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Z-17/ alternator wire protection

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jpoint(at)wi.rr.com
Guest

Posted: Sat Feb 11, 2017 6:03 am Post subject: Z-17/ alternator wire protection

Hello,



I am confused about the requirements for protection of the A/C wires 

from the alternator.  I'm planning to use Z-17 as the basis for my 

electrical design for my simple, day-VFR aircraft.  Battery will be a 

Earth-X 680, alternator is a B&C 200G, along with a B&C starter on an O-200.



The drawing that came with the alternator shows a 15A fuse in one of the 

A/C lines from the alternator to the regulator, as well as a 15A breaker 

between the crowbar relay and the power bus. However, Z-17 omits the 

fuse in the A/C wires but does put a fusible link between the crowbar 

relay and the battery (via the hot post of the starter contactor.)



Other Z- drawings using the SD-8/ 200G also omit the fuse in the A/C 

wiring.  The only drawing I've found which includes it is the one from B&C.



Is the fuse in the A/C wires required?



Thanks.



Jeff Point



Milwaukee WI

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 11, 2017 7:18 am Post subject: Z-17/ alternator wire protection

At 07:54 AM 2/11/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jeff Point <jpoint(at)wi.rr.com>



 Hello,



 I am confused about the requirements for protection of the A/C wires from the alternator.  I'm planning to use Z-17 as the basis for my electrical design for my simple, day-VFR aircraft.  Battery will be a Earth-X 680, alternator is a B&C 200G, along with a B&C starter on an O-200.



 The drawing that came with the alternator shows a 15A fuse in one of the A/C lines from the alternator to the regulator, as well as a 15A breaker between the crowbar relay and the power bus. However, Z-17 omits the fuse in the A/C wires but does put a fusible link between the crowbar relay and the battery (via the hot post of the starter contactor.)



 Other Z- drawings using the SD-8/ 200G also omit the fuse in the A/C wiring.  The only drawing I've found which includes it is the one from B&C.



 Is the fuse in the A/C wires required? 	


   The two-fuse combination of protection considers the fact

   that energy capable of burning wires in the

   PM alternator system comes from TWO directions.



   (1) fault in the R/R that places high load on

   alternator and (2) fault - perhaps the same one -

   that loads the battery.



   I recommend 15A inline fuses at both locations.

   This fuseholder is one of several options suited

   to the task. 



  http://tinyurl.com/gmpr8j2



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sat Feb 11, 2017 7:42 am Post subject: Re: Z-17/ alternator wire protection

No, the AC fuse is not required because the generator is self current limiting.  The alternator could overheat if the output is shorted or very heavily loaded.  A fuse might protect against that.  On the other hand, a fuse in the AC output is one more thing that could fail and cause the aircraft to lose electrical power.

The output of an alternator does not normally have over-current protection.  However the "B" lead is protected by a fuse at the battery end.  That fuse protects the battery and the "B" lead from battery current, not from alternator output current.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 11, 2017 8:54 am Post subject: Z-17/ alternator wire protection

At 09:42 AM 2/11/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 No, the AC fuse is not required because the generator is self current limiting. 	


    Yeah . . . mostly . . . indeed, an SD-8 turning

    4K RPM max is at little risk for smoke due to

    hard fault. But that's a condition I'll check

    next time I get on the test bench.



    The 200G on a Continental is belt driven with

    a pretty high ratio. This is why, with the SAME

    magnetics, it is rated at 12A output. It's almost

    a certainty that this machine would smoke seriously

    if the R/R presents a hard fault.



 



 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sat Feb 11, 2017 9:02 am Post subject: Re: Z-17/ alternator wire protection

Oops.  Bob posted his reply while I was still composing mine.  And my reply contradicts his.  So now I am confused.  Why doesn't Z-13/8 or Z-17 have a fuse protecting the dynamo AC output?

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Sat Feb 11, 2017 11:49 am Post subject: Z-17/ alternator wire protection

On 2/11/2017 11:02 AM, user9253 wrote:

 	  Quote: 	
		   



 Oops.  Bob posted his reply while I was still composing mine.  And my reply contradicts his.  So now I am confused.  Why doesn't Z-13/8 or Z-17 have a fuse protecting the dynamo AC output?



 --------

 Joe Gores

Hi Joe,
	




Any chance you're thinking about a regular field type alternator, and 

the one being discussed is a dynamo?

jpoint(at)wi.rr.com
Guest

Posted: Sun Feb 12, 2017 6:23 am Post subject: Z-17/ alternator wire protection

On 2/11/17 10:51 AM, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		  



 The 200G on a Continental is belt driven with

    a pretty high ratio. This is why, with the SAME

    magnetics, it is rated at 12A output. It's almost

    a certainty that this machine would smoke seriously

    if the R/R presents a hard fault.

On my O-200 it is mounted on the vacuum pad and is gear driven from the 
	


cam gear.  Nevertheless I will take your advice and put a 15A fuse in 

both locations.  Final question- the drawing from B&C only shows the 

fuse on one of the two A/C wires from the dynamo to the regulator.  

Since there is no polarity to these wires, I assume this is because it 

is AC voltage?



Jeff

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 12, 2017 11:03 am Post subject: Z-17/ alternator wire protection

At 08:17 AM 2/12/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jeff Point <jpoint(at)wi.rr.com>



 On 2/11/17 10:51 AM, Robert L. Nuckolls, III wrote:



  	  Quote: 	
		  



 The 200G on a Continental is belt driven with

    a pretty high ratio. This is why, with the SAME

    magnetics, it is rated at 12A output. It's almost

    a certainty that this machine would smoke seriously

    if the R/R presents a hard fault. 	
On my O-200 it is mounted on the vacuum pad and is gear driven from the cam gear.  Nevertheless I will take your advice and put a 15A fuse in both locations.  Final question- the drawing from B&C only shows the fuse on one of the two A/C wires from the dynamo to the regulator.  

 Since there is no polarity to these wires, I assume this is because it is AC voltage? 	


   No, it's because the alternator output is

   a loop that goes to zero current when

   opened anywhere in that loop . . . one

   fuse suffices for both leads.



 

 

   Bob . . .

blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Mon Feb 13, 2017 8:47 am Post subject: Re: Z-17/ alternator wire protection

"No, it's because the alternator output is 

a loop that goes to zero current when 

opened anywhere in that loop . . . one 

fuse suffices for both leads." 







Would I be assuming correctly this is also true for a three phase PMA?

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Feb 13, 2017 9:00 am Post subject: Re: Z-17/ alternator wire protection

No, to stop three phase current, at least two of the three phases must be opened.

_________________
Joe Gores

blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Mon Feb 13, 2017 9:03 am Post subject: Re: Z-17/ alternator wire protection

Agree...found my notes on this topic along with a drawing by Bob on how to disconnect 3 phase PMA.

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