DennisRhodes

DennisRhodes

Well Known Member
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///???
 
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.
:cool:
 
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.
 
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.
 
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.
 
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
 
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.
 
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.
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THanks Joe. That might be the way to rule out the Dynon and signal wire . I can get to the shunt andadd some test leads. OR at least provide some direction to troubleshoot the issue.
 
DennisRhodes said:
THanks Joe. That might be the way to rule out the Dynon and signal wire . I can get to the shunt andadd some test leads. OR at least provide some direction to troubleshoot the issue.
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Testing here is difficult, as it is intermittent and you can't easily be near the components with the engine running. I would replace the terminals on all wires terminating at the shunt and check each of 4 wires for resistance, with special attention on the low voltage wires. It would be best to disturb the wires/bundles while you do this. You want end to end continuity, so take the DB-25 off the D120 to do this. Then I would do another flight and re-evaluate. If you suspect the shunt, that should be easy to test by rigging an experiment (disconnect power lines, run one new wire to a battery and another to some 12v load and measure the millivolts on the to sense leads - it will either be stable or fluctuate, confirming a diagnosis). However, I suspect resistance or frrayed wire in the low voltage lines.

Larry
 
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Mich48041 said:
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:
Click to expand...

Actually most aviation shunts built in the US drop 1mv per amp. So a 40A shunt drops 40mv, a 60A shunt drops 60mv etc. Check the Mfg documentation to be sure.

You can read the 60A / 60mv rating engraved on the Dynon shunt

:cool:
 
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Thanks Galin, Not sure I would have been able to read the value on mine and would have never thought to look at the part on Dynon. It`s buried up high in the forward most bay on a slider canopy model. Maybe several days before I get back in the trouble shooting mode but will post when I get some solution. Thanks for all the ideas. I`m betting on the signal wire thing with maybe a bad crimp. DRR
 
I realize you stated your alternator is internally regulated, so this may not apply.

But, I had this symptom years ago with an externally regulated alternator and, three replacement regulators later, I was able to find the field wire grounded to a wire guide in which the grommet had worn through.

So the field wire was occasionally grounding to the engine, which would show up as amperage going to max for a few seconds at a time.

Perhaps your internal regulator has a similar issue....just a thought.
 
DennisRhodes said:
Thanks Galin, Not sure I would have been able to read the value on mine and would have never thought to look at the part on Dynon. It`s buried up high in the forward most bay on a slider canopy model. Maybe several days before I get back in the trouble shooting mode but will post when I get some solution. Thanks for all the ideas. I`m betting on the signal wire thing with maybe a bad crimp. DRR
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Check that you have a 60 or 40 Amp shunt actually installed. Both will work just fine with any ammeter calibrated for 1mv per amp. Just that the 40A shunt can't handle above that value without possibly exceeding the rated accuracy and giving wrong current values.
:cool:
 
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You state nothing else in the system. I assume you do not have a solid state "fuse" panel?
 
lr172 said:
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
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I would go one further and say it is physically impossible to have current double with no voltage drop. I am sure you have an indication issue. You need to cross check somehow. I would run some additional wires from the shunt to a digital volt meter and go flying and see if the readings make sense. Or put a clamp type current meter on the main wire going to the bus. Whatever, just get an independent measurement.
 
Yes Scott that's exactly where I'm headed with my next TS efforts. And I also agree on the statement about impossible to have amps double without a voltage drop. NO solid state breakers but do have a 50 amp main on the alternator.
 
Reading post #1 again:
Turned off all electrical one at a time EXCEPT the Plasma II + and still experienced spikes but smaller.
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Since the magnitude of the current fluctuations varies directly with the load, that indicates to me that the shunt is at fault.
 
Got back onto trouble shooting the gremlin today and believe we've found the problem. I had installed the 1 amp fuse as recommended by Dynon on the low voltage (mv signal wires). I had forgot about the additional connections on that signal wire. They were on the sub panel vertical face and accessible from the co pilot side panel take out. With that was introduced four crimp on spade lugs. Of the four two failed the "tug" test. Looks like the lugs were for a larger size wire. Replaced the two and recrimped the other two. Run up confirmed that the wires were reinstalled on the correct terminal and i believe next flight will confirm the signal wire gremlin will be gone.
 
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DennisRhodes said:
Yes Scott that's exactly where I'm headed with my next TS efforts. And I also agree on the statement about impossible to have amps double without a voltage drop. NO solid state breakers but do have a 50 amp main on the alternator.
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It's a completely different issue, but what current capacity alternator do you have? Some of the older alts supplied by Van were 35A, but just about everything in common use these days is at least 45A; typically 60A. If you have a newer alternator, that 50A protection is a nuisance trip hiding in the woodwork. (Also implied is a check of the alternator B lead wire gauge.)

FWIW,

Charlie
 
The new one that went on last weekend was a 45 amp. Usual load less landing lite is 12 maybe up to 15 amps. The landing light pushes loads upward of 25 amps. I can say I have never used it except to see if it work!
 
Flight today indicated all back to normal. Evidently was bad indication on mv signal wire across the shunt due to bad crimp connections. THANKs to all who responded. BY the way I now have a spare 45 amp alt on the shelf if anyone needs one to get home .
 
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