Berchmans

Berchmans

Well Known Member
I have an electrical issue that I am a little stumped by. During a flight yesterday I noticed an indication on my Dynon FlightDEK 180 of low battery voltage, 11.8v, I switched screens and noted that I was showing zero amps and the low voltage. On the main display the reading was M of 11.8, and I of 16.3. The ?I? reading was rock solid the entire flight at 16.3. On the secondary display after a few seconds the amp indication went from zero to plus 8 and the battery voltage began returning to the normal range. During the course of the flight the amp reading would occasionally drop back to zero and the battery voltage would start to drop once more. At conclusion of the flight the amp reading seemed to have stabilized at about +8 with the battery indicating 13v. The idiot light for the alternator never came on during the flight. Is this a failing alternator or some other problem? The engine is a Lycoming YIO360M1B, new from the factory with 97 hours on it.
 
It does sound like a problem to solve.
It would be useful to know what alternator/regulator you have.
If you shut off your alt field when its working, what is its behavior? Trying to determine if your alternator is self exciting or not.
 
Intermittent operation is often a result of worn brushes. The good news is the brush pack on most alternators is very easy and very inexpensive to replace. Being cheap, easy, and a likely cause makes brush replacement a great place to start troubleshooting.

Of course making sure the wiring connections are tight to the field, ground, and B lead is also cheap (free) and easy.
 
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Alternator

The alternator is the standard Plane Power 60 amp unit that Van's supplies for Lycoming Engines...will be popping the cowling tonight to check connections and such.
 
The I reading is the voltage of the Internal battery. The M is the Main voltage. It does sound very strange. I would start looking at the field wiring and the alternator itself. Also, how is your ammeter shunt wired?
 
I need to look at the diagram for the wiring, but did not re-invent the system, used the standard installation. hasn't been an issue before.
 
Wiring

The installation is per the electrical diagram provided by Van's Aircraft for the 6,7,8...I check connections and found the connection on the starter solenoid to be less the tight. After tightening took the plane for a spin, all was well for about 20 minutes then the amps dropped to zero and the battery voltage immediately dropped as well. I cycled the alternator and upon turning it back on it remained a zero amps for about 30 seconds then began output once more to 7 to 8 amp...on landing it was all normal again. Could this be a battery issue? The battery voltage seems to drop kind of fast.
 
If the battery is able to start the engine, it is HIGHLY unlikely that the battery is causing the voltage drop.
Remove the connector from the alternator. Connect an automotive brake light bulb to the field terminal of the wiring harness and to the engine ground. Turn on the master switch. The light bulb should illuminate. Measure the voltage across the light bulb. It should equal battery voltage. If not, find out where the voltage is being dropped. Measuring voltage without a load is not a good test because high resistance in the circuit will not drop the voltage without current flowing through it.
 
After reading your posts again, it seems that your ammeter measures alternator output current. So if a battery cell was shorting out, the ammeter output would go up, not down. Therefore, the battery is definitely not the problem. Since the engine only has 100 hours since new, the alternator brushes should not be worn out already. I think there is a bad connection someplace. The most likely location is the alternator connector. Make sure each fast-on is gripping tightly (assuming fastons). If not the alternator connector, then the previously posted voltage test will help to locate a bad connection. The alternator field on-off switch is also suspect.
 
Are you using one of the solid state electrical management systems, like the DC Load Center or standard fuses/breakers and switches?
 
Electricity needs a round trip circuit. The ground is just as important.

Either the indication is wrong,

or voltage at the point of indication

or at the alternator. Lots of things to check.

0. Belt tension
1. Connection at the alternator (fast on plug)
2. Ground between alternator and engine case.
3. B lead power wire at alternator, including a good tight connector.
4. Engine case to battery ground connections, tight. Cable connectors too if applcable.
4a. Trace field supply wire back through the system to ensure it is getting voltage.
5. Power wire from alternator at the contractors. Cable end connector too.
6. Voltage indication wire to Dynon.
7. Dynon grounds.

Brain fade . . . .
 
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Update

OK, finally got some time to pop the cowl off and check the belt on the alternator...it did seem just a bit loose so I tightened it up just a bit and put an hour and a half on the plane...problem seems to be fixed...thanks for all the suggestions.
 
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