500-hr Gremlins

[JordanGrant]

I just clicked over 500 hours in my RV-6 (since first flight in 2006). It's been a pretty reliable airplane over the years, but I've recently started having some gremlins creep in that I need to chase down. I post this here in case others may have some advice or ideas, and so that future RV owners can compare experiences.

#1. Ammeter spiking to 45 amps for no apparent reason. Flying along, minding my own business, with a total load of about 20 amps, when my amperage audio alarm goes off and the amperage has rapidly spiked up to 45 or so. Turn off alternator, drops to 25. Turn off battery for 15 seconds and re-boot engine monitor, and back to normal. Weird.
Configuration:
-AFS engine monitor (ACS 2002 / AFS-2500 model)
-AFS Hall Effect current sensor, mounted on firewall sensing alternator output prior to battery buss
-40-amp B&C alternator
-B&C LR3-14 external regulator

#2. #1 CHT indicating 150 deg cooler than the rest. Don't think that's really possible. Reset calibration in engine monitor for the 32 deg F point. Interestingly, the AFS-2500 only has one calibration for CHT, i.e. you can't calibrate each sensor individually, as far as I can figure. It seemed to get back to a more normal indication - currently keeping an eye on it.

#3. Right side fuel tank sensor intermittently going to zero. Probably a short of some type (hopefully not inside the tank), or possibly a failing fuel tank sensor module. Swapped sensor modules to try and isolate if its the module or a connection. Test flight of 30 minutes had no problem this time - keeping an eye on it.
Configuration:
-Van's capacitive fuel tank sensor setup
-AFS supplied modules converting capacitance to voltage

#4. Electric Turn/Slip indicator doesn't spin up anymore. Might be done for.

I'll try to remember to post the problem/solutions if and when I find them.

Cheers,

 

[kbelue]

Do you have an APRS transmitter? I've seen them cause gauges to periodically spike when they transmit.....

 

[rzbill]

#1. Ammeter spiking to 45 amps for no apparent reason.

Jordan, I fixed this on my plane recently but mine was already rampantly bad, not the one-off you saw (my debugging was easier). Changed regulator, no joy. Talked to B&C to ask about three phase ripple but they steered me towards checking the voltage sensing line that goes from the main bus to the regulator. In your LR3, there is a dedicated sense line that is separate from the field switch control. On mine, the field switch is the voltage sense line (it is a Ford VR-166). So, I bypassed my field switch wiring harness and made a jumper that went direct from main bus to the regulator, started the engine and all was instantly good. Removed jumper, installed ohmmeter on my harness (measured 4 ohms harness vs .1 ohm for the jumper), started jiggling the harness and sure enough, I found a loose Fast-On spade connector. I squeezed the grippy bits and slid it back onto the spade nice and tight. Viola'. Voltage and current meters stable again.

For your convenience, here is a link to the LR3 trouble guide:

LR3 Troubleshooting

Good luck. I'm confident you have a connection quality problem like I did. I hope you can find it at this early stage of intermitant failure..

 

[JordanGrant]

Thanks, Bill! I'll definitely check that sense line closely - it's the best lead I have so far, for sure.

 

[Elwell81]

I'm no expert in aircraft engines but it would seem like the current sensing is the problem. If you shut off the alternator shouldn't it read zero current, or negative for that matter? When it drops from 45 to 25 amps, that is a difference of 20 amps, which is the original current you where reading. It appears that the sensor is showing 25 amps of "false" current. Just an observation, take it for what it's worth.

 

[rzbill]

Yeah Elwell, I saw that when rereading everything after my post. The 25 amp "no alternator" indication may invalidate what I suggested.

 

[JordanGrant]

Current Sensor Issues

Update to current sensor: Today, I verified that the current sensor will still show erratic and erroneous indications when the alternator field is off and the alternator is not putting out voltage. When I turn the alternator field off and/or pull the alternator field circuit breaker, the buss voltage drops from about 13.5-14.0 (alternator output) to battery-level voltage (11.5-12.0), so I'm confident the alternator is not generating power in that condition. The current sensor is located on the output line from the alternator, so it should show 0 amps, but the AFS2500 is showing a high load, erratically displaying up to 100 Amps or dropping off the screen altogether. Of course, if it were really putting out over 60 amps, my firewall fuse would be blowing out, so I'm now fairly sure this is a sensor problem of some sort. Next step is to isolate which of the following is probably happening:
1) Current sensor module (Hall Effect sensor) is failing? Rob Hickman has mentioned on his support forum that he knows of no known Hall Effect sensor failures.
2) Cable from current sensor to AFS-2500 computer is shorting out or otherwise failing?
3) Cable connection to AFS-2500 is failing?

Continuing to troubleshoot...