What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

master switch / alternator switch

miyu1975

miyu1975

Well Known Member
First, let me say I am very grateful to this site and forum...especially for the questions, advice and education I have gained from it.

I am currently working on my panel and wiring. I have a question on the master switch. From my reading of bob nuckolls I believe I need a 2-3. I am trying to confirm this and how to wire this up. I have the PP alternator. Do I run the field wire from the PP alt to the master switch?

My initial thinking is to use a separate switch for the alt and master, just a simple on/off switch for each. I suppose on the master switch one wire would go to the main bus and the other to the battery contactor. Again, I have reading and studying the nuckolls book but all his diagrams show the b/c alternator/regulator....so my wiring diagram would be a little different with the pp alt internally regulated.
please advise.
 
Many ways to skin a cat. I have two simple on-off toggles, one for the battery and one for the alt field. With the PP alternator, you can also add an alternator out light (no switch needed) or not if you choose.

Greg
 
What Greg said. I like simple.

One simple toggle switch for the master. One 5a breaker for the alternator field, which is placed above the master switch.
 
OK..Thanks... I like simple too. I will go with off/on switches one for the master and one the alt field. Still not clear on the wiring of the Master on/off switch. don't I need a wire from the switch to battery contractor and another wire to the main bus fuse block? right?
 
miyu1975 said:
OK..Thanks... I like simple too. I will go with off/on switches one for the master and one the alt field. Still not clear on the wiring of the Master on/off switch. don't I need a wire from the switch to battery contractor and another wire to the main bus fuse block? right?
Click to expand...

The MASTER switch should complete a ground to close the master solenoid. And all you really need for the PP alternator is a 5A pull type breaker and no switch.
 
Typical master solenoid has only one small terminal. Goes through your switch seeking ground. The positive for the solenoid coil is connected internally. If you have a 4 pole master a small jumper goes from one small terminal to the big terminal on the battery side. Then the other goes through switch to ground. That means that if your switch wires ever short to ground you won't make fire. It just turns the master on.
 
Maybe this will help. Copied/snipped/modified from the Aeroelectric Z11 diagram.

i-Q34VWRS-X3.jpg


The switch is 3 position double pole double throw. The terminals are numbered; they correspond to the numbers on the diagram. It's helpful to have a volt/ohm meter when you are doing this stuff, so you can verify circuits.

Note that I'm not recommending this design over any other; merely clarifying how to connect a Plane Power alternator and a master switch using Nuckoll's design.
 
Lars said:
Maybe this will help. Copied/snipped/modified from the Aeroelectric Z11 diagram.

i-Q34VWRS-X3.jpg
Click to expand...
For connecting the main buss to alt field, why does Bob show both a fuselink at the buss AND a 5A ALT FLD c/b after the switch?

Why not just go from the main buss, right to a 5A ALT FLD c/b then to the switch then to the alternator F terminal? This is how Van's does it in their drawings and others that I've seen.

Just curious. I've mostly followed Aero Bob but this one has always stumped me.
 
alpinelakespilot2000 said:
For connecting the main buss to alt field, why does Bob show both a fuselink at the buss AND a 5A ALT FLD c/b after the switch?

Why not just go from the main buss, right to a 5A ALT FLD c/b then to the switch then to the alternator F terminal? This is how Van's does it in their drawings and others that I've seen.

Just curious. I've mostly followed Aero Bob but this one has always stumped me.
Click to expand...

I seem to recall reading his logic for doing it that way, but I can't dredge it out of my feeble memory right now. Guessing, I would say to protect the wire between buss and switch.
 
alpinelakespilot2000 said:
For connecting the main buss to alt field, why does Bob show both a fuselink at the buss AND a 5A ALT FLD c/b after the switch?

Why not just go from the main buss, right to a 5A ALT FLD c/b then to the switch then to the alternator F terminal? This is how Van's does it in their drawings and others that I've seen.

Just curious. I've mostly followed Aero Bob but this one has always stumped me.
Click to expand...

The circuit breaker protects the wiring to the alternator. The fuselink protects the wiring between the bus and master switch.
 
