Low bus voltage

i have been noticing that my voltage on my main bus is less then it used to be. I always showed 14.2-14.3 volts while flying. The last 4-5 flights I have noticed it has been consistently 13.9-14.0 volts. I was wondering if this an indication of my battery getting bad (5 year old PC680 that had several complete discharges last year when I was having hot start problems) or can it mean my alternator is going bad?

Maybe the regulator, but I would check the belt tension first. Then check the field wire for loose connections, including the plug to the alternator - look close.

Good luck!

In addition to the above check you amp reading with the engine running and only the master and alternator on. If the amperage is higher than it used to be then, yes, I would suspect the battery. 5 years is a bit long for a PC-560.

Mike Robertson

We have a winner

BillL said:

Maybe the regulator, but I would check the belt tension first. Then check the field wire for loose connections, including the plug to the alternator - look close.

Good luck!

Click to expand...

I had not flown in a couple of weeks but got up yesterday and still notice the bus voltage low. Took the cowl off and found the belt was slipping. Unfortunately/fortunately I found the the bracket attaching the alternator to the engine boss had both lugs sheared completely off. Unfortunate because the fix is a little harder the just belt tensioning. Fortunately I caught this before any thing bad happened in flight.

Yet again another proof of my 3 step process to preventive maintenance:
1) pay attention to your instruments and notice when things change
2) ask the smart experienced people on this forum for suggestions
3) check out and trouble shoot based on step 2.

Step 4) Don't ignore step 1 for too long.