Master Contacter

[gammaxy]

Gordon,

The starter used by the Aerovee has an integrated solenoid that can be used instead of a starter contactor.

The experimental aircraft wiring diagrams on this page shows it connected that way:
http://www.skytecair.com/Wiring_Diag.htm

I have big welding wires running directly from the battery to the starter. This is the main difference. Smaller gauge wires (with a fuse near the battery) run through the automotive relay and into the cockpit where everything including the starter button is powered.

I turn my master key to "on" and hear a tiny click from the relay letting me know the cockpit has power and that the starter button is "armed".

I don't have a digital copy of the schematic, but if it still doesn't make sense, I can scan one in.

I'm not recommending anyone else do it the same way I did. There are some downsides--most notably the inability to completely remove the battery from the circuit. If the starter solenoid somehow got stuck "on", there'd be no way to turn it off other than wait for a dead battery. The relay seemed simpler and more elegant at the time, but I just as easily could have gone the typical route.

[Bryan Cotton]

Chris,

I like that solution. I have never had a starter contactor weld itself. I had also considered a pull-start like on the Cessna 140, but that seems like a lot of work to prevent a problem that is not terribly likely.

[GordonTurner]

Interesting idea. I'll think about that one.

Gordon

[Bryan Cotton]

So, I have this crazy idea. Rather than a large power robbing master, how about a disconnect switch like this one:


This one is from harbor freight.
https://www.harborfreight.com/battery-c ... 63425.html


Switch would mount on the engine side of the firewall. I would replace the red plastic key with a short steel part which would go through a hole in the firewall. I would rivet an aluminum tube to the steel part and have it penetrate the panel so I could turn it on and off. It would be a mechanical master switch, and would use no power.

Thoughts?

[wlarson861]

I don't see why it wouldn't work. That's the type of switch used in motorhomes and large travel trailers to shut down the house batteries so they don't discharge in storage. Does the same thing as a master contactor and probably less likely to fail.

[NWade]

I would rivet an aluminum tube to the steel part and have it penetrate the panel so I could turn it on and off. It would be a mechanical master switch, and would use no power.

Thoughts?

Just note that you're poking an extra hole in your firewall and an al tube will melt in a fire fairly quickly; letting the flames through the firewall quite readily. Its up to you to judge the risks of that and determine if you're OK with it or not - no one can make that judgment for you.

Personally, I'm not sure I understand what the upside is over a master contactor; given that the parts will also weigh more than a small-gauge wire and a small switch? I'm not saying there is no upside; just that I am not understanding what it is you're seeking to improve by implementing this.

--Noel

[sonex892.]

H Bryan
I'm an electrician and I like the simplicity. I have always viewed master contactors as another failure point. I put my faith in a fuse for everything other than the starter which is DOL to the relay.
Steve
Sonex 892

[Bryan Cotton]

Noel,
If I implement this, there would be a short steel rod going through the firewall, and the aluminum tube would only be in the cockpit. I'll weigh the switch. It is pretty light - and has no coil. Besides saving the weight of the coil (traded by the actuation rod) I am also saving the juice needed to run it. With only 20 A available in cruise, that is a good thing.

[GordonTurner]

Brian, ive been pondering the same thing. It basically saves an amp!!!!

Gordon

[n982sx]

Bryan,

I did contemplate using a cutoff switch on the Sonex. Ultimately I did go with a contactor but was concerned about the amount of current they draw with a Sonex alternator.

You can always trade dollars for convenience so that is why I went for the contactor instead of the switch. Convenience of installation and use. I still had concerns about power draw so I traded money again for electrical efficiency with one of the Tyco EV200 units with an economizer. It draws only .13 amps at 12v. Very nice match for the Sonex alternator.

You can find them on eBay for widely varying prices. However, some people on eBay sell them without the economizer which just makes no sense for our purposes.

I did use one in my new build for my second battery. It is mounted under a seat. A standard contactor converts its near one amp draw to heat and the one I installed first just got too hot for the location. So I switched to a Tyco unit for that reason. I got it for $45 on eBay but had to wait awhile to find one at that price.

I think Tyco has a new model now so that most of the ones out there seem to be new old stock or salvage.