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Andy J

Well Known Member
While waiting for the delivery of my next kit I decided to familiarize with the POH. I ran across something that I don?t fully understand. From page 6-5:

WARNING - Engine operation depends upon there being battery power sufficient to run the ignition system and fuel pump.

I thought the engine ignition system was independent of external power(That is what the Rotax operator manual says on page 9-4). I know the fuel pump has been discussed in another thread, and it seems the engine should continue to run without it.
Is there perhaps some circuitry on the RV-12 main bus that closes the ignition switch circuits when the main switch or battery is off? I noticed some relays next to the ignition switches that make me wonder about this.

Could some of you please comment on this? For builders with running engines: Does your engine stop if the Master is switched off, but the ignitions both on?
 
The Rotax 912 runs with the master off. It does not require the battery to run.

The mechanical pump will continue to pump fuel if the electrical power is off.
 
Thanks Larry for confirming that - Really is how I would expect it to work. Still curious as to the reason for the Warning in the POH.
 
Just guessing - those may be needed for start only. Best bet is to check with Van's.
 
Geico266 said:
The Rotax 912 runs with the master off. It does not require the battery to run.

The mechanical pump will continue to pump fuel if the electrical power is off.
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Correct. Mine continues to run after I pull the masters until I turn it off with the key!

This raises the issue of how to properly shut down the 912. I had always been taught to pull the masters (gen then batt) first, then switch the ignition off. However, I've seen others turn the key off first.

TODR
 
The warning at the top of page 6-5 applies in the event of a generator failure or runaway generator. In that emergency situation battery power would be needed to keep the ignition powered up and the engine running.
 
Bruce Russell said:
The warning at the top of page 6-5 applies in the event of a generator failure or runaway generator. In that emergency situation battery power would be needed to keep the ignition powered up and the engine running.
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Hmmm. My understanding is that each EI is powered by an independent coil in the generator.

TODR
 
Bruce Russell said:
The warning at the top of page 6-5 applies in the event of a generator failure or runaway generator. In that emergency situation battery power would be needed to keep the ignition powered up and the engine running.
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Thanks Bruce. I was unaware the ignition could run off the battery-That's what made me question the warning in the POH. I received a similar response from a phone call to Van's.

The Rotax manual states the ignitions each have their own independent charging coils. I'm just trying to fully understand this system. I wish I had a schematic to clear it all up for me.
 
Andy J said:
The Rotax manual states the ignitions each have their own independent charging coils. I'm just trying to fully understand this system. I wish I had a schematic to clear it all up for me.
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Take a look at the Rotax Operator's Manual, Section 9.4, which has a diagram of the ignition system and states:

"The ROTAX 912 A engine is equipped with a dual ignition unit of a breakerless, capacitor discharge design, with an integrated generator.

The ignition unit is completely free of maintenance and needs no external power supply.

Two independent charging coild located on the generator stator supply one ignition circuit each. The energy is stored in capacitors of the electronic modules. At the moment of ignitio, each of the 4 external trigger coils actuate the discharge of the capacitors via the primary circuit of the dual ignition coils."

From my understanding, I don't think the ignitions can run on battery power. This is consistent with my understanding that the engine needs about 300 rpm during start to generate enough power for the EIs.

TODR
 
mrt890 said:
There is a 12V power schematic in the Maintenance Manual Pg 17-17
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Unless I am missing something, I don't see any connection between the battery and ignition on that schematic. So, would the ignition lose power in the event of a generator failure?
 
Bruce Russell said:
Unless I am missing something, I don't see any connection between the battery and ignition on that schematic. So, would the ignition lose power in the event of a generator failure?
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Well, the EI gets power from the generator, but it's totally separate electrically from the battery charging portion. So, if you lost some part of the system that only handled the battery charging portion (e.g., voltage regulator), the EI still runs. If you have a mechanical problem that affects the entire generator (e.g., overtemp, fire, etc), then the EIs might fail.

TODR
 
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