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Thread: Overvoltage question

  1. #1
    Gordon Misch's Avatar
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    Overvoltage question

    I have a Plane Power alternator and voltage regulator and Odyssey battery. Beginning last May I started getting over voltage indications of 15-16+ volts. I would pull the field breaker, wait till the battery voltage declined into the upper 11's, then reset. All would be fine until the battery was fully charged again. Over the last several months the problem has become more frequent, and recently the overvoltage crowbar has tripped the field breaker a few times. I suspected a poor connection somewhere, but found none. I have ordered a new Plane Power regulator.

    My question, that just occurred to me this evening - could an old battery cause this problem? My battery is 10 years old, but seems to hold charge well and cranks the engine well.

    Before I simply install the new regulator, voiding its returnability, I'd appreciate opinions from you folks. Thanks!
    Gordon

    N4328M KTDO
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  2. #2
    irishfield's Avatar
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    Not sure on the plane power wiring, but 9 times out of 10 overcharging is a ground issue, as in the voltage regulator not well grounded. If it's a two field alternator, having one wire break off the voltage regulator will = runaway full field voltage. Check for a perfect ground on the voltage regulator case... zero ohms case of regulator to case of alternator.

  3. #3
    Gordon Misch's Avatar
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    Thank you. I did check the regulator ground wire at the regulator terminal. I measured between 0.1 and 0.2 ohms. (My Fluke meter zeros at 0.1 ohm.) The Plane Power troubleshooting guide specs 0.1 ohms, I believe (it's been a few days since I read it). I will check reg case to alt case tomorrow.
    Gordon

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  4. #4
    hotrod180's Avatar
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    If it was me, I'd change out that 10 year old battery just because.
    I had some electrical issues earlier this year, changed out my 5 year old Odyssey just because.
    A cheap way to eliminate a possible issue. Or what could become an issue before long.
    Turns out the problem was the regulator going haywire.
    But I don't regret changing out the battery.
    Cessna Skywagon-- accept no substitute!

  5. #5

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    When you check the crimps on your connections push and pull on them. I had a gremlin I chased for 2 years, it was a crimp that allowed the cable to slide forward so when you would tug on the wire it would reseat and feel good. It would hold for a while them get loose again.
    DENNY
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  6. #6
    wireweinie's Avatar
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    Look at the diagram for the Plane-Power system. The wire coming from the field circuit breaker provides power to the regulator, at the 'enable' position. There is also a jumper wire from the 'enable' position to the 'sense' position, where the voltage is monitored. A poor or intermittent connection anywhere along this circuit will cause incorrect voltage output from the system. And keep in mind that this circuit should also run through one pole of the master switch, if wired correctly, although this is not shown on the Plane-Power diagram.

    To do a basic trouble shoot of this circuit, turn on the master switch and make sure the charging system is powered on (engine does not need to be running here). With a digital voltmeter, measure bus bar voltage. Now measure the voltage at both terminals of the field breaker and the master switch (field power side only). Then measure the voltage at the 'enable' and 'sense' terminals on the regulator. Note ANY change in voltage from bus voltage. This will tell you what component or section of wire that is causing issue. A poor connection or any high resistance, such as a corroded breaker or switch, will cause the regulator to see a lower voltage and cause the regulator to increase the systems output voltage.

    Another trick I use for these installs is to run the ground wire from the regulator to the alternator case. It's not that common, but this will eliminate any ground issues that might exist between the alternator and the airframe.

    Web
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  7. #7
    wireweinie's Avatar
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    Trying for a better copy of the diagram.

    Web
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  8. #8
    wireweinie's Avatar
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    Found a better diagram. This time it has the field circuit routed through one pole of the master switch.

    Web
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  9. #9
    Gordon Misch's Avatar
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    Thank you much. I will double check crimps and voltages as suggested. What's odd is that voltage is well regulated at 14.3 or 14.4 until the battery is fully charged. Then it starts to spike in a non-smooth manner - i.e. the voltage hops around erratically from 16+ back to 14.2. If I leave it alone it eventually crowbars out. If I pull the field breaker and let the battery run down just a bit, then upon re-energizing the field the system regulates properly again.

