Why does my 2nd ignition circuit breaker keep popping?
Posted: Wed Apr 08, 2020 1:00 pm
by Bacon8tor
I recently finished the electrical system and didn’t have this problem before. I could have the master and 2nd (electronic) ignition on all day with no problems. Now, when I turn on the master then the 2nd ignition switch the 5 amp breaker pops after about 30 seconds. I re-checked the wiring and everything seems okay. I’m using the Dyna S Ignition. I’m running 16 gauge wire from one of the coils to the switch, then breaker, then bus. I’m assuming the ignition is grounded to the engine block.
I’m wondering if this has anything to do with an electric carb heat plate I installed on my Zenith carburetor. These have been successfully installed on Bing Carburetors to prevent carb ice. It wasn’t until after a prolonged test on that system (15 minutes) that I started having problems with the 2nd ignition. I’m wondering if there’s a connection here. Even after letting the carb cool down the 2nd ignition breaker still pops. I checked the wiring and neither system touches the other. The carb heat plate warms quite nicely. I hope it’s not adversely affecting other components.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Wed Apr 08, 2020 1:58 pm
by Area 51%
According to my Aerovee assembly manual, there’s supposed to be a 10amp fuse/breaker in the system.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Wed Apr 08, 2020 4:12 pm
by Rynoth
Mine has a 10A fuse and 18AWG wiring. If I recall, 18AWG is probably the minimum wire size for the secondary ignition on an Aerovee, 16AWG would be just fine. It draws right around 5 amps continuously.
Remember, the fuse/breaker’s main purpose is to protect the WIRE, not the equipment.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Thu Apr 09, 2020 12:22 pm
by bvolcko38
My secondary ignition draws 10 amps
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Fri Apr 10, 2020 10:40 pm
by Bacon8tor
I think I found the answer to the problem. From two sources I’ve been told the 2nd ignition shouldn’t be turned on for more than 15 seconds to a minute without the engine running. This can cause overheating in the wires. I’m not sure which “wires” those are (coil?) but damage is most likely done to the ignition “module” which I think is the round thing on the top of the engine (I have the Dyna S Ignition on a Hummel). That would be an easy fix but if it were the coils that would most likely require engine removal for access. Ugh!
I should have specified that I have the Dyna S Ignition and not the Magnetrons like on the Aerovee. The 5 amp fuse is the correct size. I don’t know what the Aerovee says about turning on the ignition without the engine running but I wish the Dyna S manual would’ve cautioned against it. Maybe they assumed no normal person would do it in the first place. I flipped it on for the electrical test just to see if I had it wired correctly (no smoke or popped breakers). When that didn’t happen I saw no reason to turn it off immediately. I just didn’t really think about it one way or another. I was too busy sitting in the cockpit making airplane noises with various switches flipped here and there. But, lesson learned! Please don’t make this same mistake.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 12:37 am
by WesRagle
Hi John,
Bacon8tor wrote:The 5 amp fuse is the correct size.
Just an FYI, I emailed Scott and asked him what size fuse to use for the secondary ignition. He told me to use a 10 amp fuse.
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 1:59 am
by Bacon8tor
Thank you, Wes. I know of other builders who have never popped a 5 amp breaker on this system. Can’t remember where I saw where 5 was the correct size but if 10 is better my order is in!
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 9:36 am
by sonex1374
A typical 3 ohm coil supplied with 12 volts will draw approx 4 amps (Ohms Law: V=IR, so I=12/3 = 4 amps), and in doing so will generate 48 Watts of heat (P=IV: P=4*12 = 48 watts). This is a fair bit heat being generated (think of grabbing a lit 60 watt incandescent light bulb). With no cooling air flowing over them the coils could easily overheat. I think a best practice with these ignition systems is to turn them off when they are not needed, such as taxiing or when the engine is not running. Some pilots even turn them off for periods in flight to save the current draw and help recharge the battery.
In any case, I think a 5 amp fuse for a single coil or 10 amp for two coils would be appropriate.
Jeff
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 10:50 am
by WesRagle
Hi John,
sonex1374 wrote:I think a best practice with these ignition systems is to turn them off when they are not needed, such as taxiing or when the engine is not running.
