75 Amps On Gear Retract

[ARFlyer]

So today, I was flying our Piper Arrow with my CFI student doing some high work. I noticed our airspeed was flipping around during the flight and turned on the Pitot Heat which solved the issue. A while later we proceeded into do some power off 180s. On landing I noticed a Low Voltage Warning and saw the Bus voltage at 12.5v and dropping with the ALT at 35 Amp. My student looked down and saw that the Pitot Heat was still on and flipped it off. This fixed that problem on taxi back. System was holding 35-40 Amps with 13.8v Bus. Well on our next landing a guy pulled out and caused us to go around. When my student threw the gear up the ALT surged to 75 Amps and it took the gear twice as long to come up and lock. Went out did some trouble shooting and threw the gear down and saw no issue. The system stayed at a cozy 40 Amps. The mechanic went up with another CFI and found nothing wrong. They believe me but just couldn't replicate the issue. So the mechanic said it must have been the low power setting and everything known to man turned on. Any of you guys got an idea ?

Aircraft PA-28R-201 Glass Cockpit
ALT: 14v 60 Amp
Bus Avg: 13.8v
ALT Avg: 40 Amp

 

[hindsight2020]

For reference, my pa-28R-200 cycles between 16-22 amps with the strobe beacon , position lights and master avionics on (Garmin 430W, King radio, xpndr,intercomm and DC electric flight instruments). 40 amps as a steady state load seems rather high to me.

Gear actuation on mine increases load circa +25 from baseline. The three landing lights on do about +30 from baseline. I cannot actuate the gear with all three lights on without overloading the alternator. I can see how with an already high baseline of 40amps, cycling the gear puts you above the limit. Time to figure out why your baseline is 40amps.

 

[Datadriver]

They believe me but just couldn't replicate the issue.

I was flying IFR into Houston when the gear pump in my Arrow started running for no reason. A minute later it stopped, I aborted and returned to base.

Not the answer you were looking for, but yes, dumb things happen that cannot be recreated.

 

[hindsight2020]

I was flying IFR into Houston when the gear pump in my Arrow started running for no reason. A minute later it stopped, I aborted and returned to base.

Not the answer you were looking for, but yes, dumb things happen that cannot be recreated.

LOL. Do realize that's considered normal operation of the pump. The arrow gear is held up by hydraulic pressure, not uplocks. After a while, pressure leaks off and the gear stops making contact with the microswitch, triggering the pump in the direction the gear handle is placed (with the noted exceptions of auto-extend system, which I'll skip for the sake of this thread).

Now, if the pump was running for minutes on end, that would be one thing. But if it's intermittent operation spread throughout a lengthy flight, it is considered normal.

 

[ARFlyer]

Would running a full glass cockpit with the stobes, beacon, recog lights, landing lights, 2-430 GPS, Digital transponder, and three backup gauges cause it to avg 40 amps?

Normal gear operation will cause it to spike above 60 Amps like yours. But it never gets above 65 Amps.

 

[Dan Thomas]

The Pipers use an ammeter shunt. The current runs through it and the ammeter, basically just a milliammeter, is connected across it. The shunt has a tiny resistance, and as more current flows through it, more tries to bypass it through the milliammeter and drives it up.

If that shunt develops corrosion or looseness between its terminals and the shunt strip itself, the tiny fixed resistance is now much larger, the milliammeter reads much too high, and the current is restricted and gear operation is slower because the delivered voltage has fallen under load.

That shunt is sometimes found in the cabin, on one side or the other, behind the sidewall paneling and against the outside skin, where it gets condensation on it. The maintenance manual should have a definite location of it for that particular airplane.


Dan

 

[weirdjim]

Would running a full glass cockpit with the stobes, beacon, recog lights, landing lights, 2-430 GPS, Digital transponder, and three backup gauges cause it to avg 40 amps?

Normal gear operation will cause it to spike above 60 Amps like yours. But it never gets above 65 Amps.

Do you all get charged by the character to post stuff?

If not, what is a recog light? I can translate "stobes", but if there are strobes, what is a "beacon"?

