Eliminate Master Contactor ??

[RKellogg]

I am considering elimination of the master contactor to save weight and electrical load. Could use three 20A toggle breakers as "masters" to control the electrical systems. Any comments? Any experience?
- Roger

[skybolt31]

The Christen Eagle is setup without a master contactor, everything goes through a 20amp switch/breaker. It saves weight perhaps cuts down on electrical load and makes things a little simpler. The two drawbacks that I have identified (so far) is that if your starter contactor sticks, the starter will crank until the battery dies and if you do have a dead battery and jump the plane to start it, the charging current to the battery will exceed the 20amp breaker's capacity and it will trip when the rpm's are increased. Sounds like if you use several of them, this will not be a problem.

Bruce Green

[MCA]

You can't run the starter load through those switches so you'll have the issue described above. Further, you won't be able to isolate power form coming into the cabin area.

The contactor draws about 0.7 amps at 14v. What is the weight delta between three beefy swithces and the contactor?

[Neal@F14]

If you ever have an electrical fire start up during a flight. The ability to kill all your electrical power via shutting off a "master relay" is the next best thing to having a parachute (and enough altitude for it to work) onboard.

[gasman]

How about a manual master switch? Harbor Freight has this........

http://www.harborfreight.com/catalog...battery+switch

Heavy Duty Battery Cutoff Switch
Item #66789
Only:$9.99
U.S. General #66789


This will carry starting load and also be able to switch it off manually if you need to isolate the battery load just like the master relay except it is a manual switch that does not use any power.

[Crossbow]

Originally Posted by RKellogg

I am considering elimination of the master contactor to save weight and electrical load. Could use three 20A toggle breakers as "masters" to control the electrical systems. Any comments? Any experience?
- Roger

I am still a good ways from this point, however the same thought has crossed my mind, therefore I am interested in the replies.

After all, Aircraft Spruce sells a little item that is called a "PULL SWITCH" (part number: 16-140) for $ 9.50 that can pull 75 Amps. Anyway, I should think that one can use a device like this as opposed to the Master Contactor unit.

[rocketbob]

Originally Posted by Crossbow

I am still a good ways from this point, however the same thought has crossed my mind, therefore I am interested in the replies.

After all, Aircraft Spruce sells a little item that is called a "PULL SWITCH" (part number: 16-140) for $ 9.50 that can pull 75 Amps. Anyway, I should think that one can use a device like this as opposed to the Master Contactor unit.

Your starter will draw 300-350A initially.

[szicree]

Originally Posted by gasman

How about a manual master switch? Harbor Freight has this........

http://www.harborfreight.com/catalog...battery+switch

Heavy Duty Battery Cutoff Switch
Item #66789
Only:$9.99
U.S. General #66789

No offense, but the idea of a Harbor Freight item keeping my plane in the air makes me very uncomfortable.

[Crossbow]

Originally Posted by rocketbob

Your starter will draw 300-350A initially.

Wow! That sure is a lot of current all right.

However, if one kept the wiring for the Starter Contactor seperated from the other wiring, then that 300A to 350A should not be a factor.

So am I thinking about that correctly?

[Neal@F14]

Using a master relay solenoid (contactor) is a tried and proven recipe. They don't weight or cost all that much, and there's very good reasons why virtually every production and homebuilt piston engine aircraft on the planet has one.