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Master Switch/Contactor and Starter Questions

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dgaldrich

Joined: 24 Apr 2009
Posts: 267
Location: Naples, Fl and Belfast, ME

Posted: Sun Jun 30, 2013 8:07 am Post subject: Master Switch/Contactor and Starter Questions

Hi Robert et al.



Two issues to discuss



Under what circumstances could you recommend/condone the use of a simple mechanical master switch (as in Z-17) rather than a traditional battery contactor?



I am building an aircraft with very similar loads to Z-17 but will have an 18 amp dynamo/PMG and an Odyssey 680 battery so I guess the real question is, do those two items change the ability to use a switch versus the additional complexity and "hold" current usage of a contactor?



Second issue is wiring the starter.  Mine has two separate terminals.  One for the serious current and one for the solenoid.  I'm planning to wire the battery directly to the starter with #2AWG cable and use #16AWG from the solenoid to the start switch and back through a 5 or 10 amp CB.  All of the Z- diagrams show a start contactor so I'm wondering if my planning passes the "idiot" test.



Thanks.



Dave

peter(at)sportingaero.com
Guest

Posted: Sun Jun 30, 2013 1:09 pm Post subject: Master Switch/Contactor and Starter Questions

Dave,



Here's a couple of ideas for you to consider,



1. If a switch is used as the 'master switch' as you suggest, some 

distance from the battery, consider installing a 20 or 25A (or similar) 

c/b close to the battery, and in reach of the pilot, so if need be 

breaker can be pulled and the system will be cold from there on.

2. Fit a starter relay close to the battery - that way you do not have 

hot thick wires running to the engine all the time. The issue then is 

the starter relay welding itself shut, where releasing the starter 

button will not stop the starter. Some modern starters with an on board 

solenoid allow for the path energising the solenoid to be broken - such 

as SkyTec NL series. If a switch is added in the cockpit in this path 

then the starter can be turned off with a welded starter relay.



Regards, Peter



On 30/06/2013 17:07, dgaldrich wrote:

 	  Quote: 	
		   



 Hi Robert et al.



 Two issues to discuss



 Under what circumstances could you recommend/condone the use of a simple mechanical master switch (as in Z-17) rather than a traditional battery contactor?



 I am building an aircraft with very similar loads to Z-17 but will have an 18 amp dynamo/PMG and an Odyssey 680 battery so I guess the real question is, do those two items change the ability to use a switch versus the additional complexity and "hold" current usage of a contactor?



 Second issue is wiring the starter.  Mine has two separate terminals.  One for the serious current and one for the solenoid.  I'm planning to wire the battery directly to the starter with #2AWG cable and use #16AWG from the solenoid to the start switch and back through a 5 or 10 amp CB.  All of the Z- diagrams show a start contactor so I'm wondering if my planning passes the "idiot" test.



 Thanks.



 Dave





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=403652#403652

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Jun 30, 2013 3:45 pm Post subject: Re: Master Switch/Contactor and Starter Questions

The FAA doesn't require a battery contactor and you car doesn't have one. The contactor per FAA "must disconnect the battery with one hand in the event of an emergency" e.g. crash. 



Nascar has the same issues, but the cars' enormous vibration has pretty much forced racecar builders to use battery switches instead.



I recommend Flaming River remote battery switches, but there are others.



The entire experimental aircraft can be built without contactors, and I think it's a good approach.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

decaclops(at)gmail.com
Guest

Posted: Fri Jul 05, 2013 10:28 am Post subject: Master Switch/Contactor and Starter Questions

So....on the SkyTec permanent magnet starter, the diode goes from the 

little terminal to where - ground on the starter case? By the way, I 

only measure approximately .3 ohms from the small terminal to the 

starter case. I thought the coil would have more resistance than that. 

The starter comes from SkyTec with a jumper from small terminal to the 

fat wire terminal.



Ed Holyoke

On 7/4/2013 6:18 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   If the starter is a PM version, the builder can

   take advantage of the "I" terminal on many modern

   starter cotactors and use it to SUPPLY current

   to the engagement solenoid. This provides for

   instant removal of coil power when the starter

   switch is opened and prevents 'delayed disengagement'.



