n3ckf
Well-known member
So. I've been doing a little reading around about what's called "V2G" (vehicle to grid) applications.
There's a ton of research about "how to use electric cars as buffers for the grid", ie. you charge one during low periods, and if the grid needs power, you discharge them into the grid.
So how would you do that?
Well first, you need to bypass the "onboard charger" in the vehicle straight away. The charger will only take A/C and make it into DC (to charge the batteries) but not the reverse.
What's more, you wouldn't want to carry around additional hardware *in the car* if you're hooking it to your house anyway (your house can hold that itself, and its not going anywhere).
So you need a direct connection to the car battery (ie. a "DC" connection).
Enter ChaDEMO. Thats exactly what it is, a direct connection to your battery with a bunch of control logic to control the external charger that pumps amps *in* to your batteries.
(this is what that cool box that QuickChargePower sells for the Rav4EV does).
What's more we want that fancy control stuff in there, because we don't want your car battery to go flat while you're imitating Grand Coulee Dam in your garage.
There's *another* piece of hardware that a lot of people have that works like the reverse of what the DC charger does though, and thats the Grid Tie Interactive Inverter a lot of people have on their solar power systems.
Example here
Thats a 9000watt Grid Tie inverter (its very close to the one on a friend of mine's house), and it takes up to 21amps of DC power at 300-480volts and converts it to 240Volts A/C and synchronizes it with the Grid.
So what happens if you put these 2 items together?
Hook the batteries in your car, to a grid tie inverter which inverts the DC and turns it into A/C?
(I'm a little worried about the fact that your car's batteries can generate a ridiculous amount of current if they want to, unlike the solar panels on your roof. How do you keep them from vaporizing the inverter by sourcing near-infinite current into it?)
The motor can take 115KW out of the batteries (its rated capacity), that's 156HP and 115KW at 386 volts (the nominal voltage) = 297amps (holy arc-welder man!)
(Ludicrous mode in the Model S apparently uses *1500* amps. Gee wow.)
The cool thing about grid-tie inverters is the MPPT ones will actually track the voltage on the input to generate an "efficient" conversion from the solar panels to the grid (think of it as a big switching power supply). So as the batteries in your car "discharge" this looks just like the sun moving on your solar panels, and the inverter will continuously re-adjust (until the voltage goes below the drop-out point which is around 300V for a 240Volt feed.)
So folks who know more about this stuff than i do, tell me why I die if i try turning my car into a generator
(a little more researchfound this discussion in the spec sheets for a particular kind of grid interactive inverter. Apparently the MPPT circuit in this inverter type effectively raises the input voltage tracking to limit current to the inverter's max capability. (I dont know how it does that exactly) but that would tend to prevent too much battery current from flowing into it).
Slightly more research produces and engineering app note on a 3K solar inverter system
There's a ton of research about "how to use electric cars as buffers for the grid", ie. you charge one during low periods, and if the grid needs power, you discharge them into the grid.
So how would you do that?
Well first, you need to bypass the "onboard charger" in the vehicle straight away. The charger will only take A/C and make it into DC (to charge the batteries) but not the reverse.
What's more, you wouldn't want to carry around additional hardware *in the car* if you're hooking it to your house anyway (your house can hold that itself, and its not going anywhere).
So you need a direct connection to the car battery (ie. a "DC" connection).
Enter ChaDEMO. Thats exactly what it is, a direct connection to your battery with a bunch of control logic to control the external charger that pumps amps *in* to your batteries.
(this is what that cool box that QuickChargePower sells for the Rav4EV does).
What's more we want that fancy control stuff in there, because we don't want your car battery to go flat while you're imitating Grand Coulee Dam in your garage.
There's *another* piece of hardware that a lot of people have that works like the reverse of what the DC charger does though, and thats the Grid Tie Interactive Inverter a lot of people have on their solar power systems.
Example here
Thats a 9000watt Grid Tie inverter (its very close to the one on a friend of mine's house), and it takes up to 21amps of DC power at 300-480volts and converts it to 240Volts A/C and synchronizes it with the Grid.
So what happens if you put these 2 items together?
Hook the batteries in your car, to a grid tie inverter which inverts the DC and turns it into A/C?
(I'm a little worried about the fact that your car's batteries can generate a ridiculous amount of current if they want to, unlike the solar panels on your roof. How do you keep them from vaporizing the inverter by sourcing near-infinite current into it?)
The motor can take 115KW out of the batteries (its rated capacity), that's 156HP and 115KW at 386 volts (the nominal voltage) = 297amps (holy arc-welder man!)
(Ludicrous mode in the Model S apparently uses *1500* amps. Gee wow.)
The cool thing about grid-tie inverters is the MPPT ones will actually track the voltage on the input to generate an "efficient" conversion from the solar panels to the grid (think of it as a big switching power supply). So as the batteries in your car "discharge" this looks just like the sun moving on your solar panels, and the inverter will continuously re-adjust (until the voltage goes below the drop-out point which is around 300V for a 240Volt feed.)
So folks who know more about this stuff than i do, tell me why I die if i try turning my car into a generator
(a little more researchfound this discussion in the spec sheets for a particular kind of grid interactive inverter. Apparently the MPPT circuit in this inverter type effectively raises the input voltage tracking to limit current to the inverter's max capability. (I dont know how it does that exactly) but that would tend to prevent too much battery current from flowing into it).
Slightly more research produces and engineering app note on a 3K solar inverter system