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Master Switch/Contactor and Starter Questions

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nuckolls.bob(at)aeroelect
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Posted: Sun Jun 30, 2013 12:23 pm Post subject: Master Switch/Contactor and Starter Questions

At 11:07 AM 6/30/2013, you wrote:

 	  Quote: 	
		  

<dgaldrich(at)embarqmail.com>



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?


	


   It needs to serve the same purpose as any other form

   of battery master . . . offer the pilot direct control

   of the battery by means located as close as possible to\

   the battery . . . generally less than 1 foot.  EVERY OBAM

   aircraft could use a manual master switch as long as it

   was in convenient reach of the pilot.



 	  Quote: 	
		  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?


	


   You CAN purchase a low-hold current contactor . . . but

   have you done a load analysis? What are your full up

   running loads?



 	  Quote: 	
		  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.


	


   It's not generally done that way . . . opening the

   battery master is supposed to take the system max-cold.

   This would include fat wires to the starter.

   What kind of airplane/engine combination are we discussing?

   Do you have night lighting?  What drove your decision for the

   680 as opposed to a smaller battery?





   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jun 30, 2013 8:38 pm Post subject: Master Switch/Contactor and Starter Questions

 	  Quote: 	
		  



The entire experimental aircraft can be built without contactors, 

and I think it's a good approach.


	


   I took dual instruction in a TriPacer back in '61 that

   mounted the battery under the pax seat. The battery master

   was a switch that you could reach under the seats between

   pilot and co-pilot. The starter was a manual push button

   in a similar position between the pilot's knees.



   A contactor is not required . . . just a battery master

   disconnect. If you can acquire manual switches suited to

   the task and they can be mounted for convenient access

   the choice is yours.



   Bob . . .

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dgaldrich

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

Posted: Mon Jul 01, 2013 1:30 pm Post subject: Re: Master Switch/Contactor and Starter Questions

Based on everyone's inputs and logic, I will use a normal aircraft style contactor for the battery.  The aircraft is a Pietenpol with a Corvair engine and my arms are not long enough to reach the battery in the engine compartment from the rear cockpit.  I would be interested in a low current one if it could handle the starter current when closed.



The aircraft will have LED lights/strobes, Microair radio and transponder, individual electric instruments, and conventional ignition.  No landing light or heated pitot.  I'm figuring a maximum of 10 amps so the dynamo has enough output to "hold" a contactor in addition to the normal load.  The 680 battery was chosen for no better reason than it works in motorcycles and ATVs.  Would love to use something lighter if it will turn over the engine reliably.  I am not primarily concerned with a long endurance capability.  Any kind of electrical issue, or mechanical for that matter, is a land at the nearest suitable field signal and I fly on the east coast where 30 minutes of battery power will generally get you on the ground, even at Pietenpol airspeeds.



The Corvair uses a Subaru starter which has an almost zero weld closed failure rate so I'm still thinking of running a large wire from the battery contactor to the big lug on the starter and using the starter solenoid as an independent way to turn the engine over.  Two less junctions in the high current path.



Thanks Bob and others for the information and advice.



Dave

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jul 02, 2013 9:45 am Post subject: Master Switch/Contactor and Starter Questions

At 04:30 PM 7/1/2013, you wrote:

 	  Quote: 	
		  

<dgaldrich(at)embarqmail.com>



Based on everyone's inputs and logic, I will use a normal aircraft 

style contactor for the battery.  The aircraft is a Pietenpol with a 

Corvair engine and my arms are not long enough to reach the battery 

in the engine compartment from the rear cockpit.  I would be 

interested in a low current one if it could handle the starter 

current when closed.


	


   It's easy to craft a contactor-coil-current-manager.

   See:



http://tinyurl.com/bolkoyc



   Contactors like the EV series from Tyco will

   do something similar . . . although probably

   in a micro-cotroller.



 	  Quote: 	
		  The aircraft will have LED lights/strobes, Microair radio and 

transponder, individual electric instruments, and conventional 

ignition.  No landing light or heated pitot.  I'm figuring a maximum 

of 10 amps so the dynamo has enough output to "hold" a contactor in 

addition to the normal load.


	


   Okay, you're not 'hurting' for energy under

   normal conditions. A e-bus alternate feed path

   that bypasses the contactor could be crafted for

   your panel bus.



 	  Quote: 	
		     The 680 battery was chosen for no better reason than it works in 

 motorcycles and ATVs.  Would love to use something lighter if it 

 will turn over the engine reliably.


	


   The 680 will crank an IO720 . . . there are many

   batteries will crank the Corvair engine.

 	  Quote: 	
		     I am not primarily concerned with a long endurance 

 capability.  Any kind of electrical issue, or mechanical for that 

 matter, is a land at the nearest suitable field signal and I fly on 

 the east coast where 30 minutes of battery power will generally get 

 you on the ground, even at Pietenpol airspeeds.


	


   Do you plan to carry a hand-held?



 	  Quote: 	
		  The Corvair uses a Subaru starter which has an almost zero weld 

closed failure rate so I'm still thinking of running a large wire 

from the battery contactor to the big lug on the starter and using 

the starter solenoid as an independent way to turn the engine 

over.  Two less junctions in the high current path.


