[DeTomaso] Interesting ammeter situation.

[jgkrenton at comcast.net]

Mike: 

A bit more, I found this on a Piper Aircraft site. Similar statements show up on Cessna and some Marine/boat sites: 

""The Piper Service Manual's troubleshooting chart says that "excessive 
ammeter fluctuation" can be caused by a defective voltage regulator or 
excessive resistance in the field circuit."" 

and 

"The delay between the request of the voltage regulator and the response of the alternator is what causes the ammeter fluctuation ." 

The root cause of this seems to be corrosion on the field/sense lines so the regulator isn't getting good feedback on the results of it's commands to the alternator. 

The answer seems to be clean all the terminals in the circuit to ensure any high resistance connections are eliminated. There is some discussion that corrosion on the Alternator output wiring will also cause the problem, but that is likely to cause a lot of heat.. 

and speaking of a lot of heat, did you look at the terminals on the back of the ammeter? We all know the trouble they can cause. 

Also, is the resistor by-pass still on the back of the idiot light on the dash? 

Good luck 

Jeff/2467 





----- Original Message -----

From: "Mike Drew via DeTomaso" <detomaso at server.detomasolist.com> 
To: "DeTomaso Mail List" <detomaso at server.detomasolist.com> 
Sent: Tuesday, February 14, 2017 7:19:28 PM 
Subject: [DeTomaso] Interesting ammeter situation. 

Guys, 

Yesterday I accompanied the new owner of a '74 Pantera from Sacramento to his home in San Diego. 

We almost made it. 

As we entered the worst of the LA megopolis, the charging system suddenly didn't. The am we had been dancing around for hours and it finally stabilized deep in the discharge zone. With headlights and fans on, crawling in stop and go traffic, it wouldn't be too long before the car quit completely so we dove off the freeway into a gas station and then enjoyed a two-hour tow truck ride (gotta love AAA premium!) 

Today we started troubleshooting. The new owner is almost devoid of tools, but we started by changing the regulator since its cheap. The result was an ammeter that now danced violently either side of center. 

Next suspect was the alternator. Although it was new, it was a standard Ford remain and thus probably only 50A. We took it to a nearby alternator/starter shop where they rebuilt it and converted to 90A in just over an hour. They said it tested good beforehand, but since we were there, why not improve it? 

With the rebuilt ammeter installed, the needle swing was even more pronounced, wider at idle, and reducing at about 3000 rpm. 

Now armed with a recently purchased voltmeter, we tested voltage at the battery and found it cranking out 14.3-14.6 volts depending on rpm and electrical load (headlights etc) 

After a quick call to SOBill Taylor (bless him!!!!) we reinstalled the old regulator to see what would happen. 

Ammeter jumping stopped, replaced with a constant discharge. Voltmeter testing at the battery revealed 12.5 volts--the battery was powering the car and the alternator was doing nothing. 

We reinstalled the new, electronic (as opposed to stock-style mechanical) regulator, and once again had proper charging indications at the battery, but the ammeter continued its wild ways. 

I shot a video and stupidly oriented my phone vertically. Only idiots shoot videos like this, so my profound apologies: 

http://youtu.be/lLKf2Z23P_Q 

So what do you think the next course of action should be? I have at least one extra stock ammeter and several regulators, so I am thinking of loaning them to him for troubleshooting purposes. Do any of you have any suggestions? 

(No, don't suggest he just bypass the gauge or switch to a voltmeter--a voltmeter would not have warned us of our charging system failure and would have left us stranded on the freeway!) 

Thanks in advance for any constructive advice (other than to learn how to hold a phone properly when shooting a video!) 

