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Low Volts Light staying on above 1100 RPM, initial troubleshooting done, expert input needed!!!

Philly5G

Registered User
England
On my last flight (before the schedule of planned remedial work I've been working to) I noticed the Low Volts warning light staying on in the climb.

I tightened the generator belt and then ran on the ground, the low volts light flickered (rapidly) on/off above 1100

I did the recommended generator troubleshooting I found on line and the generator was producing no output and in the course of this, I found the field tab connector was hanging on by a thread, so replaced the connector

I cleaned the "points" in the Delco Remy Voltage Regulator with fine abrasive paper and then the low volts light remained solidly on above 1100 rpm

The generator was then overhauled and reported as working fine on the bench.

I refitted the generator and found the same problem with the low volts light staying on above 1100 rpm

With master switch on I can measure battery voltage (to ground) to as far forward as the voltage regulator, but obviously not at the generator

Due to the maintenance work and therefore being in the hangar, I haven't run the engine since the test above, but intend to do that this week and measure battery voltage from the ammeter to ground and see if the voltage does increase at rpm above 1100 and therefore point to a faulty low volts light, but other than that I'm thinking voltage regulator, maybe something to do with the field circuit, the thing about "flashing/polarising" the generator (although the generator shop said it wouldn't need this), or WHO KNOWS?!!!!!

I'd really appreciate any thoughts/steers/troubleshooting steps on this please :)

Thanks

Philly
 
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Can't find the generator trouble shooting instructions on Zeftronics new website. Pretty easy to diagnose, will post the instructions when I get to the hanger. I would put a meter on the buss to start with.
 
HI Philly,

You most likely need to flash the field.

Tim

Thanks Tim!! Is this the thing where I touch a lead from the battery +ve to the field tag?!

I'd really appreciate a step by step action point list of how to do this if that's not too much of a hassle, but my basic questions are:

How long do I hold the +ve lead on the field tab
Do I need to disconnect cables and loosen off the drive belt first?
Does the master switch need to be on or off

Thanks again man :)

Philly
 
Can't find the generator trouble shooting instructions on Zeftronics new website. Pretty easy to diagnose, will post the instructions when I get to the hanger. I would put a meter on the buss to start with.

Thanks Steve!! Is the bus the same as putting the meter from the ammeter to ground?

Cheers

Philly
 
The buss is where your circuit breakers etc attach to the main power from the battery and generator. Should see 12-12.5 volts with engine off and 13.5- 14 or so when engine is running above 1200 rpm or so. Here is the trouble shooting instructions and the info on Zeftronics regulator with a good explanation of how the system works with schematic.
 

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The buss is where your circuit breakers etc attach to the main power from the battery and generator. Should see 12-12.5 volts with engine off and 13.5- 14 or so when engine is running above 1200 rpm or so. Here is the trouble shooting instructions and the info on Zeftronics regulator with a good explanation of how the system works with schematic.

Brilliant!! Thanks Steve!! Yes, I was doing exactly this voltage measurement from the buss to the rudder cables yesterday when trying to work out why the new radio circuit switch I'd just fitted wasn't working AT ALL!! Turned out that the connector from the battery supply lead (via the ammeter and master switch) to the Buss had broken off when changing the switch!! The fun of working with 71 year old aircraft and aging components!!! :)

Ps The battery voltage was 12.54v so pretty healthy despite all the testing I've been doing while fitting the new radio :)
 
The buss is where your circuit breakers etc attach to the main power from the battery and generator. Should see 12-12.5 volts with engine off and 13.5- 14 or so when engine is running above 1200 rpm or so. Here is the trouble shooting instructions and the info on Zeftronics regulator with a good explanation of how the system works with schematic.

I've looked at the docs now, thank you and obviously they refer to the Zeftronics GCU which has a GEN FLD switch (or is this a switch on the aircraft? mine doesn't have one if yes) can I do the polarity test up to the point of flushing the field as they describe? and if is reverse polarity, do you know what the flushing procedure is for a none Zeftronics Voltage Controller?
 
Thanks Tim!! Is this the thing where I touch a lead from the battery +ve to the field tag?! ...

