Amps going negative intermittently

[Andy]

I just got it back from annual and the shop said they loosened the alternator belt because it was too tight.

I thought mine was very tight at airworthiness insepction and at the next two condition inspections. That was based on the tension I have used for road vehicle alternator belts and the alternator belt on my PA-28. I did not change the tension and have never seen negative amps in flight.

I don't know what spec CubCafters is using for setting alternator belt tension but maybe that high tension is appropriate for that alternator and pulley combination.

Pete - what belt tension spec is used in production and what is it based on?

[dkelley]

Pete - what belt tension spec is used in production and what is it based on?


CC is shipping their CC363i engines with the
LYCOMING SI 1129D as the method to tension belts. However, I just snug it up.

[Andy]

CC is shipping their CC363i engines with the LYCOMING SI 1129D as the method to tension belts.

Thanks for the reference but it doesn't help much as it states "There are three methods to complete a check of the belt tension:".

Which method is used?

The belt deflection method is what I have used when setting tension but I have always used a "feels about right" method. Belt deflection needs to consider the unsupported span of the belt and that varies between installations.

Excessive belt tension caused premature failure of alternator and generators that used plain bushings rather that ball races for the aft end of the armature. I doubt it is a significant problem when the armature runs in a ball race at both ends.

[Andy]

Just a bit of info on typical alternator output since a standard CubCrafters aircraft only shows battery current:

In cruise flight at 2150 rpm in my FX-3 with standard G3X avionics plus G5, GPS175, and GAD 29, and with landing lights flashing and strobes on, my battery is charging at 3 A and the alternator is giving 10 - 11 Amps. If alternator output was lost the battery drain for this condition would be about 7 Amps.

[stautz]

I took the cowling off today and sure enough the alternator tensioning arm was beautifully powder coated. I will remove this weekend and grind off the powder coating as written up by Dave Embry and then give a report.

Update:
I ground the powder coating off and reinstalled the alternator bracket. I started up the engine and the alternator was charging at 20Amps and slowly decreased down to +3 amps when fully charged. I flew for about an hour and a half and everything looked good.

[Pete D]

Thanks for the reference but it doesn't help much as it states "There are three methods to complete a check of the belt tension:".

Which method is used?


Excessive belt tension caused premature failure of alternator and generators that used plain bushings rather that ball races for the aft end of the armature. I doubt it is a significant problem when the armature runs in a ball race at both ends.

We use the torque at the pulley method.

I have never seen an alternator fail due to bearing failure, if they fail it tends to be reported as low or no output.