Matronics Email Lists :: View topic - Alternator B Lead protection

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Alternator B Lead protection

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

dean.psiropoulos(at)veriz
Guest

Posted: Sun Apr 16, 2006 8:32 pm Post subject: Alternator B Lead protection

Lectric Bob:



I'm using a version of your Z-12 architecture modified for a single 60 AMP

alternator (no backup YET, after the airplane flies I'll add an SD-.  My

question has to do with alternator B lead fusing and I'll get right to the

point.....



Is it really necessary to put a fuse, breaker or ANL in this circuit?



My thinking on this goes as follows:  

1) The B lead would be routed from the alternator to the contactor on the

engine side of the firewall only (no heavy wire inside the cockpit).

2) I'm using an 8 gauge Tefzel wire provided in Van's wiring kit. 

3) An 8 gauge Tefzel wire will experience appx 30 degree (C) temperature

rise at the 60 amps provided by the alternator at maximum output.

4) Even sitting next to a 200 degree (F) engine crankcase the temperature

rise on the wire should be within the capability of the wire insulation. 

5) Even under extreme charging circumstances the full 60 amps of the

alternator will not be flowing in the wire for long periods, limiting the

duration of the temperature rise and insulation stress

6) B&C 60 amp externally regulated alternator with LR-3 reg/OV protect



The only condition that I can think of that might cause trouble and where a

fuse/breaker/ANL would mitigate a possible hazard is:



An alternator fault that allows a dead short between the battery positive

and crankcase ground through the alternator windings and the B lead.  This

could burn up the windings in the alternator and possibly melt the B lead.



Is this the scenario that the ANL on the B lead is designed to mitigate?

What are the probabilities that such a scenario would occur in the field?

Any experience with this type of fault in 40 years of working on spam cans?

Would you advise against leaving this ANL out or is it just "extra

insurance" for some other scenario I'm missing?  Thanks.



Dean Psiropoulos

RV-6A N197DM

Crimping and soldering

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckollsr(at)cox.net
Guest

Posted: Mon Apr 17, 2006 5:11 am Post subject: Alternator B Lead protection

At 12:25 AM 4/17/2006 -0400, you wrote:



 	  Quote: 	
		  

<dean.psiropoulos(at)verizon.net>

Lectric Bob:



I'm using a version of your Z-12 architecture modified for a single 60 AMP

alternator (no backup YET, after the airplane flies I'll add an SD-.  My

question has to do with alternator B lead fusing and I'll get right to the

point.....



Is it really necessary to put a fuse, breaker or ANL in this circuit?


	


   Cars don't do it . . . and if you're comfortable with that in your

   airplane too . . . you don't need to do it there either. But I believe

   there was a recent case where a car caught fire in a parking lot . . .

   don't recall the extent of the damage but I think the story cited

   some form of failure in the alternator. Now, in all fairness, that

   might have been a soft fault wherein b-lead protection would not

   have opened and stopped progress of the event. Without detailed

   analysis we're left with best hypothesis supported by what we hope

   is good common sense and lots of experience. Unfortunately, it doesn't

   take too many fertilizations of myth and bad science to turn

   a perfectly understandable event into Scary Story version 1456.3

   useful only for hangar flying over a pitcher of suds.

 	  Quote: 	
		  My thinking on this goes as follows:

1) The B lead would be routed from the alternator to the contactor on the

engine side of the firewall only (no heavy wire inside the cockpit).

2) I'm using an 8 gauge Tefzel wire provided in Van's wiring kit.

3) An 8 gauge Tefzel wire will experience appx 30 degree (C) temperature

rise at the 60 amps provided by the alternator at maximum output.

4) Even sitting next to a 200 degree (F) engine crankcase the temperature

rise on the wire should be within the capability of the wire insulation.

5) Even under extreme charging circumstances the full 60 amps of the

alternator will not be flowing in the wire for long periods, limiting the

duration of the temperature rise and insulation stress

6) B&C 60 amp externally regulated alternator with LR-3 reg/OV protect



The only condition that I can think of that might cause trouble and where a

fuse/breaker/ANL would mitigate a possible hazard is:



An alternator fault that allows a dead short between the battery positive

and crankcase ground through the alternator windings and the B lead.  This

could burn up the windings in the alternator and possibly melt the B lead.



Is this the scenario that the ANL on the B lead is designed to mitigate?


	


    That's it. Rare and in fact, I've not heard of one in many moons

    with our customers. But the folks at Kelly see them come in from

    time to time.



 	  Quote: 	
		  What are the probabilities that such a scenario would occur in the field?

Any experience with this type of fault in 40 years of working on spam cans?

Would you advise against leaving this ANL out or is it just "extra

insurance" for some other scenario I'm missing?  Thanks.


	


    I prefer not to deal in probability slicing. If the risks are not

    zero -AND- potential for hazard under the fault condition is high,

    then I prefer to design in plan-b hazard mitigation.



    It's your airplane and I would not propose to dictate design

    philosophies to you.



    Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum