My plane is a '56 180 with an interav alternator. I do not however, have a separate alternator field switch in my panel - it has just a breaker which is actually kind of hard to pull out due to the side panel. I'm trying to educate myself about whether I need the newer split master switch (cessna added it in '73 as I understand it). It allows you to individually turn off the alternator field.

What are the benefits of retrofitting this switch if any?

I may have found the answer to my questions - I'm just looking for validation that I need to investigate this and have my plane retrofitted. Is it to improve the longevity of my charging system (to allow starting with the alternator field disconnected)? Page 14 of this article seems to claim this is not necessary.

http://www.aeroelectric.com/articles/Alternators/Know_Your_Charging_System.pdf

Here's the switch for cessnas:
https://www.aircraftspruce.com/catalog/elpages/cessnasplit.php?clickkey=87446

And a wiring diagram:
http://www.steinair.com/wp-content/uploads/2016/03/CESSNA-SPLIT-MASTER-SWITCH-DWG.pdf

You could just put a pull switch in instead of the dual switch. That's how my 180 is setup.

Greg,

I was always led to believe that the primary purpose of having an alternator field switch was to enable you to disconnect/disable the alternator in the event of a malfunction. With the separate switch, you can disconnect field current to a malfunctioning alternator, and still run your minimal avionics off the battery.

You can, of course, do the same thing with what you have....a circuit breaker. Maybe not as pretty, but....you could install a standard switch or maybe a switch/breaker if you don't feel like installing the split switch.

I think the logic of having the alternator field off during starts was to avoid spikes as the alternator comes up to speed. These days most planes have avionics master switches to prevent that kind of damage to avionics and actually, most avionics these days are pretty tolerant.

MTV

soyAnarchisto wrote: My plane is a '56 180 with an interav alternator. I do not however, have a separate alternator field switch in my panel - it has just a breaker which is actually kind of hard to pull out due to the side panel.....

My last airplane, a C150/150TD, had an Interav alternator and a 50A alternator breaker. It also had both an alternator field CB and a alternator field toggle switch. I thought that was unnecessary redundancy and was gonna get rid of the toggle switch, but upon inspection I found that they were not wired in series and seemed to be on separate circuits. So the CB you reference might not be doing the same thing as an alternator switch.

If it was me & I determined that a separate switch was a good thing, I think I'd add a toggle switch (or wire it to a spare pull button switch) instead of fooling with a split master.

Hey Greg,
I have the same interav alternator installed in my plane. The manufacturer instructions and diagram indicate at what point in the wiring the field switch should be installed for the STC. Note, the Circuit Breaker your referring to is for the externally mounted over voltage relay device which is unique to the Interav setup. Pulling this can sometimes cause a voltage spike and Interav has issued the following note in their manual: "Don't open Alternator circuit breaker at any time when Alternator is operating if manual-type Circuit breaker is used. Leave in "ON" or closed position at all times."

As MTV mentioned, installing the field switch allows you to isolate the alternator when troubleshooting electrical issues or to prevent spikes during start-up. I've noticed that a lot of cessna airplanes that originally had generators don't have the field switch and it seemed to be over looked when the interav kits were installed.

Link to Interav Diagram

Hope this helps,
Alec

Thanks for the responses, guys.

I don't know what brand alternator conversion I have, but it came with the split master switch. I recall when my IA installed it, we discussed the split master, and he said that the only time to operate them separately was to kill the feed from the alternator if it should ever malfunction. He also installed an avionics master at the same time, along with a separate sub-panel to replace the fuses with circuit breakers. One of those CBs is for the alternator, too, so it can be disabled with both the split switch and the CB. In any event, I haven't had to do either, as it's worked just fine for the last 12 1/2 years.

Cary