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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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 Posted: Thu Aug 06, 2020 7:48 am Post subject: Re: Rotax install |
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I would NOT buy an external alternator now, but wait until you determine that
it is actually needed. I added up your loads and the total came to 13 amps. I
did not include intermittent loads: landing - taxi lights, or charging two
batteries. Run the engine and measure the actual alternator output with all
continuous loads turned on. If the total current is 15 amps or less, an aux
alternator is not needed.
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Joe Gores |
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meat_ball
Joined: 05 Aug 2020
Posts: 27
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| Posted: Thu Aug 06, 2020 10:07 am Post subject: Re: Rotax install |
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| user9253 wrote: | I would NOT buy an external alternator now, but wait until you determine that
it is actually needed. I added up your loads and the total came to 13 amps. I
did not include intermittent loads: landing - taxi lights, or charging two
batteries. Run the engine and measure the actual alternator output with all
continuous loads turned on. If the total current is 15 amps or less, an aux
alternator is not needed. |
Okay! I'll give that a shot. However, I will need to wire the plane to make it easy to add the external alternator if needed. So I go back to my previous question about the "master switch".
| Quote: | Attached is the Rotax 914 Electrical Diagram (hopefully you can make sense of it). It shows just what kenryan suggests as far as the fuel pumps. What about the master switch toward the bottom? From what I see when you turn it on, the battery gets connected to the bus, but that also gives a ground to the master relay which allows the Internal and External Alternators to connect to the bus/battery. Now turning off the Master Switch will kill all power to the Bus Bar and battery from the Alternators. Am I missing something? That seems like a bad thing...
Is this where I would wire in the s700-2-10, 3 position ON-ON-ON switch?
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How would I wire this switch to make it work for the single alternator, and also in the case that I add an external?
Again, thank you for indulging my ignorance.
Rob
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Fri Aug 07, 2020 5:34 am Post subject: Re: Rotax install |
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There is more than one way to wire the alternators. You can use the
3 position OFF-Battery-Both switch or separate switches.
Since you might eventually add a second alternator, to make it less confusing
for you or future pilots, I would use 3 separate switches:
Master battery contactor switch, alternator-1 switch, and alternator-2 switch.
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Joe Gores |
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meat_ball
Joined: 05 Aug 2020
Posts: 27
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| Posted: Fri Aug 07, 2020 6:15 am Post subject: Re: Rotax install |
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| user9253 wrote: | There is more than one way to wire the alternators. You can use the
3 position OFF-Battery-Both switch or separate switches.
Since you might eventually add a second alternator, to make it less confusing
for you or future pilots, I would use 3 separate switches:
Master battery contactor switch, alternator-1 switch, and alternator-2 switch. |
Of course!! Next question is about the fuses. I want to use the fuse blocks instead of breakers, but is there a hard and fast rule about which components should have a panel circuit breaker instead of the fuse?
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Fri Aug 07, 2020 7:56 am Post subject: Re: Rotax install |
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Some builders use all circuit breakers. It is a matter of personal choice.
I prefer fuses. They are lighter weight, cost a lot less, and never fail to open the
circuit when required. Some breakers have been known to smoke instead of opening.
Circuit breakers should be used for circuits that might be expected to
momentarily draw too much current. Perhaps a landing gear pump.
Bob's drawings use a circuit breaker in series with the over-voltage crowbar module.
Your Rotax 20 amp alternator will be heavily loaded, thus unlikely to put out too high
voltage. If you have a lead acid battery, it will absorb extra current for a
short time. You might risk not having over-voltage protection. Van's Aircraft
designed the RV-12 without over-voltage protection. Over 500 of them are flying.
If you have a lithium battery, over-voltage protection is highly recommeded.
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Joe Gores |
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meat_ball
Joined: 05 Aug 2020
Posts: 27
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| Posted: Sat Aug 08, 2020 5:47 am Post subject: Re: Rotax install |
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Thanks again, Joe! I appreciate everyone’s input. I’ll try to iron this out, but I’m sure I’ll be back with more questions.
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meat_ball
Joined: 05 Aug 2020
Posts: 27
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| Posted: Sun Aug 09, 2020 11:12 am Post subject: Re: Rotax install |
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Hello everyone. I’ve taken my first stab at the wiring diagram. I based this off of a Rotax 914 because that drawing has the turbo charger electrics depicted. The one thing it doesn’t show is the electronic ignition wiring so I had to go it alone on that part...hopefully I’ve done it correctly.
After looking at the system a bit more in depth, I realized they were a few things I left off the initial list of “Consumers.“ The most significant thing I had forgotten was the cabin heater. That will put me over the edge for electrical usage as far as a single alternator goes. There is a 15 amp external alternator which will sufficiently handle the extra loads so I plan on wiring that for constant use along with the internal generator. I have the essential bus in the top left corner of the drawing but am unsure how/where to connect it. Also, I would like to add the crowbar unit (I’m uncertain if I will use lithium or not) but don’t completely understand how that would work in this setup. As I understand it, it measures bus voltage and removes the alternator from the bus if that voltage is too high. The way I have it wired, how would it know which is the offending alternator since they’re both in an always-connected-to-the-bus-state? would I need one for each alternator?
Will some of you be so kind as to take a gander and offer your input?
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meat_ball
Joined: 05 Aug 2020
Posts: 27
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| Posted: Tue Aug 11, 2020 4:56 am Post subject: Re: Rotax install |
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| user9253 wrote: | There is more than one way to wire the alternators. You can use the
3 position OFF-Battery-Both switch or separate switches.
Since you might eventually add a second alternator, to make it less confusing
for you or future pilots, I would use 3 separate switches:
Master battery contactor switch, alternator-1 switch, and alternator-2 switch. |
Of course!! Next question is about the fuses. I want to use the fuse blocks instead of breakers, but is there a hard and fast rule about which components should have a panel circuit breaker instead of the fuse?
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http://www.matronics.com/Navigator?AeroElectric-List |
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