Low Voltage light Help!

SeanDL

Filing Flight Plan
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SeanDL
Just wanted to see if anyone else had this problem. We are having a hard time finding the source that triggers the low voltage light. Here is what happens and a summary of what we have fixed:

The plane is a turbo 182 (1981).

On the way to Oshkosh low voltage light comes (indicates discharge on JPI of 23.4 volts) on after 30 mins of flying. Follow the procedure in the POH (turn off radios, turn off master, turn on master, turn radios on) and the the system resets and the low voltage light disappears. The battery is being charged showing 28.3 volts on the JPI. As the flight proceeds the low voltage light comes on 10 mins, 5 mins, sometimes every 2 mins. Each time it is reset. The longer the flight the more frequent the low voltage light comes on. It does not come on during descent or around the pattern or on the ground. Only climbing or level flight (maybe something to do with engine cowl temperature?)We landed and replaced the alternator which was 10 years old. Test flew the plane and 1st hour of flight LV comes on. Replaced the master switch which had corroded wires. Same issue on test flight. Limped the plane back to California and replaced main wire from alternator, replaced wire from battery, checked all grounds and replaced the voltage regulator. Same problem after 30 mins of flight. During flight we have tried to isolate the problem to a piece of electronics but the LV still comes on when each piece of equipment is shut off. Any similar problems out there?

Thanks

Sean
 
Is the alternator getting enough cooling air? Sounds like it's getting hot.
 
Was the voltage regulator changed when the alternator was replaced? Was the old alternator tested?

I've had a similar failure with the alternator dropping offline repeatedly but it was much more frequent than you experienced. That particular failure was the voltage regulator. Replaced with a Zeftronics unit and was good to go.

It is a bit of a pain but it is possible to monitor the field voltage so you can see what the voltage regulator is doing. I don't know where the VR is on a 182 so it might be even more of a pain than it was for me in the 'kota.
 
Was the voltage regulator changed when the alternator was replaced? Was the old alternator tested?

I've had a similar failure with the alternator dropping offline repeatedly but it was much more frequent than you experienced. That particular failure was the voltage regulator. Replaced with a Zeftronics unit and was good to go.

It is a bit of a pain but it is possible to monitor the field voltage so you can see what the voltage regulator is doing. I don't know where the VR is on a 182 so it might be even more of a pain than it was for me in the 'kota.

The voltage regulator was changed a month after the alternator and I am not sure what brand it is but I will check. The old alternator was not tested. The voltage regulator is mounted on the pilot side right in front for the firewall above the air filter. Some more history: The plane has flown for 10 years with no problem. During those years it had a complete panel upgrade and was fine. It sat idle for 6 months and during those six months we put in a garmin ADS-B transponder. After that the plane was flown for 10 hrs and then the VL appeared. We isolated the garmin transponder by shutting it off and the VL still came on while we were flying. We are going to take a look at the transponder and the wiring to see if something does not look right just in case.
 
The attached is for a 14 volt system, but it should be similar.
I would be looking at the over voltage sensor, sounds like it is getting hot and preventing voltage to the regulator. Should be under the instrument panel, possibly on a heat sink.
 

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  • 14V ALT Cessna -TSN.pdf
    337.1 KB · Views: 27
Silly response from me- bad battery issue? Is the battery getting too hot when charging? Alt charges more when the RPMs are up (climb, level)? Easy to swap batteries and check.
 
The overvolt sensor is a small cylinder, about the size of a pill bottle, usually tied to the wiring bundle behind the panel on the pilot's side. It has three wires: one is connected to the alternator side of the master switch, one goes to the alternator breaker, and a third goes to ground. If any of those are loose, the regulator shuts off and you get the low voltage light. (The light is connected to the "I" terminal on the regulator.)

So check the orange wire connection at the ALT switch, red at the breaker, and black at the ground connection.

Now, around the time your airplane was built, electronic alternator control units were showing up. They had the overvolt sensor built into them. If you have a new one, it's probably OK. But those electronic units had another problem: their voltage sensing input from the aircraft's system was supersensitive and any sort of transient spike would trip them off. Right in the Cessna manual it tells you to check the com antenna cable connections for looseness, corrosion or crud. If the shielding isn't well-grounded, RF escapes when you push the PTT and RF floods the aircraft's wiring and trips the ACU.

Voltage regulator:

07-01897a.jpg



ACU:

R25S01.jpg
 
The OP hasn't mentioned and no one has suggested actually measuring the system voltage when the light is on.

