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Alternator field current?

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Jerry Cochran

Joined: 10 Jan 2006
Posts: 111
Location: Wilsonville, OR

Posted: Wed Mar 07, 2007 10:24 am Post subject: Alternator field current?

Folks,

 

I may be having a brain lockup, but trying to determine field  current for 

the old 14184 type Van's alternator. I just began running my engine  for the 

first time, and thought I had it wired per Z-11. I had inserted a 5a  fuse onto 

the field circuit at the bus because I thought this would be  equivalent to 

inserting one inline after the switch as Z-11 shows instead  of the 22AWG 

fuselink. Z-11 looks like this circuit has double protection with  the fuselink and 

5a fuse on the same circuit

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rvreynolds(at)macs.net
Guest

Posted: Wed Mar 07, 2007 12:57 pm Post subject: Alternator field current?

Jerry

My B&C 60A draws about 4 amps.



Richard Reynolds

Norfolk, VA RV-6A, 350 hours

On Mar 7, 2007, at 1:22 PM, Jerry2DT(at)aol.com (Jerry2DT(at)aol.com) wrote:

[quote]  Folks,

  

 I may be having a brain lockup, but trying to determine field current for the old 14184 type Van's alternator. I just began running my engine for the first time, and thought I had it wired per Z-11. I had inserted a 5a fuse onto the field circuit at the bus because I thought this would be equivalent to inserting one inline after the switch as Z-11 shows instead of the 22AWG fuselink. Z-11 looks like this circuit has double protection with the fuselink and 5a fuse on the same circuit

 .

 Well, upon first start, the 5a fuse on the buss blew, so I have two questions for Bob and/or other smart people on this list. 

  

 1) Why the "extra" protection on the field circuit?

  

 2) What typically would the current draw be on the field circuit for this 35a alternator. I checked the archives and manuals, no joy... 

  

 BTW, if it matters, this is the "Generic Ford" regulator as per Z-11

  

 Any/all advice/input appreciated...

  

 If you have an immediate answer, please email me as well at jerry2dt(at)aol.com (jerry2dt(at)aol.com)

  

 Jerry Cochran

 RV6a FAA inspection tomorrow!!! 



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Hopperdhh(at)aol.com
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Posted: Wed Mar 07, 2007 2:03 pm Post subject: Alternator field current?

Jerry,

 

The field current is not necessarily related to the output current rating of 

the alternator.  It would normally be smaller for a small alternator, but not 

always in direct proportion.  It should be less than 10 amps for sure.  Try a 

temporary 10 amp fuse in place of your 5 amp fuse.  If that blows, you have a 

problem.  If it works, measure the current and use a fuse rated for about 1.5 

to 2 times that current.

 

I think the field fuse or switch/breaker is just a way to disable the 

alternator if it should become necessary for any reason -- like an overvoltage 

condition.  Some automotive internal electronic regulators may not turn off if the 

"field" breaker is turned off.  They must get power from some other source.  

There has been a lot of discussion about this on various lists.

 

Dan Hopper

Automotive engineer, ret.

RV-7A

N766DH Just flew yesterday, finally -- weather has been awful here in IN this 

winter.

 

 

In a message dated 3/7/2007 1:26:21 PM Eastern Standard Time, 

Jerry2DT(at)aol.com writes:

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gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Thu Mar 08, 2007 2:34 am Post subject: Alternator field current?

 	  Quote: 	
		  Subject: Alternator field current?



I may be having a brain lockup, but trying to determine field current 

for  the old 14184 type Van's alternator. Z-11 looks like this circuit has 

  >double protection with  the fuselink and 5a fuse on the same circuit.
	


   

  5 Amps is plenty. Remember you are protecting the wire NOT the 

regulator or alternator.

   

  To answer your question I would guess the draw at max output 

to be about 3 amps, 3.5 amps. 

   

  The Z-11 dwg? In general you have two protections in the charge 

system. One from the battery or battery bus (via the starter contactor

typical of Bobs scheme) to the output of the alternator (B-lead). This 

fuse, cuircuit breaker or fusible link must be at least 35 amps to 

handle the output but still protect the wire.  I assume the field wire is 

at least 6  awg. The protection is near the battery or where the B-lead 

attaches to the pos circuit.

   

  The second protection is the HOT wire (+A terminal) to the voltage 

regulator (VR). This fuse or CB is about 5 amps, near the pos source. 

   

  You should NOT see two protections in series on one wire.

  George

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jmsears(at)adelphia.net
Guest

Posted: Thu Mar 08, 2007 3:09 am Post subject: Alternator field current?

 	  Quote: 	
		   5 Amps is plenty. Remember you are protecting

 the wire NOT the regulator or alternator.


	


I agree with George on this.  The fuse or breaker is only to protect the 

wire.



