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Nathan Young wrote in message . ..
On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts" wrote: I am now able to reproduce my charging problem. Engine off, Bat and Alt on: Bus voltage: 24.8 Supply to Voltage Regulator: 22.6 Voltage Regulator Output to Alt Field: 21.6 I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A circuit breaker, the Alt side of the master switch, and the Overvoltage relay. John, I didn't see your original charging problem, so cannot comment on that, but will make a few general comments on this post. 21.6 Volts seems like a high field voltage to drive the alternator. What kind of load was on the system during this measurement? I'm not certain, but believe wih minimal load, the field voltage on my 14V system was around 6-7V. The 2.2V drop between the master bus and VR is not good and can lead to several problems in the electrical system. I would fix this before doing anything else. #1. The bus voltage will be high. The VR will crank up the field voltage until its input 'sees' 24V. Given a constant drop of 2.2V between bus and VR, the bus will be at 26.2. #2. If the resistance causing the 2.2V drop is caused by a bad CB, switch, or loose/corroded connection before the OVR, the resistance will vary depending on temperature and turbulence knocking the system around. This will cause OVR cutouts as the OVR will occasionally see the full bus voltage which is 24V + the voltage drop from a second ago (26.2V or higher). #3. Resistance between the master bus and the VR input sets up an RC circuit which (when extreme) can cause charging system oscillation. I like your idea of trying to eliminate the drop between the bus and the VR input by direct connecting it to the bus. (Make sure to have your avionics master OFF when doing this kind of troubleshooting!). Another approach would be to measure the voltage after each of the field CB, field switch, OVR, and VR input. This will probably tell you where the drop is, and you can do this without the plane running. BE EXTRA CAREFUL when probing around under the panel, it is easy to short things with voltmeter probes. -Nathan Nathan, As posted elsewhere I did finally solve the problem. The main problem was the filter capacitor inside the alternator had come loose and was bouncing around in there. Explained my intermittent charging, and then eventually it wiped out the alternator completely. After replacing the alternator the bus voltage was higher than desired, but we were expecting this. We jumpered from +bat to the VR input as described above, and the voltage came down-- confirming the resistance problem. We cleaned the connections on the master switch and on a connector to the VR itself. That solved the high bus voltage problem. It also eliminated my "bouncing ammeter/flickering panel lights", which had been that way ever since we got the plane so I didn't even think it WAS a problem! Thanks for everyone's input-- it's been a great learning experience! Cheers, John Clonts Temple, Texas N7NZ |
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