It might be a good place to start.
 
The OP hasn't mentioned and no one has suggested actually measuring the system voltage when the light is on.

It might be a good place to start.
Might wanna read the OP again...
 
Might wanna read the OP again...

I did that before posting, and did it again just for you. I don't see any indication a multimeter was used to measure the bus voltage or any other point on the system. I just see reference to the light and the indication on the JPI. It's unlikely that the two together aren't correct, but changing parts hasn't fixed it. I wouldn't change an alternator without even bothering to bench test it but that's just me.

I would look at the components that Dan Thomas mentioned as a start, and since the problem began occurring after the installation of the ADS-B equipment a good look behind the panel is in order.

On the way to Oshkosh low voltage light comes (indicates discharge on JPI of 23.4 volts) on after 30 mins of flying. Follow the procedure in the POH (turn off radios, turn off master, turn on master, turn radios on) and the the system resets and the low voltage light disappears. The battery is being charged showing 28.3 volts on the JPI. As the flight proceeds the low voltage light comes on 10 mins, 5 mins, sometimes every 2 mins. Each time it is reset. The longer the flight the more frequent the low voltage light comes on. It does not come on during descent or around the pattern or on the ground. Only climbing or level flight (maybe something to do with engine cowl temperature?)We landed and replaced the alternator which was 10 years old. Test flew the plane and 1st hour of flight LV comes on. Replaced the master switch which had corroded wires. Same issue on test flight. Limped the plane back to California and replaced main wire from alternator, replaced wire from battery, checked all grounds and replaced the voltage regulator. Same problem after 30 mins of flight. During flight we have tried to isolate the problem to a piece of electronics but the LV still comes on when each piece of equipment is shut off. Any similar problems out there?
 
I did that before posting, and did it again just for you. I don't see any indication a multimeter was used to measure the bus voltage or any other point on the system. I just see reference to the light and the indication on the JPI. It's unlikely that the two together aren't correct, but changing parts hasn't fixed it. I wouldn't change an alternator without even bothering to bench test it but that's just me.

I would look at the components that Dan Thomas mentioned as a start, and since the problem began occurring after the installation of the ADS-B equipment a good look behind the panel is in order.
You are right. The JPI sensor is undoubtedly bad. Thank you eversomuch for showing me the light.
 
You are right. The JPI sensor is undoubtedly bad. Thank you eversomuch for showing me the light.

The fact remains that apparently no one has confirmed the system voltage using an independent source.

Why do you think it's appropriate to post replies that are denigrating and pretty much indicate you're an a sshole? What makes you think your abilities to troubleshoot an electrical system problem are superior to mine?

I spent ten years working on the TTL logic of large UPS systems in the 1990s and am a licensed electrician that has built dozens of data centers with multiple megawatt power systems over the last 25 years. I've seen a lot of things stranger than an electronic monitoring system displaying erroneous information.
 
The fact remains that apparently no one has confirmed the system voltage using an independent source.

Why do you think it's appropriate to post replies that are denigrating and pretty much indicate you're an a sshole? What makes you think your abilities to troubleshoot an electrical system problem are superior to mine?

I spent ten years working on the TTL logic of large UPS systems in the 1990s and am a licensed electrician that has built dozens of data centers with multiple megawatt power systems over the last 25 years. I've seen a lot of things stranger than an electronic monitoring system displaying erroneous information.
Well for one thing the JPI data matches that which is expected for a system that is charging initially and then shows voltage that is correct for a discharging battery.

I think it is wonderful that you claim to be an electrician and have built wonderful things. I will note that you said nothing about a multimeter until I pointed out that the voltages were reported in the OP. I will also note that you evidently believe any suggestion you make should be treated as gospel even though all information presented suggests the contrary. In other words I think you are full of crap. I’ll ignore the personal attack and put that down to ill temper or inebriation. I will suggest that you learn to be more temperate in your remarks particularly when you are so obviously in the wrong. HTH and HAND.
 
Regarding my OP, looking at a display and measuring voltage are two distinctly different activities, so I'll consider your original comment as being based on poor reading comprehension skills.

The mention of my qualifications to comment on the thread topic are no different than other posters stating they hold an A&P or IA certification, which is common in this forum.

I will stand by my opinion that determining the voltage present in various parts of the electrical system by measurement using a multimeter is a basic starting point for troubleshooting.

Anyone who thinks I'm "full of crap" for espousing this point of view isn't qualified to comment on the subject of the thread.
 
