Not a builder but very mechanical. I've owned my RV9 for about 1-1/2 years. Been through it top to bottom with my A&P and on my own. One on going issue that I have yet to resolve. Voltage has always read in the green no matter whether a short flight in the pattern or a long haul of a few hours. However, the amprage has always indicated a negative number and when the mike key is engaged the amperage will show a momentary drop. Any thoughts or suggestions?
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Low Amperage Reading
- Thread starter Dunntexas
- Start date
Ammeter fluctuations
Mark,
You said, when the mike key is engaged the amperage will show a momentary drop. Any thoughts or suggestions?
This is a common issue. Mine does the same. Not very scientific but I understand that it's due to spurious electrons floating around behind the panel with the gauges not being of the highest quality. I'm sure others will provide a better explanation.
Jim 7A
Mark,
You said, when the mike key is engaged the amperage will show a momentary drop. Any thoughts or suggestions?
This is a common issue. Mine does the same. Not very scientific but I understand that it's due to spurious electrons floating around behind the panel with the gauges not being of the highest quality. I'm sure others will provide a better explanation.
Jim 7A
A shunt style amp meter is basically a volt meter reading the voltage drop across a very low resistance (that is what the shunt is) point in the power cable.
If the wires are connected backwards the meter will act the same as a volt meter connected backwards.... it will give a correct reading but the polarity will be reversed.
Swap the two wire connections at the shunt and it will probably read normal, except for the transmit jump... that can be caused by shunt wires being adjacent to coax cable, etc. (the voltage read by the meter is very low values and can easily be effect by stray EMI, etc.)
If the wires are connected backwards the meter will act the same as a volt meter connected backwards.... it will give a correct reading but the polarity will be reversed.
Swap the two wire connections at the shunt and it will probably read normal, except for the transmit jump... that can be caused by shunt wires being adjacent to coax cable, etc. (the voltage read by the meter is very low values and can easily be effect by stray EMI, etc.)
rapid_ascent
Well Known Member
Depending on where the shunt is installed in your system the negative reading might be correct for reversed sense leads. It all has to do with how your systems is wired, where the shunt is in your circuit and what you are really trying to measure.
By drop did you mean the value got more negative? That would technically actually mean the magnitude got bigger so to me that wouldn't be dropping. A detail I admit but it makes a difference. If the magnitude actually dropped then that would indicate something else is wrong. I'll assume you meant it got more negative. The reversing of the leads will just change the sign of the current. If the magnitude seems about right its probably just that they are connected reversed.
So getting back to my original statement. Do you want to measure alternator output current or load on the battery. If you want to see load on the battery then you may see negative currents when you are charging the battery and little or no electrical load. Check to see where the shunt is installed so you have a good picture of what should be happening. It may not be wired the way that you would like it to operate.
By drop did you mean the value got more negative? That would technically actually mean the magnitude got bigger so to me that wouldn't be dropping. A detail I admit but it makes a difference. If the magnitude actually dropped then that would indicate something else is wrong. I'll assume you meant it got more negative. The reversing of the leads will just change the sign of the current. If the magnitude seems about right its probably just that they are connected reversed.
So getting back to my original statement. Do you want to measure alternator output current or load on the battery. If you want to see load on the battery then you may see negative currents when you are charging the battery and little or no electrical load. Check to see where the shunt is installed so you have a good picture of what should be happening. It may not be wired the way that you would like it to operate.
The way most RV's are wired, the AMP meter will show a positive charge regardless of the configuration, as long as the alternator is operating.
So it is highly likely that the wires are reversed.
I agree that there are a lot of different configuration possibilities. Unfortunately, with a detailed tutorial a lot of people don't understand what you are talking about or it starts a big debate on which is correct (almost as bad as primer wars....).
But I do agree that people should learn how their system is configured so that they no what the instrument is telling them (actually, once you understand the different configurations that are possible, it is easy to tell what any particular airplanes configuration is just by what the instrument says in flight).
Thank you!
Thank you all for your replies. The reversed leads would make sense as several have explained. The amp meter always shows a negative reading somewhere below zero. When the mike is keyed it will show a more negative reading of several amps. I will start tracing things out and try reversing leads. The collective knowledge of this group is ever impressive.
Thank you all for your replies. The reversed leads would make sense as several have explained. The amp meter always shows a negative reading somewhere below zero. When the mike is keyed it will show a more negative reading of several amps. I will start tracing things out and try reversing leads. The collective knowledge of this group is ever impressive.
Jesse
Well Known Member
As others have said, there are really 3 different places to put the shunt (3 correct places) in the schematic.
