wireweinie
FOUNDER
Palmer, AK
Whatever
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It doesn’t sound like the shunt is the issue, but I’ll share something to be aware of.
If a builder mis-wires the shunt, and attaches the sense wires to the buss(es), the display you are using to indicate both voltage and amps can interpolate that value in strange ways.
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Rest assured, I corrected the issue.
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Transmitted from my FlightPhone on fingers...
Are you having similar issues? Can you descibe them?
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If you have correct voltage on the bus (around 14 volts, positive, with engine running) and the negative amps is a steady reading, then check the two small wires connected to the shunt. They may be flipped. This shouldn't hurt anything but it will give a negative reading instead of a positive reading.
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Yes. New Carbon Cub build. First engine start and taxi and showing -6 to -7 amps at idle. Sounds like perhaps I have the wrong GEA wires on the shunts?
You should see negative current before engine start and positive current after engine start in a normally functioning system. Only if BOTH are reversed do you have a sense wire reversal.
If current is negative before and after engine start then your alternator is not charging the battery. That can be confirmed by checking VOLTS 1 before and after engine start. (I have the same shunt, display, and alternator in my FX-3 but my aircraft is modified to also monitor and record alternator current)
ok thanks but what do you mean if “both” reversed?
Just to verify info: you have the shunt installed on a feed wire from the battery to the bus? OR, do you have the shunt installed on the alternator output wire?
Just to verify info: you have the shunt installed on a feed wire from the battery to the bus? OR, do you have the shunt installed on the alternator output wire?
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Before start and after start current both opposite to expected sense, i.e reversed. Positive current before engine start and negative current after engine start.
In brief - check the current before start. You should see about about -3 A. If it reads + your sense wires are reversed.
Well I guess it’s not the Small wires. First flight ……. Turn on master and ignition switch and it goes to -3 volts. Start engine and avionics switch on and it goes down to -7. Flying and it continues to go to -12 volts and stays there. Obviously nothing coming in from the alt.
i guess I don’t understand the flow from the alternator to the battery to charge it. I see power coming in from the battery onto the shunt. Then shunt to main bus and then distributed to the other buses. The alt wires all go from the alt circuit breaker, voltage regulator, field circuit breaker etc. how does the power go back to the battery and recharge the battery? Does it go backwards?
How do you test the wiring vs the alternator?
I'll start by assuming all the numbers in the first paragraph are amps not volts but I suppose you should confirm that.
Two sources can supply current to Main Bus, the battery and the alternator. If Main Bus voltage is greater than battery voltage then current from Main Bus passes through the shunt to the battery. The battery is charging and the indicated current will be positive. This can only happen if the alternator output voltage exceeds battery voltage.
If the alternator output voltage is lower than Main Bus voltage then the battery will be providing current to Main Bus and the indicated current will be negative.
All a properly functioning alternator needs to provide power is field excitation and rotation. The 40 A alternator used by CubCrafters has an integrated regulator. Check the field terminal is powered at the alternator when master is on. Check for continuity between the alternator output terminal and the 50 A alternator breaker. Check for continuity between the alternator 50 A breaker and Main Bus. If these tests are ok then the alternator or its integrated regulator may be defective.
The GDU SD card log may be helpful. Can you post a link to it?
The bus bar requires power. When the engine is shut down, the bus bar will pull power from the battery, through the master relay, and to the bus bar. Since your shunt is installed in this circuit, it should read negative amps at this time. When the engine is running and turning the alternator, alternator voltage is greater than battery voltage (14.2 volts vs 12 volts). When this occurs, the bus bar will pull it's power from the alternator instead of the battery due to the higher voltage. The path of current flow for the alternator is from the large output terminal, through the output breaker, and to the bus bar. Also occurring at this time is the battery recharge. This happens as the alternator voltage becomes greater than battery voltage causing current flow to reverse and flow back into the battery. At this time amp readings will be positive. The amp readings for a recharging battery will be several amps, depending on the battery and the alternator used, and will taper down to an amp or two after several minutes.
You describe a constant negative current flow and slowly decaying voltage. That tells me that the circuit from the battery to the bus bar should be wired correctly. Therefore you should start troubleshooting at the alternator. Turn on the master switch and check for battery voltag at the 'IGN' and 'L' terminals on the alternator. If you don't have both, check the wiring. If you do have battery voltage on both, make sure that the voltage on the 'IGN' terminal comes on and goes off with the alternator field breaker. Then check that the voltage on the 'L' terminal comes on and goes off with the alternator output breaker.
Let us know what you find.
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'B' terminal is the large wire. The 'IGN' terminal is the smaller wire.
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This is my fault. Instead of checking the 'L' terminal, I should have told you to check the 'B' terminal. Apologies.
But, the voltage on the 'IGN' terminal should be controlled by the field breaker. I'm curious about what would put a voltage on that terminal when the circuit should be powered down. You'll need to sort that out as it could lead to being unable to shut power off to the field in case of an electrical emergency. Check the wires at the overvoltage module as per your diagram above. Maybe disconnect the alternator and check the 'IGN' and 'B' terminals again.
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