231LV Posted October 22, 2020 Report Share Posted October 22, 2020 Just took a flight and noticed the amp output on the JPI 900 jumps from -9 to +15 amps and everything in between on every cycle. Voltage holds steady around 13.8...maybe hits 13.9v then drops back to 13.8v. My gut tells me this is not something to monitor but wanted some input from other 231 drivers regarding what they typically see. Am I missing a problem developing? Quote Link to comment Share on other sites More sharing options...
PT20J Posted October 23, 2020 Report Share Posted October 23, 2020 What’s a “cycle”? By ohms law, current = voltage divided by resistance (i.e., load). If the load is constant and the voltage is constant, the error is in the instrumentation. Skip 1 Quote Link to comment Share on other sites More sharing options...
milotron Posted October 23, 2020 Report Share Posted October 23, 2020 Check for a broken wire at the alternator. i had the same condition and the large wire had broken at the crimp connector and making intermittent contact but was hidden by the rubber boot over it. Quote Link to comment Share on other sites More sharing options...
231LV Posted October 23, 2020 Author Report Share Posted October 23, 2020 1 hour ago, PT20J said: What’s a “cycle”? By ohms law, current = voltage divided by resistance (i.e., load). If the load is constant and the voltage is constant, the error is in the instrumentation. Skip Sorry...couldnt think of a more appropriate word....the output would show -9 then +15 then -2 then +11 then -4 and so on and so on... Quote Link to comment Share on other sites More sharing options...
231LV Posted October 23, 2020 Author Report Share Posted October 23, 2020 1 hour ago, milotron said: Check for a broken wire at the alternator. i had the same condition and the large wire had broken at the crimp connector and making intermittent contact but was hidden by the rubber boot over it. will do....thanks Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2020 Report Share Posted October 23, 2020 As Skip says above, it’s an indication error. It would be impossible to have no alternator output(negative current indication) and still have positive voltage indication. Look for loose wires at the alternator shunt. Clarence Quote Link to comment Share on other sites More sharing options...
Z W Posted October 23, 2020 Report Share Posted October 23, 2020 Ours did something similar once. Turned out to be the voltage regulators. Quote Link to comment Share on other sites More sharing options...
jlunseth Posted October 23, 2020 Report Share Posted October 23, 2020 I tend to agree it is probably in the circuitry, the wiring or the voltage regulator. The coupler in the drive mechanism is a weak spot but it tends to be binary, in other words it works or does not work it is not often a matter of intermittent slippage. That does not mean that it never fails in that mode though. Quote Link to comment Share on other sites More sharing options...
Geoff Posted October 26, 2020 Report Share Posted October 26, 2020 If the above doesn't solve the issue, beware of a failing alternator clutch. Quote Link to comment Share on other sites More sharing options...
buddy Posted October 27, 2020 Report Share Posted October 27, 2020 I’m not to sure what the back of your master switch looks like but when I owned my 1980 M20J I had the same problem. Mooney uses spade connectors (push on connectors) on the back of the master switch and every couple of years I would get wild swings on my amp. gauge. I used a screwdriver and pushed the spade connectors in tight and that solved the problem. My master switch had several wires attached to it. PM me if you want I can probably explain it a little better. 1 Quote Link to comment Share on other sites More sharing options...
231LV Posted October 27, 2020 Author Report Share Posted October 27, 2020 23 hours ago, Geoff said: If the above doesn't solve the issue, beware of a failing alternator clutch. Voltage is steady on at 13.8v....only amps popping around Quote Link to comment Share on other sites More sharing options...
N231BN Posted October 27, 2020 Report Share Posted October 27, 2020 Check the wires from the ammeter shunt to the JPI, it is an indication issue. 2 Quote Link to comment Share on other sites More sharing options...
Mike A Posted October 27, 2020 Report Share Posted October 27, 2020 I recently had a similar issue where my Amp meter would randomly go crazy. My voltage on the JPI would also vary. It got resolved by spraying the master switch connections with contact cleaner. Got the idea from another thread on the site. Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 28, 2020 Report Share Posted October 28, 2020 If not familiar... Amp meters are technically volt meters, reading voltage difference across the shunt... the shunt is a precise low resistance resistor... all of the electrons Being used by the plane are coursing through the shunt... The amp meter is reading the voltage drop and displaying it on the gauge that is calibrated in Amps... there are two thin wires going from both ends of the shunt to the gauge... one probably got loose... Use caution with shunts... not a lot of insulation near the device that carries a lot of electricity... Accidentally shorting this thing to ground... can melt aluminum... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
wpbarnar Posted October 28, 2020 Report Share Posted October 28, 2020 On 10/22/2020 at 8:43 PM, milotron said: Check for a broken wire at the alternator. i had the same condition and the large wire had broken at the crimp connector and making intermittent contact but was hidden by the rubber boot over it. I experienced the exact same failure and intermittent contact in my Encore. Bill Quote Link to comment Share on other sites More sharing options...
David Lloyd Posted October 28, 2020 Report Share Posted October 28, 2020 10 hours ago, carusoam said: all of the electrons Being used by the plane are coursing through the shunt... The amp meter is reading the voltage drop and displaying it on the gauge that is calibrated in Amps... Depends on how the shunt is connected in the system. As a load meter, it would measure what is being used by the airplane. Without looking, I don't know if Mooney included the battery load or not. Could be either way. My airplane has the charge/discharge meter only showing a couple amps going into the battery to keep it charged, or if the alternator failed, a discharge showing the load of equipment and radios. Yep, three different schemes for measuring amps, all used by various mfgrs at various times. OP, amps jumping and volts steady, sounds like a loose connection of the shunt circuit. Quote Link to comment Share on other sites More sharing options...
231LV Posted December 1, 2020 Author Report Share Posted December 1, 2020 OK...as a followup for anyone else experiencing something similar...turns out the master switch connection appears to be the culprit...lose wire BUT if it persists, a replacement master switch will be necessary since my mechanic found a lose pole on the switch...still, after he re-tightened the wire, he could not get it to fail so that's a plus....all other avenues were explored and eliminated...this was all done during annual... 2 Quote Link to comment Share on other sites More sharing options...
Mike A Posted December 2, 2020 Report Share Posted December 2, 2020 On 10/27/2020 at 5:36 PM, Mike A said: I recently had a similar issue where my Amp meter would randomly go crazy. My voltage on the JPI would also vary. It got resolved by spraying the master switch connections with contact cleaner. Got the idea from another thread on the site. Winner winner chicken dinner? 1 Quote Link to comment Share on other sites More sharing options...
larryb Posted December 2, 2020 Report Share Posted December 2, 2020 In my J I had the master switch fail in this way. It was a loose rivet on one of the field circuit terminals. Your symptom is indicative of a bad connection somewhere in the field circuit. It could be anywhere, including internal to the master switch. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 2, 2020 Report Share Posted December 2, 2020 The teamwork makes the dream work prize goes to.... Great follow-up 1LV! Fantastic input Mike A! Excellent related Experience larryb! Go MS! Best regards, -a- Quote Link to comment Share on other sites More sharing options...
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