Regarding my OP, looking at a display and measuring voltage are two distinctly different activities, so I'll consider your original comment as being based on poor reading comprehension skills.

The mention of my qualifications to comment on the thread topic are no different than other posters stating they hold an A&P or IA certification, which is common in this forum.

I will stand by my opinion that determining the voltage present in various parts of the electrical system by measurement using a multimeter is a basic starting point for troubleshooting.

Anyone who thinks I'm "full of crap" for espousing this point of view isn't qualified to comment on the subject of the thread.
Well I see you persist with the personal attacks. A digital multimeter display is no different than a JPI display. Perhaps in the future you can learn to evaluate data and suggest useful things rather than time wasters. Perhaps not.

As for your qualifications, well claim away. It is clear to me that you are quite full of crap and unable to admit a fundamental flaw when assessing data. Don’t worry about it. It’s just the internet. Your income won’t be affected by the display of your skills here. HTH and HAND
 
Well, no wonder. ****ing *******. I have zero respect for licensed electricians. The experiences I've had with them, they either flat out lied or didn't know what they were doing and I found their error.
As best I can tell passing an electric code test has nothing to do with troubleshooting...it’s about knowing code...
 
Well, no wonder. ****ing *******. I have zero respect for licensed electricians. The experiences I've had with them, they either flat out lied or didn't know what they were doing and I found their error.

That's a well reasoned observation. Unlike you, I don't use Google to manufacture replies on subjects I have no knowledge of.
 
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Well I see you persist with the personal attacks. A digital multimeter display is no different than a JPI display. Perhaps in the future you can learn to evaluate data and suggest useful things rather than time wasters. Perhaps not.

As for your qualifications, well claim away. It is clear to me that you are quite full of crap and unable to admit a fundamental flaw when assessing data. Don’t worry about it. It’s just the internet. Your income won’t be affected by the display of your skills here. HTH and HAND

So I'm led to believe you think the OP's mechanic was performing a well thought out plan by changing the alternator, the voltage regulator, the alternator primary conductor, the master switch, and the conductor between the battery and the B+ bus without measuring any voltages at the several points to isolate the extent of the problem. He apparently didn't test the items he removed and replaced either.

Where does the JPI obtain its voltage information? Is relying on a voltage sample that doesn't represent all parts of the charging system good practice?
 
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As best I can tell passing an electric code test has nothing to do with troubleshooting...it’s about knowing code...

In my case you would be quite wrong. As I mentioned I have extensive experience in performing board level repair on TTL systems. It's a dead industry, but that doesn't mean skills I have are inapplicable in other fields.

Regarding the license, in Texas a journeyman must have at least 8,000 hours of on-the-job training under the supervision of a master electrician and pass a journeyman electrician examination administered by the state.

To obtain a master electrician license, the applicant must have at least 12,000 hours of on-the-job training under the supervision of a master electrician, have held a journeyman electrician license for at least two years and pass a master electrician examination administered by the state. That means I worked 40 hours a week for six years to obtain my license, a little more involved than "passing an electric code test".

Acting as project manager for a general contractor Installing 12 mW electrical services, multiple 2 mW generators and 600 kW UPS systems in parallel operation requires a little more than reading a code book. But please, continue to display your ignorance. You too, Glenn..
 
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Even a licensed electrician needs to consult the schematics of both the aircraft's charging system and the regulator's internals. That low voltage light does not specifically indicate low voltage; it indicates that the regulator has been turned off, either via the alternator switch or by the overvolt sensor. The alternator could die entirely--broken belt or worn brushes or whatever--and it would not light.

Edit: Corrected to read "alternator could die entirely..."

Was only halfway through first cup of coffee..
 
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The voltage regulator was changed a month after the alternator and I am not sure what brand it is but I will check. The old alternator was not tested. The voltage regulator is mounted on the pilot side right in front for the firewall above the air filter. Some more history: The plane has flown for 10 years with no problem. During those years it had a complete panel upgrade and was fine. It sat idle for 6 months and during those six months we put in a garmin ADS-B transponder. After that the plane was flown for 10 hrs and then the VL appeared. We isolated the garmin transponder by shutting it off and the VL still came on while we were flying. We are going to take a look at the transponder and the wiring to see if something does not look right just in case.

