Elijah Posted Sunday at 02:07 AM Report Posted Sunday at 02:07 AM On my flight to Wyoming today, the over voltage protection started tripping. This has happened in the past but so intermittently I could never pin down the problem. The alternator has been checked and seems fine, good brushes etc. So, I am thinking voltage regulator but I thought I'd see if anyone has experience with this or any other thoughts. What's happening now is within a minute of powering on the field breaker (sometimes immediately, sometimes a minute, kinda random) the charge current spikes and the voltage goes up to 14.8, 15 and then the OVP trips, the voltage light comes on, and the bus voltage returns to the battery resting voltage. Cycle the field breaker and it all repeats. The charge current can spike almost to 60a very briefly. It's gotta be the regulator right?
DC_Brasil Posted Sunday at 02:45 AM Report Posted Sunday at 02:45 AM I've had this problem. In my case it was the VR802 voltage regulator. A technician removed it and changed a fried component (very quick diagnostic and repair) and bench tested it. It has worked great ever since.
Elijah Posted Sunday at 03:29 AM Author Report Posted Sunday at 03:29 AM 42 minutes ago, DC_Brasil said: I've had this problem. In my case it was the VR802 voltage regulator. A technician removed it and changed a fried component (very quick diagnostic and repair) and bench tested it. It has worked great ever since. I'm happy to hear that, I imagined it was all potted in plastic and nothing repairable. Maybe it can be fixed. I think I'll take it out tomorrow. I remember it's under the dash on the firewall and not real easy to get to.
Elijah Posted Sunday at 04:27 AM Author Report Posted Sunday at 04:27 AM I just found this thread, this sounds exactly like what I'm seeing. I'm going to take a close look at the canon plug... https://mooneyspace.com/topic/47294-voltage-regulator-alternator-or…/page/2/#findComment-838077
DC_Brasil Posted Sunday at 11:20 AM Report Posted Sunday at 11:20 AM 7 hours ago, Elijah said: I'm happy to hear that, I imagined it was all potted in plastic and nothing repairable. Maybe it can be fixed. I think I'll take it out tomorrow. I remember it's under the dash on the firewall and not real easy to get to. Older Voltage regulators like the one I have in my 1990 J are actually not very complex equipments. They're circuit boards with very simple and easy to find components like resistors, capacitors, etc. An electronic technician can easily work with them to troubleshoot. Most of the times (not always) electrical problems are easier to pinpoint than mechanical. You can get point to point readings with a multimeter to isolate where some faults are coming from. 1
PT20J Posted Sunday at 03:45 PM Report Posted Sunday at 03:45 PM The voltage regulator controls alternator output by sensing the bus voltage and regulating the field current to maintain the proper voltage. So, too high a voltage can be caused by either a failure in the regulator, or a voltage drop where the regulator senses voltage. The latter can be due to an intermittent short or loose connection. When it fails, that momentary surge in current is going somewhere that may not be good for your electronics.
Mooneymite Posted Sunday at 03:51 PM Report Posted Sunday at 03:51 PM (edited) The intermittent alternator over voltage light came on a couple of times for no apparent reason. Not wanting to be stranded, I took the precaution of buying a solid state VR and stored it in my baggage compartment. The light never came on again. I have since sold the plane, but still have the VR. As far as I know the "fix" is still working. Anyone need a spare "over-voltage preventer" for their baggage compartment? Edited Sunday at 03:52 PM by Mooneymite 2 2
dc0341 Posted Sunday at 06:40 PM Report Posted Sunday at 06:40 PM I had the same issue. Tested the alternator and battery, everything was okay. The A&P adjusted the old voltage regulator and it didn't work. I just ended up buying a Zeftronics regulator, no issues since. 1
Elijah Posted Sunday at 07:40 PM Author Report Posted Sunday at 07:40 PM 3 hours ago, Mooneymite said: The intermittent alternator over voltage light came on a couple of times for no apparent reason. Not wanting to be stranded, I took the precaution of buying a solid state VR and stored it in my baggage compartment. The light never came on again. I have since sold the plane, but still have the VR. As far as I know the "fix" is still working. Anyone need a spare "over-voltage preventer" for their baggage compartment? I would be interested in that, I'll PM you. I am going to go look through things today and hopefully I can find a wiring issue but if not, I'd love to have that on hand. Yeah I have actually had some luck fixing voltage regulators in the past. Of course not for certified aircraft but they all work similarly. This one seems to control field currently by PWM. I studied it a bit last time this happened but I could never get the problem to show up again. Of course now that I'm on a trip now it shows itself! At least it's very consistently failing now.
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