   In this case, the builder would do well to have

   diode coil suppression on BOTH the external contactor

   coil AND the solenoid/contactor coil on the

   starter.



   Bob . . .

billp(at)wwpc.com
Guest

Posted: Fri Jul 05, 2013 10:59 am Post subject: Master Switch/Contactor and Starter Questions

Ed,

Do you get the same resistance reading in both directions? What if you 

swap your meter leads? If there's an internal snubbing diode there, 

you'll get a really low resistance reading in the direction the diode 

conducts in and you'll read the coil resistance with the meter leads 

swapped the other way around.

.3 ohms at 14V would pull about 47 amps. Probably more than your starter 

switch can handle. I'm thinking it should be like 30 ohms or more.

Bill

On 7/5/13 11:28 AM, Ed wrote:

 	  Quote: 	

 So....on the SkyTec permanent magnet starter, the diode goes from the 

 little terminal to where - ground on the starter case? By the way, I 

 only measure approximately .3 ohms from the small terminal to the 

 starter case. I thought the coil would have more resistance than that. 

 The starter comes from SkyTec with a jumper from small terminal to the 

 fat wire terminal.

 Ed Holyoke

 On 7/4/2013 6:18 AM, Robert L. Nuckolls, III wrote:

> If the starter is a PM version, the builder can

>   take advantage of the "I" terminal on many modern

>   starter cotactors and use it to SUPPLY current

>   to the engagement solenoid. This provides for

>   instant removal of coil power when the starter

>   switch is opened and prevents 'delayed disengagement'.

>

>   In this case, the builder would do well to have

>   diode coil suppression on BOTH the external contactor

>   coil AND the solenoid/contactor coil on the

>   starter.

>

>   Bob . . .

decaclops(at)gmail.com
Guest

Posted: Fri Jul 05, 2013 8:29 pm Post subject: Master Switch/Contactor and Starter Questions

decaclops(at)gmail.com
Guest

Posted: Fri Jul 05, 2013 8:55 pm Post subject: Master Switch/Contactor and Starter Questions

I knew on some level that low ohms means high current. That's why I 

questioned it, but I didn't do the math. 35 amps is a bunch! I'm not 

planning to throw away my starter contactor anytime soon. I did measure 

the coil both directions and it is the same.



Ed Holyoke



On 7/5/2013 12:29 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 01:58 PM 7/5/2013, you wrote:

> 

>

> Ed,

>

> Do you get the same resistance reading in both directions? What if 

> you swap your meter leads? If there's an internal snubbing diode 

> there, you'll get a really low resistance reading in the direction 

> the diode conducts in and you'll read the coil resistance with the 

> meter leads swapped the other way around.

>

> .3 ohms at 14V would pull about 47 amps. Probably more than your 

> starter switch can handle. I'm thinking it should be like 30 ohms or 

> more.

>

> Bill



   40 amps . . . yeah that's about right.

   See:



 http://tinyurl.com/op5cs2g



   Bob . . .

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Sat Jul 06, 2013 5:20 am Post subject: Master Switch/Contactor and Starter Questions

 	  Quote: 	
		   I knew on some level that low ohms means high current. That's why I

 questioned it, but I didn't do the math. 35 amps is a bunch! I'm not

 planning to throw away my starter contactor anytime soon. I did measure

 the coil both directions and it is the same.

 

 Ed Holyoke


	


And that's why you don't re-invent the wheel, but rather follow the

conventional wisdom of using a "standard" starter contactor ahead of the

solenoid built into the starter OR use a buffer relay to energize the

solenoid just as all modern cars do and as Bob has explained in a previous

post. (your starter won't operate without the built in solenoid as that is

what engages the pinion with the ring gear)



Bob McC

_________________
Bob McC
Falco #908
(just starting)

decaclops(at)gmail.com
Guest

Posted: Sat Jul 06, 2013 7:42 pm Post subject: Master Switch/Contactor and Starter Questions

Howdy Bob,

     

     When I said contactor, I meant the firewall variety, a B&C unit.     That's the one I'm not throwing away,   I did not measure the     coil resistance on that one. 

