85KW Battery Pack discharge capability - Technical musings...

85KW Battery Pack discharge capability - Technical musings...

I'm very curious how TM can have the twin motor Model X Performance version, produce 50% more torque. It was discussed here before that the MS P85 is basically maxed out on the discharge rate of the battery pack. Meaning, with the larger inverter, the limiting factor to power and torque is not the drive-train, but the battery pack capacity and discharge. Now, comes the MX with twin motors, and the Performance version is claimed to produce 50% more torque. This to me mean either bigger pack, or Tesla found a way to get more juice out of the existing pack, but either way something could be very much different in the pack design.
Can '50% more torque' mean 600+ lbs-ft directed to the wheels under WOT?
This opens another huge possibility. A twin motor MS super performance version, with higher gear ratio in the two differential units will give both higher top end speed, and faster acceleration.

logicalthinker | January 27, 2014

I think a lot of us will be thrilled if there turns out to be a bigger pack. But I'm not getting my hopes up.

Dramsey | January 27, 2014

It could be that they're using the same physical (size) battery pack, but that it's wired differently; perhaps as two semi-independent 42kWh packs.

Just guessing here, of course. I have no idea at all how the current pack is wired.

Chuck Lusin | January 27, 2014

@Dramsey sure it's not two 40kWh packs :)

AoneOne | January 27, 2014

Based on my very limited knowledge of motors, I'd guess that the low-speed torque is limited by the current available from the inverters, not the power available from the batteries. A separate inverter for the front motor would provide extra torque at low speeds and could be limited to avoid overloading the battery at higher speed.

jdesmo | January 27, 2014

It's kind of the opposite. Considering existing 85KW pack and drive train, i.e not increasing electric power supply in the X: In the P85, the inverter is large enough so that the motor achievable output is only limited by the capacity and discharge rate of the pack, and internal impedance. At zero rpm and low speed, the P85 motor can produce it's max torque up to about 5000 rpm. Torque is a direct function of the current draw into the electric motor. At higher speed, the motor (any electric motor) starts to produce back emf, which cuts down on the current draw and thus torque output. So by definition, the battery pack supplies less and less current as the speed builds up. The Battery pack can only give what it can give, no matter how many motors and inverters are connected. At low /zero speed, the current draw can be shared and produced torque can be split to any varying degree between the two motors, but total combined can not exceed the max. that would be available from the rear motor of the P85, since we know it already can absorb by itself all available discharge from the pack in the S Performance model. This makes the X behave similar to ICE AWD from stop and in low speeds. It's at higher speed, when the draw from the motor(s) is reduced due to the back emf, that more juice is available to the second motor from the pack, and total torque to the wheels can be increased. But having more torque to the wheels at high speed is not very practical or useful.