Ed,

 

Yes, I was kidding about everything except my question about current draw for ignition coils.  (Apparently my winky emoticon ;) wasn’t big enough)

 

I did not know that you built your own EFI system – that explains a lot.  Have you ever looked at the MegaSquirt system?

 

Thanks,

 

-Jeff

 

You are kidding – aren’t you, Jeff.

 

My memory is doing good to tell me who the stranger in the mirror is in the morning – particularly before 1^st cup of coffee.  But, I do keep a whole lot of files (over 10 years worth) and every once in a while they bring up a nugget. 

 

But the greatest is having the internet to find data quickly.  Since I designed and built my own Electronic Fuel Injection System Monitor (EFISM), I had to learn to think in terms of injectors and engine parameters – sometimes I even get it correct.

 

Well, I briefly (very briefly) consider those other elements you mentioned – but, decided Naaahhh, back of the envelope is the excuse for ignoring such 2^nd, 3^rd and 4^th order effects.  Or as some of my instructors used to say – take that one for home work {:>)

 

Happy Thanksgiving to you as well, Jeff.

 

Ed

 

 

Ed,

 

Do you keep all these stats in memory? I’m impressed!

 

(Although, I must say that I’m a little disappointed that you did not include more detail on the electro-magneto dynamics of solenoid field saturation, collapse, and back EMF at higher frequencies, and maybe a little on flyback suppression…;)

 

Now, as I continue down my list of electrical loads, I come to ignition coils. 

 

So Ed (or anyone else), I would like to order another mini EE Masters Thesis on the load drawn by typical ignition coils on a Renesis.

 

 

Thanks for the wealth of information and have an over-stuffed Thanksgiving,

 

 

-Jeff

 

 

Hi Jeff,

 

Since your Renesis injector is the saturated type, it probably has a resistance on the order of 12 ohms (could be anywhere between around 8 – 16 ohms – would have to measure it to be certain.

 

Given a 13.8 Volt system that would mean it would draw I = E/R = 13.8/12 = 1.5 amps when there is sufficient current to pull it open.  Perhaps a bit more or a bit less.  The dynamics of current changing in a magnetic field makes this a non-linear relationship – but for a back of the envelope approach lets ignore that little detail.  Its unlikely the current draw would be more. 

 

This shows the current vs time for a typical saturation type injector.  As you can see the current appears pretty much proportional to the amount of time the injector is open up to the point it stabilizes.  Which I think would be around 1 msec (but just a guess in this case)

 

At WOT at 6000 rpm the maximum PW would be 10 msec (because that happens to be the injection cycle for the rotary at 6000 rpm).  So at that point the injector would be open/on continuously.  So lets consider that the maximum power draw case – whenever the injectors are “locked Open” – you don’t’ want to operate there {:>).  But, your one injector would be open continuously - drawing 1.5 amps. 

 

However, that would equate to the engine consuming 29.16 GPH (4 x 460 cc/min injectors) which is highly unlikely at 6000 rpm and no boost – your engine would probably bog down and flood at that flow rate at 6000 rpm.

So something less than that is probably the case..

 

Let’s say our engine will “realistically” produce 200 HP at 7500 rpm that would equate to approx 20.0 gph fuel flow using a BSFC of 0.55 to make the calculation.

 

For 4 x 460 cc/min injectors to give you that fuel flow  at 7500 rpm would require them to be open approx 5.1 msec

The injection period at 7500 rpm is around 8 msec (so we have not “lock open” the injectors at this point)

 

So the duty cycle would be 5.1/8 =  64%

 

Therefore if one injector draws 1.5 amps when open all the time then 4 would draw 4 x 1.5 =  6 amps

 

So with a duty cycle of 64% they would have  a combined current draw of approx 6 * 0.64 = 3.825 amps at 7500 rpm.  Now as the power requirement decreases the injectors do not have to stay on as long and so your long-term current draw is undoubtedly less than this – unless you run WOT all the time {:>)

 

I’m doing some electrical load analysis and need some stats for fuel injectors.

 

What does a typical fuel injector used on a Renesis draw?  I’m looking for 3 numbers:

1. If I’ve got an injector on the bench, what is the energized load?
2. When the injector is running in the engine, it is getting a PWM signal.  What it the typical duty cycle at full throttle?  This will help calculate average load over time. 
3. Or - is there some rule-of-thumb number that is used for engine at full throttle?

 

TIA

 

-Jeff

 

 

Jeff Luckey

Direct Connection Systems

www.DCSIT.com

949-645-8832

 

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