Surefly SIM, Hot Starts, & Kick back

[Bcone1381]

Installation instructions are a good thing. Is the SureFly SIM powered directly from the battery? If not, every circuit breaker and/or switch can become a point of failure for your ignition. The only time you want to use a backup battery is with your second SIM. The first should go directly to the battery. Don't go down a rabbit hole with speculation, call SF tech support. The most tested piece of the puzzle is the SF SIM. Be open to looking elsewhere.

That said, I'm a little concerned that you still don't understand you have a problem with your aircraft. By using a separate battery for SF SIM power, you confirmed that your aircraft has an electrical issue (after a lot of finger pointing at the SureFly). Installing a Band-Aid backup battery is not the answer, nor is it part of the installation unless it is the second SIM.

P-Lead: It is a simple ground-open circuit. The ground tells the unit to turn off, the open to turn on. Check the wire and switch.
Ground: Check all terminals for proper crimps and corrosion.
Battery: Even though it spins the prop, doesn't mean it is good. Try a new one. If you are powering the SF SIM through a circuit breaker, switch, bus bar, or relay fix this immediately! Wire it directly to the aircraft battery.

I had a similar issue when I first installed the SureFly generation 1, many years ago. I cleaned the starter pad as that is the ground for the starter. Checked and cleaned all the terminals. Beefed up the engine to firewall ground. This not only fixed the SureFly issue but suddenly my starter worked as it should!

You echo Chat GPT. It helped me put into words the following conclusions. I see similarities.

The breakthrough came when SureFly had me create an entirely isolated electrical system for the right ignition module. The isolated system did not interact with the aircraft electrical system. The left SureFly was turned off, and the engine was started using only the isolated right ignition module.

The result was dramatic: the engine hot-started really well! I could tell Fuel was still causing spits and sputter…but the single SIM was firing all it could. Never seen that before.

This test was valuable because it isolated the SureFly module from several possible influences at the same time:

• Voltage sag during start and compression events.
• Ground potential issues caused by the high current flow of the starter (200–400 amps).
• Electrical noise or current effects associated with the P-lead circuit.
• Interactions with the aircraft electrical system.
• Shared return paths through the aircraft grounding system.

This does not yet identify the root cause, because several variables changed at once. However, it does provide an important conclusion:

The right SureFly module is capable of performing correctly when isolated from my aircraft’s electrical system.

My original installation did not follow SureFly’s recommended installation procedure. SureFly specifies that the module power supply should be connected directly to the aircraft battery. Instead, I connected the right module to an always-hot battery bus that is supplied from the battery side of the master relay. Although measured voltage during cranking appeared acceptable (approximately 11 volts), the hot-start problem remained.

This raises an important possibility: voltage alone may not tell the entire story. An electronic ignition module may respond not only to average voltage, but also to transient voltage changes during cranking. Each compression event places a varying load on the starter, which can create fluctuations in the electrical system that we saw as small and un-noteworthy on the oscilloscope.

SureFly’s recommendation to connect the module directly to the battery was likely made for a reason. The specific concerns behind that requirement have not been shared with me, so my battery-bus installation is now a strong area for further investigation.

The next step is additional experimentation with the power supply, the ground reference, the P-lead circuit, electrical noise.

At this point, we know the SureFly system can hot-start the engine reliably when removed from my aircraft’s electrical system.

This is Experimental Aviation.

 

[pecanflyboy]

My original installation did not follow SureFly’s recommended installation procedure. SureFly specifies that the module power supply should be connected directly to the aircraft battery. Instead, I connected the right module to an always-hot battery bus that is supplied from the battery side of the master relay. Although measured voltage during cranking appeared acceptable (approximately 11 volts), the hot-start problem remained.

That says it all. Good luck and stop blaming SureFly when you are not willing to follow the directions.

