[DeTomaso] Interesting ammeter situation.

Tue Feb 14 23:10:10 EST 2017

My first guess would be a bad diode in the alternator, BUT since it was just rebuilt, that should not be.
I can only provide therotically, but I would want to see if there was ANY AC voltage on the 14 vdc when it is charging.
There shouldn't be, but I can't provide what the expected AC would be nor when it is bad,
I have thought about how to smooth out the mechanical regulator (capacitor on the field current), but would think the electronic would provide a smoother output

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at server.detomasolist.com] On Behalf Of Mike Drew via DeTomaso
Sent: Tuesday, February 14, 2017 22:19 PM
To: DeTomaso Mail List
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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