 	  Quote: 	
		  > In general you have two protections in the charge system. One from the 

> battery or battery bus (via the starter contactor

typical of Bobs scheme) to the output of the alternator (B-lead). This fuse, 
	


cuircuit breaker or fusible link must be at least 35 amps to handle the 

output but still protect the wire.  I assume the field wire is at least 6 

awg. The protection is near the battery or where the B-lead attaches to the 

pos circuit.<<



Again, I agree with George.



 	  Quote: 	
		   The second protection is the HOT wire (+A terminal) to the voltage > 

 regulator (VR). This fuse or CB is about 5 amps, near the pos source.


	


And, this is what I'm using in my RV with no problems.  I'm using a 35amp 

alternator, as well.



 	  Quote: 	
		   You should NOT see two protections in series on one wire.


	


Let me add a small addition, here.  In addition to the 5amp fuse or breaker, 

let me suggest an over voltage protection device, if you don't have one 

built into your system at the voltage regulator.  This device checks the 

voltage to see if the alternator is putting out more voltage than it should. 

The limit is set at about 16V on the one I have.  If the volatage surpasses 

the limit, the device triggers a direct short in the field wire that causes 

the fuse or breaker to fail.  That protects the avionics, not the wire, 

against a runaway alternator if the voltage regulator fails.  It's not 

needed when the regulator is functioning well; but, it can save you some 

money if the regulator fails.



As for the fuse or breaker, let me suggest the breaker.  I used a fuse in 

mine and ran into trouble with that idea when I was sorting out a problem in 

the charging system.  I went through several fuses before all was said and 

done.  The OV protection kept blowing the fuses, even when the new regulator 

was functioning well.  I figured out it was the OV protection device that 

was failing in error.  I sent it back for repairs.  Shortly, I'll be putting 

the OV device back into the system and will do away with the fuse in favor 

of a new 5 amp breaker.



Jim Sears in KY

RV-6A N198JS (Scooter)

RV-7A #70317  (On hold due to laziness)

EAA Tech Counselor

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n616tb(at)btsapps.com
Guest

Posted: Thu Mar 08, 2007 6:21 am Post subject: Alternator field current?

I have had this happen in my 170.  The regulator went gunnysack and the OV

protection kicked in.  But apparently it was of a type the smoked itself

inside to break the circuit and the alternator quit working.  The problem

was when the OV blew it made smoke in the cockpit.  Since I didn't know what

was going on at the time I shut down all electrical and made a steep spiral

to a landing on an extreme high crosswind dirt landing strip just north of

Lancaster, CA.  I had to keep the plane running on the middle of the runway

while my wife got out and held the tail.  Then I could shut down and get off

the runway.  The good side was all my avionics were in good shape.

Tim



 

 	  Quote: 	
		   > You should NOT see two protections in series on one wire.

 

 Let me add a small addition, here.  In addition to the 5amp fuse or

 breaker,

 let me suggest an over voltage protection device, if you don't have one

 built into your system at the voltage regulator.  This device checks the

 voltage to see if the alternator is putting out more voltage than it

 should.

 The limit is set at about 16V on the one I have.  If the volatage

 surpasses

 the limit, the device triggers a direct short in the field wire that

 causes

 the fuse or breaker to fail.  That protects the avionics, not the wire,

 against a runaway alternator if the voltage regulator fails.  It's not

 needed when the regulator is functioning well; but, it can save you some

 money if the regulator fails.

 

 As for the fuse or breaker, let me suggest the breaker.  I used a fuse in

 mine and ran into trouble with that idea when I was sorting out a problem

 in

 the charging system.  I went through several fuses before all was said and

 done.  The OV protection kept blowing the fuses, even when the new

 regulator

 was functioning well.  I figured out it was the OV protection device that

 was failing in error.  I sent it back for repairs.  Shortly, I'll be

 putting

 the OV device back into the system and will do away with the fuse in favor

 of a new 5 amp breaker.

 

 Jim Sears in KY

 RV-6A N198JS (Scooter)

 RV-7A #70317  (On hold due to laziness)

 EAA Tech Counselor

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jmsears(at)adelphia.net
Guest

Posted: Thu Mar 08, 2007 6:35 am Post subject: Alternator field current?

 	  Quote: 	
		  > I have had this happen in my 170.  The regulator went gunnysack and the 

> OV protection kicked in.  But apparently it was of a type the smoked 

> itself inside to break the circuit and the alternator quit working.  The 

> problem was when the OV blew it made smoke in the cockpit.<<


	


Yep, this is how I learned about the device in my Cheetah.  It, too, failed 

and had to be replaced.  Fortunately, I was able to replace the regulator 

with one that had OV protection built in.  Since it was a commercially built 

aircraft, and one that required a more expensive FAA approved regulator, I 

opted to spend the few extra dollars to keep from having to by a regulator 

and OV protection seperately.  I

do have them seperate in the RV because I can use a $12 regulator in it.  If 

I chose, I can even roll my own OV protection device for a few dollars.



Jim in KY

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