voltage light came on

[eman1200]

my voltage light came on....reset the field breaker and all looked fine after that.  on the return trip it did the same thing.  some more details:

my battery has been showing signs of weakness.  granted it is well over 6 years old but cranks the plane every time.  I do have a new one waiting for the right time to install.

if you look at the attached image of my ammeter, green dot location 1 is where the needle is in cruse almost all the time (uh, except today), and very stable in that position.

voltage light came on, I cycled the field breaker.  with the breaker pulled, the needle dropped down to red dot position 2.

with breaker back in, needle jumped to red dot position #3 for probably not more than a minute, maybe even less.  needled stabilized back at position one for the remainder of the flight.  the above steps and results from each makes sense to me.

I have one of those cigar lighter voltmeter thingamajiggys and after the breaker reset, it was fluctuating between 14.2 and 14.7, bouncing back and forth between those #s.  usually it is much more stable at the lower end of 14.

the tension on the alternator belt seems normalish, maybe even slightly tighter than I remember but that could just be my brain playing games now that a blinky light came on (actually it wasn't blinking, it was on solid).

I'm going to get the specs on my voltage regulater and alternator, but other than that I'm not sure what my next steps are. I am a bumbling idiot when it comes to electrical stuff.  when I was 5 I stuck a popsicle stick in an outlet and that was when I wrote off anything and everything electrical.  please form replies as if you were talking to that 5 year old (pre-popsicle stick incident), because that is about where my electrical skills are up to.

thank you.

[skykrawler]

J manuals say steady red light with field circuit breaker tripped is an OVERVOLTAGE.

How does OVERVOLTAGE occur? Good question.   The regulator adjusts the voltage to the alternator field to control the voltage that the alternator will produce.  Higher current demand causes the voltage to drop and the regulator responds by increasing the output to the alt field.  If the regulator 'sees' a lower output from the alternator it will increase output to the field.

The ammeter indicates current between the battery and the alternator.  If the alternator doesn't keep up with system demands (avionics/lights) the needle moves to the negative side because the battery makes up the deficit.

The first thing to always check are the connections to the alternator.   Also check the ground between your engine/alternator and the airframe.  14.7 volts is getting up there.  Some regulators are adjustable.

 

 

[ArtVandelay]

Sounds like the right time to install the battery, easy to do and since you already have it, after 6 years the battery doesn’t owe you anything and you’d hate to be grounded away from home because of it.

If that doesn’t work out, check all connections on alternator and voltage regulator are clean and secure.

If that doesn’t work, try a new voltage regulator.

[EricJ]

This is unlikely to be a battery issue, it sounds like the alternator stopped producing power and the reset fixed it.    This may be an alternator or regulator or wiring issue, but the first thing I'd look at is that the wires at the alternator are clean and secure.   The field wire in particular is a common source of issues, so just inspecting that the connection isn't loose at the alternator is a good first step.   This means checking the connection at the alternator and that the wire is secure in the crimp to the ring terminal.   

Edit:   Often when cycling the breaker fixes it it is an indication that the regulator went a little wack for a minute, but it doesn't mean the regulator needs to be replaced.    If the wires are secure and clean you might try just flying it to see if it recurs.

[eman1200]

Sounds like the right time to install the battery, easy to do and since you already have it, after 6 years the battery doesn’t owe you anything and you’d hate to be grounded away from home because of it.

If that doesn’t work out, check all connections on alternator and voltage regulator are clean and secure.

If that doesn’t work, try a new voltage regulator.

Based on the symptoms and outcomes I was leaning towards a bad VR. But what I wanted to avoid was putting the new battery in then something going wrong (either VR craps out or alternator) thus damaging the NEW battery.

[eman1200]

This is unlikely to be a battery issue, it sounds like the alternator stopped producing power and the reset fixed it.    This may be an alternator or regulator or wiring issue, but the first thing I'd look at is that the wires at the alternator are clean and secure.   The field wire in particular is a common source of issues, so just inspecting that the connection isn't loose at the alternator is a good first step.   This means checking the connection at the alternator and that the wire is secure in the crimp to the ring terminal.   
Edit:   Often when cycling the breaker fixes it it is an indication that the regulator went a little wack for a minute, but it doesn't mean the regulator needs to be replaced.    If the wires are secure and clean you might try just flying it to see if it recurs.

I will do this today/tomorrow, thank you.

