I have written about my discharging battery problems (charging problem). This mechanic has gone through three alternators and two voltage regulators. Now, he is sending the original out for a re-build. I can not find any information in the MML archives and downloads on this topic. Can someone please help. It has been nearly two months and I have not flown the plane yet.
Editor’s note: This person had been advised that everything he needed was in the BAC archives, but he indicated he had been too busy to join BAC (and apparently still chose not to do so). I won’t belabor the obvious about what that choice has cost him (so far).
Search keys: 1971 Ford Truck, 1971 Ford Pickup, Ford Alternator
Bob Steward, A&P-IA
Let’s start with a “Mechanic-ectomy” so that you can get someone that actually understands charging systems. Throwing parts at the problem is obviously not working for him THIS time. There are a few basic measurements that must be made, and with that information the right part can be installed (if any parts are actually needed).
The fact that he’s wasted more than $1,000 of your money on 3 alternators ($330 each) and 2 regulators ($115 each), and STILL has no clue what’s wrong, ought to be reason enough for you to dump this loser and ferry the plane to someone that CAN fix it.
I think that Mike Rellihan has already advised you to check the BAC archives, since Yahoo messed up the search function a long time ago, and you can not effectively search the MM archives for older topics.
What one MUST know, before even starting the engine:
1. Battery voltage = 12.6V fully charged.
2. Verify voltage TO the VR on the “S” terminal = within 1 volt of battery voltage.
3. Verify voltage FROM the VT on the “F” terminal = 6-10 Volts.
4. Measure resistance from wire removed from F terminal to ground ~4-10 ohms.
After this is known, then you can see if the VR has power and is exciting the alternator. If there is no power TO the VR, then it’s a fuse/CB/wiring issue, and you trace the wires according to the factory maintenance manual wiring diagram.
If there is power FROM the VR, and there is NOT an open or shorted circuit on the wire taken off the F terminal and measured to ground, then the Field windings in the alternator are probably OK, as is the wire TO the alternator.
At this point, you start it up, and measure the system voltage. If not 13.8-14.2V, then you now troubleshoot why the alternator is off line or putting out too little voltage. If you did your homework in the above paragraphs, then you probably ALREADY found the problem.
If you can’t seem to get the alternator to charge the battery, the step BEFORE buying an expensive $300 “aircraft” rebuilt unit is to take the old one to AutoZone or Pep Boys and have them spin it up for free. Tell them its a 1971 Ford P/U with AC, and they can test it just fine. This is the original actual application for the Ford DOFF-10300J alternator found on most Sundowners and other 70’s Musketeers. According to Kelly Aerospace, 80% of the “core” alternators returned for OH are just fine.
Personal consultation is available off list. But I’d start by finding a REAL mechanic, and ditch this one that fell asleep in class the day they discussed charging systems.