GPS drop out (Alternator)

[AJ85WA]

Hi All

Just wanted to post an issue I have been having for some time and see if anybody can give me some tips.

I Have an MGL EFIS system and for a long time now on the ground only my GPS will drop out and come back alive on repeat.

I then started playing around with the idea that interference from some device is causing the drop outs and very long story short I have managed to pin down the issue to my alternator. **only during idle RPM**

After my aircraft idles for about 5min @ (800rpm) I will consistently get these "GPS not available...... GPS available" notifications. If I switch off the alternator the problem goes away instantly.

I have got a capacitor wired in the alternator system already, just wondering what other modifications I can make to try and remove the interruptions/interference.

I have a backup battery to the efis running as well so voltage drop is not the issue.

Thoughts?

Thanks in advance
AJ

[flightlogic]

Is the capacitor a "noise filter" by design? Lone Star sells a nice filter that works for some.

[AJ85WA]

Hi

Thanks for the reply
I currently have a 10000uF 50V cap sold by aeroelectric.com



Thanks for the noise filter recommendation.

[amerkarim]

Hi

I would check your grounding to the alternator and the EFIS, but especially the alternator.

Had a similar, and other problems with a G3X setup. Gauges were all out and things kept switching on and off randomly. Turned out it was an insuffient alternator ground contact. The alternator mounting brackets were all powder coated so the ground contact was not good. Adding a large size extra battery cable from the alternator casing mounting bolts to the engine block sorted out all the issues.

Just something to check. Good luck

Best Amer

[snopercod]

Where is your GPS antenna located and does it have a good ground plane?

[lr172]

Do you have an external voltage regulator? If so, I would suggest replacing it. At idle, the VR pushes a lot of volts on the field, as it keeps asking for more and more. The alternators typically produce only a small output at idle and can't keep up with demand.

You can load up a lot of power drains at higher RPMs to get the Alternator to pump a lot of amps. If this does not create GPS problems, it would seem less likely the alternator (excluding the VR) or a ground is the problem, though it could be a bad ground to the VR.

Larry

[AJ85WA]

Hi Guys

Thanks for the replies.

I have tried 2 different GPS antenna's and also moved the location of them to several different spots, still received the problem during idle only.

My alternator in internally regulated. (DENSO)

I will confirm its grounding first, possibly even run a ground strap to it for testing to see if it solves the problem.