[PT20J]

I agree with @EricJ. I’d check ALL the wiring connections and the alternator brushes before replacing anything. A quick search of the site will find lots of instances of people replacing regulators and alternators that did not fix the problem.
 

Also, agree it’s not the battery. They will “work” until they won’t crank anymore because the alternator, not the battery, supplies power during flight. However, the capacity (amp-hours) decreases over time, and even though the battery may still “work”, if the alternator dies, you might only have battery power for a few minutes. This is an important consideration if you fly IFR, and it’s a good idea to get a capacity test annually.
 

[ArtVandelay]

Based on the symptoms and outcomes I was leaning towards a bad VR. But what I wanted to avoid was putting the new battery in then something going wrong (either VR craps out or alternator) thus damaging the NEW battery.

Crapping out won’t hurt the battery unless you drain it completely.

Overcharging can, but 14.2-14.7 wont, here’s a chart of ideal battery voltages (I assume you have an AGM):

[mike_elliott]

The io360 has been known to have the field wire at the alternator break continuity .Check this here and at the VR

[Mooneymite]

On my 74 C which I believe has an electrical system like yours, I had the overvoltage light come on twice within about a month.  Both times it reset with no more spurious indications.  Suspecting the vr was going bad, I ordered the Zeftronics vr for my make and model and put it in the baggage compartment just in case I had got stranded on a trip.  That vr stayed unopened in my baggage compartment for years until I sold the plane without a single recurrence.  My advice is buy a zeftronics and put it in your baggage compartment.  

[eman1200]

update:  went on the hunt for loose/goobered up wiring.  on the back of the alternator there is a threaded post with several wires/ring connectors on it.  the nut was loose and all connections behind it were loose.  I cleaned up those connections and tightened the nut.  went on a test flight and had zero issues with the voltage light coming on.  that's only one flight but still, so far looking good.  I really hope that was it and will be a little embarrassed but upon visual inspection I don't think I ever would have caught that it was so loose.  will update after another flight or three.

[A64Pilot]

16 hours ago, ArtVandelay said:

Crapping out won’t hurt the battery unless you drain it completely.

Overcharging can, but 14.2-14.7 wont, here’s a chart of ideal battery voltages (I assume you have an AGM):

Issue with the chart is it’s assuming a three stage charger, which we don’t have. The higher voltages are absorption voltages which are used to charge quickly but will over time cook a battery, so a three stage drops to float voltage in usually a couple of hours.

Automobile charging systems, which is what we have in truth should maintain 13.8 to 14.2 on average, so above float but below absorption, it’s not ideal, but it obviously works.

Of course our systems don’t know flooded from AGM etc so again it’s not optimal, but good enough to get by.

Point is if you’re running high 14’s or low 13’s over time it will ruin the battery, probably ought to get it fixed.

Edited August 6, 2023 by A64Pilot

[PT20J]

Chart from Concorde

[gabez]

I had to deal with this twice in less than a year because the first time wasn't done right, basically for me was the alternator coupling slipping. 

[eman1200]

FYI, second flight with no voltage light coming on.  thanks for all the helpful suggestions!  of course now my CHT gauge is going wonky.  looks like similar symptoms from when my EGT probe busted.

 

[Pinecone]

On 8/6/2023 at 10:28 AM, PT20J said:

Chart from Concorde

It would seem that some smart company would design a voltage regulator that automatically adjust output voltage to temperature.

 

[ArtVandelay]

It would seem that some smart company would design a voltage regulator that automatically adjust output voltage to temperature.
 

Already have them, common in boating world, certified aviation world, no.

[A64Pilot]

1 hour ago, Pinecone said:

It would seem that some smart company would design a voltage regulator that automatically adjust output voltage to temperature.

 

They do as was said for the boating world, that’s because we had HUGE battery banks that cost bunches of money and wanted to charge them as fast as possible, but also to protect them as well as the alternator, a LifePo4 bank in particular will cook an alternator because it can accept way more than an alternator is capable of making.

if your curious this is what I had on our sailboat 

https://balmar.net/wp-content/uploads/2017/12/MC-614-Installation-Operation-Manual.pdf

It’s fully programmable three stage regulator with voltage compensation, ways to protect the drive belt if necessary and even a temp sensor that would turn down current when the alternator reached a certain temp to protect it.

