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More Contactor - Newbie questions

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jdalton77(at)comcast.net
Guest

Posted: Mon Jan 08, 2007 8:59 am Post subject: More Contactor - Newbie questions

Hello,

  

 I'm sorry to be asking such basic questions, but I  am still confused about the use of contactors and relays.  I've been  reading Bob's book, but I'm not always sure how to interpret the  schematics.

  

 In terms of the battery contactor, I know the  hot lead goes from the battery to the large post, and that the "output"  side  (leading to the starter) is not engaged until I flip, or depress, the  starter switch.  But how does the 8AWG wire that connects to the main  bus from the contactor's"small" terminal become "hot?"  Is it  always hot?  I see a switch for "turning on the main bus" but how does that  work?  Doesn't the switch need to be hot in order to turn on the current to  the main bus from the battery contactor?

  

 Also, in the back of the book there is a schematic  for connecting a ground power plug (Piper style).  A contactor is shown  here also.  Why do I need one here, and in a similar vein, wouldn't I need  a powered switch to turn it "on" to allow current to pass through it?  What  would activate the contactor when I plugged in the external power.  And  would this be a "continuous duty" contactor or more like a starter  contactor?

  

 Finally, on two batteries.  Is there any  reason two batteries could not be connected in parallel, without using another  contactor, or another switch?  Why would that kind of setup not give me  redundancy if one of the two batteries were to perish while flying?  I'm  not challenging anything in the book here - I just don't understand  it.

  

 I've learned a ton in the two weeks I've been  reading the book - but I'm just starting to learn the language.

  

 Thanks,

  

 Jeff



   [quote][b]

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Dennis Glaeser

Joined: 10 Jan 2006
Posts: 53
Location: Rochester Hills, Michigan

Posted: Mon Jan 08, 2007 6:17 pm Post subject: More Contactor - Newbie questions

Jeff,



This is Dennis in Rochester Hills.  You need to give me a call and come over

to see my electrical system and I think things will fall into place quickly!

Call me at 248-953-0374.  My wiring is done to the point that I can show you

how the contactors work, and how power flows through the system.



I'm not sure what you mean by the "contactor's small terminal" that has an

8AWG wire connected.



The small terminals on the contactor should have small (20 or 22AWG) wires -

one from the big "+" terminal, the other leads to the master switch.  The

battery provides the power for the solenoid coil - the master switch

provides the ground.  There should be a diode across the small terminals as

well.



If you have 2 batteries, each one needs a contactor for safety.  In normal

operation, both contactors are closed and the batteries are in parallel.

But you need to be able to connect/disconnect them separately 1) for due to

failure modes where one battery could bring down the other one, and 2) each

battery typically powers different things in battery-only mode (when the

alternator fails).



The external power connector has a contactor for the same reasons - control

and potential failure modes.  The power for this solenoid comes from the

external power source - again the switch just provides a ground.



Dennis Glaeser

Rochester Hills, MI



----------------------------------------------------------------------------

-------------------------

Subject:      More Contactor - Newbie questions

From:      jdalton77 (jdalton77(at)comcast.net)

Date:      Mon Jan 08 - 8:59 AM



Hello,



I'm sorry to be asking such basic questions, but I am still confused

about the use of contactors and relays.  I've been reading Bob's book,

but I'm not always sure how to interpret the schematics.



In terms of the battery contactor, I know the hot lead goes from the

battery to the large post, and that the "output" side  (leading to the

starter) is not engaged until I flip, or depress, the starter switch.

But how does the 8AWG wire that connects to the main bus from the

contactor's"small" terminal become "hot?"  Is it always hot?  I see a

switch for "turning on the main bus" but how does that work?  Doesn't

the switch need to be hot in order to turn on the current to the main

bus from the battery contactor?



Also, in the back of the book there is a schematic for connecting a

ground power plug (Piper style).  A contactor is shown here also.  Why

do I need one here, and in a similar vein, wouldn't I need a powered

switch to turn it "on" to allow current to pass through it?  What would

activate the contactor when I plugged in the external power.  And would

this be a "continuous duty" contactor or more like a starter contactor?



Finally, on two batteries.  Is there any reason two batteries could not

be connected in parallel, without using another contactor, or another

switch?  Why would that kind of setup not give me redundancy if one of

the two batteries were to perish while flying?  I'm not challenging

anything in the book here - I just don't understand it.



I've learned a ton in the two weeks I've been reading the book - but I'm

just starting to learn the language.



Thanks,



Jeff

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jdalton77(at)comcast.net
Guest

Posted: Mon Jan 08, 2007 7:01 pm Post subject: More Contactor - Newbie questions

Dennis,



Thanks for your offer.  I just received my shipping docs for my wing kit.



I'll be out of town until the 17th but will call you when I get back.  I 

definitely want to see your plane and your wiring.



Jeff

248-709-4775

---

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