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EFI engine shutdown

svyolo

Well Known Member
Is there a preferred method for shutting down an EFI Lycoming? Just turn off the master like on a car, or shut the fuel pump off?

Obviously both will shut the engine down. I was interested because of a wiring logic I would like to use.
 
I have been using EFII for 4 years and 800 hours now in my RV10. Shutting down starts with shutting both ECU units, then master.
 
engine should run with master contactor open

Is there a preferred method for shutting down an EFI Lycoming? Just turn off the master like on a car, or shut the fuel pump off?

Obviously both will shut the engine down. I was interested because of a wiring logic I would like to use.

IMO opening the master contactor should not kill the engine. In case of fire in the cockpit you should be able to open the master contactor and still have engine power and if the master contactor fails you should still have engine power. Stop the engine with coil, injector, or pump power your choice but kill them and the ECU within a few seconds of one another. SDS in their 6 cylinder dual ECU installation instruction says to "NEVER switch off ECU power to verify coil pack operation" so I take it as good advice to shut down the coilpacks before the ECU for EFI systems in general.
 
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IMO opening the master contactor should not kill the engine. In case of fire in the cockpit one should be able to open the master contactor and still have engine power and if the master contactor fails one should still have engine power. Stop the engine with coil power, fuel pump power, or ECU power your choice but kill them all within a few seconds of one another.

Having the engine continue to run with the battery disconnected or master off was my intention and the reason for the question.

Thanks for the responses.
 
I have mine set up so that I can toggle an emergency bus switch which will give power to the essential buss that the engine runs on. So on a normal shutdown I just turn the master off and the engine dies. If I engage the emergency bus switch first, the engine will keep running with the master off.
 
Is there a reason you can't just pull the mixture to cutoff first?

The mixture knob will reduce the AFR by 50% so if idle is set up for about 13 to 1 at the normal 12 O'clock position, this should kill the engine too. Just don't forget the position when you try to restart again.
 
I also starve the engine by killing the fuel pump2, than coils, ECUs, & O2 in that order. Convenient because it is basically a right to left sweep of the hand.
 
I wasn't planning on have the ECU's switched. I thought the SDS install stuff said it was optional.

Thanks for the responses. I will probably turn off the pump. Or put a big red guarded momentary stop switch that does the same.

I would prefer to not have to flip a bunch of switches to power up and start the engine. Master on, start. At most master on, start, then avionics master on.
 
How does every car manufactured in the last 30 years do it?

They do it by turning the master off (ignition key off, or stop button). Hence my question.

If my battery BMS turns my battery off, my master contractor fails "open", etc, I would like the engine to continue running off the alternator. Unfortunately that wiring logic will cause my engine to continue running, if I turn my master switch off. I will also have a second battery on a diode and a switch in parallel to also power the engine bus.

I asked because I thought others had thought of the same thing. My first choice was to turn off the fuel pump. But I haven't found any other reference stating how others did it.
 
If my battery BMS turns my battery off, my master contractor fails "open", etc, I would like the engine to continue running off the alternator.

Caution - here there be dragons.

What you propose is possible with some setups - but certainly can result in widely varying voltage swings on the system without a battery to damp them out, and your high-dollar electronics are exposed to all those swings. You'll want to test this, and in the testing you are risking your electronics - so caution is advised.

I accidentally tested this myself in my airplane by bumping the master BATT switch off to open the master, with the ALT switch still on - and my airplane reacted well to that, but there are no guarantees.
 
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Caution - here there be dragons.

What you propose is possible with some setups - but certainly can result in widely varying voltage swings on the system with a battery to damp them out, and your high-dollar electronics are exposed to all those swings. You'll want to test this, and in the testing you are risking your electronics - so caution is advised.

I accidentally tested this myself in my airplane by bumping the master BATT switch off to open the master, with the ALT switch still on - and my airplane reacted well to that, but there are no guarantees.

I've done this with my ND clone in my lathe test stand. Removing the battery bumped the charging voltage from 14.5 to 15.5, but I only had a small cooler hooked up as a load, only 12V thing I could find I didn't mind if I fried.

More testing to follow but the analog and digital meter I had didn't seem to show voltage variance even when I was cycling the load on and off.
 
I've done this with my ND clone in my lathe test stand. Removing the battery bumped the charging voltage from 14.5 to 15.5, but I only had a small cooler hooked up as a load, only 12V thing I could find I didn't mind if I fried.

More testing to follow but the analog and digital meter I had didn't seem to show voltage variance even when I was cycling the load on and off.

I think you'll find that as you increase the load the output voltage will remain more stable. I've got a full glass panel and electric-only fuel pumps, so I'm pulling a good 15-18 amps constantly and my voltage held pretty steady in the mid-13 to high 14 range. All those are steady loads, as you bring on things that are temporary or pulsing like strobes and radio transmissions, that's where you'll get voltage swings.
 
I think you'll find that as you increase the load the output voltage will remain more stable. I've got a full glass panel and electric-only fuel pumps, so I'm pulling a good 15-18 amps constantly and my voltage held pretty steady in the mid-13 to high 14 range. All those are steady loads, as you bring on things that are temporary or pulsing like strobes and radio transmissions, that's where you'll get voltage swings.

