4 ms·

I'm pretty sure the warranty limitation line is to prevent liability. (mostly for people trying to hook up directly to the ~375V battery pack). The 12V battery

I'm pretty sure the warranty limitation line is to prevent liability. (mostly for people trying to hook up directly to the ~375V battery pack). The 12V battery wiring and/or DC/DC charger is probably also not designed to have a continuous ~165+ amp draw for a long period of time. (2000W / 12)

stonkdonk 6y ago
Not to mention the main battery would have to constantly recharge the 12v battery, which is probably bad for both batteries. Going from the high-voltage battery to the 12 volt to the inverter sounds really inefficient too. I usually see people using marine batteries as pc backup power, but only using a couple of hundred watts for an inverter. https://teslatap.com/articles/12-volt-battery-compendium/ https://teslatap.com/articles/12-volt-battery-compendium/ The batteries mentioned here have 40 or 45 Amp-hours, which I believe would be 480 or 540 Watt-hours (amp hours * 12v), which is not enough to run a 2000W inverter for very long. Ideally, there would be circuitry to hook up directly to the main battery safely and efficiently.
- fy20 6y ago
  > Not to mention the main battery would have to constantly recharge the 12v battery, which is probably bad for both batteries. I don't know about a Tesla, but this is how regular ICE cars work. The power from the alternator varies depending on the speed of the engine, so if you are stopped at a red light with your radio, wipers and head lights on, the alternator may not provide enough power. This is why the 12v battery is still connected after the engine has started, not just to charge itself, but effectively as a big capacitor to balance the 12V power supply to the car. As long as the inverter is normally drawing less power than the high voltage to 12V system can supply, it shouldn't damage the 12V battery. This is also why cars with start-stop usually use AGM batteries, as the battery will be run down a lot more while the car is stopped (and the engine isn't running), which would quickly damage a regular lead acid battery.
nkingsy 6y ago
pulling that kind of wattage from a 12v car battery will destroy it in short order, and I’m not sure it can even discharge that fast. Last time our power went out I charged my 48v ebike battery off of my leaf’s 12v, then used that to power a big inverter to run the fridge. Now I have some dedicated solar that can charge the ebike, so no need for shenanigans. Anyone looking to do this, there are challenges, and don’t do it with a battery that isn’t built for serious discharge (mine is 1.7kwh and rated for 3k watt bursts). Most off the shelf ebike batteries will not tolerate that kind of abuse.
- benlivengood 6y ago
  All car batteries will provide over 3KW since they're rated for 300-900 cold-cranking-amps but efficiency and capacity are pretty low at those rates.
  - turtlebits 6y ago
    Most batteries are rated to pull very high amps for a short period of time. Not for hours on end.

stonkdonk 6y ago

Not to mention the main battery would have to constantly recharge the 12v battery, which is probably bad for both batteries. Going from the high-voltage battery to the 12 volt to the inverter sounds really inefficient too. I usually see people using marine batteries as pc backup power, but only using a couple of hundred watts for an inverter. https://teslatap.com/articles/12-volt-battery-compendium/ https://teslatap.com/articles/12-volt-battery-compendium/ The batteries mentioned here have 40 or 45 Amp-hours, which I believe would be 480 or 540 Watt-hours (amp hours * 12v), which is not enough to run a 2000W inverter for very long. Ideally, there would be circuitry to hook up directly to the main battery safely and efficiently.

fy20 6y ago
> Not to mention the main battery would have to constantly recharge the 12v battery, which is probably bad for both batteries. I don't know about a Tesla, but this is how regular ICE cars work. The power from the alternator varies depending on the speed of the engine, so if you are stopped at a red light with your radio, wipers and head lights on, the alternator may not provide enough power. This is why the 12v battery is still connected after the engine has started, not just to charge itself, but effectively as a big capacitor to balance the 12V power supply to the car. As long as the inverter is normally drawing less power than the high voltage to 12V system can supply, it shouldn't damage the 12V battery. This is also why cars with start-stop usually use AGM batteries, as the battery will be run down a lot more while the car is stopped (and the engine isn't running), which would quickly damage a regular lead acid battery.

nkingsy 6y ago

pulling that kind of wattage from a 12v car battery will destroy it in short order, and I’m not sure it can even discharge that fast. Last time our power went out I charged my 48v ebike battery off of my leaf’s 12v, then used that to power a big inverter to run the fridge. Now I have some dedicated solar that can charge the ebike, so no need for shenanigans. Anyone looking to do this, there are challenges, and don’t do it with a battery that isn’t built for serious discharge (mine is 1.7kwh and rated for 3k watt bursts). Most off the shelf ebike batteries will not tolerate that kind of abuse.

benlivengood 6y ago
All car batteries will provide over 3KW since they're rated for 300-900 cold-cranking-amps but efficiency and capacity are pretty low at those rates.
- turtlebits 6y ago
  Most batteries are rated to pull very high amps for a short period of time. Not for hours on end.