That’s exactly what I intend to do. Also keep in mind that with the Hummel the primary ignition is an impulse mag. To be as kind as possible to the starter you can/should start the engine on primary ignition alone. Just do a quick check of the secondary before taxi and then re-engage the secondary in the run-up area while doing the “formal” run-up.
I’m going to go ahead and say this too while I’m thinking about it. Since the Hummel primary ignition is an impulse mag, and the Zenith carb has no mixture cut off, we need to be especially mindful while handling the prop. A single point of failure, like a broken P-lead, combined with that distinctive clunk of the mag, could lead to a very bad day. As an added precaution, on the final flight of the day, I intend to kill the engine by turning the fuel valve off and letting the fuel in the float bowl burn before turning the ignition off.
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 11:38 am
by Bacon8tor
Thanks Wes. So many people here have given good advice. This is my first build and it really has been a learning process.
I saw your post about your fuel valve placement on the tank and not going with the revision from Sonex. After seeing that I did the exact same thing. I ordered the smaller valve based on the part number you gave and also installed it on the forward side of the tank “drop down.” Let me know how it goes shutting off the valve to kill the engine. I prefer not to put stress on the valve fitting but I’m not comfortable with leaving fuel in the carb either.
Regarding turning off the second ignition during various phases of flight I’m concerned about possibly fouling the plugs?
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sat Apr 11, 2020 11:58 am
by WesRagle
Hi John,
Bacon8tor wrote:I saw your post about your fuel valve placement on the tank and not going with the revision from Sonex. After seeing that I did the exact same thing.
My not going with the revision from Sonex was an accident. I have an old kit and didn’t pay enough attention to print revisions. By the time I asked Kerry about the valve I had already installed the OOPS fittings and really didn’t want to back up. I confirmed that my fuel flow is adequate, but not stellar, with a fuel flow test.
There are multiple advantages to taking fuel from the bottom of a Onex tank. For one, the forward face of the sump is not “slanted” like it is on the Sonex tank I am familiar with. So, in the three point stance/landing attitude the fuel valve is pointing upward making the last bit of fuel unavailable. There is also the opportunity for water to collect in the sump only to be released when the tail is lifted. I have a gascolator down stream of the sump so I convinced myself that overall the risk was manageable as long as I took a fuel sample at the gascolator prior to first flight and after fueling.
I would never advise anyone to go against the factory recommendations on something as critical as the fuel system. If you look at my post (ref. http://sonexbuilders.net/viewtopic.php?f=5&t=4903&start=30#p37662), I edited it last September and put in big red letters that the fuel system prints had been revised.
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sun Apr 12, 2020 1:09 am
by gammaxy
Bacon8tor wrote:From two sources I’ve been told the 2nd ignition shouldn’t be turned on for more than 15 seconds to a minute without the engine running.
I think the official Dyna S instructions say no more than 5 minutes to avoid overheating and damaging the coil.
Interestingly, I’ve noticed that after ~2 seconds of no engine spinning, the triggers on my Aerovee stop providing power to the coils. So, at least as long as the engine isn’t running, the secondary ignition isn’t drawing any current. Not sure if this is typical of Dyna S ignitions or is a change Aeroconversions made to their similar-looking trigger modules.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sun Apr 12, 2020 7:52 am
by Rynoth
gammaxy wrote:
Bacon8tor wrote:
Interestingly, I’ve noticed that after ~2 seconds of no engine spinning, the triggers on my Aerovee stop providing power to the coils. So, at least as long as the engine isn’t running, the secondary ignition isn’t drawing any current..
This has always been my impression as well, that the Aerovee secondary coil draw is RPM dependent, i.e. how often it’s actually firing. Come to think of it, I do have an ammeter at my battery to measure charge/discharge, but I’ve never tried switching the alternator off at high RPM to see just how much the secondary coils draw at 3000+ rpm. It’s may be in the 8 amp range (4 per coil as Jeff suggested).
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sun Apr 12, 2020 9:13 pm
by gammaxy
Rynoth wrote:This has always been my impression as well, that the Aerovee secondary coil draw is RPM dependent, i.e. how often it’s actually firing.
This is not quite what I meant. I was pointing out that on the Aerovee, at least, the secondary ignition almost completely shuts down when it hasn’t been triggered in a couple of seconds so you shouldn’t have to worry about it overheating when the engine isn’t running. This might be different than how the Dyna S works.
