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Alternator Voltage Fluctuations

Rhino889

Well Known Member
I tried the search function and couldn't find help so I thought I would ask...

Replaced alternator 28hrs ago. It's been solid at 14.1 volts that entire time.

Sunday I flew with my oldest son for 1 hour in the morning and volts at 14.1 never moving. Sunday afternoon I flew 1.4hrs into Georgia to drop off my brother-in-law. The entire flight my charge showed volts 14.1 solid. It was a 15minute turn and I was off again for the return flight home. Returning home my volts were 14.4 on climb out and fluctuating constantly between 14.3-14.6 the entire flight?

I know 14.6 is not high, but the fluctuations were what was concerning me (it hasn't moved off 14.1 ever). I have an alert set for 14.6 because I use a Ballistic lithium battery and like the charge below 14.5volts. When the volts hit 14.6 I pulled the prop back 150rpm and that dropped the volts back to 14.4volts. I cruised at 10,000' and OAT was 50F. 60amp alt, I never draw more then 8amps.

Question: Do you think my regulator is "beginning" to fail? Maybe the quick turn heat soaked the alternator in 15 minutes? (I've done many a fuel stop in much hotter OAT temps)

Info added in edit: I have always started my engine with the Alt switched off then I brought the Alt online. This was the 1st day that I followed something I read on VAF and started with the field energized as not to "shock" the already spinning Alt. (recommendations I read and figured it made sense)

Solid 14.1
f75d1f78a225a9c751146f94f6363352_zpseb59ac39.jpg


14.3-14.6
0f711d5f32e3b49b46a3b32d7c6ac32e_zps5c983675.jpg


Thanks in advance for any insight or comments.

Regards,

Scott
 
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This is characteristics of a bad alternator field switch or a loose or corroded connection in the field circuit. What kind of Master/Alternator switch did you use?
 
Vern,

Thanks for the reply. I didnt think about the switch. (Why i posted on VAF, more brains on the subject)

Switch is just a simple toggle switch from NAPA. Its only a year old so it shouldnt be corrosion. However, these switches do not seem robust to any degree. Ill switch 2 switches today and see what the outcome may bring.

I have an unused toggle mounted for future add ons. It should be fresh.

Thanks,

Scott
 
I replaced the Alternator switch yesterday. I pulled the cowling and checked connections, verified the belt tension. (switch is a 2 pole metal toggle from vans)

Start up and initial charging looked promising. The 26amp intial charge from engine start kept Volts at 14.0

By the time I got to the runway Amps were back down to 6amps. Volts started climbing to 14.3 in the runup.

Test flight with a lot of rpm fluctuations and altitudes. Volts were definitely effected by the RPM. I shut off the Alternator field twice when volts hit 14.9volts.

Noted in one of the graphs: RPM below 1100 now does not charge and actually draws a -3amps.



My belief: I have eaten an alternator in 28hrs!?

Any other opinions or insight would be welcome



Thanks in advance,

Scott
 
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I think Vern meant to also check all connections that are in the loop external to the alternator for the field reference. Also check for grounds too. Check tightness of fasteners and wire-to-terminal connections.

To answer your last question: maybe. It is possible the new alternator is fried, but it sounds like the root cause remains. Connectors can look good but be a bad connection. If the resistance was high at a point it would have gotten hot, and that can make the resistance even worse. Check your wiring diagram, and check the end of each wire, maybe even along the wire run. Once the root cause is found, then check the alternator.

Long (related) Story: The lights were unsteady one night as I drove up to my house in my old Volvo. It was dark and with the engine idling, I opened the hood (before getting a flashlight) and saw some sparks below the alternator down by the crank damper. Unbelievably, the alternator indicator light wire and the power wire draped under the damper with 12-18 inches of insulation gone and the wires dangling under there. They had gotten so hot that insulation melted away, and the copper oxidation scale keep them from shorting directly. After replacing 2-3 feet of wiring and securing it under the damper, all was well until sold @ 180k miles. The alternator, nor regulator, ever failed, but I did replace bearings and brushes at 120k miles (on condition). Lesson: look carefully, very odd things happen.

Good luck tracking it down.
 
Alternator with built-in integral regulator?

It's very possible, and not all that uncommon to suffer "infant mortality" with anything containing solid-state electronics.

You mentioned having a lithium battery... I have no direct hands-on experience with lithium batteries used as a primary battery in a vehicle alternator charging system, but I do know that our automotive-derived charging systems are designed for use with a lead-acid battery in mind and need to see some kind of a load like a battery acting as a "big capacitor" across the alternator's output. Automotive alternators are infamous for frying themselves if the battery is suddenly removed from the circuit while the engine is running. Here's a wild guess that might need some further investigation... maybe these new lithium batteries do not put a sufficient capacitor load on the alternator once they're fully charged and might need to be also equipped with a very large electrolytic capacitor across the alternator's output to act like an electric "shock absorber". Plausible? This is, again, just a wild guess here.

An external voltage regulator with an adjustable voltage level might also me a good idea for use with lithium batteries too. Some alternators with internal regulators can be modified fairly easily to use an external regulator.
 
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Thanks for the replies.

Where do I source an external regulator? Local dealership? Something other then vans? I'm learning my lesson to try and use parts that can be purchased in local areas for WHEN something goes out and your flying far from home.