Did you use the original wire harness and plug? The original pins are old. Wire jackets crack. I had a similar issue in my 180. I chased it with some of the best local resources for years. It didn't go away with replacement OEM alternator and regulator. Ultimately I gutted the airplane and re-wired it nose to tail and installed a B&C alternator and regulator by field approval. No problems since. I believe the re-wire is what fixed my electrical demons. I doubt there had been anything wrong with the newer OEM alternator and regulator.
 
Even a licensed electrician needs to consult the schematics of both the aircraft's charging system and the regulator's internals. That low voltage light does not specifically indicate low voltage; it indicates that the regulator has been turned off, either via the alternator switch or by the overvolt sensor. The regulator could die entirely--broken belt or worn brushes or whatever--and it would not light.

I don't disagree at all. The schematic is necessary to work through the system and inspect wiring and devices one by one. Your earlier post above was informative and provides a good starting point to locate the problem on the OP's aircraft.
 
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This is the basic stuff. I adapted the circuit diagram from an old automotive manual to show how the aircraft is wired. You can see that the low voltage light is fired by the battery, through the light, to several paths to ground inside the regulator: through three resistors (.04, 10, and 50-ohm), through the normally-closed voltage limiter relay and though the field coil, and through the 14-ohm resistor and voltage limiter coil. If the field relay is closed (by someone turning the Alt switch on), the relay contacts short directly across the light and reduce its potential to zero. It goes out. That's why you can turn on the Master and Alt switches and the light doesn't come on, even though the alternator isn't turning and the system voltage is low. Turn off the Alt switch and it will light up. Basically, the overvolt sensor does just that. It's in the line between the breaker and Alt switch. The regulator could flash on and off if either the red or orange wires are loose, or it will trip off and stay off until reset if the black (to ground) is loose; the sensor loses its reference and thinks there's a problem and trips off.

upload_2017-10-26_18-37-54.png
 
In my case you would be quite wrong. As I mentioned I have extensive experience in performing board level repair on TTL systems. It's a dead industry, but that doesn't mean skills I have are inapplicable in other fields.

Regarding the license, in Texas a journeyman must have at least 8,000 hours of on-the-job training under the supervision of a master electrician and pass a journeyman electrician examination administered by the state.

To obtain a master electrician license, the applicant must have at least 12,000 hours of on-the-job training under the supervision of a master electrician, have held a journeyman electrician license for at least two years and pass a master electrician examination administered by the state. That means I worked 40 hours a week for six years to obtain my license, a little more involved than "passing an electric code test".

Acting as project manager for a general contractor Installing 12 mW electrical services, multiple 2 mW generators and 600 kW UPS systems in parallel operation requires a little more than reading a code book. But please, continue to display your ignorance. You too, Glenn..
I understand that you focus on little jobs. That is fine. There is still no requirement for troubleshooting in passing the code tests. Anybody on the internet can claim whatever they want. In this thread you ignored reported readings and decided that certain observations should be made. Those observations are pointless. You cannot erase that. HTH and HAND.
 
So I'm led to believe you think the OP's mechanic was performing a well thought out plan by changing the alternator, the voltage regulator, the alternator primary conductor, the master switch, and the conductor between the battery and the B+ bus without measuring any voltages at the several points to isolate the extent of the problem. He apparently didn't test the items he removed and replaced either.

Where does the JPI obtain its voltage information? Is relying on a voltage sample that doesn't represent all parts of the charging system good practice?
I understand that you like to imagine things. That is fine. Do try to understand that other folks don't particularly agree with your imaginings and perhaps have good reason to discount them. If you can't understand that it's okay. HTH and HAND.
 
This might help.
 

Attachments

  • CPA Cessna Alternator Operation Notes.pdf
    562.8 KB · Views: 32
In my case you would be quite wrong. As I mentioned I have extensive experience in performing board level repair on TTL systems. It's a dead industry, but that doesn't mean skills I have are inapplicable in other fields.

Regarding the license, in Texas a journeyman must have at least 8,000 hours of on-the-job training under the supervision of a master electrician and pass a journeyman electrician examination administered by the state.

To obtain a master electrician license, the applicant must have at least 12,000 hours of on-the-job training under the supervision of a master electrician, have held a journeyman electrician license for at least two years and pass a master electrician examination administered by the state. That means I worked 40 hours a week for six years to obtain my license, a little more involved than "passing an electric code test".

Acting as project manager for a general contractor Installing 12 mW electrical services, multiple 2 mW generators and 600 kW UPS systems in parallel operation requires a little more than reading a code book. But please, continue to display your ignorance. You too, Glenn..
Impressive! However, it does not change the experiences I've had with licensed electricians.
 
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