Help troubleshoot my alternator(s) problem

[glbtrottr]

I have a TSIO360MB4 on my 14v M20K (A trophy conversion).  The engine was just reinstalled.  I suspect I have multiple issues.

I suspect we'll have to remove them and bench check them, but I figured I would ask the wise ones.

If I turn on both alternators, the voltage drops steadily, all the way down to 11.9....

If I turn off the left field switch, voltage starts going up immediately.

Pressing the PTT to talk on the horn creates a drop of nearly a voltage.

On the climb, voltage again drops all the way to 11.9. 

Occasionally the voltage holds steady at 13.7, sometimes even 13.9, and sometimes will drop to 12.0.

All 3 lights (strobe, nav and headlights) causes a drop over time all the way down to 12.0.

Voltage sometimes is intermittent. 

After the climb last night, when I went from WOT to cruise, voltage went from 11.9 to 13.7 on the single alternator. 

BTW, this data is from a couple of flights.  The mechanics have checked for a "loose connection" .  I suspect a loose cable, and possibly a bad coupling on the alternator...the situation may be hard to reproduce while on the ground. 

Aside from removing and reinstalling alternators, any ideas as to what may be happening? 

 

 

[Geoff]

I had a simmilar issue with my LB1 engined K.  Although I only have one alternator.  I would get 13.7 for a while then suddenly drop to 11.5 with no load changes.  Sometimes I could get more voltage via more throttle, other times not.  Mine turned out to be the alternator coupling along with the regulator/rectifier.  The up/down voltage fried the RR.  The coupling on the alternator has a clutch feature so that if the alternator binds up it doesnt destroy the accessory gears.  The coupling is designed to be inspected/replaced on condition every 500 hrs.  It is easy to check when they go bad since you can spin them with your hand.  The hard part (time consuming)is getting the alternator off. 

Sounds like you have at least one failing alternator coupling and possibly a fried reg/rec.

[1964-M20E]

I'm no expert but assuming with dual alternators you have dual regulators you have two independent systems with the wire back to the battery being common.  You say that when you turn off the left alternator the voltage goes up. 

When running just on the right alternator is your voltage is maintained above 13.5V?

Did you try running just on the left alternator only to see what happens?

It may be in the paralleling circuit on the voltage regulators.  Double check the settings and jumpers on each regulator if any.

Were you experiencing this before the engine work?

 

 

[glbtrottr]

Hey guys - thanks for the help - answers within

Quote: 1964-M20E

 

 

You say that when you turn off the left alternator the voltage goes up. When running just on the right alternator is your voltage is maintained above 13.5V?

 

13.7 max

Did you try running just on the left alternator only to see what happens?

Voltage drops below 12

It may be in the paralleling circuit on the voltage regulators.  Double check the settings and jumpers on each regulator if any.

Were you experiencing this before the engine work?

 

No

 

 

[1964-M20E]

I'd focus on the regulator and the wires between the two regulators.  You may have abad coupling but I'm not sure if that would cause the output of the good alternator to go down.