Is there something going on with my voltage regulator?

[bradp]

This was something that I had never thought about in much depth and that Chris brought up on the J speed thread.  

Bus voltage is running between 13.6 and 14. 

Takeoff:  Bus voltage is between 13.8 and 14 with the ammeter showing a slight positive charging to a zero position needle.  

Cruise/Descent: Once setup in cruise I'm showing between 13.5 and 13.8 always with a slight negative needle on the ammeter indicating a possible slight discharge.  

Link from the original thread showing pictures of voltages and ammeter needle position: 

New pictures from flight this weekend indicating positive ammeter needle (sorry about the glare) after takeoff and 13.9V to cruise with 13.8 V and a negative ammeter needle deflection.  

Whats going on here?  Voltage regulator, battery master switch contact, alternator field?  I'm trying to wrap my head around the ammeter needle position ... Id think it should be at zero or charging slightly during normal operations.  It's been like this for years which makes me think the ammeter might be off slightly?

Thanks 

brad 

 

 

[mooniac15u]

What does it look like with the master switch on but without the alternator running?

[bradp]

I'll take a picture with that condition this weekend (next time I'll likely fly). 

[INA201]

I vote ammeter is off based on your experience.  Battery would eventually run down if it were accurate. My voltage is usually showing 13.7 to 13.8.  Amperage is higher right after startup as it is recharging the battery after starting the engine then goes down as the battery gets back up to full charge.  Turn on the pitot heat and your landing light and watch the needle,  it should deflect to the right as more amperage is being used while the voltage should stay close to the same as long as the engine is running.

[Piloto]

I think your system is working perfectly right. There would be minor voltage variations depending on the bus load and where the voltmeter is connected to.

José

[Andy95W]

I will bet that if you clean the contacts to your ammeter and the shunt that those wires are connected to you will start showing a positive charge.

The ammeter itself is just a very sensitive voltmeter that is basically measuring the voltage drop across a known resistance (the shunt).  If the resistance is different from what it is supposed to be, the ammeter will read incorrectly.

[ArtVandelay]

I think you're ammeter gauge is off.

Try pulling CBs, it would have to be a big amp draw to overcome the alternator.

2 possible items would be Landing lights and a gear motor (gear or flaps), pull those CBs to check, if a limit switch failed the motor may continue to run.

[Guest]

If your buss voltage is above in that range, the battery can not be discharging.  There is something wrong with the ammeter system. Start with the simple, cleaning connections on the shunt and ammeter first.

Clarence

[N201MKTurbo]

Where does the needle sit with the master off? That will be the zero position. Is the needle sticking? have you tried tapping on it?

As long as the buss voltage is above the voltage with the engine off, the alternator is charging the battery. If you see the voltage get much below 13.6 I would start to get concerned. If it gets below 12.6 your alternator is not working.