This one sensed battery not air temp and alternator temp directly with sensors

Heck it’s the 21st Century, pretty much anything you can think of can be done. Modern Auto’s apparently I believe control the alternator with their computer and the program even is set to help pass pollution tests, I surmise it delays pulling a load until the motors pollution controls are working, many I believe have to reach operating temp.

[PT20J]

3 hours ago, Pinecone said:

It would seem that some smart company would design a voltage regulator that automatically adjust output voltage to temperature.

 

The voltage regulators are usually mounted in the cabin, and most of the time we keep the temperature range within our narrow comfort zone. 

[A64Pilot]

1 hour ago, PT20J said:

The voltage regulators are usually mounted in the cabin, and most of the time we keep the temperature range within our narrow comfort zone. 

It’s one wire to mount a temp sensor to the neg post of the battery though, so it wouldn’t be hard, question is, is it necessary?

But I suspect that the temp in the tailcone gets to close to what’s in the cabin over time, and that in truth temp compensation isn’t as important as dropping to float would be and yet we know that leaving the battery at a voltage that is really a state of constant overcharge doesn’t hurt much as they last for years like that, so if not dropping a whole volt doesn’t hurt, does not trimming .1 or .2V really matter?

Old military helicopters OH-58, UH-1, Cobra etc had Ni-cad batteries and we would adjust the voltage regulators twice a year, a Winter and a Summer setting and they were frequently removed and the battery shop tore them apart, replaced individual cells when necessary etc., continual maintenance and expensive as Hell.

AH-64 had lead acid SLAB or sealed lead acid battery that didn’t start anything, was really just to run things until you got the APU online and as an Emergency battery, and to be truthful I don’t remember one ever failing in 15 years even in the Desert. I guess they were checked in Phase or something or maybe a calendar change item.

The old lead acid battery it seems requires very little attention, is extremely tolerant of abuse and yet lasts for years.

There is a large number of modifications sold in Aviation and I won’t name them as many are so adamant on how they are necessary and I don’t want to start a battle, but in truth operationally they don’t really seem to make a whole lot of difference. I think a “Modern” precision voltage regulator just might fit that category.

For whatever it’s worth I flew yesterday and looked after the flight with everything on my voltage at 700ish idle RPM measured by my Garmin 696 was 14.1, same as in cruise, everything means all Avionics and lights, but not pitot heat and landing light is LED. So my bone stock system holds set point at all RPM, once fully charged anyway.

[Shadrach]

23 hours ago, PT20J said:

The voltage regulators are usually mounted in the cabin, and most of the time we keep the temperature range within our narrow comfort zone. 

I believe the VR on the 75 F in question is on right side of the firewall on the engine side.  Easy to access and adjust.  In NW Washington one can claim a narrow comfort zone. Here in the Mid Atlantic, we take what we can get and lie to ourselves about the discomfort.  It does grate on you during extended ground ops. Especially when a tower controller sitting in AC'd comfort forgets your at the hold short line awaiting take off clearance.

[eman1200]

Ok so the threaded post on the back of the alternator is stripped, which is probably why it’s been so difficult to tighten it up. Any ideas how to handle a stripped post?

[EricJ]

Can't completely tell from the pic, but that looks like the brush holder assembly and those are the field wires?   If so, that assembly should be pretty easily removable from the alternator, and you could probably match the whole assembly to one in an auto parts store.

I don't know what specific alternator you have, but if it's not obvious, find a manual for that alternator and see how to remove that assembly.   Most alternators are based on automotive alternators and the brush assemblies are fairly easy to find.

You might have some short term success running a die over that to chase the threads a bit, but it looks kinda goobered.

[eman1200]

Can't completely tell from the pic, but that looks like the brush holder assembly and those are the field wires?   If so, that assembly should be pretty easily removable from the alternator, and you could probably match the whole assembly to one in an auto parts store.
I don't know what specific alternator you have, but if it's not obvious, find a manual for that alternator and see how to remove that assembly.   Most alternators are based on automotive alternators and the brush assemblies are fairly easy to find.
You might have some short term success running a die over that to chase the threads a bit, but it looks kinda goobered.

goobered, agreed.

[A64Pilot]

If you’re uncomfortable doing that often you can take them to a shop that rebuilds alternators, starters etc. They still exist but are going the way of shoe and TV repair shops.

In Fl we tell them it’s for our Airboat, gives them plausible deniability