Mike 

Sent from my iPhone 
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-------------- next part --------------

   Mike:
   A bit more, I found this on a Piper Aircraft site.  Similar statements
   show up on Cessna and some Marine/boat sites:
   ""The Piper Service Manual's troubleshooting chart says that "excessive
   ammeter fluctuation" can be caused by a defective voltage regulator or
   excessive resistance in the field circuit.""
   and
   "The delay between the request of the voltage regulator and the
   response of the alternator is what causes the ammeter fluctuation."
   The root cause of this seems to be corrosion on the field/sense lines
   so the regulator isn't getting good feedback on the results of it's
   commands to the alternator.
   The answer seems to be clean all the terminals in the circuit to ensure
   any high resistance connections are eliminated.  There is some
   discussion that corrosion on the Alternator output wiring will also
   cause the problem, but that is likely to cause a lot of heat..
   and speaking of a lot of heat, did you look at the terminals on the
   back of the ammeter? We all know the trouble they can cause.
   Also, is the resistor by-pass still on the back of the idiot light on
   the dash?
   Good luck
   Jeff/2467
     __________________________________________________________________

   From: "Mike Drew via DeTomaso" <detomaso at server.detomasolist.com>
   To: "DeTomaso Mail List" <detomaso at server.detomasolist.com>
   Sent: Tuesday, February 14, 2017 7:19:28 PM
   Subject: [DeTomaso] Interesting ammeter situation.
   Guys,
   Yesterday I accompanied the new owner of a '74 Pantera from Sacramento
   to his home in San Diego.
   We almost made it.
   As we entered the worst of the LA megopolis, the charging system
   suddenly didn't. The am we had been dancing around for hours and it
   finally stabilized deep in the discharge zone. With headlights and fans
   on, crawling in stop and go traffic, it wouldn't be too long before the
   car quit completely so we dove off the freeway into a gas station and
   then enjoyed a two-hour tow truck ride (gotta love AAA premium!)
   Today we started troubleshooting. The new owner is almost devoid of
   tools, but we started by changing the regulator since its cheap. The
   result was an ammeter that now danced violently either side of center.
   Next suspect was the alternator. Although it was new, it was a standard
   Ford remain and thus probably only 50A. We took it to a nearby
   alternator/starter shop where they rebuilt it and converted to 90A in
   just over an hour. They said it tested good beforehand, but since we
   were there, why not improve it?
   With the rebuilt ammeter installed, the needle swing was even more
   pronounced, wider at idle, and reducing at about 3000 rpm.
   Now armed with a recently purchased voltmeter, we tested voltage at the
   battery and found it cranking out 14.3-14.6 volts depending on rpm and
   electrical load (headlights etc)
   After a quick call to SOBill Taylor (bless him!!!!) we reinstalled the
   old regulator to see what would happen.
   Ammeter jumping stopped, replaced with a constant discharge. Voltmeter
   testing at the battery revealed 12.5 volts--the battery was powering
   the car and the alternator was doing nothing.
   We reinstalled the new, electronic (as opposed to stock-style
   mechanical) regulator, and once again had proper charging indications
   at the battery, but the ammeter continued its wild ways.
   I shot a video and stupidly oriented my phone vertically. Only idiots
   shoot videos like this, so my profound apologies:
   http://youtu.be/lLKf2Z23P_Q
   So what do you think the next course of action should be? I have at
   least one extra stock ammeter and several regulators, so I am thinking
   of loaning them to him for troubleshooting purposes. Do any of you have
   any suggestions?
   (No, don't suggest he just bypass the gauge or switch to a voltmeter--a
   voltmeter would not have warned us of our charging system failure and
   would have left us stranded on the freeway!)
   Thanks in advance for any constructive advice (other than to learn how
   to hold a phone properly when shooting a video!)
   Mike
   Sent from my iPhone
   _______________________________________________
   Detomaso Email List is not managed by POCA
   Posted emails must not exceed 1.5 Megabytes
   DeTomaso mailing list
   DeTomaso at server.detomasolist.com
   http://server.detomasolist.com/mailman/listinfo/detomaso
   To manage your subscription (change email address, unsubscribe, etc.)
   use the links above.
   Members who post to this list grant license to the list to forward any
   message posted here to all past, current, or future members of the
   list. They also grant the list owner permission to maintain an archive
   or approve the archiving of list messages.