voltage regulator?

[Todd Makiyama]

I have a '59 K35, very much upgraded with most of the latest toys, including a huge investment in modern avionics.  I have three voltmeters on the panel (panel guage, JPI 730, and a Davtron).  

Inflight, my voltage jumps all over the place, probably changing twice a second.  I have a range from 13.9 to 15.1v as reported on all three, most of the time, the voltage cycling between 14.2-14.6v.

I've had two digital instruments die in the past year - my JPI700 died and was repl with a 730, and my horizon tach died and was serviced and replaced in the panel.

Question to you all - is your voltage as indicated - rock solid?  My car's indicated voltage doesn't move and is steady.  I am thinking my voltage regulator to be the culprit and am worried that this range in voltage is going to fry my mx20/gns480/autopilot etc, which are a crapload more $$$ to replace or service.

I'm planning to have the voltage regulator replaced - talked to my a&p who says it's buried in the nether regions of the panel and will require to take 1/2 the bird apart to get to.

Anybody have an opinion?

[Tom Pelz]

Todd,

On the occasion when my voltage seems to bounce around it seems to be the result of an intermittent short.   Not a long lasting one, but long enough to create a problem.

I recently found a loose screw in my pitot heat area.  The screw was not shorted to anything. It was able to freely move about.  It took me about a year to figure it out because it was not giving me a problem all of the time.  

What I did to figure out what was happening was to fly with some equipment off.  I finally figured out that the circuit to the pitot heat that was giving me the problem.  I ran all of the wires and found no shorts.   I then detached the heated pitor tube from the wing.  Lying on the pitot tube was a screw.  It was apparent that the screw had been moving around and intermittently touching the wires connecting the heated tube and a ground.  Removed the screw.   Now everything works properly.

Interestingly, the screw was from a landing light.

The point is that it may not be the voltage regulator, but an intermittent short.  

TomTom Pelz2011-02-12 14:22:48

[Bob Andrews]

Todd, Try a couple of cheap and relatively easy things before you start chasing your voltage problems with money. Do you have the same problem with the avionics switch, pitot heat and all lights OFF? If not, look in those areas one circuit at a time. If the problem still exists with all of the auxillary loads turned off look at the basic power leads such as the ground stud into the firewall. We found one with poor contact. Check closely to see that the airframe to engine grounds are intact. Both of these items will usually produce less than optimal starter performance. Your aircraft's cranking power does not go through the master relay except to close the starter relay which is approximately three anps so corroded master relay contacts will usually not affect cranking performance. However, your avionic and airframe loads depend on the master relay for stable performance. Your Beech supplied master relay is a very robust Eaton 200 amp continous duty nice piece of work but age, cycles and abuse from mechanics who wash down the electrics with high pressure water and gunk take a toll. These are expensive $400+ relays but the good news is the contacts can be cleaned. Remove the relay and disassemble. Polish the heavy contacts with crocus cloth (never aluminum oxide paper, please) and reassemble. Seal all water entry points with clear silicone seal. Polish the battery and generator / alternator electrical connections and give it a try.

  Let me know what you find.

  P.S. Your voltage regulator may be just above the copilot's right foot.

[Todd Makiyama]

Thanks Bob,

At the recommendation of Tom Pelz, I did cycle my circuit breakers.  No improvement.  To date and within 3 months of flying twice a week, I've fried a jpi700, a horizon digital tach, and 1 iPhone.

I did have my voltage regulator replaced by my A&P.  Don't know where it quite lies, but he stated it was easier than expected by taking out my glove box.  

Did the trick though.  Voltage is now rock solid at 13.9v.  No more skipping around 13.9-15.1v.  Curiously enough it also fixed some feedback whining I was getting in my headsets.  My panel lights were pulsing quite a bit and you could also hear it in my Zulu's - fortunately no more.

I was really worried about frying my 480, mx20, and my other digital instruments.

Your recommendations were all very wise and thank you for them.