As in the Dynon manual, one is between the battery and the aircraft load and alternator. Basically, this is giving a +60 to -60 Amp reading. When the engine is off or the alternator is off with the plane running, this should show a negative reading, showing that the battery is seeing a drain. When the engine and alternator are on, this will initially show a high positive reading as the battery charges back up, and will ultimately show very close to zero during a flight as the alternator will be putting out what the aircraft load is using, with the battery fully charged and basically just sitting there and stabilizing everything. The drawback in this setup is that you don't know what your bus is using (you can calculate, but you don't really know), which makes it harder to load shed if/when your alternator fails. I know that Wheeling Strobes (3 lights) uses 6-7A, the three Nav lights use around 6A, and so on. If I turn on the Nav logs and one is burned out, this amperage setup won't tell me anything.
The second place is between the alternator and the aircraft load and battery. It will only give you a reading of 0 to 60A. It will just read what the alternator is putting out. If the voltage is good, then the alternator output is equal to he aircraft load, as in the first example when it reads close to zero. If the load exceeds what the alternator can put out, then the voltage will show lower than normal as the battery makes up for the difference. If you ever get a negative reading in this setup, then you are wired backwards. As you increase aircraft load, the negative reading should become increasingly negative. If you turn on lights and pitot heat, it should become increasingly negative. If this is the case, switch the two sense wires and it should flip. The benefit of this amperage format is that it tells you what your alternator has to put out to keep your battery charged, so if a Nav lift is burned out, it will only show and increase of 4A instead of 6A when I turn the Nav lights on.
The third place is between the aircraft load and the battery and alternator. This is not as common in my experience, although it really gives you a more accurate and stable reading of what you are using because the battery is not buffering the readings, as in the second example above. This will definitely help you determine if your Nav lights, strobe lights or landing lights are not working, because amperage will be showing exactly what you are using. This will also show negative is it is wired backwards, although showing negative is acceptable if you want to think of it as a high amperage reading being bad in the case of an alternator failure.
With examples 2 and 3, voltage is more importante to indicate the healt of your electrical/charging system than in example 1. In fact, I personally would MUCH rather have a good voltage reading than an amperage reading at all.
What had not been mentioned is the possibility that you have a Hall Effect sensor. If so, it is a ring and has a wire passing through it instead of being a shunt that has a wire connected to each end. A Hall Wffect sensor is less accurate, but can be installed in any of the above ways. If it is reading backwards, you just need to disconnect the end of the cable it is reading, and flip the ring so it is pointing the other direction to get a positive reading.
As for the mic key creating a different reading, it is likely the fact that the radio is drawing a LOT more power when transmitting, at least a couple of Amps. However, especially if your antenna cable is low quality, one of your ends has a bad crimp, or you antenna is not well grounded, it can cause a lot of electrical "noise", making some reading read kind of crazy. I have more than once seen oil temperature readings go crazy when transmitting.
THis should cover the possibilities of what you are seeing.
As in the Dynon manual, one is between the battery and the aircraft load and alternator. Basically, this is giving a +60 to -60 Amp reading. When the engine is off or the alternator is off with the plane running, this should show a negative reading, showing that the battery is seeing a drain. When the engine and alternator are on, this will initially show a high positive reading as the battery charges back up, and will ultimately show very close to zero during a flight as the alternator will be putting out what the aircraft load is using, with the battery fully charged and basically just sitting there and stabilizing everything. The drawback in this setup is that you don't know what your bus is using (you can calculate, but you don't really know), which makes it harder to load shed if/when your alternator fails. I know that Wheeling Strobes (3 lights) uses 6-7A, the three Nav lights use around 6A, and so on. If I turn on the Nav logs and one is burned out, this amperage setup won't tell me anything.
The second place is between the alternator and the aircraft load and battery. It will only give you a reading of 0 to 60A. It will just read what the alternator is putting out. If the voltage is good, then the alternator output is equal to he aircraft load, as in the first example when it reads close to zero. If the load exceeds what the alternator can put out, then the voltage will show lower than normal as the battery makes up for the difference. If you ever get a negative reading in this setup, then you are wired backwards. As you increase aircraft load, the negative reading should become increasingly negative. If you turn on lights and pitot heat, it should become increasingly negative. If this is the case, switch the two sense wires and it should flip. The benefit of this amperage format is that it tells you what your alternator has to put out to keep your battery charged, so if a Nav lift is burned out, it will only show and increase of 4A instead of 6A when I turn the Nav lights on.
The third place is between the aircraft load and the battery and alternator. This is not as common in my experience, although it really gives you a more accurate and stable reading of what you are using because the battery is not buffering the readings, as in the second example above. This will definitely help you determine if your Nav lights, strobe lights or landing lights are not working, because amperage will be showing exactly what you are using. This will also show negative is it is wired backwards, although showing negative is acceptable if you want to think of it as a high amperage reading being bad in the case of an alternator failure.
