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How to Start Rotax 912 if Odyssey Battery Fails?

Piper J3

Well Known Member
I don’t want to get stranded with a dead battery caused by either the battery itself or the voltage regulator going on the fritz. The Rotax 912 uses capacitance discharge (CD) ignitions vs. magnetos as used on most other aircraft engines. The consequence is that you cannot hand prop the engine if the electric starter doesn’t do its job. The CD ignitions need ~ 500 rpm to self-generate enough voltage to create spark. You’re not going to hand prop (read: backdrive) a 2.4:1 gearbox – ain’t going to happen.

So, I’ve been thinking about what to do if the Odyssey battery ever lets me down in a remote location. No problem if battery goes dead in flight – engine keeps running. But can’t restart if you shut engine off.

For total cost of $70.40 I bought the following items on eBay to put a starter package together:

  • LED 82800mAh Portable Car Jump Starter Pack Booster Charger Battery Power Bank J
  • 8 Gauge Silicone Wire 10 feet (2x5') 8 AWG Silicone Wire Flexible Silicone Wire
  • Jumper Cable EC5 Connector Alligator Clamp Booster Battery for Car Jump Starters

The RV-12 Odyssey PC680 is rated 12 Volt / 16 Ah / 170 CCA. The 82800mAh Lithium Starter Pack with advertised 200A Starting Current is able to start up to 5L gas or 2L diesel engine. The 912ULS is 1.35L so the Starter pack should crank it just fine. I used 8 AWG silicone wire to allow the battery to sit on ground and still connect to the Odyssey airplane battery. Then I added a second set of clamps just in case a Good Samaritan would come along and provide a 12-volt power source.

When completed, I tested the starter pack by jumping a totally dead 26 HP garden tractor. Cranked fast and fired right up...

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82800mAh Portable Car Jump Starter Pack

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Battery Clamps w/ Fuse

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Ring Terminal for 8AWG

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Remove Plastic Insulation

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Crimp Wire and Insert Under Copper Jaw

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Finished Battery Clamp with 8AWG Extension Wire

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Completed Assembly

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82800mAh Lithium Battery

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99% Remaining After Cranking/Starting Dead 26HP Tractor

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Ready for RV-12 Baggage Compartment
 
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This guy seems to think you can hand-start a Rotax:
https://m.youtube.com/watch?v=-JUBrHYsh4E

I see a couple problems with this guy's procedure.
#1, You should never lift that leg. If your other foot should slip, the momentum of that leg will pull your body through the prop arc.
#2, When propping a carbureted engine, the fuel should be turned off. There will be plenty of fuel in the carburetor bowl to keep the engine running until you can turn the fuel on.
 
This guy seems to think you can hand-start a Rotax

Yes, he is starting a 80 hp 912 UL which has compression ratio of 9.1:1. Might also have 2.27:1 gearbox.

912ULS is 100 hp and compression ratio of 10.8:1 with 2.43:1 gearbox.

Give it a shot and let me know how it works... :D
 
I?ve been thinking about a similar rig, but I?m trying to figure out he best location for a positive post so I can jump it from the cockpit.
 
Maybe it's just me but no way I'm carrying a rather large cheap LI battery in the airplane.
 
I?ve been lucky so far and have not been stuck out of town yet! Thank you for sharing a field expedient remedy for when the battery gives out. All lessons learned and fixes are truly valued by most of us,
 
Maybe it's just me but no way I'm carrying a rather large cheap LI battery in the airplane.

I understand your concern. Airlines can no longer accept bulk shipment of Lithium batteries in cargo hold. Likelihood of a major incident is magnified with thousands of tightly packed batteries. Individual Lithium batteries are allowed in the cabin and in carryon luggage.

Actually the LiPo (Lithium Polymer) here is same used for large scale radio control airplanes. Chemistry and battery construction is mature. Battery will only be charged perhaps twice a year to top it off. Self-discharge for LiPo is very slow reaching 70% in 3-4 months. Chemistry is similar as EarthX, however, unlike charge/discharge cycling of main battery in aircraft this battery will sit at full charge unless needed. LiPo's are designed for very heavy discharge - sometimes as much as 50-60 times rated capacity. Charging is done at low current and very controlled. This will be accomplished on a bench and not in the airplane.

These Portable Car Jump Starter Packs have been thrown around by tow truck drivers, highway patrol, and AAA road assist for years.
 
I carry a similar battery pack in my RV6 when away from home. They advertise the compact battery pacs will start a healthy discharged battery, but not one that has issues like a dead cell or internal short. I had a one year old PC680 that crapped out on me and the lithium ion pac overheated trying to start the plane. It has however started many airport loaner cars so worth having and may someday hide the embarrassment of leaving the master on.
 
Assuming the cells inside are cylinders like common 18650s, the main hazard is crushing them verically in shipping type handling. The negative contact is everything but the top and the insulator between the top and the balance of the shell case.

Cells can be dumb and managed by the device like a laptip battery or each cell can have a control chip.

Recharge it outside the plane away from easy igniteables just in case.

Easy to google if interested.

My concern in upping cable size is though more efficient, the smaller cable may be done on purpose to limit current. I would make sure the unit does not overheat using the larger cables. If 10 feet of 8 gauge acts like the thinner, shorter OEM cable, nice flexibility added.
 