 

[lr172]

I would suspect that the likelihood of lower battery voltage would be starting the engine cold not when the engine is hot just after the alternator has had a chance to recharge the battery. Usually in my experience a hot engine take less power to crank over than a cold one. I would still suspect a problem with the SF and or wiring issues.

That is true and one of the reasons I still think the heat related issues may be inside the simm. Eaton's experience also reinforces that speculation.

 

[lr172]

At this point, we know the SureFly system can hot-start the engine reliably when removed from my aircraft’s electrical system.

unfortunately we don't know the why so still difficult to say that the simm is without fault.

 

[lr172]

That says it all. Good luck and stop blaming SureFly when you are not willing to follow the directions.

You have no confirmation that his installation is the root cause. why does it work when cold if the installation is wrong? Eaton posted that his first unit worked well, hot or cold, for 1000 hours and the rebuilt unit did not; no change to his installation. you cannot design an ignition system that requires adedicated battery to start when hot. The test results are interesting, but something else is at play here.

 

[Bcone1381]

Curious if your original setup had the SIM power connected directly to the battery (using the supplied fuse holder) or if it was powered through a switch. And did you just swap the power wire over to the second battery, or is it a new power wire now?

I did not connect the Surefly to the battery using the supplied fuse holder. It is not powered through a switch. Its always powered on. I deviated knowingly from the Surefly Installation instructions. It seemed to me at the time the functionality and craftmanship of using Hot Battery Bus was superior to having another wire run all the way to the battery.

My original setup has the Battery supplying power to the Master Contactor bolt. That Bolt battery supplying power to a Hot Battery Bus. The Hot Battery Bus is a Fuse Block supplied by B&C that uses auto fuses. The Battery bus directly powers the Right Ignition module. The craftsmanship and wiring supplies and tooling used on this installation are all supplied from B&C. AMP ring terminal ends and .250" Faston tabs at the fuse block.

For yesterdays test I fabricated a new power supply wire and ground wire. I used speaker wire. I would only use speaker wire for a temporary test. Hehehe...The Auto manufacturing Industry calls this an MVP.... "Minimally Viable Product". Just get it tested. The testing wires were removed and saved after the successful hot start and the aircraft returned to an airworthy state.

 

[Bcone1381]

You have no confirmation that his installation is the root cause. why does it work when cold if the installation is wrong? Eaton posted that his first unit worked well, hot or cold, for 1000 hours and the rebuilt unit did not; no change to his installation. you cannot design an ignition system that requires adedicated battery to start when hot. The test results are interesting, but something else is at play here.

Thanks for the backup Larry.

I think how I think. Maybe I am "Unwilling to follow instructions." We Bearhawk Builders naturally have an environment that is creative and imaginative. The Bearhawk Patrol is not like an RV. We dont have drawings, or instructions, or complete kits with all the hardware like you guys. Our firewall forward package is a nose bowl. Thats it. NOTHING else. i built my engine cowl by hand from scratch. And this was a Quick Build kit.

We must make choices. We read books, and design solutions, and bounce ideas around each other and come here for help. All our stuff is sourced outside the kit. Every bolt, and wheel, and part. So to design my electrical system using Bob Knuckols Z101 digram, and assume it provides a sound source of electrons for a Surefly seemed at the time reasonable to me.

So thats the context behind "Unwilling to follow instructions." I'll take that badge. And Like you say, Larry...it still might a good power supply.

 

[lr172]

Thanks for the backup Larry.

I think how I think. Maybe I am "Unwilling to follow instructions." We Bearhawk Builders naturally have an environment that is creative and imaginative. The Bearhawk Patrol is not like an RV. We dont have drawings, or instructions, or complete kits with all the hardware like you guys. Our firewall forward package is a nose bowl. Thats it. NOTHING else. i built my engine cowl by hand from scratch. And this was a Quick Build kit.

