Because I could never get the primary, magnetron ignition to work on my Sonex, I now have TWO electronic ignitions, an SDS Coil Pack Ignition and the AeroConversions Secondary. I’d like a backup battery for one of the ignitions, so if the Rectifier/Regulator or the stator, or the main battery (Sealed Lead Acid) take a nap, I can fly for 30 minutes or so and get the airplane on the ground. A few things I’ve learned:
It looks like the AeroVee R/R fail LOW, and stop charging, vice failing HIGH in an overvoltage condition, based on my review of the forums. Thus, there may not be much utility in “Crowbar” overvoltage protection schema.
B&C does have a regulator for Permanent Magnet alternators, that includes a bunch of nice features, including true “Crowbar” overvoltage protection, but they are not clear it’s ever been installed on an AeroVee. PMR1D Regulator, 14v (Homebuilt) - B&C Specialty Products
B&C no longer sells the “Crowbar” modules as a separate thing, but http://olsentechllc.com/ still does.
The backup battery should be the same chemistry as the main battery, due to different charging characteristics.
Olsen Tech has an “automagical” solution, that manages charging the auxiliary battery, preventing overvoltage to the smaller battery, and switches without pilot intervention in the even the main bus voltage drops below a set point. I think this is the way I will go, after the first of the year, during my first Condition Inspection.
As near as I can tell, the AeroVee secondary draws about 6 amps and the SDS about half that.
The Olsen tech module will protect the aux battery from an over voltage. Good to know failing high is a possibility. The way my R/R is mounted I’d have to pull the front of the airplane apart to replace it.
That’s really cool. I’d like to learn more about the SDS system. 3 amps saved is significant. I find that when we do night patterns our MFD squawks about low voltage on the ground - with 20A from takeoff until abeam the numbers, and probably near zero the rest of the time, it doesn’t charge well enough. We shut off our secondary on the ground. If we are doing night XC it is fine, as we are getting the whole 20A and we turn off the secondary in flight.
I haven’t seen the Olsen Tech battery backup IPB (automagical) but it looks pretty neat. Wouldn’t be an issue for you, but it looks like it’s limited to 5 or 10 amp depending on the model. It looks like you’d also need a relay to control the alternator output in place of the alternator field circuit for the OV protection to work since I suspect it’s not rated to 20A. This would also control it for the main battery.
Ross Farnam of SDS recommends 3.4 Ah for a 30 minute reserve with a single Coil Pack Ignition. Injected Rotax would need more, to run fuel pump(s), etc. Brent Olsen makes an IPB with OV Protection, but I’ve decided I don’t need it. My electrical system actively resists modifications for Reasons, so simple is better on my airplane.
I should have been more clear that this is not for me since I’ve got a completely different system for redundancy built into the engine design. Seeing electrical system failures and doing research on it I feel it should be thought about more for electrically dependent aircraft so it’s good to see different solutions.
My ears perked up when I read in your recent note about using the SDS CPI system. I am currently working on replacing my Revmaster 2300 ignition system with the SDS version. I would like to discuss installation and operation matters with you regarding the SDS system. I will also discuss back-up battery info with you. If possible, please send me a private message to 984dm for contact information.
Thanks, Dave M
Regarding simplicity, it is still worthwhile to figure out the magnetrons and use the SDS as the secondary. They really work well, and kept the engine running for us during two total electrical failures.
I concur with Bryan, but in order to do it I would have to pull the engine and the flywheel, so I went a different way. Multiple changes of Magnetrons didn’t pan out, I think the coil charging magnets on the flywheel were damaged. Only component we didn’t change.
I changed my magnet the last time I had the flywheel off. It’s been off a lot! The joy of flying behind a VW.
I had some missing on my primary ignition unless I had it really leaned out. So I replaced everything when I had it apart and it’s really good again. Much less sensitive to mixture now.
Sonex calls for a 0.010” air gap between the magnetron and the flywheel. I could never get mine to work with this gap, they even sent me a new magnet for the flywheel. I did get them to work reliably by closing the gap to 0.004”