I don't know who came up with the term "flashing the field" but as seen in this question to me it seems kinda misleading.
When polarizing the generator, a much better term IMHO, you momentarily touch a jumper from the battery terminal to the armature terminal at the regulator.
It'll spark, then you're done. The master doesn't need to be on.
It was easy to remember with the Bosch regulator on my old Harley panhead: B+ to D+.
Dunno if you'd hurt anything connecting the battery to the field, but it wouldn't polarize anything.
 
I don't know who came up with the term "flashing the field" but as seen in this question to me it seems kinda misleading.
When polarizing the generator, a much better term IMHO, you momentarily touch a jumper from the battery terminal to the armature terminal at the regulator.
It'll spark, then you're done. The master doesn't need to be on.
It was easy to remember with the Bosch regulator on my old Harley panhead: B+ to D+.
Dunno if you'd hurt anything connecting the battery to the field, but it wouldn't polarize anything.

Thanks HotRod, so basically just take a lead from battery +ve and touch it on the armature terminal on the Voltage Regulator, just the once briefly and with all cables connected and the master switch off? :)
 
Brilliant!! Thanks Steve!! Yes, I was doing exactly this voltage measurement from the buss to the rudder cables yesterday when trying to work out why the new radio circuit switch I'd just fitted wasn't working AT ALL!!
Rudder cables ??
 
This is the flash instructions from an old manual. Just be aware that if this generator was working recently you will not need to flash the field. "Flashing the field" as stated earlier just restores residual magnetism, of the correct polarity, in the pole shoes. Also be aware that if done incorrectly it WILL destroy stuff by dumping battery power directly through components. Flashing is usually done after major parts replacement on generators or when the generator has not operated for an extended time (usually several months).

Web
 

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Easiest way to fix that generator is to call B&C and buy an alternator. You will have good voltage all of the time. You will take some weight off the front of your airplane. You will never have to worry/wonder about it again.
 
Easiest way to fix that generator is to call B&C and buy an alternator. You will have good voltage all of the time. You will take some weight off the front of your airplane. You will never have to worry/wonder about it again.

Yes, they work great!! I fitted one to my BA4B and really pleased with it!! This PA12 is potentially a money pit, so I'm looking to fix wherever possible, but an alternator is definitely on my list of "Would Likes" :)
 
I have not read and understood this complete thread so please excuse my butting in .But , If this is a situation is like I had with a generator paired with a zeftronics regulator not working on an L21 20 amp gen it was because the way it was wired ,when the starter was energized the surge caused the regulator to shut down the charging circuit . So now I must pull the generator breaker before I start the engine and after the start reset the breaker while the engine is idling and all works as designed .
 
I've looked at the docs now, thank you and obviously they refer to the Zeftronics GCU which has a GEN FLD switch (or is this a switch on the aircraft? mine doesn't have one if yes) can I do the polarity test up to the point of flushing the field as they describe? and if is reverse polarity, do you know what the flushing procedure is for a none Zeftronics Voltage Controller?
The first document is of the standard Delco Remy system. Piper used the master switch to turn on the field of generator. Your PA12 should be wired like this diagram for the PA18.
PA18_Electrical_Schematic.jpg
 

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Please do some research, because I don't think that is correct. It is the residual magnetism in the field core that needs to be re-magnetized by current in the field winding. Here's a start http://www.davidsonsales.com/FlashGenerator.htm.

I dunno who Davidson is, or what kind of vehicles he's referring to, but here's his procedure (from the link):


  1. Remove exciter field leads F+ and F- from the voltage regulator. CAUTION: Failure to remove the field leads from the regulator during flashing procedures may destroy the regulator.​
  2. Measure the exciter field resistance from the F+ to the F- lead. You should be able to read some resistance as you are measuring a continuous winding. An infinite resistance reading would indicate an open in the exciter field. Also check to be sure there is no path to ground.​
  3. Connect F+ to the positive pole of the battery.​
  4. Hold the F- lead by the insulated portion of the lead wire, touch F- to the negative pole of the battery for about 5 to 10 seconds, then remove.​
  5. Reconnect F+ and F- to the regulator. Repeat the procedure if the generator fails to build voltage


    Here's what the Cessna series 100 manual says:

    polarizing generator.jpg[SUB][SUP]
    [/SUP][/SUB]

 

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Welcome to the club...
Myself and a man in Washington state are the co-Presidents. You can be our CEO.