Your point has come up in the past and inspired me to attempt to capture exactly what’s going on:
I used the waveform to estimate what the average current per coil will be at a range of typical RPMs. It decreases by about 13% across the range I considered. I feel that this is is probably barely noticeable in practice. Last time this came up, I expected a much larger change and jerry09w said when he measured it with VOM it was barely noticeable: viewtopic.php?f=6&t=3831&start=10#p33386
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Sun Apr 12, 2020 9:58 pm
by WesRagle
Hi Chris,
That’s good stuff.
So the wave form is just a series of RL charging curves with the R being the 3 Ohms shown on the side of the coil (Ref. https://www.electronics-tutorials.ws/inductor/lr-circuits.html).
I suspect the Dyna S works the same way the AeroVee ignition works. I haven’t studied either closely but the button on top of the Dyna S looks suspiciously like the magnet used on the AeroVee secondary ignition.
I’ve never really questioned how these ignition systems work but now I’m curious. These questions may sound a little geeky but inquiring minds want to know. So here goes.
-
Would it be correct to say that what we are calling a coil is actually a transformer?
-
Is the high voltage generated by the transformer secondary a result of the near instantaneous change in current (and therefor flux in the transformer core) in the primary when the ignition fires?
-
I guess what I’m trying to ask is, are these “Coils” nothing more that a flyback transformer?
Thanks,
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Mon Apr 13, 2020 12:58 am
by gammaxy
Wes,
Yeah, you’re absolutely correct and it’s not just our ignition coils, but all/most ignition coils are really transformers designed to deliver energy in impulses. Wikipedia’s article on “Induction Coil” says these were the first type of transformer, so the confusing name seems to go way back. And you’re correct that the sharp drop of current in the primary raises the voltage across the secondary high enough to fire both spark plugs.
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Mon Apr 13, 2020 9:38 am
by WesRagle
Chris,
Back in the day we always used the terms coil, choke, and inductor interchangeably, but we never called a transformer a coil. I suppose if you cut one open you would find two secondarys. I’ve always just hooked the “coils” up and never really understood how the worked. Now I do. Thanks.
Back to the problem John is having:
I recently finished the electrical system and didn’t have this problem before. I could have the master and 2nd (electronic) ignition on all day with no problems.
Without the engine running, as Jeff calculated and as you measured, we should expect 7 to 8 amps of current draw by a secondary ignition with two 3 Ohm coils. That is unless the crank happens to be positioned such that one of the coils is shut down (firing) in which case the current draw would be half that. That might explain why the problem seemed to be related to the installation of the carb heat plate. Maybe only one coil was energized but sometime during the process of installing the carb heat plate the engine was rotated enough to cause both coils to be “turned on”. Maybe a little “post hoc ergo propter hoc” goin’ on here 
Thanks,
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Mon Apr 13, 2020 11:51 am
by sonex1374
Wes,
That’s a very plausible scenario. The coil consumes battery power all the time until the triggering magnet aligns with the triggering module which interrupts the flow of power to the coil (there’s a small transistor inside the triggering module that does this switching). This interruption causes the stable magnetic field that has built up inside the coil to collapse all at once, and this collapsing magnetic field generates the high voltage surge that fires the spark plug. If the engine just happens to be rotated such that the trigger magnet and module are aligned, then no power will flow thru the coil. Move the magnet a smidgen, then current flows again.
Kinda improbable that is works out like this, but once or twice in a blue moon the stars will randomly align.
Jeff
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Mon Apr 13, 2020 12:22 pm
by WesRagle
Jeff,
sonex1374 wrote:Kinda improbable that is works out like this, but once or twice in a blue moon the stars will randomly align.
Looking at the duty cycle of the current waveform, and considering that there are two coils that could be turned off, it looks like the probability of one coil being turned off is about 15%. At least for Chris’ ignition.
Wes
Re: Why does my 2nd ignition circuit breaker keep popping?
Posted: Mon Apr 13, 2020 1:45 pm
by gammaxy
Wes,
I just tested your idea and you are correct that if the magnet is stopped next to the trigger, that coil won’t draw any current even when it is first powered on. This might not be all that unlikely, especially if the timing had recently been set by pointing the magnet at a trigger.