Detail steps to reproduce the issue encountered:
Just fire up a C172 classic and play around with the power settings and the alternator.
I was able to identify which variable this is using: āELECTRICAL BATTERY LOADā in Instrument_Subtemplates.xml. I am not convinced that this is just an inversion of the correct behaviour, since low rpm is correct at this point.
There is nothing wrong if ELECTRICAL BATTERY LOAD is the variable.
That variable would measure the amount of power the battery is putting out.
In the first instance, with the alternator off, there would be a huge load on the battery, and that is what the gauge shows.
With the alternator on, load on the battery is reversed, it is getting power.
So with high RPM it is getting a lot of power, as it would, and this shows as a large negative load.
At low RPM it would not get so much power from the alternator, so the negative load would be small, and the gage actually does show that, slightly below zero.
In a car, if it has an Ammeter, it indicates how much the battery is Charging ā¦ ie + = alternator is putting current INTO the battery, ā ie Alternator OUTPUT
In the C172, the whole concept is different ā¦ The Ammeter is measuring how much current is being drawn FROM the battery.
So Its backwards, from a car ā¦
Think of it as Battery Discharge amount ā the more +ve it is, the more it is flattening your battery.
Use the Starter motor, and it maxes out POSITIVE.,
So, when the Plane is running, you do NOT want to see it go Positive, you want to see it stay negative.
Difficulty to remember, as one is so use to the Ammeter in a car.
Maybe Think of it as AMMETER WARNING ā¦ the more Positive it reads, the HIGHER the WARNING. ie it is measuring battery LOAD
is BAD
is GOOD
EDIT 1/6/2020
DISREGARD all above. The issue is the c172 Ammeter Gauge, most likely in a reversed animation.
> + is GOOD Charging > - is BAD Discharging ā eventaully leading to a flat battery, and being unable to start the Plane.
Never really though too much about it before, but strange that the C172 Ammeter does not have a GREEN band, from 0 to say -45A
Then, Ammeter āin the Greenā is a good, working state.
Anything +ve is eventually going end up with a flat battery
Anything more negative than -45A probably indicates the battery has an OVERCHAGE issue, which will also, over time, cause issues.
Finally, the best source to solve this problem is the 172SP POH. Here are some interesting excerpts:
INSUFFICIENT RATE OF CHARGE:
If the overvoltage sensor should shut down the alternator and trip the alternator circuit breaker (ALT FLO), or if the alternator output is low, a discharge rate will be shown on the ammeter followed by illumination of the low voltage annunciator (VOLTS). Since this may be a ānuisanceā trip out, an attempt should be made to reactivate the alternator system.
STARTING ENGINE (With External Power)
e. Engine RPM ā INCREASE to approximately 1500 RPM (as engine RPM increases, alternator output should increase to meet the system load requirements).
f. Ammeter and Low Voltage Annunciator ā CHECK (the ammeter should indicate in the positive direction, showing that the alternator is supplying current and the Low Voltage Annunciator (VOL TS) should not be lighted).
AMMETER:
The ammeter/vacuum gage is located on the lower left side of the instrument panel. It indicates the amount of current, in amperes, from the alternator to the battery or from the battery to the airplane
electrical system. When the engine is operating and the master switch is turned on, the ammeter indicates the charging rate applied to the battery. In the event the alternator is not functioning or the
electrical load exceeds the output of the alternator, the ammeter indicates the battery discharge rate.
Iām not disagreeing, all Iāve said is that given that variable, the gage probably reads correct.
It does indicate the load.
Obviously, that is not the correct way this gage should operate.
It needs to take a lot more into account than that one amperage reading, as you have shown above.
That, as you have discovered, is probably the source of the problem.
Precisely. I was about to reply to your other (edited) post. Your line of thought seems correct for the āLoadmeterā as far as I could verify. I do agree that the POH is not very clear about charging being positive or negative though.
There are some clues in the manual though that points for āchargingā been positive and ādischargingā being negative.
e. Engine RPM ā INCREASE to approximately 1500 RPM (as engine RPM increases, alternator output should increase to meet the system load requirements).
f. Ammeter and Low Voltage Annunciator ā CHECK (the ammeter should indicate in the positive direction, showing that the alternator is supplying current and the Low Voltage Annunciator (VOLTS) should not be lighted).
The ammeter in the steam 172 being reversed is a known bug. Charging should read in the positive range, and not the negative.
Sadly, that plane is one of those that are locked down. If you had access to the xml source, it would likely be as simple as an errant ā-ā sign in the gauge code. But those files are encrypted for the upgrade package planes.
I experimented other variables that showed inverted āmore correctā values, but Sometimes the low rpm also got inverted (showing charging). I think they should investigate it since it maybe that they quite donāt have the correct variable in this case yet.
It should only affect another aircraft if that aircraft used that gage.
I would be more concerned with other systems in the 172 classic that may also use that reading in their programming.
The instrument is indeed reversed. Iāve flown a real C172SP.
And the values are quite unrealistic as well.
When alternator is off, it should read slight negative value indicating a discharge. When on, it should read either 0 or a slight positive, depending on engine RPM. The needle skyrocketing either full up or down is completely wrong, there is never such a huge charge/discharge, even with all the electrical systems running at once.
Also, the alternator needs at least about 1000 engine RPM to actually be able to charge the battery at all.
Itās a standard procedure while on the ground, that before you do anything at all (be it taxi, checklists, engine runupā¦) you first increase RPM to at least 1000, and only then you operate switches, radios, flapsā¦
Here it is for your convenience:
Simvar: ELECTRICAL BATTERY LOAD
File: Instrument_Subtemplates.xml
Additionally, this is the path so you donāt have to spend too much time looking for it: Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Official\OneStore\fs-base-aircraft-common\ModelBehaviorDefs\Asobo\Common\Subtemplates\Instrument_Subtemplates.xml
Until Asobo fixes it, it seems like it is quite easy to fix with a simple MOD, (just for the C172 Steam)
I suspect the animation in the C172 for the Ammeter is backwards ā¦ because it works correctly for the C150.
So, all that appears to be needed is a Mod, for the C172 Classic, that has a modified Instrument_Subtemplates.xml in it ( and none of the other files or folders on that
āModelBehaviorDefs\Asobo\Common\Subtemplatesā path needed.
The edit needed to the Instrument_Subtemplates.xml is to swap the MIN & MAX values in the Ammeter_SubTemplate
I did this, and now my C172 Steam gauge, has a correct way round Ammeter,
ie Goes negative when you use the Starter Motor etc etc etc
Not really a big deal ā¦ just annoying, but since its not a big deal, who know how long Asobo will take to fix it.
Iām surprised it hasnāt been mentioned yet in this threadā¦ but literally every aircraft Iāve played with in this sim has its ammeter readings reversedā¦ whether or not its an analog gauge or a readout on the Garmin displays.
Itās not just a C172 bug. The accuracy of what the value should read at whatever load is another discussion in and of itself for each aircraft, but Asobo seems to have consistently modeled a negative value to mean āChargingā across the board and that needs to be fixed.
