N6893U Posted November 28, 2011 Report Share Posted November 28, 2011 Since I''m here, I have another issue. Recently had to have the generator rebuilt on my M20C. Unfortunately, we were three hours from home when it died. Left the plane with a local AI and eventually brought it home. Some new and different indications were observed, and I would appreciate your thoughts. First, the digital voltmeter I have plugged into the cigarette lighter cycles up and down form 11.8 to 13.9 after the battery becomes fully charged. I know this sounds normal, but it never did this prior. It always read a steady number, usually @ 13.8 or so. Secondly, the ammeter bounced back and forth full scale in synch with the voltage changes. Tried turning off various items, no help. Prior to this, it was always steady and rarely more than a couple ticks of the lower peg. Upon shutdown, the battery showed a solid 12.7 volts It almost seems like the ammeter and voltmeter are no longer connected the same as they were. Thanks, Jerry Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 29, 2011 Report Share Posted November 29, 2011 Jerry, You have hit on one of my favorite topics. If you haven't done so already. Look up Zeftronics digital voltage regulator for your generator. It is a low cost, like for like, replacement for the original springs and screws type controller originally in your plane. Your electrical system is stone simple. Generator, controller, and battery. When one part of the system breaks, it usually takes another part with it.... Search this site for details on Zeftronics. One of our members even posted graphs of voltage output comparisons. As you can imagine, digital output is smooth and steady. Analog output looks like chicken scratch on paper. There are also several discussions on generator vs. alternator. If you don't need to idle on the ground, waiting an hour for an IFR clearance, I preferred the generator. Launching into IMC with a dead battery would not be ideal. Go digital.... Note: it is worth going over each of the connections to make sure they are tight. Most of the connectors are reachable with the copilot side panel removed from the cowling. Cooling tube should still be connected to the generator also. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
DrBill Posted November 29, 2011 Report Share Posted November 29, 2011 I concur with carusoam. The regulator is not controlling the generator properly. The regulator's job is to control the field winding of the generator. When the field is grounded, the generator trys to put full output. When grounded through a resistor, it provides partial output. The electronic regulator will control the field current to maintain 13.6-14.1 v on the power bus with the engine at 1000 rpm or more. Given the wiring is solid and we have to "assume" it is since it was just worked on, then the regulator must be at fault. For those of your with Alternators, the field terminal is similar operation however the alternator will produce maximum output when the field is tied to 12V (not grounded like a generator). Hence a regulator on an alternator equipped plane varies the voltage to the field terminal to control the output current. With the plane running at 1000 rpm or more, a voltmeter on the field terminal, the bus and the generator/alternator output will quickly identify the problem device. Bill Quote Link to comment Share on other sites More sharing options...
garytex Posted November 30, 2011 Report Share Posted November 30, 2011 Also check the security of your connections at the master switch, especially if they are the slip on (spade) connections. One side of the switch is alternator field, tho other is everything else. When the field circuit becomes intermittent charging jumps around. The spade type are the weak ones, but easy to fix, just slide them back and forth a little. If really loose pinch the female side down a little bit with pliers. The ring and screw ones can give trouble too. The other place that will jump up and bite you is corroded battery terminals. They will look fine assembled, but have corrosion at the contact points. Two mechanics and I fought that one, replacing voltage regulators, checking the generator for several months. DOH! Gary Quote Link to comment Share on other sites More sharing options...
DaV8or Posted November 30, 2011 Report Share Posted November 30, 2011 You could have an intermitant short in one of your circuits. A short will simultaneously drop voltage on your meter and peg your amperage gauge. Simply turning systems off may not be enough to isolate it. Try pulling breakers if you haven't already. If that turns up nothing, then visually checking wiring on the other side of the breakers is next. Particularly where it goes through, or clamped to metal. A dead short in an airplane can lead to a pilot's worst nightmare... a fire in the cockpit! Quote Link to comment Share on other sites More sharing options...
Lionudakis Posted December 3, 2011 Report Share Posted December 3, 2011 It sounds like everything is working electrically, cause its charging, 13.9 volts shows that, then shuts off generation, so now your going to show straight battery voltage, 11.8. The on and off of the charging is why your seeing a charge and dis-charge on the ammeter, the ammeter just shows which way the electrons are flowing, either in or out of the battery (+ for charge, - for dis-charge). It sounds like the regulator is simply turning the field on and off and not modulating it. Like CARUSOAM said, if it doenst have one, get a zefftronics ! I installed one om my old 150, made a huge difference in charging. Quote Link to comment Share on other sites More sharing options...
N6893U Posted December 29, 2011 Author Report Share Posted December 29, 2011 Thanks all for sharing your knowledge. It's been working fine in the few hours I've flown it since my post. Jerry Quote Link to comment Share on other sites More sharing options...
jetdriven Posted December 30, 2011 Report Share Posted December 30, 2011 standby Quote Link to comment Share on other sites More sharing options...
gregwatts Posted December 30, 2011 Report Share Posted December 30, 2011 Check it with the strobes off. Quote Link to comment Share on other sites More sharing options...
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