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Thread: Volts constant but amps will fall off and run negative

  1. #121
    frequent_flyer's Avatar
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    I was away at the hangar and missed most of the action.

    From my scan of the test results I'd want to check how voltage appears on the IGN (Field) terminal of the cable harness when it is disconnected from the alternator and the field CB is pulled.

    I suggest checking the harness field terminal voltage in these 4 condition:

    Field breaker in, master on, alternator main breaker in
    Field breaker pulled, master on, alternator main breaker in
    Field breaker pulled, master on, alternator breaker pulled
    Field breaker pulled, master off, alternator breaker pulled

  2. #122

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    Quote Originally Posted by wireweinie View Post
    I'd test the wires two ways. First, with all wires connected at the alternator. Then unplug the 'IGN' wire and disconnect the 'B' wire. See if there is a change.

    Web
    sorry but I don’t guess I’m following.

    1. Measuring the voltage “at the alternator”…….. are you referring to placing the leads of the voltmeter onto the actual alternator “spade” “IGN” connector on the alt? If so, are you first plugging in the wire to that spade with the “B” (big, main wire) connected? If so, then how do you get the voltmeter lead onto that spade on the alt with it plugged in? Do you just barely plug it in and leave enough spade exposed to get a reading? The big wire “B” is not problem with the wire connected because it’s a post with a nut on it. Easy enough.
    2. In the measurement you suggested earlier, we’re you referring to measuring the v “on the alt” or the wires going “to the alt”?
    3. In this post you said to measure with the IGN and the “B” wire disconnected? If they are disconnected, what am I measuring then! The wires and not the alt itself?

    Sorry. This just isn’t making sense for me as I really have a hard time figuring this out with the OV relay, etc wire and alternator connections. I’m not sure how to make these measurements. All the wiring is connected correctly per the schematics so I’m assuming the OV Relay or the alt must be bad?

  3. #123
    wireweinie's Avatar
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    Leave the wires connected as if it was operating. Connect the black lead from the voltmeter to a clean, unpainted spot on the airframe. With the master switch on and the alternator field and output breakers pushed in, use the red lead from the voltmeter to measure voltage at the 'IGN' terminal and the 'B' terminal on the alternator. On the plug used for the 'IGN' connector push the voltmeter probe through the back of the connector past the wire. If the probe is to big, use a paper clip or a short piece of safety wire to slip inside the connector and touch the red lead to the clip/wire. Note the voltage. Then touch the red voltmeter lead to the stud for the output terminal. Again, note the voltage.
    Now remove the 'IGN' connector from the alternator and remove the 'B' wire from the stud on the alternator. Touch the red voltmeter lead to each of those wires and note the voltage.

    Web
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  4. #124
    40m's Avatar
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    I suspect this is not related to your problem and others could explain this better than I but it's important to understand the roll of the most common installation of the IBBS battery system in the Carbon Cub with a G3X. If you have installed a three battery system than the purpose of the IBBS battery is to supply warm up/emergency power to the G3X. The thin ~1x5x7 inch battery is your right ignition back up power source.

    From Genesis: "And God promised men that good and obedient wives would be
    found in all corners of the earth."

    Then he made the earth round... and He laughed and laughed and laughed!

  5. #125

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    Ok. Thanks for explaining. Here is what I got with every configuration I could think of. Thanks Web!

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    Quote Originally Posted by wireweinie View Post
    Leave the wires connected as if it was operating. Connect the black lead from the voltmeter to a clean, unpainted spot on the airframe. With the master switch on and the alternator field and output breakers pushed in, use the red lead from the voltmeter to measure voltage at the 'IGN' terminal and the 'B' terminal on the alternator. On the plug used for the 'IGN' connector push the voltmeter probe through the back of the connector past the wire. If the probe is to big, use a paper clip or a short piece of safety wire to slip inside the connector and touch the red lead to the clip/wire. Note the voltage. Then touch the red voltmeter lead to the stud for the output terminal. Again, note the voltage.
    Now remove the 'IGN' connector from the alternator and remove the 'B' wire from the stud on the alternator. Touch the red voltmeter lead to each of those wires and note the voltage.

    Web

  6. #126

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    Yes. I wondered about that too. The IBBS (Integrated Backup Battery System) is a good system I’m use to. I know this one worked because it actually automatically activated on my first flight when the colts dropped below 12.0.

    its the backup battery for the G3X system. It has a separate switch and breaker. When the switch is on, it alone boots up the system without the master being on. Good to flip on before starting it as it will boot up the system and have it ready when you hit the master switch to start the engine.

    The CB for the IBBS does not power that backup battery system itself. Pulling that cb will not shut down the G3X or the IBBS system. It is controlling whether or not you want to charge that battery. If the cb is in, the battery will recharge when the master switch is on. If the engine is not running, it will charge from the main battery.

    i always leave it on for quick refueling stops after i shut down the engine and turn the master off.

