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OMEX PWM control of electric water pump


sideways_stu
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Hi - does anyone have any experience with the OMEX 600 using Aux 1 as PWM output with a temp vs PWM table to control an electric water pump?  I'm planning an engine swap where I use a EWP110 water pump - a solid state relay driven by PWM from the OMEX ECU would be a neat solution vs another stand-alone controller.

I use the same engine & pump on a stage rally car but since its purely competition it runs 100% duty.

 

Thanks Stuart

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Not Omex but again, used that method. Used to drive a water/methanol injector and the HP pump that supplied it. 

 

Don’t know that ECU but if it has the feature, you can tune for best result by tweaking PWM frequency to suit the hardware you are using. 

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@Arm and @corsechris - Any recommendation on SSR model or type and any SSR protection you added given you are switching an inductive load would be very interesting.  From what I've read a lower frequency and flyback diode are both good ideas and the OMEX PWM output can be adjusted 250-25Hz.

 

Thanks Stuart

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I used an ordinary relay to drive the pump as it had a simple on/off requirement so I set the map to 0% below threshold and 100% above. The meth injection was done by an ‘HSV’ high speed valve) that was basically like a fuel injector so was driven directly by the ECU output.

 

It may well be that the ECU can drive the load directly?

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If using a SSR in the engine bay, watch out for the temperature de-rating.

Either use an overly rated one to operate at engine bay temps or place it in the cockpit or forward of the rad. You’ll also need a heat sink for the SSR.

 

Another spec to check is the maximum switching frequency. Some are low like 50Hz. Low PWM drive frequencies can sound nasty as something on our cars will resonate.


You’re right about the inductive switching, but a diode could control the recirculating currents and protect your SSR. You just need the right spec.
 

Software is another potential problem; is the ECU setup to control the PWM relative the engine temperature and is it tuneable?
 

Craig Davies do a digital water pump and fan controller kit. Merlin Motorsport sell them. Might be the easier option.

 

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Thanks @Westy119 - integrated aluminium heat sink/base plate and then mounted onto a metal surface seems the way to go to control SSR temps.

The CD controller is a perfectly good solution but its standalone, another add-on and the Omex PWM control allows a map of PWM duty cycle vs coolant temp which is just what is needed.

I'll do some looking into appropriate diodes and then it sounds like time to test!

 

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I see the EWP110 is rated at 10.5A. I think I’d want at least a 100% overhead on that, maybe even as much as a 30A capable device, with good flyback protection.

 

Copy the output stage of the Davies Craig controller??

 

Or as suggested on those links, 2 or 3 very over-spec MOSFETs in parallel.

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I have some 40Amp DC/DC SSRs sat in the garage and will add 2 x 20Amp Schottky diodes - around 25% of rating should be very safe. 

I'll jury-rig a test off the car to prove it first and see what sort of duty cycle range & PWM frequency works best.

It will probably be several weeks before I get to this but I'll endeavour to post results in case others find it useful.

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  • 2 months later...

I did finally get to test this with mixed fortunes so far - sharing this in case others consider this and to save them time.

With a restricted inlet & full 12.5v the EWP110 flows about 1 litre per second measured on my sophisticated dyno 🙂

The User1 pwm output on the Omex is easy to configure and the pump seems happier with 84Hz or higher and needs 10% duty cycle or higher.

However the pump flow at 10% PWM duty cycle is 90% of full flow and from 30% duty cycle it is 100% (current draw matches this).

I wonder if the solid state relay I am using is slow to switch off so Omex specified duty cycle isn't reflected at the EWP.

Now coming round to the idea that PWM alone isn't sufficient and it may need the long duration pulsing as well as PWM for reduced voltage - in fact as the Davies Craig controller does!

Next steps are to try another brand of SSR and may also consider building a 2 stage flip-flop circuit to give slow pulses / more pulses / 100% selected by 2 omex outputs responding to coolant temp.  Otherwise it is fit another controller and another coolant temp sensor etc.

 

Will post the final outcome probably near Christmas.

 

ewp test.jpg

Screenshot 2021-09-15 at 12-35-52 EWP® DIGITAL CONTROLLER INSTALLATION INSTRUCTIONS - 1484524180 18922-LCDEWPFANDigitalCont[...].png

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There is some restriction with the tap - probably around 15mm bore down from 38mm which is a 85% reduction in cross section - if the flow charts are to be believed that is equiv to around 4 psi.

 

I'm thinking of using 2 astable circuits in series driving a relay for the pump to give 10sec on / 30 off and then 10 on / 10 off and finally full on switched by 2 aux outputs on the omex using temp thresholds - pretty similar to the standalone controller behaviour above.

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