Scudrunners

Scud

If it still has a cigarette lighter you can get a voltmeter that plugs into it.

As for the alternator light pulsating. Have you tried turning off the strobes and beacon to see if it makes any difference? Otherwise have a look at the front alternator for any obvious sketchy wiring. High resistance at the alternator connections can cause your symptoms

I think I've mentioned here before, that with the help of my engine monitor,
I was able to deduce that the condensor (really capacitor) across the points
in my right magneto, started to break down and allow the points to arc above
150F. 90 hours in service. Good job!

Heat-related failures are not exactly rare, but good luck figuring that out with
engine steam gauges.

Scudrunner wrote: Sun Aug 01, 2021 3:25 pm
Now here’s one for you electronic gurus. I have noticed the front engine ALT NOT CHARGING light will kind of pulse on and off.

The rear is fine, but when I shut off the rear alternator the front works fine.

I’m not familiar with the 337’s system, but had this problem recently on the Navajo and it turned out to be a voltage regulator issue. The lights comes on for the alternator, not if it’s not charging, but if it’s lower than the other. The difference between the outputs was 0.1 v as I recall, and only showed up when the power was in between idle and cruise or take off. Was a problem for us since that stupid variation in voltage had downstream effects, but not sure that would be more than an irritation for anyone else.

EDMs are money savers in the long run, blew a plug recently and knowing which one it was I think saved the mechanics a bunch of time on discovering which one it was. As an example over the years.

Big Pistons Forever wrote: Sun Aug 01, 2021 4:10 pm Scud

If it still has a cigarette lighter you can get a voltmeter that plugs into it.

As for the alternator light pulsating. Have you tried turning off the strobes and beacon to see if it makes any difference? Otherwise have a look at the front alternator for any obvious sketchy wiring. High resistance at the alternator connections can cause your symptoms

I’ve got one coming, I had to find one capable of 28v
https://www.aircraftspruce.ca/catalog/e ... -15538.php

Probably could have found one cheaper but I was clicking buttons on spruce and well it happens.

I’m going to play with it more might be something stupid , the guru around the airport said his front alternator on his 337 packed it in every 200-300 hours.

Scudrunner wrote: Sun Aug 01, 2021 5:40 pm


Probably could have found one cheaper but I was clicking buttons on spruce and well it happens.

You know how those gambling web sites have a feature that lets people register so you can’t log on, well my wife things aircraft spruce should have the same feature for me

Twins have a complicated balancing circuit between the two engine electrical
charging systems that you should be aware of. It deals with different voltages
produced by the two charging systems.



Back to your problem. It could be a regulator oscillating under light load - nothing
to push against.

Another thing worth checking is for fried diodes in the alternator, which results in
ripples in the no longer-DC-output, which will make life harder for the voltage regulator.

If Cessna put a scat hose to the alternator for cooling at the factory, make
sure it's there now, and not blocked or broken. Heat is the enemy of electronics.

PS You can see ripples with an array of instruments. I prefer Saleae. When
diodes fail, you can sometimes hear a howl in the audio which varies with
RPM and disappears when you pop the field.

So if I’m following the way the parallel coils work. Unlikely, but…

If the rear alternator has an intermittent higher voltage the front alternator is possibly being controlled by its coil opening the contact point?

Then when you shut down the rear alternator the front one just runs happily along.

All I know for sure, is that you have to look pretty hard to find an AME that knows the difference between a volt and an amp.

They're often great with a wrench or a screwdriver or pliers or a socket, but not so much a multi-meter or oscilloscope or
logic analyzer. I would wager you could count on the fingers of one hand, the number of AMEs in Canada that own a
scope or Saleae.

Squaretail wrote: Sun Aug 01, 2021 4:59 pm

Scudrunner wrote: Sun Aug 01, 2021 3:25 pm
Now here’s one for you electronic gurus. I have noticed the front engine ALT NOT CHARGING light will kind of pulse on and off.

The rear is fine, but when I shut off the rear alternator the front works fine.

I’m not familiar with the 337’s system, but had this problem recently on the Navajo and it turned out to be a voltage regulator issue. The lights comes on for the alternator, not if it’s not charging, but if it’s lower than the other. The difference between the outputs was 0.1 v as I recall, and only showed up when the power was in between idle and cruise or take off. Was a problem for us since that stupid variation in voltage had downstream effects, but not sure that would be more than an irritation for anyone else.

EDMs are money savers in the long run, blew a plug recently and knowing which one it was I think saved the mechanics a bunch of time on discovering which one it was. As an example over the years.

Interesting, I got the digital cigarette plug coming (ETA Thursday) so Ill be playing with it.
I think its more of annoyance than an issue so far. Nothing I could figure throws up a major flag .

One weird thing I've discovered while going through the electrical diagrams is the 2 D Cell Batteries for the Alternator Restart Batteries.

Never seen that before, although I usually just break the planes let someone else fix them

Scudrunner wrote: Sun Aug 01, 2021 3:25 pm

Now here’s one for you electronic gurus. I have noticed the front engine ALT NOT CHARGING light will kind of pulse on and off.

The rear is fine, but when I shut off the rear alternator the front works fine.
4AB5C73F-FCF0-479A-8037-CE072A38B2B2.jpeg

I've driven a few mixmasters and a couple of them did this. I believe that it is just the voltage regulator spazzing out a little bit, probably isnt doing any harm.