Ha ha ha ha ha ha ha ha ha ha ha!!!!!!!!!! AND you guys don't have the shipping costs and import duty and value added tax amounts to worry about :)
 
I dunno who Davidson is, or what kind of vehicles he's referring to, but here's his procedure (from the link):


  1. Remove exciter field leads F+ and F- from the voltage regulator. CAUTION: Failure to remove the field leads from the regulator during flashing procedures may destroy the regulator.​
  2. Measure the exciter field resistance from the F+ to the F- lead. You should be able to read some resistance as you are measuring a continuous winding. An infinite resistance reading would indicate an open in the exciter field. Also check to be sure there is no path to ground.​
  3. Connect F+ to the positive pole of the battery.​
  4. Hold the F- lead by the insulated portion of the lead wire, touch F- to the negative pole of the battery for about 5 to 10 seconds, then remove.​
  5. Reconnect F+ and F- to the regulator. Repeat the procedure if the generator fails to build voltage


    Here's what the Cessna series 100 manual says:

    View attachment 37889[SUB][/SUB]


Hmmmmmm the Delco Remy Voltage Regulator has 3 connectors - Battery, Armature and Field. I wonder which of these (if any) are the F+ and F- leads?
 
The first document is of the standard Delco Remy system. Piper used the master switch to turn on the field of generator. Your PA12 should be wired like this diagram for the PA18.
View attachment 37885

Wow, thank you!! So if all is working correctly, turning on the Master Switch should immediately show battery voltage measured between the Generator Field Tab (on the generator) and Ground? :)
 
http://www.venselenterprises.com/techtipsfromdick_files/generators.pdf Here is a good explanation of how your generator and regulator work together. Since your generator was overhauled we can assume the commutator and brushes are OK and you probably have a regulator problem. If everything works OK but the north and south poles are swapped on the field poles the ammeter will show current flow in the discharge direction. Since you have a low voltage light you probably have a regulator problem.
 
Here is a good explanation of how your generator and regulator work together. Since your generator was overhauled we can assume the commutator and brushes are OK and you probably have a regulator problem. If everything works OK but the north and south poles are swapped on the field poles the ammeter will show current flow in the discharge direction. Since you have a low voltage light you probably have a regulator problem.

Thanks Cruiser!! That's a really good explanation!! It still doesn't answer an earlier question though-when the master switch is turned on and without the engine running, should there be battery voltage measurable between the generator field tab and ground? I'm guessing yes from the wiring diagram????

And a supplementary question, even before the low volts light problem, I never saw the ammeter needle (+/- 30A scale) move significantly at all, just flickering around the +1 to +5 and hardly showing any kind of charge......... I've got the ammeter out now and can take measurements, but what kind of current readings would you expect to see in a normally working Delco Remy Generator?
 
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Thanks Cruiser!! That's a really good explanation!! It still doesn't answer an earlier question though-when the master switch is turned on and without the engine running, should there be battery voltage measurable between the generator field tab and ground? I'm guessing yes from the wiring diagram????

And a supplementary question, even before the low volts light problem, I never saw the ammeter needle (+/- 30A scale) move significantly at all, just flickering around the +1 to +5 and hardly showing any kind of charge......... I've got the ammeter out now and can take measurements, but what kind of current readings would you expect to see in a normally working Delco Remy Generator?
If you read the schematic you will see that when the master is turned on there will be power from the battery, through the 30 amp fuse, through the master switch to the field contact on the voltage regulator.
 
If you read the schematic you will see that when the master is turned on there will be power from the battery, through the 30 amp fuse, through the master switch to the field contact on the voltage regulator.

Thanks Steve, I'm actually reading it that when the Master Switch is on, the voltage will flow from the battery/30A fuses, through the MSwitch and ammeter to the bus/jumper, through the 15A circuit breaker to the Battery terminal on the Voltage Regulator and then (if the Voltage Regulator does this) out of the VRegulator Field tab via the other MSwitch contact to the field tab on the Generator and hence my question on whether battery voltage SHOULD also be present on the field tag of the generator on MSwitch switch on :)
 
I've never seen any control cables that were grounded, except through the clevises and hinges.
 
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