I was wondering wether tesla would use both motors for regen.

Would it actually increase or decrease the amount of energy recovered when say taking your foot of the pedal at 50 miles/hour and coming to a stop?

And assuming they would use both motors for regen, could it have an impact on handling when turning? I've seen threads that advise to turn regen to low on icy roads because of the possibility the car loses grip.

Thanks.

Arne

Would it actually increase or decrease the amount of energy recovered when say taking your foot of the pedal at 50 miles/hour and coming to a stop?

And assuming they would use both motors for regen, could it have an impact on handling when turning? I've seen threads that advise to turn regen to low on icy roads because of the possibility the car loses grip.

Thanks.

Arne

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## Comments

Will it also increase the net energy recovery? Will it, under the exact same conditions, recharge the battery more or less compared to a single regen setup?

now with both motors sucking power (converting kinetic energy) they could slow the car down faster - but the amount of energy returned to the battery should remain roughly the same…

I'm sure Tesla is tuning the regeneration so that it's a controlled burn and not very abrupt due to the additional generator coming online…

remember you can not get more energy out of system than you put into it…in fact you can't even get the amount you put in due to loss of conversion and overhead.

dual regen can return _MORE_ power to the battery over a unit of time - i.e. they can charge the batter at 2x the rate of one motor…

but the presence of dual motors does not change the total amount of energy in the system…

so dual motors could slow the car down at a faster rate of deceleration - but they do not in of themselves add more energy back to the battery - they can not because the potential amount of Kinetic energy in the system is no greater than a Model S

so I would assert the Tesla sales representative is wrong - he has to be otherwise the conservation of energy laws of physics would be violated.

dual motors will allow a greater rate of charge (if the tesla software lets them) - i.e. faster deceleration

dual motors will _NOT_ be able to recover more energy other than some minor variation possibly due to regenerating the energy faster due to less loss to rolling resistance or aero-dynamics

example slowing the car down from 60 mph in 2 seconds vs. 3 seconds (dual vs. single regeneration) there may be some gain in that less energy was lost to aerodynamics and rolling resistance in the 1 second difference in the 60 to 0 mph test - but I would be surprised if this was significant in any way…

now the Model X being heavier than a Model S - it has MORE kinetic energy than a Model S at the same speed (60 mph) - but it also took more energy to get the Model X to 60 MPH - nature always balances the books - but you will still only recover X% (where X is less than 100% due to loss) of the energy due to regeneration. So technically you will recover more energy in a Model X - but that is because you used more energy to get it up to speed - and will use more energy again to get it back up to speed…

I would not be surprised if the Model X could recover 80 kw of energy under full regen braking (vs. 60 kw indicated on my model S). But while that is more energy per-second under deceleration (80 vs. 60) - that simply means the energy is being drained from the system quicker -not that there is more energy in the system. i.e. the Model X could slow down faster - but it would hard to say it recovers more energy because it has two motors…

think of a pump moving water into and out of pool - this is the tesla converting electricity to motion - it's adding kinetic energy into the system…

when you are accelerating the pumps/motors are pumping water into the pool to fill it up - the amount of water in the pool equals the amount kinetic energy in the system - this is kilowatts used minus the overhead of aerodynamic/weight/rolling resistances…

when you are decelerating using regenerative braking the pumps are pumping water out of the pool and storing the water back into the battery - minus some conversion overhead - this conversion causes the car to slow down and stores some of the energy back into the battery…

the pumps can not recover more water than they put in…two pumps can empty the pool faster (harder more aggressive deceleration) - this will empty the pool faster (car will slow down more quickly) but two pumps do not change the amount of water in the pool…

having two pumps can empty the pool faster - but they can not change the amount of water in the pool - the amount of water is the pool is related to how much was pumped into the pool when the car was accelerating - minus the overhead of maintaining the speed due to external drag/friction.

the two motors on the Model X could slow the car down faster (up to the limits of traction of the tires and tesla's software settings) but they will not "add" any water to the pool - so they can not recover "more" energy…because the simple fact is there is not more energy in the system.

gotta balance the books…

All irrelevant. The limitation on regen right now is the max current the battery can accept, 60 kW as I recall. That is subject to revision in the new car. If TM wants more regen, it will have it.

Ok so the new car can empty the pool at say 100 kW - there still isn't more energy to be had - it will just capture that energy quicker - but it will not capture more energy...

We're dealing with a fixed budget of kinetic energy..the only difference will be the rate of regen - it can not be the total amount.

So basically dual motor regen could slow down the model x faster compared to a model s, but it will not capture more energy. (Only capture that same energy faster)

Just this, because you have losses in two places now, will it actually recover less energy?

but for the most part I'm getting good enough with my Model S that I never use the brakes under normal circumstances…so if you are already getting the car down to zero using nothing but regen dual motors aren't going to recover more energy…

but yeah I could see more regen capturing more energy as being perceived as improving regen because now even more people won't use the brakes.

of course this is all in theory - right now the 60kw regen is pretty noticeable and I would question how much more you can ramp up the regen before people will prefer a softer impact - i.e. I might be able to regen at 200 kw due to two motors -but the drag/deceleration caused by that much load may be quite abrupt and unacceptable in daily use…so it's also a matter of tuning the software as to what amount of regen is allowed…

also if the current limit is 60 kw due to the batteries ability to accept regen charge - then again two motors doesn't change that particular aspect of the system…

I think dortor's thinking is basically right.

Don't understand 60 kW "current limit", kW is a unit of power not current. Maybe power limit was what was meant. I have a question about that. It's my understanding that the MS circuitry can accept about 120 kW of power from the Superchargers. Is that right? If so, is that the power limit for regen or are there two power limits?

Anyway, if you go from speed x mph to zero, you will have y kinetic energy loss available. Some goes to air and rolling friction. The rest goes to regen. If regen is 80 per cent efficient, that's what's left for the battery. Doesn't seem like 1 or 2 motors will make much of a difference.

The supercharger is straight DC. I believe the motor there for the regen is AC so the 60kW limit maybe in the AC to DC conversion.

do not confuse kW with kWh. The car at 50 mph only has 0.158 Kwh of of kinetic energy. Regenerating at 60 kW will take all of the of kinetic energy (stop the car) in 10.8 seconds. You only get back the 0.158 Kwh minus some system efficiency losses. You get about 0.5 miles more range then if you had stopped using conventional brakes.

As a collateral issue, I was just confused about where 60 kW came from.

But, if you say so...

sorry my response was intended to be to hpjtv's post not your post. I am the one that got confused.