Interesting thought on the lithium battery interacting differently with the regulator. It's becoming very common in motorcycles. These alternators really are just auto alternators. I'd think we would here of charging issues from the wheeled vehicle users.

*** something I thought about: recently I've had a fan blow up into the cowl exit and out the nose after flights. Thinking I was dissipating the heat from heat soaking the components under the cowl. I might have in fact blown the 300+ F cylinder air right into the alternator. With the cowl and air intake capping that area off... Heat soaking that exact location?
 
Deleted: was not the altenators fault.

Smoke oil misting from newly installed nozzle in #1 exhaust was found inside the altenators internal regulator.
 
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Thanks for the replies.

Where do I source an external regulator? Local dealership? Something other then vans? I'm learning my lesson to try and use parts that can be purchased in local areas for WHEN something goes out and your flying far from home.

A readily available regulator that has seen widespread use on RVs is 1975 Ford LTD, available at your local auto parts store.

Wire it like this:

I -- no connection
A -- jumpered to "S"
S -- jumpered to "A", also connected to your alternator switch from the field CB
F -- connect to field terminal of your alternator
case -- securely bonded to ground (i.e. mount on firewall and insure good electrical bonding)
 
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The Ford LTD regulators do work very well indeed. That's what I installed on my RV-6 when the original Vans-supplied Chrysler style 2-wire regulator failed shortly after I bought the airplane. It's not adjustable however, it's fixed and gives me about 14.2-14.4 volts in cruise flight. I have the older Honda Civic 35 amp alternator that Vans used to sell.

The 60 amp ND alternator with internal regulator can be modified to use an external regulator, I think I saw a post on the AeroElectric forums showing how to do it.

A brand of aftermarket adjustable regulator that seems to be popular with boaters and other off-road vehicle enthusiasts and that works well with ND alternators is "Transpo". They even make one with a remote mounted control so that you can fine tune your voltage while flying by twisting a knob on your panel.

I can't remember the exact website where I saw these for sale, but I think it was a marine supply company somewhere in Florida. A little googling should probably turn up numerous resellers of Transpo regulators.
EDIT: Here's one such place that sells them http://www.motorcityreman.com/unvore.html
 
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Neal,

Thanks for the post and the link!

The Ford LTD regulators do work very well indeed. That's what I installed on my RV-6 when the original Vans-supplied Chrysler style 2-wire regulator failed shortly after I bought the airplane. It's not adjustable however, it's fixed and gives me about 14.2-14.4 volts in cruise flight. I have the older Honda Civic 35 amp alternator that Vans used to sell.

The 60 amp ND alternator with internal regulator can be modified to use an external regulator, I think I saw a post on the AeroElectric forums showing how to do it.

A brand of aftermarket adjustable regulator that seems to be popular with boaters and other off-road vehicle enthusiasts and that works well with ND alternators is "Transpo". They even make one with a remote mounted control so that you can fine tune your voltage while flying by twisting a knob on your panel.

I can't remember the exact website where I saw these for sale, but I think it was a marine supply company somewhere in Florida. A little googling should probably turn up numerous resellers of Transpo regulators.
EDIT: Here's one such place that sells them http://www.motorcityreman.com/unvore.html
 
Alt switch problem?

Last Saturday, cranked up, alt charging normally after engine start; got to end of rw, final instrument check before t/o, alt not charging; alt & batt switches on/off several times, no soap.

Fortunately there is a starter/generator/alternator rebuilder on the field at KAWM - took both alternator and external regulator there, checked paired together - both working fine ---- ???? wire or switch problem advised the electrical doc......check 'em all.

Suspect the dual, red, alt/batt switch -- will report further, later.

Also, confirming Sam Buchanan's wiring for the Ford LTD regulator, Part #R400P at Advance Auto Parts (aviation section), $21.99; works good lasts a long time.
 
Replaced Split Master Switch

01/26/15: first day that it's been warm enough to go to my hangar; replaced Cessna split master switch with new one from Spruce; ops normal, alt charging normally.
 
Thanks for the reminder to update on my experience.

Replaced the switch and still had a over-charging situation. Took off the cowl again and this time I noticed a very faint oily cloud around the area. I had just installed my smoke system 2 weeks earlier. The spray nozzle in exhaust #1 was slightly canted away from the alternator. Canted away means the nozzle was misting directly toward the alternator.

I tightened the nozzle down flush with the exhaust as should have been done in the 1st place. I pulled the alternator, but it looked clean of oil. I opened up the internal regulator and found oily residue throughout the internals.

$89 at pep boys for a new Alt, 16hrs more flying as of today and all systems normal.
 
unsteady alternator voltage

I am getting in a little late on this BUT------------------
When we had a problem with the alternator voltage being 14.0 for a while, then 12.6 for a while, then 15.5 for a while we found the problem to be the wiring of the alternator circuit.
We did not use shielded wire for either the power (large wire) or the field (small wire) and we ran the wires parallel to each other and in close proximity to each other and we believe we were getting induced voltage from the power wire that was affecting the alternator field wire. We shielded the field wire and the problem went away.
I would recommend shielded wire for both the power and the field and would try to keep those wires away from anything electronic.
 
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