Generator Current Issues

[8342]

I found that the wiring diagrams in the IPC are very helpful.
Figure 43 or 43 should be what you need.

Rick

[6643]

I found that the wiring diagrams in the IPC are very helpful.

Yes! I think it's the same diagram, only bigger and easier to read.

[bill_e]

I just got a copy of the 120/140 maintenance Reference Manual from the store here. Chapter 2300 has that same Figure 19 drawing from the IPC along with the excellent reference schematic drawn by Ed Lawrence and Barry Warren. Nice to have someone else's interpretation of the system as further guidance.
Using those references, I've already found (I think) that my ammeter is incorrectly installed in the line between the "B" terminal of the voltage regulator and the main bus. Explains why it's never worked the way I expect an ammeter in an airplane to work (only shows positive values). Lots more work and diagnostics to go. I think my winter project is going to involve cleaning up a lot of wiring behind the panel.

[bill_e]

I had a very productive work session over the weekend addressing this problem. I managed to confirm that both the generator and voltage regulator were working correctly, found the wiring fault that was preventing the battery from charging, and corrected the ammeter wiring.
Before touching anything, I put a voltmeter between the "A" terminal of the regulator and ground and did a ground run. I wanted to see what the generator was delivering to the regulator prior to doing any work. At 1000 RPM, I measured about 8.5V and that increased to about 15V by 1800 RPM. Given that, it seemed likely that the generator and the field control function of the regulator were working correctly.
Next, I moved the voltmeter over to the "B" terminal of the regulator and ran the engine again. I wanted to see what the regulator was delivering to the main bus. I saw battery voltage until around 1500 RPM when it jumped up to 13.4V, then stabilized at about 14.5V by the time I got to 1800 RPM and above. I turned loads on and off, but it held at that voltage. However, the voltage across the battery terminals was still about 12.8V, so it seemed clear there was a wiring fault somewhere between the regulator output and the battery. Still, breathed a sigh of relief that I probably didn't need a new generator or regulator.
Working under the panel, I confirmed that the ammeter was incorrectly wired between the regulator output and the input side of the generator breaker and that the battery was connected directly to the main bus via the positive terminal of the starter contactor. The wires behind the panel were routed oddly and seemed to indicate some previous owner had moved them from where they were supposed to be. In moving terminals so that the ammeter was correctly placed in the circuit, I noticed a too-long screw securing the generator breaker to the main bus. The screw was digging into the plastic of the breaker and preventing the bus bar from making good contact with the breaker terminal. I shortened the screw and tightened everything back down.
After checking, rechecking, and triple checking all connections that were touched, I ran the engine again. Now, I see about 14.3V across the battery terminals, and my ammeter shows positive charge that decreases as the battery recovers from the start, and displays a discharge when I turn the generator off. Final inspections and logbook signoff are needed before I go fly, but I think I can put this one to bed.

[6643]

Good work!

[V529]

Bill, I know we discussed this at Decorah, who knew you were going to have to get so involved to sort it out. I guess I should have considered, "prior installations, and non-standard wiring techniques"