I bought a plane.

[Scudrunner]

Hi RockSalty welcome to the forum!

I took my son out Dino hunting over Drumheller today and played around with the issue.



Looks like the rear engine is pumping out 29v - 29.3v and the front 27.9v 28v

[Colonel]

Depending upon the amperage load, you can probably just leave the
front alternator off all the time, and let the back carry the load.

If it were my airplane, I would change voltage regulators so that they
were the same voltage, but I was dropped on my head as a small child.

[Scudrunner]

Ya it’s going to bug the shit out of me now, I’m going to have to do something.

[vanNostrum]

Not trying to be a smart ass
Have you checked the pulley, belt, brackets, worn out bearings
and brushes
Diodes can be checked with a multimeter
If the multimeter blocks DC while set to AC you can also test for ripples
in the alternator's output

[Big Pistons Forever]

I think the Col is right. Your most likely problem is the regulator.

[Colonel]

It's not a big deal ....

When the aircraft left the factory, it probably had identical voltage
regulators front and back, that maintained the same voltage.

But, over the decades, you might replace one. And it might be
FAA/PMA approved for your airplane, but it might be of different
manufacture, and maintain slightly different voltage.

I am far too familiar with 12V regulators on aircraft. I know one
brand that likes to maintain 14.3 volts (and is prone to oscillation
on the ammeter). I know another brand that maintains 13.7V and
does not oscillate on the ammeter needle.

Both are legal. Is one better than the other? Probably not. But
if you look at your (external) voltage regulators, I suspect they
are from different manufacturers.

Pro Tip™: go with the single combined box, that is both the
regulator and over-voltage relay. Note that aircraft alternators
(certified, that I have seen) have external voltage regulators.
Modern automotive alternators have the voltage regulator
inside them. Saves money - no external voltage regulator box
required. No field wire (input).

PS You mentioned something about little batteries. I have a shot
in the dark about that one. Simple scenario: you have a dead
battery on a single, and you hand-prop it. Engine starts. Problem
is, the battery might be dead enough that it cannot energize the
field of the alternator - the voltage is too low. You don't need a lot
of amps to light up an alternator field - just a few volts. I've always
suspected a 9V battery would do it marvellously.

Anyways, with no volts, the result is that the alternator cannot produce
a charge. I suspect your little batteries are for this scenario - to kick-start
the alternator field, when the voltage of the system is near-zero. See
any diodes on the wiring diagram near them? Diodes are like one-way
check valves (most of the time).

Sorry about all this drivel. I used to be an electrical engineer. We
worried about useless shit like this.

PPS If you know about "flashing" a generator - which will charge up
from zero volts - you're probably too old to hold a pilot medical

[Scudrunner]

Going to open the books see what the mtc log says is installed on it. Other partner in plane has them and is away.

Maybe someone did something nice and It’s a simple adjustment but my 6 year old didn’t want to stick around to pull cowls (kids these days)

And yes little batteries !

I think I’m missing something
Duracell or Energizer ? meh I’ll go Kirkland or just fund Jeff’s Penis rocket

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[David MacRay]

I used to love Duracells but they keep leaking when I forget to change them. So we’re friends off for now.

[Colonel]

Alternator restart! That is so COOL!

Four D-cells is 6V to the field. As I said, the alternator field doesn't need many amps.

Some EE gave a shit about his job

[David MacRay]

Hey Scud, I got that exhaust manifold welded up for you.

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