Ah that would make sense. I'd like to try some more tests with better varying loads. My concern was tripping the OVM, which is set to 16V if I recall? I'd have to look that up.
 
Running on generator without battery

Apart from providing a load to hold the generator voltage in check the battery also provides a low source impedence for the switching regulator power supplies in the power circuits of most glass display systems (Dynon, Garmin etc.) Switching power converter control loop stability is negatively affected by an increase in source impedence from the power source as when running on the alternator without a battery. This may not damage the switch mode power supply but could possibly damage the display electronics and result in unreliable operation. One solution to this problem is to install a large capacitor (22,000 microfarad rated at 50 volts) in the bus circuit. This will also damp the high frequency voltage variation from the alternator rectifier diodes. Asking Dynon tech support for regulator control loop stability margin information got the same response as asking for definition of the two port parameters for the EMS-220. It was like speaking a unknown foreign language and expecting a rational answer. Garmin may provide more information and a least understand the reason for the concern.
KT
 
Apart from providing a load to hold the generator voltage in check the battery also provides a low source impedence for the switching regulator power supplies in the power circuits of most glass display systems (Dynon, Garmin etc.) Switching power converter control loop stability is negatively affected by an increase in source impedence from the power source as when running on the alternator without a battery. This may not damage the switch mode power supply but could possibly damage the display electronics and result in unreliable operation. One solution to this problem is to install a large capacitor (22,000 microfarad rated at 50 volts) in the bus circuit. This will also damp the high frequency voltage variation from the alternator rectifier diodes. Asking Dynon tech support for regulator control loop stability margin information got the same response as asking for definition of the two port parameters for the EMS-220. It was like speaking a unknown foreign language and expecting a rational answer. Garmin may provide more information and a least understand the reason for the concern.
KT

That's good advice - BUT - you will want to install that capacitor with about a 1-ohm high wattage resistor across the bus power to the capacitor, to limit the current surge into the capacitor when you turn on the master. Otherwise it's going to instantaneously try to pull about 1.21 gigawatts and arc the contacts on the master. A 1-ohm resistor will limit the current flow to a more manageable 13-14 amps surge when you bring the master online, and will not be enough resistance to damp the effects of having the capacitor in the system.
 
At the point of master closure the instantaneous current is defined by the resistance and inductance of the wiring and the equivalent series resistance (ESR) of the large electrolytic capacitor. Unless the wiring is wound in a coil the inductance will be very small so the voltage across the contacts of the master solenoid as a result of adding the capacitor will never rise above line voltage. The current will rapidly drop as the capacitor charges (negative exponential) The total enery transferred will not cause the master contacts to overheat or the capacitor to explode. Having a 1 ohm in series with the capacitor is defeating the point of putting the capacitor in the circuit. Having a defined resistor in the circuit is good from an analytical viewpoint but in practice the ESR of commercially available electrolytic capacitors is sufficient to limit the inrush current to safe levels without compromising the integrity of any circuit components. Remember rate of change of current in an inductor gives induced voltage and rate of change of voltage in a capacitor gives induced current.
KT
 
Kill injector or coil power or turn off the pump. No need to overthink any of this or add more electrical parts.
 
Thanks again, Ross. Will do.

I did ask B&C about running their alternator without a battery hooked up. They asked what my electrical load would be. I said 18 to 20 amps. They said it should be fine. My second battery will be brought on line anyway.
 
They do it by turning the master off (ignition key off, or stop button). Hence my question...

I see the functionality of the automotive ignition switch differently. In the car it's a single switch with a "chassis" function (the accessory position) and an "engine" function (start/run). In my airplane the master switch controls the airframe functions and another switch controls the engine functions. I have an airframe buss and battery and an engine buss and battery. My engine stops when I turn off the "engine switch", killing power to the entire engine buss (ECU, coils, injectors, fuel pump)

Airframe On/off; engine on/off. Simple.
 
I see the functionality of the automotive ignition switch differently. In the car it's a single switch with a "chassis" function (the accessory position) and an "engine" function (start/run). In my airplane the master switch controls the airframe functions and another switch controls the engine functions. I have an airframe buss and battery and an engine buss and battery. My engine stops when I turn off the "engine switch", killing power to the entire engine buss (ECU, coils, injectors, fuel pump)

Airframe On/off; engine on/off. Simple.

I asked the question to solicit opinions. I didn't expect that one. I will think about it. I have EFI, single big EFIS, 1 com, 1 Xponder/adsp.

Again, thanks.
 
My architecture and integration wins points for theoretical reliability (few failure points), but certainly falls short of airliner redundancy. There are plenty of threads discussing electrical architecture, but concerning the topic of this thread, I simply kill all the engine systems with a single dedicated switch to shut down (like a car).
 
I would like to have my setup so simple that most pilots can fly it without me telling them what sequence to turn things on. Right now that is just master and start, and maybe then avionics master. I would like to not have to do the avionics master every start but GRT recommends it for their EFIS.

If I am really slick I will figure out how to get the start button to start when the engine is off, and shut the engine off when it is running.
 
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