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Old 04-07-2019, 08:50 AM
jaybhansen jaybhansen is offline
Join Date: Feb 2018
Location: Simi Valley
Posts: 2
Default 912 ULS Ammeter

The ammeter is my RV12 shows a negative reading. I understand that the two battery wires can be interchanged. Also the two generator wires. I have tried any combination on my current and a new rectifier and get the same results. Any advice would be appreciated.
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Old 04-07-2019, 12:06 PM
rvbuilder2002 rvbuilder2002 is offline
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,286

It would be helpful to have more details.
Standard avionics kit from Van's?
Skyview? Garmin.
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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Old 04-08-2019, 06:14 AM
BigJohn BigJohn is offline
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,585

Ditto what Scott says. Also, it is troubling to me when you say you have been swapping wires around hoping for a better result. That is a real good way to damage additional expensive components. Suggest you take a big step back and look for the basic cause of the problem. There are people here on the forum that will be glad to help you, but we need much more complete information about your configuration and the circumstances of the failure.
John Peck, CFII, A&P, EAA Tech Counselor, Flight Advisor.
“Master Pilot” Award, UFO Member.
RV-12 N37JP 120176 Flying since 2012.
One Week Wonder Build Team, OSH 2018.
VAF paid through 10/2019.
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Old 04-08-2019, 07:33 AM
Mich48041 Mich48041 is online now
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,886

Assuming that you have Dynon avionics, interchange the two wires going to
EMS pins 24 and 25. Like BigJohn said, switching other wires could cause big
problems. What is the voltage? If less than 13, then negative amps is
expected and normal.
Joe Gores
RV-12 Flying
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Old 04-08-2019, 09:54 AM
MMiller MMiller is offline
Join Date: Oct 2010
Location: Babylon NY
Posts: 52

Jay, your ammeter should fluctuate between positive and negative amps. Reading into your post, I assume you are telling us your system is not charging, and you are referring to the wiring at the voltage regulator connector. Yes, the individual wires within those pairs can be swapped, but doing so is pointless because the the two “generator” wires supply AC and the two white battery wires are jumped together in both the harness and inside the regulator.

If your system is not charging you need to measure the voltage at the regulator “C” terminal (referenced to ground.) you can measure this with the engine OFF and master switch ON. The C pin voltage be must equal battery voltage.

Last edited by MMiller : 04-08-2019 at 10:09 AM.
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Old 04-08-2019, 11:41 AM
Mich48041 Mich48041 is online now
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,886

I never thought to read between the lines like Mike Miller did. So is the problem actually a low voltage problem and not an ammeter problem?
If so and this RV-12 has Van's original control board, then a burned circuit board trace will result in no voltage on regulator terminal C. There is no fuse protecting the terminal "C" wire. If that wire shorts to ground, even for a second, the control board will be damaged. Some people elect not to have the control board repaired. Instead, they jumper regulator terminals "B" and "C" together. The disadvantage to doing that is that it will not be possible to shut off electrical power if there is smoke in the cockpit, unless the engine is stopped.
Joe Gores
RV-12 Flying
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Old 04-08-2019, 12:20 PM
DHeal DHeal is offline
Join Date: Sep 2006
Location: Windsor, California
Posts: 824

As Mike noted above, during the course of a normal flight (RV-12 w/ 912ULS) the ammeter will likely show you "plus" and "minus" readings. Typically the "minus" readings occur at low RPM settings (e.g., taxiing, power-off approach, etc.) when the 912's dynamo/generator does not supply sufficient power to supply all of your electrical demand -- the battery is then providing the additional power required and is slowly being discharged. As you add RPMs you should see your ammeter stabilize at a small "plus" reading -- in cruise, my readings are stable at 13.9 volts and +1 amp. If you constantly see a "minus" ammeter indication at high RPMs then that is another problem.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 825+ hours (as of Sep 2019)!
VAF donation through June 2020.
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Old 04-09-2019, 09:19 AM
pilotyoung pilotyoung is offline
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 124
Default 912 ULS Ammeter

Question for Joe. The electrical diagram for the RV-12 shows a 1 amp fuse in the line that powers the C terminal of the Voltage Regulator. I blew the one in my airplane last summer. I called Van's asking for the location of it, I could not find it, and they told me it is internal to the circuit board of the switch module. They also said that it could only be repaired at Vans.

Before I shipped it back to them, they gave me the alternative wiring which you mentioned of jumpering the C and B terminals.

You mention a circuit board trace which melts or separates. Does that circuit board trace function as a fuse or is there really a 1 amp fuse soldered onto the circuit board?


John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 140 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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Old 04-09-2019, 11:19 AM
Mich48041 Mich48041 is online now
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,886

You mention a circuit board trace which melts or separates. Does that circuit board trace function
as a fuse or is there really a 1 amp fuse soldered onto the circuit board?
The answer is both. It all depends on which version of the control board you have. The original D-180
control board did not have a fuse. In that case a short circuit caused a circuit trace to burn open.
Newer control boards have a fuse. Since my RV-12 has the original control board, I do not know
where the fuse is physically located or how to replace it on newer control boards.
Joe Gores
RV-12 Flying
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Old 04-09-2019, 11:29 AM
NinerBikes NinerBikes is offline
Join Date: Dec 2018
Location: Granada Hills
Posts: 186

Anyone have an idea what it would cost to replace a D-180 with a Skyview D1000 Touch, with GPS 2020 receive antenna, on an older RV-12, pre 2013 finish build date?
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