Intermittent electrical problem now

[drgwentzel]

Flyers,

We seem to now have an intermittent electrical problem on our 71 Cardinal RG. (related to our past transponder problem? Hmmm. Maybe) Every once in a while the alternator will go off-line and we will get a discharge on the amp meter. If not caught (no Hi-Lo Voltage Light) it will drain the battery pretty quick. What would do this? Voltage Regulator, Bad Alternator, Bad Battery (we have new battery in May '09).

I put a voltmeter on the bus and saw 14.6 volts on average with little load. I turned on all lights and pitot heat and still saw 14.5 volts, but then I turned on the avionics master and it went right to 11.9 to 12.3 volts. Clearly discharging the battery.

As an aside, the transmit lights on my radios and stuck mic light came on my audio panel at this time. That was a new one. Recycling the radios, avionic master and the master switches did not stop this. I cycled the PTT switches and still had transmit lights on. After engine shut down I went back and put the Master back on and the transmit lights returned to normal. Hmmm. But I digress. Back to the alternator...

Any thoughts? Weak alternator?

Gene Wentzel

 

[gismo]

Flyers,

We seem to now have an intermittent electrical problem on our 71 Cardinal RG. (related to our past transponder problem? Hmmm. Maybe) Every once in a while the alternator will go off-line and we will get a discharge on the amp meter. If not caught (no Hi-Lo Voltage Light) it will drain the battery pretty quick. What would do this? Voltage Regulator, Bad Alternator, Bad Battery (we have new battery in May '09).

I put a voltmeter on the bus and saw 14.6 volts on average with little load. I turned on all lights and pitot heat and still saw 14.5 volts, but then I turned on the avionics master and it went right to 11.9 to 12.3 volts. Clearly discharging the battery.

As an aside, the transmit lights on my radios and stuck mic light came on my audio panel at this time. That was a new one. Recycling the radios, avionic master and the master switches did not stop this. I cycled the PTT switches and still had transmit lights on. After engine shut down I went back and put the Master back on and the transmit lights returned to normal. Hmmm. But I digress. Back to the alternator...

Any thoughts? Weak alternator?

Gene Wentzel

I think your voltage regulator is set too high. It should be more like 13.8 to 14.2 volts. A high setting on the regulator could result in an overvoltage trip. A weak battery makes this more likely due to the higher internal resistance that causes. How old is your battery?

I don't understand the part where you measured 14.5 with lights on and then saw less than 12 volts when you turned the avionics on. I assume this was with the engine running or you wouldn't have been able to get 14 volts. Was the alternator still online when the voltage dropped? If so does turning on the avionics master always kick the alternator offline?

Edit: That was supposed to be 13.8 to 14.2 not 13.0

 

[SCCutler]

14.6v? That's excessive. You're looking for a nominal 13.8.

What voltage regulator do you have?

 

[Let'sgoflying!]

Nominal charging voltage
from Zeftronics:
http://www.zeftronics.com/
left hand side: Troubleshooting>Basics>Alt Charging Systems
(this is for the generic '12v system')
"After troubleshooting the system, finding and resolving any faults, run the engine at 1500 RPM. The bus voltage should be 13.8 – 14.3 volts."

Mine has crept up lately to 14.3 and I got a momentary overvolt warning on my JPI recently...need to tweak it.

 

[John Collins]

Gene,

As others have stated, the voltage regulator is on the high side. I suspect the alternator is going off line as a result of an over voltage. To reset the over voltage, you have to turn off both sides of the master/alternator switch and turn them back on. I have seen Cessna's that have a habit of resetting have a noticeable tick in the battery load meter, especially when the beacon or strobes are on. Often this is due to a bad right side of the master/alternator switch.

 

[drgwentzel]

I think your voltage regulator is set too high. It should be more like 13.8 to 14.2 volts. A high setting on the regulator could result in an overvoltage trip. A weak battery makes this more likely due to the higher internal resistance that causes. How old is your battery?

I don't understand the part where you measured 14.5 with lights on and then saw less than 12 volts when you turned the avionics on. I assume this was with the engine running or you wouldn't have been able to get 14 volts. Was the alternator still online when the voltage dropped? If so does turning on the avionics master always kick the alternator offline?

Edit: That was supposed to be 13.8 to 14.2 not 13.0

Yes, the engine was running and for some reason with the master aviontics turned on and radios turned on the multimeter went from 14.5 to anywhere between 11.9 to 12.3. I did not look at the amp meter to see if it was showing a charge or dis-charge. The plane is in the shop now for the new Garmin 330 and wiring it to my audio panel for traffic alerts and to my 696 for traffic. Also they are putting in an outside antenna (probably don't need this, the internal antenna has always worked perfectly) and they are wiring it directly to ship's power. I love that because I hate a lot of wires running around the cabin.

I am going to ask the shop to test the battery and the voltage regulator. Thanks for the great advice!

Gene

 

[Dan Thomas]

Gene,

As others have stated, the voltage regulator is on the high side. I suspect the alternator is going off line as a result of an over voltage. To reset the over voltage, you have to turn off both sides of the master/alternator switch and turn them back on. I have seen Cessna's that have a habit of resetting have a noticeable tick in the battery load meter, especially when the beacon or strobes are on. Often this is due to a bad right side of the master/alternator switch.

The overvoltage sensor cuts the alternator off at 18 volts. 15 won't do it. If the OP is seeing his voltage drop when the avionics are turned on, the alternator is most likely at fault. When is the last time the brushes were checked in it? They do wear out and can reduce the output while they're making minimal contact. The slip rings can get crudded up and introduce resistance to the field current, which is what I would check first here.

Much less likely possibilities:

loose overvolt sensor ground terminal

Worn regulator field relay contacts


Dan