    I will follow through with your suggestions today. If that all seems correct, will see how the new regulator behaves.

    This all began at the same time I discovered a loose connection on the "downstream" terminal of the master relay (Thank you, Steve of Steve's Aircraft for helping me discover that). So I wonder if the regulator might possibly have been "spiked" by that in some way.
    Gordon

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  10. #10
    Gordon Misch's Avatar
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    Well, I wiggled the wires at crimps, measured resistance to ground, and voltages as suggested. Each of those things seems right. Then flew for a little while and the system behaved. So - - I'll keep watching it, and install the new regulator, assuming the system continues to be erratic.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  11. #11
    wireweinie's Avatar
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    Is your regulator ground wire tied to the firewall or did you route it to the back of the alternator case? Cycle the field circuit breaker and master switch rapidly to break up any corrosion or burnt spots on the contacts. You've got a poor connection somewhere. Replacing the reg won't fix that.

    When you do voltage checks, keep the ground lead from the meter connected to the same point for all checks. And be aware that even .1 volt drops will cause issues on a sensing circuit. I.e. bus bar voltage is 11.8. Voltage measured at the output terminal of the breaker is 11.6. This means that at operation,when the bus voltage is actually 14.2 volts as per the regs setting, the reg will only see 14.0 volts and try to increase the alternator voltage.

    To make matters worse, a fixed resistance produces a higher and higher voltage drop as the current in the wire increases. Example; .8 ohms resistance will produce a drop of .2 volts if the current flow is .25 amps. If the reg senses an under voltage and increases current flow to .75 amps, the voltage drop will be .6 volts. So the greater the current draw the more inaccurate the sensing circuit becomes.

    Web
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  12. #12
    Gordon Misch's Avatar
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    Thanks Web, all of that makes sense to me, at least in principle. A couple thoughts:

    The system has worked fine for 10+ years, until this summer. So it's wired correctly.

    My regulator is 10 or 11 years old, and there is no "sense" terminal connection like shown on the schematic. That terminal location is labeled "N/C" on the face of the regulator and nothing is connected to it.

    Compared to Buss voltage of 11.9 V, with field energized, I measured a 0.1 V drop at the "Enable" terminal of the regulator. Then I measured an additional 0.1 V drop at the "Field" terminal of the regulator. That seemed reasonable to me given that there is field current through that circuit?? My Fluke low impedance meter has a 0.1V resolution, so each of those could be .05V in error.

    Alternator and regulator ground terminals are both independently routed to a ground buss which is in turn grounded to the airframe. Those ground paths measure 0 ohms.

    Again, when the battery is less than fully charged, the system reliably regulates correctly (14.3 - 14.4 V). It's only when the battery is peaked (around 12.5V, in flight, radio etc turned on, with the field breaker pulled) that it gets goofy.

    Am I still missing something? Thanks again for your help!

    Edit: Alternator case to ground is about 7 or 8 ohms. I discounted that, assuming that the alternator ground terminal is all that really matters. Am I wrong about that?
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  13. #13
    wireweinie's Avatar
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    Can you post a pic of the regulator and it's label? Never seen one without the sense terminal.

    What size wire is used as the alternator ground? If the alternator case shows 8 ohms resistance to ground, it doesn't make sense that the alternator ground wire shows 0 ohms to ground as the ground wire is connected directly to the case. Maybe post a pic of the alternator case where the ground wire is connected? Should be 0 ohms from the alternator to the engine, from the engine to the airframe, and from the airframe to the ground post on the battery.

    Web
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  14. #14
    Gordon Misch's Avatar
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    Gordon

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  15. #15
    Gordon Misch's Avatar
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    This is the only pic I have right now. I will go over to the airport and try to get a better pic and answers to your questions. Thanks again...
    Gordon

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  16. #16
    Gordon Misch's Avatar
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    Ok, well, I have egg on my face. Again.

