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Permalink Reply by Bob Pustell on August 11, 2011 at 9:58pm

The master contactor is basically a heavy duty relay that connects the battery to the aircraft electrical system. It is available from aircraft spruce or any other aircraft supply company. You can control it with a simple toggle switch "master switch" or you can use a keyed switch to activate it.

 

Many homebuilts are built similar to automotive systems, where the electrical system is alway "hot". The advantage to the master switch/master contactor system is you can deactivate the electrical system before an emergency landing and minimize the chances of an electrical fire. The advantage to the automotive style is less complication and one less thing to break. If it is not installed, it cannot break.

 

A good compromise is to install an automotive racing battery disconnect switch. They are readily available, cheap and reliable. Normally, you leave it on, but you can turn it off if needed. Some even come with a removeable handle so that you have a disabled electrical system if you take the handle with you as you leave the airplane, sort of a theft deterrent. I plan to go this route.

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Permalink Reply by John Austin on August 12, 2011 at 10:59am

Thanks for the detailed explanation!

My confusion arises in that in one section of the EXP BUS II installation manual, it says The EXP BUS II replaces the master solenoid, all but one circuit breaker, the master switch function, and the avionics master switch function.

Then, in another section, it says The aircraft may either have a master solenoid, or use the onboard master relay.

So, I guess to add the master solenoid is just to add yet another layer of protection?

Thanks,

John

 





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Permalink Reply by David Gallagher on August 12, 2011 at 2:41pm

John,

 

 Another good source for all sorts of of aircraft electrical hardware is B&C Products.  I am using their catalog# S701-1 continuous duty contactor as my battery master solenoid.  I think, due to a previous business connection, the B&C product line-up matches well with the Bob Nuckolls recommended philosophy.

 

Good luck on your FWF & electricals, it was the most satisfying part of my build,

 

Dave

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Permalink Reply by Joe Harrington on August 12, 2011 at 7:50pm

Just ran across this new tech solid state contact switch. Also has solid state circuit breakers.

http://www.ztronlabs.com/products.php

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