DeafSoundGuy
Well-known member
Can anyone tell me how the headlights are powered up? HV battery or the 12 v battery?
Thanks
Thanks
DeafSoundGuy said:Can anyone tell me how the headlights are powered up? HV battery or the 12 v battery?
Thanks
WoodlandHills said:I thought that the higher the voltage, the lower the amperage needed for a given task. And that amps were what killed you, not volts, was I wrong?
WoodlandHills said:I thought that the higher the voltage, the lower the amperage needed for a given task. And that amps were what killed you, not volts, was I wrong?
In practice, it's probably not possible to eliminate the 12 v. battery because the many control systems that boot when the Start/Stop button is pressed depend on the 12 v. battery. The DC-DC converter likely also depends on the 12 v. battery, so it doesn't provide 12 v. until it boots from the 12 v. battery. Kind of a chicken and egg problem.fdl1409 said:The 12V battery is tiny in an i3, only 20 Ah AFAIK, much smaller than in an ICE. It would in principle be possible to eliminate the 12V battery altogether, but this is needed for some tasks like backup for emergency lighting in case of a 360V failure.
fdl1409 said:Those peripheral systems like the lights work on 12V. However, they get their juice not from the battery, but from a DC-DC converter. 360V DC from the battery is converted to 12V and from there used directly. The 12V battery is tiny in an i3, only 20 Ah AFAIK, much smaller than in an ICE. It would in principle be possible to eliminate the 12V battery altogether, but this is needed for some tasks like backup for emergency lighting in case of a 360V failure.
Frank
alohart said:In practice, it's probably not possible to eliminate the 12 v. battery because the many control systems that boot when the Start/Stop button is pressed depend on the 12 v. battery. The DC-DC converter likely also depends on the 12 v. battery, so it doesn't provide 12 v. until it boots from the 12 v. battery. Kind of a chicken and egg problem.fdl1409 said:The 12V battery is tiny in an i3, only 20 Ah AFAIK, much smaller than in an ICE. It would in principle be possible to eliminate the 12V battery altogether, but this is needed for some tasks like backup for emergency lighting in case of a 360V failure.
If true, then the connection from high voltage circuit through the DC-DC converter to the 12 v. circuit must be always exist which I doubt. If it works like my Honda hybrid, a 12 v. relay closes when the Start/Stop button is pressed thus completing the DC-DC converter connection between the high and low voltage circuits. So without a 12 v. battery, this relay could not close and the 12 v. battery could not be charged by the traction battery.wayne325 said:The converter requires nothing on the low voltage side to operate.
I would be surprised if this is true. Without a wiring diagram, I'm guessing that the 12 v. battery is always connected to the 12 v. circuit as in all cars. The DC-DC converter serves the same function as an alternator in a normal car. I.e., it is feeding the 12 v. circuit only when the 12 v. battery's voltage is a bit low or the 12 v. load is high. Running the DC-DC converter continuously when the car is in the Ready state isn't the most efficient way to operate.fdl1409 said:I think however that far more than 90% of 12V power comes directly from the DC-DC without touching the 12V battery.
The main reason that the 12 v. battery can be smaller in an EV is that the large current draw of an electric starter motor, especially in cold weather, doesn't exist.fdl1409 said:Because of that it can be reduced to minimum size in an EV.
fdl1409 said:The 12V battery is usually just sitting there and doing nothing. All the 12V power comes from the DC-DC. The battery is only a backup for certain conditions like failure of the high voltage battery or DC-DC. I agree it is also important when the car is switched off or while systems are booting up. When the 360V has been to 0%SOC it is needed to start charging. It may also balance voltage when there are short bursts of peak power. I think however that far more than 90% of 12V power comes directly from the DC-DC without touching the 12V battery. Because of that it can be reduced to minimum size in an EV.
Frank
alohart said:I would be surprised if this is true. Without a wiring diagram, I'm guessing that the 12 v. battery is always connected to the 12 v. circuit as in all cars. The DC-DC converter serves the same function as an alternator in a normal car. I.e., it is feeding the 12 v. circuit only when the 12 v. battery's voltage is a bit low or the 12 v. load is high. Running the DC-DC converter continuously when the car is in the Ready state isn't the most efficient way to operate.fdl1409 said:I think however that far more than 90% of 12V power comes directly from the DC-DC without touching the 12V battery.
Monitoring the voltage at the 12 v. accessory receptacle would clarify the DC-DC converter's operation. If the voltage is always >14 while the car is in the Ready state, then the DC-DC converter is running continuously. But if the voltage jumps between 14.x and 12.x, then the DC-DC converter is being turned on and off as necessary.
The main reason that the 12 v. battery can be smaller in an EV is that the large current draw of an electric starter motor, especially in cold weather, doesn't exist.fdl1409 said:Because of that it can be reduced to minimum size in an EV.
The main reason that the 12 v. battery can be smaller in an EV is that the large current draw of an electric starter motor, especially in cold weather, doesn't exist.[/quote]fdl1409 said:Because of that it can be reduced to minimum size in an EV.
DeafSoundGuy said:The main reason that the 12 v. battery can be smaller in an EV is that the large current draw of an electric starter motor, especially in cold weather, doesn't exist.fdl1409 said:Because of that it can be reduced to minimum size in an EV.
Of course, but since none of us has the source code for this software, we can't describe its behavior exactly, so I was stating only its likely behavior. For the past 12 years, I've driven a car with a DC-DC converter between its high and low voltage circuits. Its DC-DC converter performs the functionality of a conventional alternator (i.e., keeps the 12 v. battery charged under various 12 v. loads) but whose behavior is almost certainly more complex than that of an alternator, voltage regulator, electronic load detector, etc., just as it is in the i3.wayne325 said:The converter is far more complicated than "being turned on and off as necessary" or operating like an ICE car with a simple regulator circuit. There's a bunch of SW running in a controller in there, it'll be far more complex than you've described.
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