    1. I did NOT measure from an alternator ground post to ground. I measured from the ground terminal on the regulator, and that runs about 0 to 0.2 ohm, depending on how I hold my mouth. I'm referencing from probe wedged between copper primer line and firewall, and confirming with probe jammed into braided engine / mount strap, and from ground post on firewall. If I reverse the probes, it changes slightly - I have no idea the why on that. But my conclusion overall is about 0.1 ohm.

    2. Alternator case to ground reference is about 0.8 ohm, not the 8 I previously stated.

    Perhaps a good next step would be to wire directly from regulator ground terminal to the alternator case?

    Here is a better pic of the regulator.
    Last edited by Gordon Misch; 10-14-2020 at 07:57 PM.
    Gordon

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  17. #17
    wireweinie's Avatar
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    Humor me. Run the ground wire on the reg, to the ground stud on the rear case of the alternator. You want 0 ohms between the reg and alternator.

    Web
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  18. #18
    Gordon Misch's Avatar
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    Yep, will do tomorrow. Thanks!

    I assume you mean to retain the lead from the reg ground terminal to airframe ground, and add a new one to alternator frame?

    Edit: As has been said so many times, nowhere else can one get such timely, friendly, expert advice. I sure do appreciate.
    Gordon

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  19. #19
    wireweinie's Avatar
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    If you run the reg ground wire to the alternator case, you can skip the reg ground to airframe. You should take a moment to clean up the engine grounds or add a good braided ground from the crankcase to the airframe.

    The engine to airframe ground is hard to check for resistance. Any primer line or p-lead ground will measure low resistance but when you crank the engine, all that current needs a large ground path to return to the battery.

    Web
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  20. #20
    Gordon Misch's Avatar
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    Got it. I'll check them and clean as necessary. I have a large braided ground and a smaller 8 awg ground, each from crankcase to airframe but separate paths, like Mike MCS recommends. It seems as though the alternator frame might not be well bonded to the engine case. I'll see what I can do to check that also. Thanks again.
    Gordon

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  21. #21
    BC12D-4-85's Avatar
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    Also try charging the battery off the airframe. Look for unexpected voltage excursions as the AGM reaches charge. Takes 14.5 VDC plus to condition them. Them = several for me. They can become sulfated and resist charge via internal breakdown at + voltage.

    Gary
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  22. #22
    hotrod180's Avatar
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    Quote Originally Posted by DENNY View Post
    When you check the crimps on your connections push and pull on them. I had a gremlin I chased for 2 years, it was a crimp that allowed the cable to slide forward so when you would tug on the wire it would reseat and feel good. It would hold for a while them get loose again.
    DENNY
    I had charging issues on my last airplane.
    Took the alt off to take it down to auto-electric shop for testing.
    Checked out good.
    When I reinstalled it, I had to twist one wire to get it on the terminal.
    I noticed that while the crimp-on ring connector pushed & pulled OK,
    it turned freely on the wire.
    Cut the connector off & crimped on a new one...problem solved.
    Cessna Skywagon-- accept no substitute!
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  23. #23

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    Had a similar problem. Turned out to be a ground issue. Whomever mounted the alternator used vibration dampeners and the ground ran through the tension adjustment bar. Somewhere along, the adjustment bar broke but still held under tension and a safety wire. It failed finally showing arcing across the broken section. It did not have a separate ground wire to the back of the case. All kinds of testing resulted in confusion because of intermittent readings, which resulted in disassembly. Did me a favor, and is corrected as mentioned above with ground wire directly to regulator.
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  24. #24
    Gordon Misch's Avatar
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    Well, I added a wire from alternator frame to ground terminal on regulator. The skin on the back of my hand is rearranged but.... Flew it for about an hour and a half and the voltage remained steady at 14.2 - 14.3 the whole time. So I think it might be fixed. Thanks all and especially to Web. You were right on sir!
    Last edited by Gordon Misch; 10-15-2020 at 09:24 PM.
    Gordon

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  25. #25
    Gordon Misch's Avatar
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    Flew another hour and a half or so today and the voltage never wavered. Happy!
    Gordon

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