Need help with electrical troubleshooting, please...

[XOverZero]

RV9A has been in the hangar for a time while working on high CHT cures. We got good results on last week's test flight, but true to the doctrine of TAS (There's Always Something), a new issue arrived - intermittent high current draw of roughly 9 amps. About the only thing we know so far is that it does not follow the flap activation cycles.

Can anyone propose a troubleshooting sequence that makes good sense? We have too little practical experience dealing with electrons that have gone off the reservation.

[DRMA]

Difficult to tell from your symptoms what it might be, but to narrow it down I would suggest first that it must be one of your circuits with a breaker/fuse of at least a 9 amp rating. If the high current draw occurs while you are on the ground, DON'T DO THIS IN FLIGHT!!!, suggest you pull one breaker/fuse at a time that is rated at >9 amps until the current draw stops. If you find the breaker/fuse that opens the problem circuit, the label on that circuit should give you an idea of where to look for the problem.

I'm assuming you have breakers/fuses instead of a VPX box. If you have a VPX, you should be able to look at the currents shown by the VPX to find the problem circuit.

Hope this helps a bit.

[maniago]

What Dave said above is solid advice - process of elimination. That said, you cant have but a few 10 amp circuits I'd imagine - I can only think of one in mine in excess of 10 and thats for seat heaters.

Maybe what you can expound upon a bit is how you know its 9 amps and just how intermittent in duration it is - ie just a quick excursion or lasts for a longer period. Does it happen both when the engine is running and not? If its only when the engine is running, I'd be leaning to looking for a rubbing or burned wire ie vibration caused. If not when the engine is running, then I'd lean towards a some electrical component thats going south...which one would be determined best by the circuit involved......I will say tho that with electricity, especially intermittants, strange things abound and despite what Ive wrote above, it could easily be the opposite. No choice but to work thru the possibilities, but start with simple first - just have a look around at all your wires and their routing. You might just see something that doesnt look right.

I would be quite hesitant to fly it until you have ascertained and eliminated the problem.
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FWIW, I went and looked at my breakers, and pitot heat is another that goes over 10A......

[Mich48041]

Check all of the electrical connections on the ammeter shunt to be sure that they are tight. While you are at it, might as well check electrical connections in the charging system also.

[XOverZero]

Thanks so far for those comments. First order will be to check that the instrument itself isn't bonkers. It's an old RMI unit.
Rest assured we will not be flying until this issue is resolved.

[rv7charlie]

That's always a good idea.

Do you have any data recording? Any idea what the voltage was doing when you saw the higher current readings? Was it spiking up, or down?