    Click image for larger version. 

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    Quote Originally Posted by 40m View Post
    I suspect this is not related to your problem and others could explain this better than I but it's important to understand the roll of the most common installation of the IBBS battery system in the Carbon Cub with a G3X. If you have installed a three battery system than the purpose of the IBBS battery is to supply warm up/emergency power to the G3X. The thin ~1x5x7 inch battery is your right ignition back up power source.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #127
    wireweinie's Avatar
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    I don't think your OV module is wired correctly. Each circuit breaker (field and output) should turn power on and off as they are pulled. As per the diagram of your charging system, there are no other paths for either of those circuits to get powered on.

    Web
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  8. #128
    wireweinie's Avatar
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    You're going to have to get access to the OV module and check each terminal. It appears to be a standard 'fog light' relay so the terminals are numbered on the plastic right next to the metal blade.
    Leave the 'IGN' and 'B' wires disconnected from the alternator for this check. Pop both breakers and check all terminals for no voltage. Press in the field breaker and check that there is voltage on relay terminal 86, ONLY. Pop the field breaker and press in the alternator output breaker. Then check for voltage at relay terminal 30, only. Finally press in both breakers and check for voltage on relay terminals 86, 30, and 87, only. If you have any readings other than this, check for a proper ground on relay terminal 85.
    For these checks, 'voltage' = battery voltage and the relay should remain plugged in.

    Web
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    Thanks Diamonddave thanked for this post

  9. #129
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    I'll throw in a caution. When using a high impedance DVM for voltage measurements it is possible to see voltages that would drop to zero if any load was applied. Sometimes an old fashioned test lamp will give more honest results. I have found a few sneak paths in the FX-3 wiring. It's fun to track them down and explain them.

    E.g. - why would the stall warning still work with master off? Turns out it is fed by a capacitor on the power input of the IBBS module. Any load on main bus would quickly discharge that capacitor but, with master off, the capacitor holds charge and will sound the stall horn hours after the aircraft is powered down. Main bus remains live with master off but cannot source any significant current. This sneak path can be eliminated by pulling the IBBS breaker.

  10. #130

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    Yes. I’ve always thought that was strange.
    Last edited by Diamonddave; 05-09-2022 at 05:32 PM.

  11. #131

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    Ok Web. I did the measurements as you suggested and it all measured as you indicated.

    - Both wires disconnected at the alternator
    - pulled both CBs and there was 12.4 v voltage at the 87 terminal on the OV Relay
    - field only CB in, 12.4v at 86 and 87
    - alt CB only in, 12.4 v at 30 and 87
    - both CBS in, 12.4 v at 86, 30 and 87 and nothing at 85.

    I have traced every wire from origin to OV Relay to he alternator. From both CBs to the OV Relay. I even disconnected the wire from the alt CB completely (after first checking and there was no voltage at the cb on that wire with it pulled, so cb working). I did continuity checks on wire only to be sure they are correct as numbered.

    I checked all wires correct on the correct terminals of the OV Relay. I don’t know what a “crowbar” is or how it works but it’s there. The wire numbers are slightly incorrect in this picture. Should not be “AB... but just A08.... etc”



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    So how is terminal 87 getting power even with alt cb pulled? It always gets volts from somewhere regardless of cbs.

    HEY..... I then disconnected all the wires from the OV Relay except the 87 wire going to the alt. It still showed 12.4 v even if the master was off and no wire connected! Then I realized the alt noise filter was between that wire and the actual alternator. It must have been holding voltage (like freq flyer stated) because I took it out of line and with it disconnected, all wire then tested out correctly. I will then assume it’s bad or doing strange stuff? The alt wire came in and out on the + terminal (per schematic) and the - terminal was grounded.

    So so I guess I’ll get another one and try it out?

    Quote Originally Posted by wireweinie View Post
    You're going to have to get access to the OV module and check each terminal. It appears to be a standard 'fog light' relay so the terminals are numbered on the plastic right next to the metal blade.
    Leave the 'IGN' and 'B' wires disconnected from the alternator for this check. Pop both breakers and check all terminals for no voltage. Press in the field breaker and check that there is voltage on relay terminal 86, ONLY. Pop the field breaker and press in the alternator output breaker. Then check for voltage at relay terminal 30, only. Finally press in both breakers and check for voltage on relay terminals 86, 30, and 87, only. If you have any readings other than this, check for a proper ground on relay terminal 85.
    For these checks, 'voltage' = battery voltage and the relay should remain plugged in.

    Web

  12. #132
    wireweinie's Avatar
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    OK. You have verified that your circuit breakers and OV module should be wired correctly and the OV module seems to turn on/off correctly. This is the process of troubleshooting. Bolting parts on and hoping it will work is called 'shotgunning' and is frowned upon by all except the deepest wallets. If you wanted to further simplify the circuit for troubleshooting you could also remove the connector from the OV relay/module and install a jumper from terminal 30 to terminal 87. This will bypass the OV module completely.