With examples 2 and 3, voltage is more importante to indicate the healt of your electrical/charging system than in example 1. In fact, I personally would MUCH rather have a good voltage reading than an amperage reading at all.
What had not been mentioned is the possibility that you have a Hall Effect sensor. If so, it is a ring and has a wire passing through it instead of being a shunt that has a wire connected to each end. A Hall Wffect sensor is less accurate, but can be installed in any of the above ways. If it is reading backwards, you just need to disconnect the end of the cable it is reading, and flip the ring so it is pointing the other direction to get a positive reading.
As for the mic key creating a different reading, it is likely the fact that the radio is drawing a LOT more power when transmitting, at least a couple of Amps. However, especially if your antenna cable is low quality, one of your ends has a bad crimp, or you antenna is not well grounded, it can cause a lot of electrical "noise", making some reading read kind of crazy. I have more than once seen oil temperature readings go crazy when transmitting.
THis should cover the possibilities of what you are seeing.
Excellent write-up Jesse, and good point about the possiblity of a hall effect vs a shunt, but I disagree with your statement about configuration 1.
It is actually an excellent configuration for allowing you to evaluate load shedding and is the one I recommend to builders.
If we assume that the only reason we would likely ever be concerned with what the total and individual device loads are is when the alternator has failed, then this configuration will allow us to see the total load on the battery and the amount of load reduction as we turn devices off. This makes it very easy reduce the overall load to a value that is within the limits of the amp hour rating of our battery.
I do agree with your comment about the volt meters value. It is a good indicator of the general health of the alternator. As long as the voltage is correct, it indicates that the alternator output is able to meet the needs of the system. That is why I always recommend that builders install the measuring device (shunt, etc.) per your example 1 or 3... so that after an alternator failure they can at least determine what the total load is they have on the battery and then make adjustments as needed. The value on the volt meter will tell them whether the alternator has actually failed... no need for the amp meter to do that.
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Voltage Question
Scott (or other experts),
Could you elaborate (please) on using the voltmeter to determine alternator function?
I have both an ammeter and voltmeter and a primary and backup alternator.
When on the primary (60 amp) alternator, my volts are over 14 and after start-up amps eventually end up back at 0 to +1 (I believe I'm wired method #1 in Jesse's post)
When I switch over to the backup alternator (B&C vacuum pad mount) the amperage goes negative, slowly climbs back up to nearly a -1/zero discharge rate, but the voltage stays in the mid-high 12's...12.5 to 12.7 volts.
Is my B/U alternator working correctly based on these readings? Would seem to be, but I'm wondering why the bus voltage never makes it back above 13-14 volts as when it's on the primary.
Many Thanks and Merry Christmas!
Scott (or other experts),
Could you elaborate (please) on using the voltmeter to determine alternator function?
I have both an ammeter and voltmeter and a primary and backup alternator.
When on the primary (60 amp) alternator, my volts are over 14 and after start-up amps eventually end up back at 0 to +1 (I believe I'm wired method #1 in Jesse's post)
When I switch over to the backup alternator (B&C vacuum pad mount) the amperage goes negative, slowly climbs back up to nearly a -1/zero discharge rate, but the voltage stays in the mid-high 12's...12.5 to 12.7 volts.
Is my B/U alternator working correctly based on these readings? Would seem to be, but I'm wondering why the bus voltage never makes it back above 13-14 volts as when it's on the primary.
Many Thanks and Merry Christmas!
Carl Froehlich
Well Known Member
B&C backup alternator
You backup alternator is working correctly. When you turn off your primary alternator, the battery voltage takes a few seconds to drift down to the backup alternator output voltage. This is why you see amperage going negative and then drifting up until it stablizes.
Your backup alternator output voltage is fine at 12.5 to 12.7 vdc. If desired you can adjust the backup alternator output voltage using the pot on its regulator. Recommend not having higher than 13vdc. The automatic aspect of the backup alternator requires a lower output voltage than the primary alternator.
Carl
You backup alternator is working correctly. When you turn off your primary alternator, the battery voltage takes a few seconds to drift down to the backup alternator output voltage. This is why you see amperage going negative and then drifting up until it stablizes.
Your backup alternator output voltage is fine at 12.5 to 12.7 vdc. If desired you can adjust the backup alternator output voltage using the pot on its regulator. Recommend not having higher than 13vdc. The automatic aspect of the backup alternator requires a lower output voltage than the primary alternator.
Carl
I admit that I don't have much experience with aircraft that have dual alternators but this seems off to me.
I would be interested in hearing about the automatic aspect of a back up alternator needing to be at a lower voltage.
Some small aircraft use the B&C as their primary alternator. Does that mean the purchase a different model that is set for a higher voltage?
If a back up alternator is properly supplying the current needs of the electrical system (after failure of the primary alternator) I think it should be able to maintain a nominal buss voltage to properly charge the battery (14 - 14.2 V).