We get to make choices. We read books, and design solutions, and bounce ideas around each other and come here for help. All our stuff is sourced outside the kit. Every bolt, and wheel, and part. So to design my electrical system using Bob Knuckols Z101 digram, and assume it provides a sound source of electrons for a Surefly seemed at the time reasonable to me.

So thats the context behind "Unwilling to follow instructions." I'll take that badge. And Like you say, Larry...it still might a good power supply.

same here. i follow many/most instructions, but have encountered plenty that didn't seem to be grounded in any type of reality. In those cases, i trust my judgement, my experience and my research. Like you, when fabricating or going off the reservation, you need to be able to figure things out.

 

[lr172]

same here. i follow many/most instructions, but have encountered plenty that didn't seem to be grounded in any type of reality. In those cases, i trust my judgement, my experience and my research. Like you, when fabricating or going off the reservation, you need to be able to figure things out.

in this case, there is really nothing different at the battery than any other spot directly fed off the fat wire. not like the transients say "wohh that is the battery right there better stop doing that!" i get the recommendation as many don't think about or respect voltage drop, but with proper design and installation practices, it shouldn't matter.

 

[Bcone1381]

in this case, there is really nothing different at the battery than any other spot directly fed off the fat wire. not like the transients say "wohh that is the battery right there better stop doing that!" i get the recommendation as many don't think about or respect voltage drop, but with proper design and installation practices, it shouldn't matter.

We will see if it matters or not. My electrical system does not seem to care what I think. I'm back on the road, so the next troubleshooting steps have to wait for now.

 

[Bcone1381]

Interesting, but glad you were able to determine there is no fault with the SureFly.

As a datapoint, my SureFly is powered directly off the battery and has never suffered from voltage drop during start.

Are you satisfied with your Surefly Hot Start Performance? Does it easily Hot Start? What type of battery do you have installed?

 

[Sam Buchanan]

Are you satisfied with your Surefly Hot Start Performance? Does it easily Hot Start? What type of battery do you have installed?

My O-320 has a carburetor, never had any hot-start problems, us carbed guys usually don't. The battery is a Chinese power sport PC680 clone, and the SureFly power lead runs directly to the positive terminal on the battery (just as detailed in the SureFly instructions.......).

 

[krw5927]

in this case, there is really nothing different at the battery than any other spot directly fed off the fat wire.

Nothing different except the gauge of the fat wire strung between the battery positive terminal and the contactor. That one wire is simultaneously supplying power to whatever avionics are on, a starter(LOTS of amps), probably an alternator regulator (sucking 5-10A by itself when the engine isn't spinning), and the SureFly (likely other stuff like lights, too). Voltage drop through that wire during starting could conceivably be quite different than voltage drop directly at the battery terminal.

 

[lr172]

Nothing different except the gauge of the fat wire strung between the battery positive terminal and the contactor. That one wire is simultaneously supplying power to whatever avionics are on, a starter(LOTS of amps), probably an alternator regulator (sucking 5-10A by itself when the engine isn't spinning), and the SureFly (likely other stuff like lights, too). Voltage drop through that wire during starting could conceivably be quite different than voltage drop directly at the battery terminal.

resistance induced voltage drop for 4 awg copper is .0003 volts per amp per foot. So, a 5' cable carrying 200 amps will lose .3 volts from end to end. can't see how that makes a difference.

OTOH, the voltage drop at the battery, due to the huge draw from the starter is quite real and substantial, but that drop is consistent at ANY place on the bus, includung at the battery terminal once you account for resistance based voltage drop.

 

[Bcone1381]

I updated my signature.

Nothing different except the gauge of the fat wire strung between the battery positive terminal and the contactor. That one wire is simultaneously supplying power to whatever avionics are on, a starter(LOTS of amps), probably an alternator regulator (sucking 5-10A by itself when the engine isn't spinning), and the SureFly (likely other stuff like lights, too). Voltage drop through that wire during starting could conceivably be quite different than voltage drop directly at the battery terminal.

My fat wire is short. I'm guessing 6 inches.