    Right now I suspect the alternator itself as you have checked for correct power at the 'IGN' and 'B' terminals. Since it looks like an automotive Nippondenso style, you can most likely take it to a NAPA type store that offers testing of alternators. They can spin it up on the test bench and verify if it's working or not.

    A crowbar is just a component that is connected to a positive lead and ground. It is completely open under normal operations (infinite resistance to current flow). If the voltage rises above it's set point, the crowbar conducts, making it a direct short from the positive lead it is connected with, to ground. When this happens, the circuit breaker pops to prevent damage. Removing power from the circuit allows the crowbar to reset.

    Web
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  13. #133

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    Really? The alternator was not connected to any wire when I did the tests which showed that alternator noise suppressor was causing 12.4 v to show up on the wire even when no power present? When I removed the suppressor from the wire from the OV to the alternator it all tests out correct. Seems like bad suppressor.

    just verifying that you did read my last paragraph.

    Quote Originally Posted by wireweinie View Post
    OK. You have verified that your circuit breakers and OV module should be wired correctly and the OV module seems to turn on/off correctly. This is the process of troubleshooting. Bolting parts on and hoping it will work is called 'shotgunning' and is frowned upon by all except the deepest wallets. If you wanted to further simplify the circuit for troubleshooting you could also remove the connector from the OV relay/module and install a jumper from terminal 30 to terminal 87. This will bypass the OV module completely.

    Right now I suspect the alternator itself as you have checked for correct power at the 'IGN' and 'B' terminals. Since it looks like an automotive Nippondenso style, you can most likely take it to a NAPA type store that offers testing of alternators. They can spin it up on the test bench and verify if it's working or not.

    A crowbar is just a component that is connected to a positive lead and ground. It is completely open under normal operations (infinite resistance to current flow). If the voltage rises above it's set point, the crowbar conducts, making it a direct short from the positive lead it is connected with, to ground. When this happens, the circuit breaker pops to prevent damage. Removing power from the circuit allows the crowbar to reset.

    Web
    Last edited by Diamonddave; 05-10-2022 at 01:23 PM.

  14. #134
    wireweinie's Avatar
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    The 'suppressor' is a capacitor. It's job is to soak up voltage spikes and drain them out when the circuit voltage decreases. That suppressor is doing it's job just fine.

    You have two circuits that connect to the alternator. You have verified that the wires are installed on the right terminals and that the circuit breakers and OV module are functioning correctly. Only thing left is the alternator. But get it checked out before you replace it. Always verify before spending money.

    Web
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  15. #135

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    Dang. This should have been the first thing I did it’s so easy to remove and test. Will get a replacement under warranty from CC and that should do it. Thanks so much for your time and help!!

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    Quote Originally Posted by wireweinie View Post
    The 'suppressor' is a capacitor. It's job is to soak up voltage spikes and drain them out when the circuit voltage decreases. That suppressor is doing it's job just fine.

    You have two circuits that connect to the alternator. You have verified that the wires are installed on the right terminals and that the circuit breakers and OV module are functioning correctly. Only thing left is the alternator. But get it checked out before you replace it. Always verify before spending money.

    Web
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  16. #136
    wireweinie's Avatar
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    Let us know when you get the new one installed.

    Web
    Life's tough . . . wear a cup.
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  17. #137
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    I suppose it's hard for those who have worked with electronic components for 60 or more years to remember that there are lots of people who don't understand those components or the terms and schematic symbols that represent them.

    A capacitor is a passive charge storage device. A perfect capacitor will hold whatever voltage it was charged to - for ever! Perfect capacitors don't exist yet but the good ones have very low leakage and will hold their charge, and therefore their voltage, for a long time.

    https://en.wikipedia.org/wiki/Capacitor

    An alternator with built in rectification diodes produces a DC output with a ripple waveform superimposed. That ripple is an inevitable byproduct of the rectification of the alternators raw AC voltage. It is this ripple that can cause whine to be heard in the headphones. The alternator capacitor smoothes the ripple and helps to eliminate the whine.

    CubCrafters describes the alternator capacitor as "alternator noise filter assembly" and depicts it using the symbol for an electrolytic capacitor.



  18. #138
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    Quote Originally Posted by Diamonddave View Post
    Dang. This should have been the first thing I did it’s so easy to remove and test. ......
    All part of the learning curve.
    Remember this for next time.
    Cessna Skywagon-- accept no substitute!
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  19. #139

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    exactly right. In this case, disconnecting the noise suppressor before testing would have done the trick but not knowing it was causing bad voltage measurements it kept me going down the rabbit hole.

    Quote Originally Posted by hotrod180 View Post
    All part of the learning curve.
    Remember this for next time.

  20. #140

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    Received a warranted alternator replacement and all good. Just an out of the box bad alternator! Thanks for the comments and suggestions. Who woulda thought!
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