Alternator current weirdness?

[nigelspeedy]

I have a Dynon Skyview system with EMS. The ammeter shunt is set up so it measures the alternator output. I also have a Vertical Power VPX Pro. The VPX measures the current flowing through it and then calculates the difference between VPX current used and Alt output and figures any difference must be going to/from the battery. I have a Lithium Ion battery and at rest with no load it has about 13.3 volts. I also use solid state relays that have a quirky property that even when off there is a small voltage (~2.3 volts) on the output side. The alternator is a Plane Power 60A and only has about 50 hours on it. With the engine off, if I turn on the alternator I see about 4 amps on the #1 Alt Vse, although in flight this value alternates in the display between 0 & 1 Amp.

Recently I have started seeing some odd behavior and am having difficulty troubleshooting the culprit (EMS, Alt, Shunt, VPX, me).
It started by seeing a high current output from the alternator before start with the master switch off (I could see it on the Dynon EMS page as I turn them on with the back up battery before start). Clearly the alternator cant put out power if it isn't turning.
In flight once every couple of flight hours I will see the alternator output amps drop from the normal +15 amps to some large negative value ~-45 amps. At this point the alternator is switched on and the battery amps are ~14.3 which is above the normal battery voltage of 13.3 so I figure this means the alternator is actually still producing output current. And how could the alternator draw current through the shunt? If I then turn the alternator off the current displayed goes to zero. If I then turn the alternator back on it goes back to normal for a few hours. The screenshots below show the sequence of the discussion above.

Any tips for troubleshooting would be much appreciated.

Cheers

Nigel

 

[lgabriel]

I'd start with the shunt itself--double check the tightness of every screw on the thing (if I remember right, I had to pull the plastic cover off of mine to ensure the bar itself was secure).

Also make sure your battery lugs are secure. Good luck!

 

[nigelspeedy]

Thanks for the tip Louis, I checked all the alternator connections including the shunt and battery ones as well and all were tight.
Cheers
Nigel

 

[nigelspeedy]

Hey Dynon,

Is there a chance this is an EMS error? Any hints for troubleshooting?

Cheers

Nigel

 

[Dynon]

So we can't really fathom a way that the EMS would misbehave like this in a temporary way. One test you could do is to short both signal wires together on the shunt. Does the current ever misbehave then? If so, you likely have a loose wire upstream.

 

[nigelspeedy]

Thanks for the troubleshooting tip Dynon.

Last night I disconnected the two sense lines from the EMS to each side of the shut, just by taking out the two automotive style inline fuses. With the alternator on the voltage showed 14.3 which is normal. The amps not surprisingly showed 0 the whole flight. I will give it a few more hours like this using the voltage as an indicator of Alternator functioning. If the alternator keeps working I think it may hint at wiring between the shunt and EMS.
Cheers
Nigel