Jim

 

[gismo]

The Pipers use an ammeter shunt. The current runs through it and the ammeter, basically just a milliammeter, is connected across it. The shunt has a tiny resistance, and as more current flows through it, more tries to bypass it through the milliammeter and drives it up.

If that shunt develops corrosion or looseness between its terminals and the shunt strip itself, the tiny fixed resistance is now much larger, the milliammeter reads much too high, and the current is restricted and gear operation is slower because the delivered voltage has fallen under load.

That shunt is sometimes found in the cabin, on one side or the other, behind the sidewall paneling and against the outside skin, where it gets condensation on it. The maintenance manual should have a definite location of it for that particular airplane.


Dan

First of all it sounds like the "ammeter" was really a loadmeter. Although both measure current, an ammeter is wired between the main bus and the battery and can display negative (discharge) as well as positive (charge) current. A loadmeter is wired between the alternator output and the main bus and only shows current in one direction which is how much current the alternator is delivering. Your POH should identify which you have in the panel (assuming the electrical system hasn't been significantly altered) and the meter face itself usually tells the same story in that a gauge with zero in the center is likely an ammeter and one that has the zero on one end is likely a loadmeter.

In any case I believe the resistance of the shunt would have to increase enough that the "ammeter" would peg under light to moderate loads before you'd see a noticeable drop in bus voltage. And if you had an ammeter you would likely have seen a large discharge (negative current) when the gear was operating. But with a loadmeter the voltage regulator is usually wired to sense the main bus voltage and therefore would increase the alternator output to compensate for any excess drop across the shunt.

Typically the shunt is sized to provide 100 mv (1/10 volt) with a current that goes full scale on the ammeter or loadmeter. If the resistance doubled there would be less than an additional 100 mv drop across the shunt while the indicated current would be double. Thus even if the alternator can't deliver more power the meter is going to peg before the bus voltage drops noticeably due to a high resistance shunt.

 

[Dan Thomas]

First of all it sounds like the "ammeter" was really a loadmeter. Although both measure current, an ammeter is wired between the main bus and the battery and can display negative (discharge) as well as positive (charge) current. A loadmeter is wired between the alternator output and the main bus and only shows current in one direction which is how much current the alternator is delivering. Your POH should identify which you have in the panel (assuming the electrical system hasn't been significantly altered) and the meter face itself usually tells the same story in that a gauge with zero in the center is likely an ammeter and one that has the zero on one end is likely a loadmeter.

In any case I believe the resistance of the shunt would have to increase enough that the "ammeter" would peg under light to moderate loads before you'd see a noticeable drop in bus voltage. And if you had an ammeter you would likely have seen a large discharge (negative current) when the gear was operating. But with a loadmeter the voltage regulator is usually wired to sense the main bus voltage and therefore would increase the alternator output to compensate for any excess drop across the shunt.

Typically the shunt is sized to provide 100 mv (1/10 volt) with a current that goes full scale on the ammeter or loadmeter. If the resistance doubled there would be less than an additional 100 mv drop across the shunt while the indicated current would be double. Thus even if the alternator can't deliver more power the meter is going to peg before the bus voltage drops noticeably due to a high resistance shunt.

So then the question for the OP is what the pegged value is on his loadmeter. If it's 75 amps, he has a problem.

Dan

 

[ARFlyer]

Do you all get charged by the character to post stuff?

If not, what is a recog light? I can translate "stobes", but if there are strobes, what is a "beacon"?

Jim

Just quoting what the aircraft calls them.

Beacon = Tail Red Rotating Beacon
Recog = Recognition Lights ( These are on the wing tips)

 

[NoHeat]

ARFlyer, does your Arrow have an engine monitor that stores data? If so, maybe you can download it and view the entire history of the amps.

 

[weirdjim]

Just quoting what the aircraft calls them.

Beacon = Tail Red Rotating Beacon

Ah, what the FAR calls an "anticollision light" (91.209)

Recog = Recognition Lights ( These are on the wing tips)

Ah, what the FAR calls "position lights" (same section)

Jim

 

[ARFlyer]

ARFlyer, does your Arrow have an engine monitor that stores data? If so, maybe you can download it and view the entire history of the amps.

Unfortantely the aircraft does not. The aircraft flew all weekend and I haven't heard about any issues. I guess it was a fluke.