Alternator over voltage

cdn_7a · #1 07-29-2011, 11:27 PM

Hi,

I'm stuck in the middle of no where with an alternator that's putting out 16+ volts. What should I do?

1 leave the plane and make my way to a town
2 fly with the over voltage. Nearest airport with service is 45 minutes away.
3 fly on battery only. Not my first choice with dual electronic ignition.

Need some constructive advise.

Thanks

az_gila · #2 07-29-2011, 11:44 PM

First check for bad contacts in the wiring to your alternator and voltage regualtor... it might be something as simple as a few extra, unwanted, ohms at a cable connection.

cdn_7a · #3 07-29-2011, 11:58 PM

Checked all the connections and they were tight. Belt was also tight, although I would expect low voltage with a loose belt.

petehowell · #4 07-30-2011, 12:05 AM

- Let us know where you are, maybe someone can fly a part into you.

- What flavor of EI do you have? Would be good to know if it can tolerate overolt - we can do some research for you.

- What alternator do you have? We can try to find one close to you.

cdn_7a · #5 07-30-2011, 12:14 AM

I'm at Derby Field in Northern Nevada. I see that there is a Napa store 20 miles away so will call tomorrow. Since I have the nippo alternator there is a chance, although small.

I have dual light speed ignitions. I'm also worried about the radio. Everything else can be turned off as I have backup dial gauges.

asav8tor · #6 07-30-2011, 02:44 AM

I have a split "Cessna" type master that is mounted in such a way that opening the canopy on a rainy day can get water in the switch.

One time that happened and the water in the switch caused the exact overvoltage condition you describe.

In my case a new master solved the problem. A new alt or voltage regulator would have solved nothing. I point this out as an additional data point to a previous poster that was correct in his remark that a few ohms somewhere in the wiring, a connector, or in my case, a switch can cause an overvoltage.

RV6airplanePilot · #7 07-30-2011, 04:27 AM

I had voltage fluctuating between 14 and 17 volts last month. All my wiring checked OK, replaced voltage regulator and brushes which were almost half worn off (3 years and 600 hrs on new Nippondenso 70 amp alternator). Replacing those solved my problem. A rep of the manufacturer said overvoltage could also be caused by a defective winding; don't flog the messenger, that's what he told me. I am going to replace my brushes every 2 years and smooth the slip rings with 320 sandpaper. My experience has been that ND alternators don't like high altitude and aircraft level vibration, low time brushes and clean slip rings are my new battle plan. I flew a lot of 3 hour legs between 10,000 and 15,000 msl.
Dale
RV6a 1530 hrs
Dual Electronic Ignition, dual batteries, dual masters

chaskuss · #8 07-30-2011, 04:45 AM

Quote:

Originally Posted by cdn_7a

Hi,

I'm stuck in the middle of no where with an alternator that's putting out 16+ volts. What should I do?

1 leave the plane and make my way to a town
2 fly with the over voltage. Nearest airport with service is 45 minutes away.
3 fly on battery only. Not my first choice with dual electronic ignition.

Need some constructive advise.

Thanks

You do not mention if you have an internal or external voltage regulator. If you have an external regulator you can go to town and replace the voltage regulator. A second option would be to run with battery only till the battery voltage drops down to about 10.5 volts. At that point, turn the alternator back on and let the alternator charge it, until the voltage starts to exceed 15.0 volts. At that point, turn the alternator back off. Repeat as needed to get to that airport with service. The low battery will act as a temporary voltage control, as it will act as a heavy load on the alternator, till it approaches a full charge.

With an internal voltage regulator, your options are limited to going to town to either buy a voltage regulator and installing it yourself, or taking the entire alternator into town to have someone do that for you. FYI, if you have a Nippon Denso alternator, the voltage regulator can easily be changed in about 15 minutes, without splitting the case halves of the alternator.
I have some photos which show how this can be done, if you need them.
Gil's advice about checking for a bad wire connection won't help, unless you have a mechanical, external regulator. A poor connection to the field wires would cause an under-charge condition, not an over-charge. Your problem is caused by the voltage regulator shorting out [solid state model] or sticking [old school mechanical regulator]
The old mechanical units can sometimes be temporarily unstuck, by rapping on the cover. This would be a temporary solution, at best.
Flying without doing anything risks destroying your battery, radios and avionics.
Charlie
PS If you need the "how to" photos, contact me off list, via either email or Private Message. You can email me by clicking on my user name, then choosing the SEND EMAIL TO link. There is also a slight possibility [certain V/R designs] that the wire to one of the brushes has broken and has contacted the case of the alternator.

Ironflight · #9 07-30-2011, 05:59 AM

Hi Dave,

Boy, Derby is really out there in the middle - you're right!

You didn't say what type of EI you are flying - if you have P-Mags, you could rely on the internal power they have to get you somewhere like Winnemucca (so long as the primary battery could get you a start). But lacking that, I think you are doing the right thing calling for help and seeing if you can get someone to bring you something, or bring you to get something.

If you are going to go to NAPA, take the old alternator with you - there are a couple of slight case variations to the "standard" ND alternator we all use, and you need to make sure that the one you get will bolt in to the mount (leg dimensions vary a little).

You can think about all the possible variation of internal/external later - I would try to get back to someplace where you can more easily rig to get home - and I wouldn't risk flying it if you have to rely on the battery to keep the engine running (personally). At least now you are at an airport - you'd hate to be on some dry lakebed nowhere near a road this time of year!

Paul

flion · #10 07-30-2011, 07:04 AM

The Lightspeeds don't draw much power. A couple of weeks ago I flew Bagdad (AZ) to Flagstaff with my alternator out. All lights and radios off until I got close to Flagstaff and saw only a 5A drain with the intercom and EFIS (and, of course, the ignitions). The PC-680 was down to 11.6V from it's normal 12.8V during this 40 minute flight. That said, I have a backup battery and had already tested the rate of drain before I lost the battery, plus I had another RVer's experience flying without an alternator to back me up. But I don't think a short ferry flight would be a problem if your battery is fully charged when you start.