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Question on Aztec Electrical System?

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B-J-J Fighter

Royce Gracie in Action
Dec 1, 2001
I posted this before the webpage crashed. I can't seem to find it since the page has been back up. A guy I use tp fly with has an E model Aztec. He was taken the airplane to 2 different shops to try and diagnose as well as fix the problem. Neither one can figure out what is going on. Of course it has 2 alternators. When you are on the ground with a low power setting or idle boths ALTS will stay online at the same time, however when you add takeoff power and usually in cruise one of the alternators will kick offline. The other one will pick up the slack so the battery never goes dead or anything. Many times in flight the working alternator will kick offline and the one that wasn't working will almost instantly come up to take over for the one that kicked off. I hope I'm being clear. Basically in cruise or with a high power setting both alternators will not function at the same time and the little red lights on the right side for ALT Inop take turns flickering. One of the shops thinks it's a problem with the parralleing (sp?) in the system. It's not the voltage regulator, that was checked. Any ideas??
Thats the likely culprit, the regulators are out of parallel. Those Lamar regulators do that a lot. They are also the same type that are on Seneca's and Navajo's.

Had an Aztec, also an "E", that had a defective alternator circuit breaker. On the PA-23's, the main alternator CB also has a field circuit switch piggy backed on the back of the main CB, so that when it pops, it cuts the field current too. The field switch was getting an intermittant open making things tricky troubleshooting it.
On my E model sometimes this would happen. Most twin engine aircraft have two amp meters and your mormal check is that they are parrell within 10 amps. The Aztec does not have this. If one side is not parrell with the other the system will shut one down.
If say your left alternator go's off in flight - turn the right one off. If they both stay off turn your right on back on because your left one is OTS. If you turn the right one off and the left one comes back on line it means you are not parrell within 10. You still have two working alternators, but can use only one at a time.
When this happened my maintenance man made an adjustment to correct the problem. Hope this helps.

Paralleling between regulators...but not true paralleling in the sense you might think. I'll bet dollars for doughnuts it's a regulator issue. That they check out okay doesn't mean anything. It's the value they're set to...they can both function fine, but if one is putting out a higher, inappropriate voltage, it's going to cause the other generator to drop off line, and the bad generator remains.

Run them up, shut one down and check system voltage. Start the other up and shut the former down. Now check voltage. See how close they are. Adjust either one up or down until they're the same output, individually, and your problems will very likely disappear.
The problem with that is that the regulators are in line with the left engine prop arc. The service manual gives the proceedure to parallel the alternators. Start by removing the parallel wire that goes between the two alternators, set the voltage on the right regulator, swap the wires from the two reg's and do the same with the right engine running the left reg. Re-attach the parallel wire. It s not tough to do, just not standard.
The point I was trying to make is that if on a flight an alternator drops off line and you think you are down to one alternator, but you may still have two. You can't use but one at a time until you get the adjustment. I had this happen two times in 14 years of owning Aztecs. Don't know of any other aircraft with this systen, but it's not a problem if you understand it.


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