FlyingCanuck

Field voltage is 0 My A&P thinks the VR is the problem, that its enough putting out enough to 'excite' the alternator (Pardon my lack of electrical knowledge - definitely not my area of expertise!)

Alternator Yes on the breakers

So the saga took an interesting twist Battery was charged for five days on a Chargeminder, and then capacity tested. Feedback from two different A&Ps/two different shops was: Battery is in great health. Good! Battery went back into plane. Now, the alternator isn't charging the battery. Start-up is fine, but the volt meter (cigarette lighter) never gets above 12.5V. If I put any load on the plane (avionics master ON), the amp meter shows a discharge. A&P tested the current at the alternator and it showed zero. What's weird is that NOTHING was wrong with the charging system (VR, alternator, etc.) before the battery discharge incident that triggered all of this. Local shop thinks its a bad voltage regulator - we think its the 1976 original. I've asked them to check some simpler things too, such as the wiring at the Master switch (maybe old wires final bit the dust after me cycling the Master switch a few times? Fluke chance?) Overall: I'm perplexed how an issue of a drained battery that was re-charged and re-installed, could affect the charging system forward of the firewall? Opposite ends of the plane

It was the perfect storm of events: the week before, the bulb in my rotating beacon burnt out. On or off, I wouldn’t have told me anything. Trust me, it doubles my annoyance at myself….

M20F with a Concorde RG35AXC. 2.5-3 year old battery. After 24 years of flying, I finally did the “leave the master on” goof-up. Drained the battery to dead (whatever the lowest symbol on a Chargeminder is - the very unhappy territory). Local shop put it on a Chargeminder for a few days, and it showed good health. First attempt at flying it: after start, annunciator flashed Voltage and voltmeter in plane showed 12.3-12.5. From other threads, I suspect that’s the end of my battery. I could spend hours and $$$ chasing it - or do I just bite the bullet, accept the price of my stupidity, and buy a new battery? (Side note: I don’t profess to be handy at electrical things, so returning the battery to the plane was my first time doing that… but I’m pretty sure that’s hard to screw up as long as you put it back how you found it? )

I’m based at SBP, have an F model, and would be happy to chat Mooney. PM me and we can arrange something.

Same problem here in the Central Coast. Overcast 018 and freezing level at 030 with rain forecast. Sorry to miss this - but let’s keep the repetition going with another one in April or sooner!

Anyone around SBP/PRB/SMX interested in "Mooney pooling" up there? Happy to pick others up in the area.

26th is great. I'm hoping my Mooney will be back in the air by then. But if not, if anyone wants to stop in San Luis Obispo (SBP) and pick me up, I'll gladly share the fuel bill with you!

Thanks - do you remember what your symptoms were going into the process?

Update on this - I did a few small checks based on my very novice (but learning ) electrical skills. Checked the voltage on the field wire with battery/alt switch on. Was showing about 11V. Checked the resistance on the field wire (removed one of two wires; batt/alt off; resistance checked at terminals). Showed between 0-1 ohms. (Mostly 0 but occasionally bounced up a bit toward 1 ohm, then steady at zero) Its been suggested that this indicates issues with the brushes on the alternator that need to be replaced. What do others think? I have photos of the alternator area if that matters.

Wow… I don’t want to get too excited at the coincidences here, but… here goes: I’ve only had 4 electrical ‘moments’ with this plane: 1. ALT FIELD CB popped on a long flight from TX to DC. Reset. No issue for years after. 2. Ever since buying plane, the volts were low: 12.8-13.2. Finally at annual had the VR adjusted up. Produced 14-14.4 thereafter. 3. VOLTAGE light after lower landing gear on approach to KHHR. Local A&Ps couldn’t find any issue. Home mechanics said it was the field wire faulty. (40 hours ago) 4. The present issue in thread above. Interesting that on my first flight, the plane was damp after two weeks of heavy rain on the ramp (albeit covered but still…). On the second flight, the issue was gone: until I lowered landing gear on a bumpy approach back home at KSBP. the parallels are striking: wet/moisture and/or landing gear lowering, seems to be happening around the same time as this issue appears. I’d be curious to check out the diode resolution. does anyone have a photo of their wiring with a diode installed?

I can confirm, no CBs were popped. Only when I manually pulled the ALT FIELD circuit, and then reset it, did the system temporarily return to normal.

Hi folks - anyone have a parts manual for a 1976 M20F? Looking for parts info related to electrical system: voltage regulator, circuit breakers, and other associated bits and pieces. Thanks!