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A big concern out here in the AZ summer not leaving the jumper battery in direct sunlight where it can overheat. I carry one in my car and it has started me twice when the main battery gave up the ghost. It?s got a remarkable energy density.
 
OK, Jim thats a nicely packed emergency kit. My question is, where do you clamp the battery pack cables for that emergency start? If its to the battery itself the top cowl has to be off, and I fail to see how it can be replaced with the motor running. Or, have you installed an external heavy duty connector for this purpose?
 
Assuming the cells inside are cylinders like common 18650s, the main hazard is crushing them verically in shipping type handling. The negative contact is everything but the top and the insulator between the top and the balance of the shell case.

Cells can be dumb and managed by the device like a laptip battery or each cell can have a control chip.

Recharge it outside the plane away from easy igniteables just in case.

Easy to google if interested.

My concern in upping cable size is though more efficient, the smaller cable may be done on purpose to limit current. I would make sure the unit does not overheat using the larger cables. If 10 feet of 8 gauge acts like the thinner, shorter OEM cable, nice flexibility added.

I don't think this pack uses cylindrical cells. Pretty sure pouch form factor is used. See pic below...
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OK, Jim thats a nicely packed emergency kit. My question is, where do you clamp the battery pack cables for that emergency start? If its to the battery itself the top cowl has to be off, and I fail to see how it can be replaced with the motor running. Or, have you installed an external heavy duty connector for this purpose?

Good catch... I haven't tried actual connection to the PC680 through the oil access door. My thinking was to have rather small clamps on the jumper cable for this purpose. Looks like next step is a trip out to the hanger. I have a small pigtail installed now for trickle charger. Might need to replace with something more substantial like this Battery Quick Connector Kit rated at 175A.
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I've thought about carrying one of those little lithium 12-volt battery packs, but I don't have any real world knowledge as to whether or not they would be useful starting up a 912.

Instead, I carry in my emergency repair kit an 18-inch long piece of battery cable with a battery terminal-sized ring connector swaged on one end and and inch of bare wire strands exposed on the other end. If faced with a dead battery while on a trip, my plan is to attach this cable to my positive battery terminal, extend the bare end out through the open oil access door, hook-up a jumper battery and start the engine. Once started, I will run the engine until it is warmed-up, shut the engine down and, hopefully, the aircraft battery will have a sufficient charge to restart the engine on its own. Alternatively, I might keep the engine running, disconnect the jumper battery, insulate the bare end of the installed cable with a heavy-duty "acorn" and secure the cable inside the engine compartment -- with great caution I might add! Anyways, that's my "plan". :rolleyes:
 
Chemistry is similar as EarthX

Just a quick note here, the Lithium Polymer used in this jump pack is not the same as lithium iron phosphate chemistry that EarthX uses. They are different on many levels but here is a quick video that describes how and why they are different. And just another side note, we have developed and been selling a quick connect cable for the exact type situation for years and most will connect the cable to their battery, run it in through the oil door for a convenient quick jump if necessary.

https://earthxbatteries.com/shop/earthx-jump-pack
https://earthxbatteries.com/shop/earthx-48-quick-connect-cable
 
...Might need to replace with something more substantial like this Battery Quick Connector Kit rated at 175A.
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Exactly what I did. Accessible through the oil door. Pigtail with clamps can be removed from the cockpit.
 
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I've thought about carrying one of those little lithium 12-volt battery packs, but I don't have any real world knowledge as to whether or not they would be useful starting up a 912.

Instead, I carry in my emergency repair kit an 18-inch long piece of battery cable with a battery terminal-sized ring connector swaged on one end and and inch of bare wire strands exposed on the other end. If faced with a dead battery while on a trip, my plan is to attach this cable to my positive battery terminal, extend the bare end out through the open oil access door, hook-up a jumper battery and start the engine. Once started, I will run the engine until it is warmed-up, shut the engine down and, hopefully, the aircraft battery will have a sufficient charge to restart the engine on its own. Alternatively, I might keep the engine running, disconnect the jumper battery, insulate the bare end of the installed cable with a heavy-duty "acorn" and secure the cable inside the engine compartment -- with great caution I might add! Anyways, that's my "plan". :rolleyes:

How about insulating it and leave it connected/secured, tucked away?
 
Doug -- Sure you can do that. I just didn't want an extra wire in there. In 640 hours I haven't needed to jump the PC-680 so an "emergency jump" fix serves me OK. A plug-in mini-jumper connection does sound enticing however. -- David
 
My thought is to run a cable from the positive battery terminal through the firewall and install a post on the tunnel under the instrument panel that I can clip the alligator clamp and connect the negative clamp to the airframe. The advantage is that jumping can be done without assistance or removing the upper cowling. My car has a similar setup because the battery is under the backseat floorboard.
 
Call me a sissy if you want but when I do condition inspection I disconnect any un-protected wires from the battery for safety sake.
A contactor or fuse close to the battery is the only way to protect wiring.
 
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In case of an imminent forced landing, all electrical power should be shut off as close to the source (battery) as possible. An accident investigator once made the comment that if the battery is thrown clear of the wreckage, fire is not as likely.
 
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