Phantom battery current and weird electrical system behaviour

This has been bugging me since day 1, but i never really bothered looking into it. Im also not sure if this has been covered before.

So, there seems to be magic current battery current coming out of nowhere. I thought there was some weird configuration but ive come to conclusion that its a bug.

A simple explanation of how these simple battery circuits work. These are very basic and everyone should know this from preschool. Here are some basic rules(cases).

  1. When the alternator is off, then the battery provides ship power.

  2. When the alternator is on, then the alternator provides ship power + battery charging.
    If the battery is fully charged then the battery current is 0 and the alternator provides ship power.

  3. When the alternator is on, but the battery is disconnected, then the battery current is 0 and the alternator provides ship power.

  4. When the alternator is on and the engine is off, then the alternator is not providing power and the battery provides ship power.

Using SimVarWatcher (provided in the SDK) you can see the current going in and out, even on planes without G1000s and premium planes.

For my testing i will be using a 172 (JTA) with an alternator that can provide 100A, a battery that does not drop voltage, and the 2nd battery disconnected to make the calculations easier.

  • Case 1: When the alternator is off, then the battery provides ship power.

I have setup the lights etc to draw ~40A.
As you can see here, the alternator is providing 0 Amps, the Battery is providing 40A. Ship must obviously draw 40A

If I were to turn on the alternator, then the alternator should provide the 40A ship current however

  • Case 2: When the alternator is on, then the alternator provides ship power + battery charging…

We can already see something funky going on. Alternator current is now 46A and the battery is charging at 54A. Meaning ship current is negative 8A?

Even if you were to ignore the 54A going into the battery, the ship power has increased from 40A to 46A?

46A (ship current) + 54A (Phantom battery charge) = 100A.
Those are the 100A that the alternator is providing. But the simvar shows the alternator only providing 46A.

What seems to be happening: The Alternator is providing ship power and the rest of the current that the alternator can provide is all being burned into the battery.
Also the 6A current increase out of nowhere. I cant explain this

  • Case 3

Similar to case 3, but again this weird 6A increase on the ship load.

The main bus now seems to be burning the 54A out of nowhere.

  • Case 4

Please ignore the readout on the G1000, this is custom code i have implemented to provide a current current readout on the JTA and Diamonds. Look at SimVarWatcher!

Now we are back to 40A ship current, which is correct. However the alternator is still providing 40A, except that its not. The battery is losing 40A, and the alternator simvar is broken. Eventually the battery will drain and die

So to sum up the problems that i have discovered.

  1. The alternator causes higher current over all
  2. “phantom” current is generated from nowhere and burnt into the battery or main bus
  3. The alternator displays that it is generating current when the engine is off, but actually isnt

I hope this wasnt confusing and that the devs can take a look at this

After thinking about it. The current increase with the alternator turned on, has to do with he voltage increase from 24.4V to 28V.
28 / 24.4 = 1.148
40 x 1.148 = 45.9. The same 45.9A we see.

This isnt unrealistic, current will increase with voltage over a normal resistor. Buuuuttt, this isnt really represented by the lights or screens getting brighter.

Not to mention that electronic devices like the the avionics would actually draw less current as the voltage increases.

These are all minor things though

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Which version of the sim you are using?

an early beta build from march 33rd 2002


Not much to add to this … reply.


im using the current version of the game.

If i was using the beta, then i wouldn’t have posted it here


Here ive set the battery voltage to 28V, identical to the alternator.
As you can see there is no current increase.

Also, a 24V alternator can charge a battery to 28V.

That does not make any sense…

Also, when starting, the alternator is providing all the current, even though it should only generate 100A??

Asobo, pls fix

Ive been going through other aircraft. turns out the DA20 behaves correctly.

Alternator providing ship power and the full charged battery not drawing any current.

Engine off, battery providing ship power

Engine running, alternator providing ship power AND charging the battery slowly

However the DA20 is configured, its correct. Buuuut, because its premium, no way to look at the cfgs :confused:

That’s interesting. (wink, wink, nudge, nudge)

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@MrTommymxr Good findings have you officially logged it also in Zendesk

I found out whats wrong (or whats right)
The new electrical system is the problem. this needs to be redone. The legacy system works fine, however its too basic for most planes, atleast if you wanna do everything nativity

So apparently the existence of a 2nd battery will prevent the plane from being considered “shut down”

I have a 2nd battery hooked up to nothing, and you an hear the sound of the plane being “on”

here ive killed the line for the 2nd battery and no plane noise, just wind noise

ofc other planes like the 172 have a 2nd battery and they dont have this problem.

Perhaps ive configured something wrong, idk.

Here the DA40 with its backup battery. When i turn it on, you can hear the G1000 firing up, but its not. The battery is only hooked up to the attitude indicator and the flood lights (DG aswell, but whatever)

Asobo, pls fix

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A simple 1 line JS mod, can make the battery Simulation so much better, by adding a simulation of the battery “Internal Resistance”

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