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Smart Start wire size

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Fri Sep 18, 2009 4:32 pm Post subject: Smart Start wire size

I bought the Smart Start module from TCW and was just getting around to looking at the wire diagram and harness.  All of the Aeroelectric diagrams show a 7 amp protected 20 AWG wire going to the start switch then on to the post on the start relay.  



The Smart Start module gets power from the main buss via 2 amp breaker or fuse and the wires in the entire harness are only 22 AWG. (http://tcwtech.com/Smartstart.htm) Wire diagram is at the link.  



So two wires connect to the start switch and go into the module and one wire goes to the small terminal on the start relay.  Is the 22 AWG wire and 2 amp breaker too small.  I can't see what determines wire size for this application.   Since only 2 amps can flow into the module then the 22 AWG wire to the start relay is protected but what complication might there be with this setup.  I guess I need to go back and read "the book" for the ump-teenth time!  Thanks for any help.

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

rnewman(at)tcwtech.com
Guest

Posted: Fri Sep 18, 2009 5:24 pm Post subject: Smart Start wire size

The main current carrying wires for the smartstart module are the power 

input and the output to the contactor.   The other wires to the start switch 

and interlock switch (if used) are signal level only.    The start contactor 

will require a peak current of about 3.5 amps,  this presents no issue for 

22 awg wire as the voltage drop over 10-15 feet of wire at this current 

level is negligible.    Since the start contactor operation is such a short 

duration and is not a continuous duty load the fusing may be reduced below 

that of the continuous rating.     The SmartStart module itself can handle 

contactor currents of up to 10 amps peak.     You may certainly raise the 

fuse rating if you wish to 5 amps without bumping into any issues as 

permitted by 43.13.   However, we have found a 2 amp fuse is sufficient.

Bob Newman

TCW Technologies, LLC.

www.tcwtech.com



---

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Sat Sep 19, 2009 4:26 am Post subject: Re: Smart Start wire size

Bob,



Thanks for the explanation, I was going to email you over the weekend so you would have my message in you inbox on Monday, lucky for me you watch this forum.  



I was confused and could not figure out why the small wire would be OK  as I stated AEC Z-diagrams all show 20 AWG with 7 amp protection.  The Van's diagram calls out 18 AWG wire.  I suppose they like the larger gage wire for its durability.

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Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Sep 19, 2009 5:33 am Post subject: Smart Start wire size

At 07:32 PM 9/18/2009, you wrote:

 	  Quote: 	
		  



I bought the Smart Start module from TCW and was just getting around 

to looking at the wire diagram and harness.  All of the Aeroelectric 

diagrams show a 7 amp protected 20 AWG wire going to the start 

switch then on to the post on the start relay.



The Smart Start module gets power from the main buss via 2 amp 

breaker or fuse and the wires in the entire harness are only 22 AWG. 

(http://tcwtech.com/Smartstart.htm) Wire diagram is at the link.



So two wires connect to the start switch and go into the module and 

one wire goes to the small terminal on the start relay.  Is the 22 

AWG wire and 2 amp breaker too small.  I can't see what determines 

wire size for this application.   Since only 2 amps can flow into 

the module then the 22 AWG wire to the start relay is protected but 

what complication might there be with this setup.  I guess I need to 

go back and read "the book" for the ump-teenth time!  Thanks for any help.


	


   Wire per the manufacturer's instructions . . . but

   write to them and ask what to do about it if

   the starter contactor draws 5A. Most intermittent

   duty contactors require about that much.  Their

   instructions seem to allude to a potential for damage

   to their product if the thing is used to control

   a modern, engagement/contactor solenoid like

   B&C, Skytec or similar automotive adaptations.



   The question to ask them is whether or not they

   can handle a 5A contactor and a system powered via

   7A breaker/fuse through 20 AWG wire on pins 7 and 9.

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Tue Sep 22, 2009 5:15 pm Post subject: Smart Start Manual Updated

I received an email from Bob Newman at TCW, although they have had no issues with the system the discussion on this board made them double check the the fuse requirements and after consulting with some starter contact manufacturers they have upped the fuse requirement to a 5 amps.  The on-line version of the manual is updated.  It seems a 3 amp fuse would be fine but since the wire size will accommodate the 5 amp fuse they are making the change to 5 amps.

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

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