AOG!!!! High Voltage

travis · #1 10-04-05, 01:27 AM

Hi there all,

My latest problem hit me tonight in Florida. Sunday I flew to Deland KDED on a one stop 6.8 hour flight (4.5 over the Gulf Of Mexico) and had only one hiccup over the duration. While in flight the red volt high light came on! As per my POH I turned off the alternators and selected the alterante regulator. This seemed to cure the problem for the moment so I continued. On a flight yesterday I cycled trhought the electrical system and found that both regulators wer working properly but that of the four idiot lights only the high voltage light would illuminate with the test function. I figure that there is a bad diod somewhere that will need to be addressed. However This morning the rear boost pump was verry sluggish so I primed the front engine and used it to taxi to the fuel farm. Later on my way to X26 I lost all charging and had a steady decline in voltage below normal batt voltage. When I landed I serviced the battery (kinda low but not too bad) and noticed that the 10 amp circut breaker had popped. I reset the cb and had a run. At idle to 1500 on the rear eingine I had good charging and was happy. Then tonight Under a large load my runup produced the high voltage light agin and a reading of greater than 33v! I had the time so I tried all combinations of electrical load, alternator and regulators and found that the only constant was that I can control voltage with each alternator with engine speed. I will work more on this later this morning after I wake, but please I beg you I need a wireing diagram and some advise for a 70 337E 38amp Ford? I am currently AOG PLEASE HELP ME.

thanks

_travis

stackj · #2 10-04-05, 07:04 AM

Travis,

Go to the Home page of this web site, on the left side go to Technical Data.

Near the bottom of the Technical Data page you will find a link called "Electrical System Schematic (PCX format). It is a diagram I made up using the wiring diagram for the B model which also uses the 38 amp Ford system. It may help you out... It even may be easier to read than the Cessna one.

If it's not identical to yours it should be very similar.

Good Luck!

WebMaster · #3 10-04-05, 08:10 AM

My plane went over voltage, and the only sure cure is to replace BOTH voltage regulators.
Like you, I was over 30V, and the danger is that you can fry your radios and such.
My plane has the 337 form filled out for the Zeftronics voltage regulator. I ordered two of them from Aircraft Spruce, and it has performed flawlessly since.

travis · #4 10-04-05, 11:09 AM

I have the diagram, but is seems a little to simple for my system. There is no mention of any of the diods or the alternator board or even the idiot lights! I will check into the system a little more. I think that the problem lies somewhere before the regulator switch where both systems are affected. Also the overvoltage relay does not seem to be doing its job. Both of my regulators are Cessna replacements from a year ago when an alternator was incorrectly installed. Thanks for the input please keep it coming.

_travis

Pete Somers · #5 10-04-05, 02:06 PM

Hi Travis
Sounds like you have been having fun!

As Larry note says it does sound like both regulator are not very well and in need of changing, however what has caused this problem. Well more than likely you have had a intermittant short ciruit on the regulator output (the field to the alternator) and switching over to the standby regulator will cause that one to fail also. Before you go to the expense of two regulators have that rear alternater looked at to make sure all the wiring is secure, also the alternator turns freely with no play in the bearings. Which 10 amp circuit breaker was popped?

Will have a look thru the wiring and see if i can come up with anything else.

Pete

Pete Somers · #6 10-04-05, 02:28 PM

Travis
I have a diagram to cover rhe alternator system in the 337E.

Let me have your fax number or email address

Regards
Pete

KyleTownsend · #7 10-06-05, 09:16 AM

I had a problem with the overvolt tripping out earlier this year on my 76 P337. If I recall correctly, my service manual says that it should trip at between 31 and 32 volts. It was actually tripping under 31 volts. Per the recommendation of the Cessna Pilots Association, I had it set to trip in the upper part of the range (about 31.8 volts). I haven't had any problems since.

I know your system is somewhat different than mine, so I don't know if this helps. I would suggest looking in the service manual, seeing where it is supposed to trip, and setting it in the upper end of that range.

If you have the Zeftronics regulators, I would doubt that this is your problem. I would save replacing regulators as the last step if all else fails.

If you have a circuit breaker that is popping, then your problems clearly go beyond what I have mentioned. I would lean towards trouble-shooting that first.

The only other thing that I would mention is that, if your alternator drive couplings haven't been tested fairly recently (search the forum for my detailed post), then I would check those as well. A slipping coupling can produce all sorts of insidious problems that are extremely difficult to diagnose.

big al 08 · #8 10-06-05, 05:08 PM

the last post was correct bad alt couplings wil drive you crazy. my 73p you can adjust the reulators via a screw pot. on the front. every once in a while i adjust the so the voltage stays in range

travis · #9 10-13-05, 04:52 PM

Hi all,

Thanks for the input. After a fiew hours of late night runups in a tropical storm we found that both alternators were working very well (hence the over voltage condition) and that indeed both of the regulators that I purchacecd last year have indeed turned belly up! For future referance there should be no conductivity between any of the leads of the regulators! So I called the guys at VanBortel aircraft and had them overnight me a pair of regulators. We installed them the next day and everything was peachy again. There is still a gremlin living in the shadows somewhere in my electrical system, But I've got my traps set and am waiting for him. This time I will be ready. I also ordered the Manuals from McCurtain Technology Group on CD and will keep a copy of them in my plane. $45 (I think for parts and service manuals 64-73&76) from www.mccurtaintg.com !!! At any rate we made it back to Ft Worth with a couple of side trips to the tune of about 12 or so hours.

_travis