Erratic amp reading with steady volt.

[rogersmart]

I finished my RV8 in 2011 and it now has 350 hours. About 50 hours ago, I started getting intermittent erratic amp readings with amps jumping very high 35-50-60. This went away after about 1 minute. Since then about every 3rd flight this will happen again with a duration of 2-3 minutes. When this exists the volts remain steady at 14.4. If I turn the field off in the Alternator, the amps are still very high and erratic although a bit lower and the volts go down to 12.5 and slowly decrease. When this erratic behavior does not exist, which is about 95% of the time, I still get 14.4 volts a steady 3-10 amps as you would expect, when de-energizing the field get the 12.5 and decreasing and a negative 4-6 amps as you would expect. I have not been able to recreate the issue on the ground. I am not seeing any other instrument irregularities. The Voltage in the normal state and the erratic state appears correct and what you would expect so I don’t think I am getting output spikes from the alternator. Also if any load was creating these indicated amperage spikes I think I would see short changes in Voltage just as you do when turning on landing lights.

I have checked my EMS grounds, particularly pin 3 and connections to the shunt and see nothing. Before going further, I wanted to post this to see if someone else has had this issue and resolved it.

 

[Garrett]

You might have an intermittent connection (caused during vibration) in the wires/connections that go between the EMS and the shunt.

 

[airguy]

You might have an intermittent connection (caused during vibration) in the wires/connections that go between the EMS and the shunt.

Agreed, that sounds like the most likely culprit - a bad sense wire connection either at the shunt itself or the EMS connection.

 

[Raymo]

I saw something similar on a Cessna that turned out to be a very loose connection to the battery that was hidden by shrink wrap covering the wire into the ring terminal. The regulator detected low amps in the battery, telling the alternator to provide more but it wasn't getting to the battery.

Not saying this is the problem but is an example of what others are saying to look for.

 

[rogersmart]

Thanks Ray,
My previous inspection concentrated on the shunt and the sense wires. I finally got back out to the airport and pulled the cowling and found the large wire from the shunt was loose where the it connects to the energized lug of the master. So basically loose at the battery just as you said. Tightened, put back together and went and flew. Amps steady now. Thanks.