231 Low Voltage Symptons

[grami-air]

I have a 231 where the red VOLTS annunicator light flashes intermittently.  The POH says a flashing red light is indicative of low voltage vs a steady red light for an over voltage problem.   My mechanic has checked the voltage under no load, partial load and full load conditions and found the voltage to hold fairly steady at 13.8V.  The Mooney manual says this is an internal problem to the annunicator panel itself (I am suspecting some kind of circuit board problem).  Has anybody seen this problem before, and if so, can it be repaired by an avionics shop.  What are my options?

[chrisk]

While I did not have this problem, I did have a problem with the annunciator not indicating low fuel.  Dugosh sent it back to the manufacturer and they replaced a few components.  The price was in the order of a few hundred.   It's probably less to have them bench check it.

[FBCK]

I had the same issue on my 1981 231. The voltage regulator was replaced and the problem went away, also help with a squeal on on of the radios. Highly recommend the Zeftronic replacement.

[Tércio Rodrigues]

grami-air, I don't want to seem alarming, but I would check everithing carrefully before flying again!!!! Does your light flashes intermittently all the times or sometimes it just stops? I had this issue too, and that's what happened to me:

 

http://mooneyspace.com/topic/9660-alternator-field-1-circuit-breaker-in-climb/?p=150208

 

Good luck!

[Mike A]

I had it as well and it was the alternator coupling slipping.  A change of the voltage regulator didn't solve my problem when it happened.  I ended up replacing the alternator and the coupling to be safe.

[jlunseth]

Well, first, is this something you experience on the ground only, during taxi, or does it happen in the air, at cruise.  I went to a Mooney PPP a couple of years ago and my instructor also flies a 231.  His first question when we got in the plane and started to taxi was, "Do you ride the brakes or watch the blinking light?"  Which should tell you that this condition, on the ground, is common in the 231.  The alternator simply does not put out enough current at idle to keep up with all the electrical needs of the aircraft.  It is especially bad if you have the strobes on as well as the old, incandescent landing lights.  At one time a 100 amp alternator was being installed in the 231, the thinking being that would solve the problem, but it did not, the problem is that the gearing of the direct drive coupler is just too low.  In my aircraft, the bottom limit is somewhere around 1100 RPM's and it depends on what I have switched on.

 

If it is happening in flight, then it is a high likelihood that the alternator coupler is slipping, as has been mentioned.  It is a rubber clutch mechanism, and the clutch seems to be good for a maximum of 500 hours.  In cold climates you really have to baby the clutch when you first start the engine.  Keep the idle speed down and put up with the "Low Volts" light until the amps start to come up, which can take a few minutes.  If you put too much power in too quickly, the cold rubber clutch will burn out in a Minnesota minute.  It will eventually wear out anyway.  If you are having a low volts indication in the air, at cruise power, then you should have the clutch checked immediately.  Once you see that indication, it is a very short time, a few hours, before the clutch fails entirely, which will leave you with a completely dark panel, no avionics, engine gauges, the electrically operated HSI will go down, etc.  The single 14 volt battery does not last long.  Usually the alternator itself is fine, it is the clutch that dies. 

[grami-air]

Thanks everybody for your thoughts.

The red Low/High Voltage indicator flashes whether on the ground during taxi, run-up or in the air.  I really do not suspect a voltage regulator problem as we see 13.8-14.2 volts under no load, partial load and full load.  I will check out the alternator coupler, and another thought is to send the unit in to have it bench tested.  A company called International Avionics (Addison, TX) has been maufacturing these units for many years and still are in business.  I'll update this post when I find an answer.

[jlunseth]

There is one other possibility that dawned on me.  There is a bushing that needs to be installed when a new coupler or alternator is put on.  It goes essentially inside the coupler and allows the coupler to slide back and forth (hence the clutching mechanism). I have had non-MSC mechanics leave that out.  It will work for awhile and then you get a catastrophic failure of the coupler in flight.  If you are lucky, the only consequence is no charging.  But the failure mode involves the coupler falling off because the lack of a bushing causes the tiny cotter pin that holds the coupler to the alternator to be beaten to pieces, and the whole coupler assembly goes down into the oil pan, and if you are not lucky a piece can get picked up and thrown who knows where.

 

When it starts to work loose, you will get the flashing light intermittently.  Very quickly it becomes permanent.

[grami-air]

jlunseth - thanks for the info .... much appreciated

[grami-air]

Thanks everybody for your feedback.

We removed the annunciator unit and sent it in.  A quick bench test revealed that several resistors were way out of tolerance causing the Voltage Indicator to flash.  The technician did a complete diagnostic of all circuits and replaced a transistor, 2 resistors, 1 diode and a switch.  Installed the unit and everything is working fine.