	


   Your cranking path stresses are no worse and probably

   much less than those for tens of thousands of single

   engine airplanes. Modifications to the legacy

   battery/battery-contactor/starter-contactor/starter

   configuration has no calculable return on investement.

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jul 04, 2013 5:20 am Post subject: Master Switch/Contactor and Starter Questions

At 07:13 PM 7/3/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "dgaldrich" <dgaldrich(at)embarqmail.com>



 I agree.  It seems pointless to have 2 solenoids operating at the same time.  The other issue is that I believe the Subaru solenoid moves the gear before the contactor part puts juice to the motor brushes.  An aircraft type contactor would do both at the same time rather than sequentially.  Have not dismantled one so I may be in error. 	


   None of applications of an external contactor

   proposed for modern starters "bypasses" functionality

   of the built in solenoid/contactor. The

   starter's built in solenoids do engage the pinion

   gear before closing electrical connection for

   the starter motor.



   Variants to select from when using these modern

   starters causes the builder to decide whether

   the built in contactor is energized by the panel

   mounted, START switch -OR- energized through a more

   robust device.



   There is a problem to be solved when the panel

   mounted starter control is used to energize the

   starter's built in contactor. Unlike legacy

   'starter solenoids' controlling starters with

   Bendix drives, the modern pinion engagement 

   solenoids have a very high coil current demand

   during the first few milliseconds of being

   energized. See:  http://tinyurl.com/op5cs2g



   Failure to recognize this difference in

   solenoid/contator performance caused a

   kerfuffle over burned start switch contacts

   on the ACS-510 key swicch (clone of legacy

   Bendix/Gerdes). ACS now sells a diode with two

   terminals applied.



 [img]cid:.0[/img]



 



 

   A critical need to install this diode across the

   starter contactor engagement coil arose from the

   alarming rate at which start contacts in the key

   switch were destroyed by overstress when the legacy

   starter/external contactor combo was replaced with

   a light weight version with combination solenoid/

   contactors. Many cars suffered similar failure modes

   in their key-start switches.



   SB92-01 from ACS originally place thier diode across

   the switch contacts . . . wrong place. It was corrected

   in a subsequent revision. See  http://tinyurl.com/nva2xdy



   B&C adopted the philosophy of jumpering the starter

   solenoid coil right to the fat-wire terminal on

   the starter . . . and controlling power to the

   starter though a modern, starter contactor WITH

   built in coil suppression diode. The external contactor's

   inrush demands on the start switch are a small fraction

   of that for direct control.



   This philosophy posed a new problem when PM motor

   starters began to show up on the airplane. PM motors

   have a pronounced counter-emf during spin-down after

   the power is removed. This would delay disengagement

   of the pinion gear and was commonly called "starter

   run on" . . . in fact it was better called "delayed

   disengagement".



   Starters with wound fields (B&C and some others)

   do not suffer this indignity and function well with

   the engagement solenoid jumpered directly to the

   starter's fat-wire terminal.



   In ANY case, the builder's design goals should

   include providing a source of solenoid engagement

   power that (1) is supplied through a low impedance

   source (short and fatter than usual wires) and

   (2) avoid running this power through the panel

   mounted start switch.



   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 . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 05, 2013 11:25 am Post subject: Master Switch/Contactor and Starter Questions

At 01:28 PM 7/5/2013, you wrote:

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



 So....on the SkyTec permanent magnet starter, the diode goes from the little terminal to where - ground on the starter case? 	


   Same for ALL starters with the built in solenoid/contactor.

   

 [img]cid:.0[/img]

   



   .... or like this



 [img]cid:.1[/img]



 



  	  Quote: 	
		   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. 	


   Yup, that resistance to ground is LOW . . . it gets higher

   after the pinion gear extends but the initial current

   draw is significant. That's why you use external contactors

   or a buffer relay as shown above . . .

   

   I've added diodes to Z22 . . . something I should

   have done years ago. Thanks for reminding me.



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 05, 2013 11:29 am Post subject: Master Switch/Contactor and Starter Questions

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

 	  Quote: 	
		  



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 . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 06, 2013 5:13 am Post subject: Master Switch/Contactor and Starter Questions

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

  	  Quote: 	
		  --> AeroElectric-List message posted by: Ed <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]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 06, 2013 8:38 pm Post subject: Master Switch/Contactor and Starter Questions

 	  Quote: 	
		  



 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 	


    I like the 1N5400 series devices which are stocked

    by Radio Shack 



  http://tinyurl.com/pfwlz2v



    and Jameco



  http://tinyurl.com/qjefqzq



   if you don't mind paying for 0.08 each in

   packs of 30. They use first class parcel

   for small orders . . . these would come to

   your door for under $2.



   The 1N5400 has reasonably robust leads and

   package. Smaller diodes work too but these

   are mechanically user friendly, easy to get

   and the price is right.



   Any P/N in the 1N540x series is okay from 0 to 9



 

   Bob . . .    [quote][b]

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