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The schematic for the 912ULS calls out a 25A breaker on the charging circuit. I am planning on using Tyco W33 series switch/breakers for all of my loads. Unfortunately, I can only find the push button type of breaker for the charging circuit. I hate to have all of these nice switches and then one push-pull breaker. Any suggestions?
Thanks
tom
The Rotax uses a dynamo that feeds a rectifier- regulator. It is not a true alternator with a field current switch unless you get the accessory driven alternator. That's why the diagram has you switching off the output . The max output of the Dynamo is 15 A. You could safely use a Tyco W33 series 20 amp switch.
Like John said, if you already have a hole you want to fill, then that matching switch will work to disconnect the output, but you still do need to protect that wire. The dynamo output doesn't really have anything to do with it if the wire is sized properly. If you check out Bob Nuckolls' elegant wiring diagrams for the Rotax (such as #Z-16) you see that you can install a simple crowbar over voltage module, and an alternator OV disconnect relay, and have automatic over voltage protection AND on-off control of the dynamo output via a simple 5 amp circuit breaker (either push-pull or switch). It's not the output from the dynamo that determines what size the fuse or circuit breaker you refer to should be. You don't need heavier than a 12 AWG size wire for the output from the voltage rectifier/regulator, & that wire should be protected - THAT'S where the 25 amp protection is called for & necessary. You could use a 25 amp MAX fuse in a holder on the firewall, or alternately you could protect that 12 AWG wire with a simple inline 16 AWG fuselink that you can make yourself.
First - thank you both for your comments. I have observed that you both provide great info for builders.
So - I think you have provided me with info that will help. First - the 25 A breaker does not protect the generator. If it is just the wire that is being protected, I can use a 30A breaker with 12Ga wire - which is just fine. I don't think I need overvoltage protection.
The reason I am thinking of the 30A limit is the curve given in the book that shows 22A output at 5500 rpm. This would probably be a typical takeoff scenario - and maybe the battery would be low and it might actually output 22A. However - if this is a short circuit reading out of the generator, then I would be fine with 20A and 14Ga wire.
So - I notice that John suggested the max output of the generator was 15A vs the curve in the manual showing 22A. Is this difference because the 22A is a short circuit reading?
Thanks
tom
Tom,
John & John have have provided solid information......I checked my install manual and the purpose of the breaker, according to this install manual is to protect the regulator/rectifer (in addittion to the wire).
The 22 amp line on the chart is the maximum the system could develope at a specified tempereture and output voltage.
I believe the 15 AMP value John Mentioned, which I remember from somewhere when I did my install, is the maximum continuous output. The system can make 22 amps, but not continuously with reliability. (I wish I could find the 15 amp reference - but I recall it being a hard number for continuous output)
I'd be reluctant to go beyond the recommended 25 amp breaker.....if the output goes nuts for some reason, it can get to the point that the capacitor may make it real clear with a good pop & cloud of smoke that will remind a person why they should have stayed with the 25 amp breaker.
Sincerely,
Dave S
KF7 Trigear
912ULS Warp Drive
I think that perhaps I still wasn't very clear. The output of the dynamo is limited by design. It isn't that output that we are worried about when installing the 25 amp breaker or fuse. It's there to protect the wire, and yes the regulator, in the event of a short circuit in that wiring. The power to burn that wire up (and other things in the circuit) and potentially start a fire doesn't come from the dynamo exclusively. It comes from the battery... potentially hundreds of amps. It's specified because legacy experience and design dictates protecting branch feeders in the event of a short circuit event. That possibility is greatly mitigated by proper installation practices, but it's still there, and protection of this sort is "standard" practice, and most would argue a good idea.