# Controlling a pulsed digiital output with a tachometer input

OK I ran the oil pump on the work bench today with a 12VDC power supply and pulse generator with various OFF times . With the 42 ms input pulse I was getting 0.2 CCs of oil flow with every stroke of the pump . I ran tests on the minimum required fuel/ oil ratio of 100:1 per hour @ Idle = 49.21 CCs per hour / 0.820 CCs per minute = ( 4.1 pump strokes per minute required with 0.2 CC delivery )

Maximum requirement which is 1590 CCs of oil @ WOT per hour / 26.5 CCs for 50:1 fuel /ratio per minute = ( 132.5 pump strokes per minute required @ 0.2 CC delivery )
I haven't done the calculations for the remaining oil ratios yet at the various rpm ranges 80,70,60 :1 but that's easy enough .

I was surprised the volume of oil output was lower than I was expecting but I had tygon tubing on the inlet and outlet to the oil pump to verify oil in the lines so it is what it is . EDITED A COUPLE OF ERRORS 7/17/21

Do you think there will be a change in oil volume with temperature increase?
Paul

With the 42 ms input pulse I was getting 0.2 CCs of oil flow with every stroke of the pump.

Good job determining the pump delivery rate.

I ran tests on the minimum required fuel/ oil ratio of 100:1 per hour @ Idle = 795 CCs per hour / 13.25 CCs per minute = ( 66.25 pump strokes per minute required with 0.2 CC delivery )

At idle, if you deliver 13.25 CCs/min = 795 CCs per hour, this means you would using 79.5 liters of fuel per hour at idle. This does not appear reasonable.

Maximum requirement which is 1590 CCs of oil @ WOT per hour

What is the fuel consumption at WOT?
I would think that WOT should take significantly more than 2x the oil of idle value.

Perhaps I am misunderstanding what you are reporting, so can you please explain in more detail your bench experiments.

I did all of my original calculations in gallons and ounces based of fuel curve data I I found for my engine . Theoretical Fuel consumption per hour at WOT should be around 20 gallons based on 200 hp but actual is approximately 20.75 gallons .
I rounded up to 21 gallons per hour because a little extra lube wont anything
21 gallons x 128 ounces = 2688 ounces . 2688 / 50 = 53.76 ounces of oil @WOT per hour ( which converts to 26.5 CCs per minute )

At Idle fuel consumption is 1.3 gallons per hour (1.3 x 128 = 166.4 ounces /100
= 1.664 ounces of oil per hour ) ( this converts to 0.820 CCs per minute )

I see I messed up the conversion for Idle values I apologize for that I had posted the correct numbers in an earlier post above .
For brevity I did not include the calcs for every ratio I am planning on running
if it hits the minimum and maximum required I can fill in the blanks for the rest .

Thanks for clarifying.

Theoretical Fuel consumption per hour at WOT should be around 20 gallons based on 200 hp but actual is approximately 20.75 gallons

That's always been my rule of thumb for 2 strokes: 1 gph per 10 hp at WOT.

What I have never understood is why the oil mixture tables use 8lbs/gallon as the weight of gasoline.

Time for you to go Green and replace the 200hp monster with a 4 stoke.

Hi,

Here in Australia 1000cm3 == 1 litre.
So 795 cm3 = 0.795 litres.

Tom...

The OP was talking about the oil consumption. At idle fuel/oil ratio the fuel would have been 100x the .795 litre.

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The equipment will be located under the engine cowl so the fuel in the VST and oil reservoir will be subjected to the same temps so hopefully it's all relative
All of the oil delivery tests on the pump is performed at 70 F according to Mercury Marine so I guess my testing should be done at that temp too.

Not 'arf! It's pretty courageous to trust the health of a valuable 200hp engine to an Arduino.

Any engine with spark ignition tends to generate noise which can crash a nearby Arduino. I spent ages on shielding and filtering on a small model motor before I got its Arduino crash-free, and just plugging in the USB lead back to the PC makes both the Arduino and PC prone to crashing again.

So, watch out for this. Also, at the very least, implement a watchdog reset. This is important - don't risk wrecking the engine.

I can premix oil in the fuel and have the arduino running in the background and monitor pump oil output in a scaled 1000 cc container without risking anything .
The part of the engine I was planning on locating the arduino on is free from spark plug wires and ignition components . Is there a minimum distance from plug wires you have found?

This is from the maker of the Tach converter module . A little over 4 volts for the pulse magnitude and the duration of each pulse maybe around 1 ms

with 35 ms between pulses that would = 28.57 PPS

Unfortunately I don't know, because space was constrained on the model I was working on. I got something like 15cm separation from the HT lead, but it didn't help much. Obviously the spark current flows through the ground return as well, so maybe that can radiate as well. I don't understand the physics of EMI at all well, sadly.

Screening made the big difference. The secret is to shield both electrically and magnetically by using tin-plated steel sheet. The stuff I used was about 0.1mm, I think, and easy to cut with stout scissors but easily rigid enough. I basically enclosed the entire electronics in it. At the entry points of the wiring from the sensor leads I filtered everything with LC filters.

That got it stable and crash-free, but really I need to research standard practices for automotive electronics because they've got it really well sorted.

It will be very interesting to see how you get on with your system. I hope you'll keep us updated.