wireweinie
FOUNDER
Palmer, AK
Whatever
Web
Web
Volts constant but amps will fall off and run negative
- Thread starter aeroaddict
- Start date
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Sounds to me like you guys are talking past each other. Since I don't know enough to have an opinion, I'll say that maybe the Dynon instrument is sensitive enough that a loose wire wandering around in electro-magneto-space confuses the instrument. Maybe modern solid state computer-moderated instrumentation can behave differently than old-school galvanometers? Dunno, just tossing that out.
sjohnson
FRIEND
Boise, ID
Do I understand correctly that this is a digital measurement and representation of the current, rather than a traditional analog ammeter? If so, some AC on the what-is-supposed-to-be DC can sometimes fool the measurement circuit, which provides an erroneous reading. I've seen this on non-vehicle projects. Here, maybe the failing alternator diode put a relatively large AC signal on the output.
Steve
Steve
The magic boxes are a different animal. Sometimes you have to call em up and listen. When Dynon says a wire can cause a negative reading, I listen. And it makes sense with my experience. I failed to tighten both ends of a DB25 on my old Dynon and one end started edging out. Broke two of my egt circuits and they just wandered around, they did not go to 0. You have to tell it what you want with a closed circuit. Open means huh? I'm not an expert on instrument amps, but they are designed for a specific job, they are not general purpose voltmeters. (there is the equivalent of an amp behind each input). This is a 100% analog thing, in the analog scaling and smoothing, before the A to D conversion.
Amp means amplifier, instrumentation amplifier.
Amp means amplifier, instrumentation amplifier.
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aeroaddict
MEMBER
Boise ID area
I now have 6 hours of social distancing without electrical issues. Beautiful morning flight down along the Snake river today.
Thanks for all the help guys.
Thanks for all the help guys.
Diamonddave
MEMBER
Can you tell me what you found wrong in this? Were the small wires on the wrong posts? Thanks
wireweinie
FOUNDER
Palmer, AK
Are you having similar issues? Can you descibe them?
Web
Web
Diamonddave
MEMBER
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?
wireweinie
FOUNDER
Palmer, AK
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.
Web
Web
Diamonddave
MEMBER
Thanks Web. That’s what I was thinking too. But I thought I put them on the correct screws as shown but I’ll double check. Shows GEA11A22 goes on same side of shunt as P03A10BK.
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frequent_flyer
Registered User
Arizona, USA
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)
Diamonddave
MEMBER
ok thanks but what do you mean if “both” reversed? The 2 GEA wires? There are the 2 big power wires going to either side of the shunt and then GEA11A22 is suppose to go on the small screw on the same side of the shunt as the P03A10BK wire and the GEA10A22 on the other side with the P09A10BK. The GEA11 wire goes to the “low” input pin and the GEA10 to the “hi” pin. By “both” do you mean if both of the wires are reversed on the shunt?
frequent_flyer
Registered User
Arizona, USA
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.
Diamonddave
MEMBER
Ah ok. Got it. Thanks
wireweinie
FOUNDER
Palmer, AK
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?
Web
Web
frequent_flyer
Registered User
Arizona, USA
Standard CubCrafters fit is that the shunt measures battery current. I found this inadequate and added a Hall effect sensor on the alternator output. I'm tempted to discard the battery current shunt and use a Hall effect sensor there too.
Diamonddave
MEMBER
Battery to shunt (via 40 amp blade fuse). Shunt to main bus. Then the 2 (hi and lo) going to the GEA24 efis. See schematics in post above. Thanks
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Diamonddave
MEMBER
Well I guess it’s not the Small wires. First flight ……. Turn on master and ignition switch and it goes to -3 amps. Start engine and avionics switch on and it goes down to -7. Flying and it continues to go to -12 amps and stays there. Obviously nothing coming in from the alt. The volts continually decrease until the IBBS backup battery automatically kicked in.
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 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?
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frequent_flyer
Registered User
Arizona, USA
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?
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Diamonddave
MEMBER
oops. Yes it was amps not volts I was replying to. I have edited it. I also added that the main volts did decrease continually actually to the point of the IBBS battery automatically kicking in, so definitely not getting charge from alt. Thanks.
ok so the current can actually flow both ways. Thanks for the suggestions on how to check. I will check it out today.
ok so the current can actually flow both ways. Thanks for the suggestions on how to check. I will check it out today.
wireweinie
FOUNDER
Palmer, AK
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.
Web
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.
Web
Diamonddave
MEMBER
Ok. Thanks again for the info. I first did the tests freqflyer suggested and everything tested good as he suggested.
i just did what you suggested and here is the results. Looks like a problem with the “L” with the alt cb pulled.
Master on
Both “field” and “alt” CBs in:
-IGN = 12.5 v
- L = 12.5 v
FIELD CB PULLED
- IGN = 12.5 v
- L. = 1.2 v
ALT ONLY PULLED
- IGN = 12.5 v
- L. = 12.5 v
so ign always has volts? L always has volts except when field pulled and then it drops to 1.2?
i just did what you suggested and here is the results. Looks like a problem with the “L” with the alt cb pulled.
Master on
Both “field” and “alt” CBs in:
-IGN = 12.5 v
- L = 12.5 v
FIELD CB PULLED
- IGN = 12.5 v
- L. = 1.2 v
ALT ONLY PULLED
- IGN = 12.5 v
- L. = 12.5 v
so ign always has volts? L always has volts except when field pulled and then it drops to 1.2?
Diamonddave
MEMBER
Maybe I misinterpreted the “ign” you say to test. Here is the schematic showing the alt. The “l” has the A09C20O wire going into it. The other part of the L is just a loop wire. In the tests I did, I thought the IGN you referred to was the big wire bolted on the alternator. What I refer to as “L” in my last post referred to this wire plugged into the “L” on the alt and not the big wire?
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wireweinie
FOUNDER
Palmer, AK
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.
Web
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.
Web
wireweinie
FOUNDER
Palmer, AK
'B' terminal is the large wire. The 'IGN' terminal is the smaller wire.
Web
Web
Diamonddave
MEMBER
Thanks Web.
i redid it and pretty much the same result.
ALL CBs IN
-IGN = 12.4
- B. = 12.5
FIELD CB OUT
- IGN = 12.4
- B. = 12.5
ALT CB OUT
- IGN = 12.4
- B. = 12.5
so no change with any cb pulled.
Traced back wiring through OV relay to master and all is correct.
Strange.
i redid it and pretty much the same result.
ALL CBs IN
-IGN = 12.4
- B. = 12.5
FIELD CB OUT
- IGN = 12.4
- B. = 12.5
ALT CB OUT
- IGN = 12.4
- B. = 12.5
so no change with any cb pulled.
Traced back wiring through OV relay to master and all is correct.
Strange.
Diamonddave
MEMBER
Pardon my ignorance. This is my weak point on this build.....
when you are saying to test the “IGN” spade on the alternator, that is with that wire that goes into it.....unplugged right and I’m just testing it on the spade on the alternator or is they with the wire plugged in somehow? I tested these with only the “B” main wire connected and no others connected to the alternator.
when you are saying to test the “IGN” spade on the alternator, that is with that wire that goes into it.....unplugged right and I’m just testing it on the spade on the alternator or is they with the wire plugged in somehow? I tested these with only the “B” main wire connected and no others connected to the alternator.
wireweinie
FOUNDER
Palmer, AK
I'd test the wires two ways. First, with all wires connected at the alternator. Then unplug the 'IGN' wire and disconnect the 'B' wire. See if there is a change.
Web
Web
