steel line into the outlet housing. I would also suggest you run a booster pump in this line to keep circulation.

I have a sr20vet in the east west configuration that has the same remote mount thermostat on the inlet. Took me ages to work out what i had done wrong. I now base my water pump duty cycle on ect and radiator outlet temp. And also a full duty cycle over ride when above 80% TPS and 4000rpm.

Now i am following you Nigel,

i would not insert a thermostat in the stock location, as you say the thermostat needs to be on the suction side of the pump.

the reason i havent done it yet as it would require a custom thermostat housing that threads into the pump inlet ($$$ and machine work).

have you had success with a remote thermostat yet? my concern is even when the thermostat is fully open it will still restrict the flow as electric water pumps i have been told struggle to pump any pressure such as that caused by a restriction.

You don't need a thermostat if your PWM the pump. Just cut the center of it and put the plate back in.

In my set up I run a Davies Craig booster pump which runs with ignition on. This moves water from factory outlet housing to factory inlet housing. My main pump does not start untill above 60 Deg ECT. I run no thermostat and can get normal operating temp on a cold morning.

I can't stress enough you need to sit down and work out which way the water now flows as it won't be the same as std.

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