help troubleshooting an electrical gremlin

[DennisRhodes]

Have a RV9 with Dynon 180 and 500 hrs, been flying since 2008, Began to get spikes on the current indicator on the Dynon EMS. Normal amps with VFR equip running is 10 to 12 been that way since first flight and normally remains fairly constant. Last couple flights the current has been eradic and spiked up to +23, +30 then back to normal. Ive had the alarm set down low so at +18 it went into alarm.. The Dynon voltage remains fairly constant during these events. As wired The Dynon shunt indicates all current from alt to battery and instruments. Style "B" in installation.

I replaced the alternator last weekend thinking the internal regulator may be at fault. flew today with the new Denso 45 amp auto self regulated alt and no change to the eradic amp spikes. Turned off all electrical one at a time EXCEPT the Plasma II + and still experienced spikes but smaller. Turned off everything again except Plasma and still saw gremlin. Also checked the Shunt and sensing voltage wire to Dynon for any looseness found none.

Leaves nothing in but alt,wiring,main 50amp alt bkr., EI, 680 battery. and Dynon180. anyone ever seen this before, Any comments appreciated. STILL LOOKING///???

[vic syracuse]

If the battery is original I would consider changing it. Could be a bad cell.

Vic

[Mike S]

Dont forget to look at the grounds.

[GalinHdz]

If you are reading the amps using a shunt, check the connections to the small signal wires again. If one of them is even a little loose, you will get a high current indication while everything else seems fine. It happened to me.

[DennisRhodes]

Odyssey 680 is about 2yrs old. But think i will use a tester to check it under load. And did check the signal shunt connections ,seem to be ok but maybe need to remove and retighten maybe also a second crimp on the lug.

[Mich48041]

Although shunt failures are rare, if it develops higher resistance, the millivolt drop across the shunt will increase and cause the ammeter to show increased current, even though the current has not actually increased.

[Jesse]

Check for good continuity from the signal wires to the D-180 and also try crimping on new ring terminals to them where hey attach to the shunt. A loose wire in a crimp connector could cause this, as was mentioned. Hop down to X35 and we can pop a new shunt in also to test that.

[lr172]

I would be looking at all wiring and connections related to the shunt (both primary and secondary) or possibly the shunt itself. It is not common to see erratic current without some voltage fluctuation.

Larry

[DennisRhodes]

Yes I also agree that the voltage doesn't reflect the current erratic spikes. Does anyone know what millavolt signal indication would be on that 60amp shunt with approx 20 amps across.it? Any method of measuring that to verify if it is In fact an amp spike or just false indication. Only other item is that Dynon internal battery indicates that it is low. I believe the always hot connection to that was cut some time ago as per Dynon. Not suprised by that.

[Mich48041]

I think that most shunts used in home-built aircraft drop 50 millivolts at full current. So 20/60 x 0.050 volts = 0.016666 volts or 17 millivolts
A high impedance digital meter should be used so as not to affect the circuit.
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Quote from Wikipedia:

most shunts are designed to drop 50 mV, 75 mV or 100 mV when operating at their full rated current and most ammeters consist of a shunt and a voltmeter with full-scale deflections of 50, 75, or 100 mV. All shunts have a derating factor for continuous use, 66% being the most common. Continuous use is a run time of 2+ minutes, at which point the derating factor must be applied.