The Field Wire from the generator receives it's electrical power from which source - does the 'airframe end' of the Field Wire connect somewhere on the Vertical Power Unit? We have scoured the schematics and can't find an answer to this. We can't make a first flight until this problem is solved. RV-12 number 120188. ULS engine. Thank you all for being here - I appreciate.
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Help please - the 'Field Wire" to my RV-12?
- Thread starter E. D. Eliot
- Start date
Field wire? Vertical Power Unit? You gotta give us a few more clues about your configuration.
jaradtke
Well Known Member
sansoneservices
Well Known Member
The field wire eventually terminates at the battery positive. It may go through a master switch, fuse block, circuit breaker, battery contactor, etc.. it should not be hot all the time. Hope this helps
The aircraft has a voltage regulator, it tells the alternator to increace/ decrease voltage to maintain the set charging voltage normally 14,5 V.
If the voltage regulator senses a too low voltage on the bus, it will send an inreasing current (amp) to the alternator field winding.
Then the voltage will go up to the set value.
Good luck
If the voltage regulator senses a too low voltage on the bus, it will send an inreasing current (amp) to the alternator field winding.
Then the voltage will go up to the set value.
Good luck
sansoneservices
Well Known Member
Correct, some alternators have internal regulators, some external where the regulator controls the field. Avanza's description is better than my previous
You mention a "Field Wire from the generator". I'm not sure where you see that. Here is a picture of the generator from the Rotax installation manual. The Vans RV-12 schematic is similar.
The Rotax generator doesn't have a field winding or field wire. It is a bunch of permanent magnets on a wheel at the back of the engine spinning past some wire coils. These magnets also power the capacitor discharge electronic ignition (different set of windings), kind of like on your lawn mower. What comes out of the generator coils (Item 1 in the drawing above) is AC that is then rectified and regulated.
On a typical (B&C AVC1 in this case) Rotax rectifier / regulator you have these connections...
You've got 2 AC inputs, 2 parallel (because they carry a lot of current) DC outputs, a warning light output, and an enable / disable control input. Usually the control input (pin 6) is just directly connected to DC (pins 2 and 3) so that it is enabled all the time. At least that's the way Vans did it.
Bottom line is don't connect the VP-X Alternator output to anything. There is nothing in the generator / rectifier / regulator circuit to connect it to.
Thank you to you all - you just saved us a ton of hours trying to figure this out. Thanks again to all.
Yeah, but not on a Rotax.
Absolutely true. See Lockwood's video on the 915/16 on the RV-9 FWF kit just released. He describes the very much different electrical system of the 900 series Rotax. Has two generators, switches bus automatically on start, redundant ECU's, etc... I have run across some 912 ULS with an external alternator kit as an add on to increase the miserly electric load the original generators put out, perhaps that is what is being discussed but that is very much a non-standard RV-12 build.
One final note about the VP-X Field output. If you have a Dynon display system then even though the Field output is not used it should be enabled anyway (and configure it for the minimal amount of current, 1 amp). The reason for this is that if the Field output is not enable the Dynon will think that there is no generator output and throw up a Fault that looks like this...
The work around is just to enable the unused Field output.
The work around is just to enable the unused Field output.
