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Basic question about contactors

 
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alec(at)alecmyers.com
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PostPosted: Tue Sep 19, 2017 4:29 pm    Post subject: Basic question about contactors Reply with quote

Now that I’m looking more carefully into contactors, I’m getting confused.

The three-terminal Ford-type contactors on my Cessna - that is, the battery master contactor, and the starter motor contactor all work by grounding the third terminal, so the top of the coil must be connected to the 12v battery terminal, internally.

The three-terminal starter contactor on my Luscombe has one end of the coil connected internally to the case (ground) and operates when the third terminal is connected to 12v.

So just to make sure I’m understanding this, there are two *different* kinds of three terminal ford-type contactors? And I guess you have to make sure you use the right one?
And, surmising further, the benefit of the four terminal regulators is that they can sub for either, by connecting the second coil terminal either to ground or to 12v?

I just want to make sure I have this correct - do I?


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donvansanten(at)gmail.com
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PostPosted: Tue Sep 19, 2017 7:54 pm    Post subject: Basic question about contactors Reply with quote

Alec, There are two basic types of contactors that are either 3 or 4 terminal. Long duration ( battery contactor) And short duration ( starter). Starter contactors generally have the coil grounded through their base. Generally 4 terminal contactors are for start circuits and the 4th terminal is hot when the contacyor is "on". I use this terminal to energise the starter solenoid as this eliminates starter run on. 

On Sep 19, 2017 17:32, "Alec Myers" <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Now that I’m looking more carefully into contactors, I’m getting confused.

The three-terminal Ford-type contactors on my Cessna - that is, the battery master contactor, and the starter motor contactor all work by grounding the third terminal, so the top of the coil must be connected to the 12v battery terminal, internally.

The three-terminal starter contactor on my Luscombe has one end of the coil connected internally to the case (ground) and operates when the third terminal is connected to 12v.

So just to make sure I’m understanding this, there are two *different* kinds of three terminal ford-type contactors? And I guess you have to make sure you use the right one?
And, surmising further, the benefit of the four terminal regulators is that they can sub for either, by connecting the second coil terminal either to ground or to 12v?

I just want to make sure I have this correct - do I?



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nuckolls.bob(at)aeroelect
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PostPosted: Wed Sep 20, 2017 8:15 am    Post subject: Basic question about contactors Reply with quote

At 07:27 PM 9/19/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

Now that I’m looking more carefully into contactors, I’m getting confused.

The three-terminal Ford-type contactors on my Cessna - that is, the battery master contactor, and the starter motor contactor all work by grounding the third terminal, so the top of the coil must be connected to the 12v battery terminal, internally.

When you say 'ford type' do you mean the black
plastic devices?


Quote:
The three-terminal starter contactor on my Luscombe has one end of the coil connected internally to the case (ground) and operates when the third terminal is connected to 12v.

This is the legacy wiring convention compatible
with off-left-right-both-start keyswitches.


Quote:
So just to make sure I’m understanding this, there are two *different* kinds of three terminal ford-type contactors? And I guess you have to make sure you use the right one?
And, surmising further, the benefit of the four terminal regulators is that they can sub for either, by connecting the second coil terminal either to ground or to 12v?

Virtually all manufacturers of contactors will
offer all variants of coil termination. Here's
a sample from the Stancor catalog on the 70/71
series devices

[img]cid:.0[/img]

Note that all variants of coil termination are
offered.

I am surprised that your starter contactor is a ground-to-
energize circuit. I'm aware of no Cessnas that left the factory
that way . . . what year/model is your airplane?




Bob . . .


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alec(at)alecmyers.com
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PostPosted: Wed Sep 20, 2017 9:08 am    Post subject: Basic question about contactors Reply with quote

You're absolutely right. I was misreading the mickey-mouse diagram in the POH. When I refer to the wiring diagrams in the service manual it's much clearer. The starter contactor is indeed 12v-to-energize.

On Sep 20, 2017, at 12:15, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

I am surprised that your starter contactor is a ground-to-
energize circuit. I'm aware of no Cessnas that left the factory
that way . . . what year/model is your airplane?




Bob . . .


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