Lars said:
Guessing, I would say to protect the wire between buss and switch.
Click to expand...

longranger said:
The circuit breaker protects the wiring to the alternator. The fuselink protects the wiring between the bus and master switch.
Click to expand...

OK, makes sense. Is there some reason the ALT FLD c/b needs to be AFTER the switch? Why not put it before the switch as is the case for most everything else coming off the main buss?
 
alpinelakespilot2000 said:
OK, makes sense. Is there some reason the ALT FLD c/b needs to be AFTER the switch? Why not put it before the switch as is the case for most everything else coming off the main buss?
Click to expand...

It shouldn't matter if you place the ALT FLD c/b before or after the switch. Keep in mind if you are using a 5a pull type breaker and the dual pole switches then your have in line redundant switches. Why?

I have a single pole switch for my master and a 5a pull type breaker for my alternator field and it works as advertised. I see no reason for switching off the alternator field when the engine is powered down and you shut off the master switch. In the rare cases where you want to do that, just pull the breaker.

The 2-10 switches are more expensive and can be a PIA to wire.

My 2 cents, YMMV
 
Eleven years of flying the RV, 1200+ hours and not once did I flip the alternator side of the switch off while leaving the master on. About the only practical use case is if you were wanting to power your radios for an extended period before startup without energizing the alternator field. Even so I never did that.

My vote is to leave it out altogether. Its one of those dumb things that is generally accepted in aircraft for really no good reason. Most pilots can't tell you why there's a separate switch anyway.
 
Last edited:
Greg Arehart said:
Because more switches = cooler airplane! I've got about a dozen that don't do anything except impress passengers.:D
Click to expand...

:D Haha how right your are! Don't forget, for every switch you install, you also need to install a corresponding LED in the annunciator panel to remind you that it's on/off.

The main reason why FADEC won't work in RV's is because we will never want to give up the mixture control.
 
Whatever switching scheme you use, make sure you can't get into a condition where the alternator is energized but the master is off. This can cause a dangerous overvoltage condition!

I used the same switch Gary mentioned in an earlier post. Off-master-master+alternator. This way when the master is turned off the alternator is always de-energized before the battery is disconnected from the alternator.
 
What Mark said. You never want power to the field and no battery. Hand propping a plane can also be a real problem. It can cause a over volt problem. You always want a field switch so you can remove the alternator from the circuit. You do that by removing the voltage from the field wire with a switch. The common double switch mentioned (Cessna switch) will not allow alt on and master off but will allow the alt. off if needed without turning off your master.
I like the strategy and will be using it.
 
Perfect!!!

Greg Arehart said:
Because more switches = cooler airplane! I've got about a dozen that don't do anything except impress passengers.:D
Click to expand...

This is so perfect. Like having switch guards on stuff that doesn't need them. They look cool, I guess:eek: Like having more than 2 GPS's. I guess it is cool:eek::eek:
 
MarkW said:
What Mark said. You never want power to the field and no battery. Hand propping a plane can also be a real problem. It can cause a over volt problem. You always want a field switch so you can remove the alternator from the circuit. You do that by removing the voltage from the field wire with a switch. The common double switch mentioned (Cessna switch) will not allow alt on and master off but will allow the alt. off if needed without turning off your master.
Click to expand...
If that's the case, then you can meet this requirement by having a pullable circuit breaker on the Alternator field. In general, it will always stay connected, and you just power both Master and Alternator at the same time with a double-pole switch. If you ever need the Alternator field disabled (haven't yet, but that's not to say it can't happen), you can pull the CB.
 
Snowflake said:
If that's the case, then you can meet this requirement by having a pullable circuit breaker on the Alternator field. In general, it will always stay connected, and you just power both Master and Alternator at the same time with a double-pole switch. If you ever need the Alternator field disabled (haven't yet, but that's not to say it can't happen), you can pull the CB.
Click to expand...

With the field power coming from the main buss that is controlled by the master, why would you need a double pole switch?
 
used to be

Many certified planes don't have separate alt/master switches so you had to shut off all electronics to attempt a reset for an altenator. The separate alt/master switches allowed electronics to remain on, although people I know always turned everything off for the dual switch exercise to protect the electronics from a surge. I do have the separate switches to isolate if ever needed in the air.
 
You must log in or register to reply here.
Back
Top