     

      I  replaced the starter solenoid because it was demanding 20 - 30     starter button pushes before it would crank. The starter contactor     on the firewall clunks reliably. The new solenoid coil measured .3     ohm. I don't figure that to be very accurate, but it is repeatable.     The VOM leads measured about .5 and then .8 for the coil so I called     it .3 ohm. I was just a bit surprised that it was that low, even if     I were off a little. Now that I read your piece about contactors and     soleniods, I understand why the low resistance. My comment about     keeping the contactor was that I'd just as soon not do that to my     starter switch.

     

     By the way, the Borg Warner (BWD) part number for the starter     solenoid I just put on my PM SkyTec is:     S5613  

     I got mine at O'Rielly's auto parts for ~$25. That's much better     than $200 flat rate repair at SkyTec + shipping and wait for it.

     

     Speaking of diodes, is this overkill?

     http://www.amazon.com/Amico-Molded-Plastic-Rectifier-Diodes/dp/B009IN1KB8/ref=sr_1_6?ie=UTF8&qid=1373088088&sr=8-6&keywords=diodes

     

     I can get these, but the shipping is more than the diodes:

     http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=133108363&uq=635086673453750862

     

     Pax,

     

     Ed

     

     On 7/6/2013 6:12 AM, Robert L.       Nuckolls, III wrote:

     

     [quote]       At 11:54 PM 7/5/2013, you wrote:

        	  Quote: 	
		  -->         AeroElectric-List message         posted by: Ed <decaclops(at)gmail.com> (decaclops(at)gmail.com)

         

         I knew on some level that low ohms means high current. That's         why I         questioned it, but I didn't do the math. 35 amps is a bunch! I'm         not         planning to throw away my starter contactor anytime soon. I did         measure         the coil both directions and it is the same.

       	
       

         Which starter contactor are we talking about?

         One built onto a starter or an external       contactor?

       

         When you mentioned 0.3 ohms, the first image in

         my head was for a contactor built onto a starter.

         These DO present a very low terminal resistance in the

         de-energized mode. There's mechanism inside that

         demands a ~30A closure current and a more moderate,

         ~10A holding current. . . 

       

         Run of the mill external contactors 

       

                http://tinyurl.com/kqphmh

         

         . . . have no such shift in demand and will require

         ~5A to close and hold the contacts. Further, the models

         sold previously by us and now by B&C have built

         in coil suppression diodes.

       

         Be wary of low resistance measurements with the

         garden variety multimeter. They're not designed

         to 'wash out' the effects of lead length and their

         excitation current to a device under test is

         too low to offer useful resolution of low resistance

         measurements.

       

         This limitation is what prompted the design of a

         4-wire low resistance measurements adapter. This

         was published in a Beech shop notes bulletin some

         years back. We had a rash of unnecessary replacement

         of landing gear down-lock indicator switches on

         fielded aircraft. This was traced to the quality

         of contact resistance measurements using the

         garden variety multi-meter. The task demanded

         instrumentation better suited to the task.

       

                http://tinyurl.com/4l3tuj6

         

         A few years later I crafted this product based

         on the earlier article . . .

       

                http://tinyurl.com/6g9e7vm

       

         The value of this technique for low resistance

         measurement is described in the Grounding

         chapter of the 'Connection. The same technique

         is useful for getting meaningful data on coil

         and contact resistance of the more robust components

         in the ship's electrical system.

       

       

                

             Bob . . .                   	  Quote: 	
		  

	
       [b]

decaclops(at)gmail.com
Guest

Posted: Sat Jul 06, 2013 7:44 pm Post subject: Master Switch/Contactor and Starter Questions

I'm with you there, Bob.



Ed

On 7/6/2013 6:19 AM, Bob McCallum wrote:

 	  Quote: 	
		   

> I knew on some level that low ohms means high current. That's why I

> questioned it, but I didn't do the math. 35 amps is a bunch! I'm not

> planning to throw away my starter contactor anytime soon. I did measure

> the coil both directions and it is the same.

>

> Ed Holyoke

 And that's why you don't re-invent the wheel, but rather follow the

 conventional wisdom of using a "standard" starter contactor ahead of the

 solenoid built into the starter OR use a buffer relay to energize the

 solenoid just as all modern cars do and as Bob has explained in a previous

 post. (your starter won't operate without the built in solenoid as that is

 what engages the pinion with the ring gear)



 Bob McC

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