If it does not, I would think it is either faulty or the load on the system is higher than what the output of the backup alternator is.
Since I think the B&C is rated for a max. output of 20 amps, if you exceed that load the buss voltage would be pulled down closer to what the battery voltage is.
Rob, I suggest you test your back up system with a reduced load and see what the buss voltage is. If the voltage is still low I recommend you give B&C a call.
Roy Thoma
Well Known Member
B&C Backup Regulator operation
The install manual for the B&C SB1B-14 (standby regulator), page 5 at http://www.bandc.aero/pdfs/SB1B-14_Installation_Manual.pdf
says "If the bus voltage falls below 13.0 volts for any reason, such as a primary alternator or primary regulator failure, the SB1B-14 will energize the standby alternator" and goes on to say "Charging voltage for the SB1B-14 has been pre-set at 13.0 volts."
I'd suggest verifying operation of equipment in your plane with just the standby alternator supplying power. I had a fuse blow when my SL-30 was transmitting
and I was running off the standby alternator / regulator. Lower voltage = more current for a given power. Increased the fuse size and it worked fine (and the wire was still conservatively protected).
Regards,
The install manual for the B&C SB1B-14 (standby regulator), page 5 at http://www.bandc.aero/pdfs/SB1B-14_Installation_Manual.pdf
says "If the bus voltage falls below 13.0 volts for any reason, such as a primary alternator or primary regulator failure, the SB1B-14 will energize the standby alternator" and goes on to say "Charging voltage for the SB1B-14 has been pre-set at 13.0 volts."
I'd suggest verifying operation of equipment in your plane with just the standby alternator supplying power. I had a fuse blow when my SL-30 was transmitting
and I was running off the standby alternator / regulator. Lower voltage = more current for a given power. Increased the fuse size and it worked fine (and the wire was still conservatively protected).
Regards,
Thanks.... Good to know.
So it sounds like if operating on just the stand-by and the buss voltage is only 12.5 V, you probably need to shed a bit more load.
Electrical loads will always draw current from the source with the highest voltage. If two alternators are online, one set at 14.5 volts and one set at 13.5 volts, only the one set at the higher voltage will be supplying current. The alternator set at a lower voltage will not be producing any current.
The voltage of a fully charged lead-acid battery is close to 13 volts. If the main alternator fails and the standby alternator is putting out 13 volts, the battery will not be charging. But the battery will not be discharging either unless the load is so heavy that the standby alternator can not supply the heavy current. Then the voltage will drop as some of the current comes from the battery and some from the standby alternator.
The voltage of a fully charged lead-acid battery is close to 13 volts. If the main alternator fails and the standby alternator is putting out 13 volts, the battery will not be charging. But the battery will not be discharging either unless the load is so heavy that the standby alternator can not supply the heavy current. Then the voltage will drop as some of the current comes from the battery and some from the standby alternator.
Thanks all for the info.
My "engine off" static load on the ammeter shows a discharge of -11 to -12 amps.
That's less than the rated output of the standby alternator...So the question remains...With that load, is a reading of 12.7 vdc when running on the standby OK? Or low?
Obviously, I can call B&C on Monday, but was wondering what others similarly equipped are seeing.
Rob
Edit: I have an "either/or' setup on my backup alternator, no automatic switching. The thougbt is the SkyView will alert me to a low voltage situation, I then manually select the standby.
My "engine off" static load on the ammeter shows a discharge of -11 to -12 amps.
That's less than the rated output of the standby alternator...So the question remains...With that load, is a reading of 12.7 vdc when running on the standby OK? Or low?
Obviously, I can call B&C on Monday, but was wondering what others similarly equipped are seeing.
Rob
Edit: I have an "either/or' setup on my backup alternator, no automatic switching. The thougbt is the SkyView will alert me to a low voltage situation, I then manually select the standby.
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Yes and yes. 12.7 volts is low. It will not recharge a discharged battery. 12.7 volts is also OK as long as it does not keep going down. The purpose of a standby alternator is to allow a flight to continue to the planned destination after the main alternator fails. The aircraft electrical system will operate just fine at 12.7 volts. The battery will not be charging, but it will not be discharged either. The battery will still be available for intermittent loads like radio transmitting and landing light.
All of the above is correct with regards to the standby alternator having a lower voltage output. However, they are adjustable, and so I usually set the main alternator at 14.2 or a little higher in the case of Odyssey batteries (which like 14.5 and will last longer when charged at that voltage). Then I set the standby at 13.7 or thereabouts. It will allow the standby to come on a little sooner but it will also be more than adequate to charge most batteries and allow you to continue on the trip if you happened to break a belt on the main alternator or are in a place that you can't get it fixed.
Just my practice.
Vic
Just my practice.
Vic
