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Curiosity Re: Master Switch

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bcone1381

Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan

Posted: Thu Apr 09, 2020 8:00 am Post subject: Curiosity Re: Master Switch

In the  Aeroelectric Connection Book has notes on Master Switches. (age Z11, Note 22)  I'm curious, if an engine of not running, and the field switch to the alternator is on, how much draw is there?  



It seems to me like the bus is at 12V, and the Regulator sees 12V and wont be satisfied until the bus is at 14V, but the regulator does not see that the engine is not running and the alternator is not turning so I would think it want to open up its throttle to wide open to try to get 14 V.  And so it seems to me like there would be a rather large draw.



I don't think me logic is right.  School me.

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_________________
Brooks Cone
Bearhawk Patrol Kit Build

Dave Saylor

Joined: 11 Jan 2015
Posts: 207
Location: GILROY, CA

Posted: Thu Apr 09, 2020 8:34 am Post subject: Curiosity Re: Master Switch

My PlanePower alternator tries its best to make voltage with the engine stopped.  It pumps enough current through the field to make the alternator case hot enough to blister my fingers.  Literally.  But without any mechanical input, of course the output just stays at battery voltage.



The draw isn't enough to pop the 5A field circuit breaker.  But the case does get pretty hot.  I'm sure the lack of cooling air is a factor as well.

--Dave

On Thu, Apr 9, 2020 at 9:09 AM bcone1381 <bcone1964(at)gmail.com (bcone1964(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com (bcone1964(at)gmail.com)>

 

 In the  Aeroelectric Connection Book has notes on Master Switches. (age Z11, Note 22)  I'm curious, if an engine of not running, and the field switch to the alternator is on, how much draw is there?  

 

 It seems to me like the bus is at 12V, and the Regulator sees 12V and wont be satisfied until the bus is at 14V, but the regulator does not see that the engine is not running and the alternator is not turning so I would think it want to open up its throttle to wide open to try to get 14 V.  And so it seems to me like there would be a rather large draw.

 

 I don't think me logic is right.  School me.

 

 --------

 Brooks Cone

 Bearhawk Patrol Kit Build

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=495725#495725

 

 

 

 

 

 

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cluros(at)gmail.com
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Posted: Thu Apr 09, 2020 8:38 am Post subject: Curiosity Re: Master Switch

Here is a graph of a typical shutdown. You can see the draw from the battery go from about 10.5 to 9 when the alternator switch is selected off after shutdown. We have seen the alternator field draw as much as 3A and the builder noted that the alternator itself gets very hot if left on for a while with the engine not running. For this reason we don't turn the alternator on until after engine start and turn it off right after shutdown.



On Thu, Apr 9, 2020 at 9:09 AM bcone1381 <bcone1964(at)gmail.com (bcone1964(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com (bcone1964(at)gmail.com)>

 

 In the  Aeroelectric Connection Book has notes on Master Switches. (age Z11, Note 22)  I'm curious, if an engine of not running, and the field switch to the alternator is on, how much draw is there?  

 

 It seems to me like the bus is at 12V, and the Regulator sees 12V and wont be satisfied until the bus is at 14V, but the regulator does not see that the engine is not running and the alternator is not turning so I would think it want to open up its throttle to wide open to try to get 14 V.  And so it seems to me like there would be a rather large draw.

 

 I don't think me logic is right.  School me.

 

 --------

 Brooks Cone

 Bearhawk Patrol Kit Build

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=495725#495725

 

 

 

 

 

 

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nuckolls.bob(at)aeroelect
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Posted: Thu Apr 09, 2020 10:01 am Post subject: Curiosity Re: Master Switch

At 11:00 AM 4/9/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com>



 In the  Aeroelectric Connection Book has notes on Master Switches. (age Z11, Note 22) 

 I'm curious, if an engine of not running, and the field switch to the alternator

 is on, how much draw is there? 	


   2-3 amps



  	  Quote: 	
		  It seems to me like the bus is at 12V, and the Regulator sees 12V and wont be

 satisfied until the bus is at 14V, but the regulator does not see that

 the engine is not running and the alternator is not turning so I would

 think it want to open up its throttle to wide open to try to get 14 V.

 And so it seems to me like there would be a rather large draw.



 I don't think me logic is right.  School me. 	


   your analysis is correct. The regulator

   will go to full-bore which connects the

   field (~4 ohms) to the battery.



   This is the reason for a progressive transfer

   DC master switch . . . it lets you power

   up battery-only while leaving the alternator

   off. This reduces battery loads for ground

   ops. It also reduces potential for damage

   to field windings being fully excited without

   benefit of cooling air.



   In operation, field current will be on the

   order of 1 amp.



 

 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 09, 2020 10:05 am Post subject: Curiosity Re: Master Switch

 	  Quote: 	
		  

 The draw isn't enough to pop the 5A field circuit breaker.

 But the case does get pretty hot. I'm sure the lack of cooling

 air is a factor as well. 	


   Correct. If you don't have a split rocker or

   progressive transfer toggle switch for the

   master, then it's advisable to pull the

   field breaker for ground ops.



   Some of the z-figures used to suggest

   a simpler, easier to acquire, DPST

   master switch COMBINED with a pullable

   field breaker.



 

   Bob . . .

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