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New Roadster Goodies for 2014
- Thread starter hjr
- Start date
Is this news, or just a referring to the Model S high powered wall charger? If something new, would a Roadster be able to use with an adapter since it sounds like these are AC instead of DC?
http://green.autoblog.com/2014/09/0...-speed-non-supercharger-network/#aol-comments
http://green.autoblog.com/2014/09/0...-speed-non-supercharger-network/#aol-comments
Fluke, that is nothing new, it is Tesla's program to offer free HPWCs to destinations like hotels and motels or really any business if the business pays the install cost. The program was started last year.
Mitrovic
Member
What about the "C" rate of the new batteries? Anyone with a guess? With a bigger C rate, will the acceleration get better?
dhrivnak
Active Member
JRP3
Hyperactive Member
The larger pack size would allow higher current draw even at the same C rate, but if the PEM and/or other components are the limiting factor then it probably can't be utilized. Though with less voltage sag in the larger pack peak motor torque might move up to a bit higher RPM.
JRP3, while I understand the cost of replacing a Roadster PEM is very high, the physical size of the unit is not that large and the technology of the electronic components used is now 6 to 8 years old. The PEM for Model S surely uses improved components and design and parts used are being purchased in much greater volume. It would seem to me that when 400 mile pack is offered, an option could be offered to replace old PEM with newer, better, cheaper one. If the extra cost was not too great, I'd think it would be attractive as it would ensure the PEM would not likely fail for many years after the pack/PEM swap. Does this seem possible to you?
Jaff
Active Member
Bob, I think it is possible and will happen...but not from Tesla. I'd be willing to bet that there will be an after market "tuner" shop / shops sanctioned by Tesla to perform such customization for interested Roadster owners...
JRP3
Hyperactive Member
I agree on a possible after market solution, with or without Tesla's blessing. Anyone take measurements on a Model S drive unit for a possible swap?
I don't think the ability of the battery to source more current will improve acceleration (unless there is voltage sag). A drive for an AC induction motor maximizes the torque by maintaining a constant V (voltage) / f (frequency) ratio. The induction motor can generate constant torque at a given frequency until it can no longer increase the Voltage. At this point, it goes into a constant power mode and the torque decreases proportional to 1/f (or 1 / speed).
If you look at the torque curve for the Roadster, you get a constant torque until about 5k RPMs. After that, the torque falls off proportional to 1/f. So, unless the new battery is a higher voltage (which seems unlikely), it won't move the knee in the torque curve.
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I believe that Model S drivetrain is smaller than the Roadster drivetrain and that it would be possible to squish it in.
If you look at the torque curve for the Roadster, you get a constant torque until about 5k RPMs. After that, the torque falls off proportional to 1/f. So, unless the new battery is a higher voltage (which seems unlikely), it won't move the knee in the torque curve.
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I believe that Model S drivetrain is smaller than the Roadster drivetrain and that it would be possible to squish it in.
JRP3
Hyperactive Member
Under load the pack voltage does sag, a larger pack at the same current is putting out a lower C rate, so there would be less voltage sag. So the larger pack will have an effectively higher operating voltage under load.
I'm not sure the S drive train can be smaller since the inverter is housed on the other side of the motor, taking up room, where the Roadster inverter is mounted up in the car. Plus I thought the S motor was a little larger as well, but I could be mistaken.
I'm not sure the S drive train can be smaller since the inverter is housed on the other side of the motor, taking up room, where the Roadster inverter is mounted up in the car. Plus I thought the S motor was a little larger as well, but I could be mistaken.
The inverters in the Roadster and Model S are completely different shapes. The Roadster is a rectangular box while the Model S is a cylinder. The diameter of the cylinder is about twice the depth of the box, so you can't just squeeze it in. However, the volume of the Model S inverter may well be less than the volume of the Roadster PEM.
I'm a bit surprised the debate about this is at such a low level. Pictures of both drive trains are google search away. Data is out there.
The easiest way would be for one to take complete Model S rear assembly and fit it into a roadster - replacing suspension arms, halfshafts, reduction gearbox and motor with model S one. One would need to find a way to mount suitable rear shocks.
Roadsters rear track is 1499mm and MS's rear track is 1699mm so some addition cutting or/and shorter suspension arms would be necessary.
Original PEM would also go away, one would need to fit new PEM/motor liquid cooling into Roadsters liquid cooling circuits.
And mount smaller wheels
The easiest way would be for one to take complete Model S rear assembly and fit it into a roadster - replacing suspension arms, halfshafts, reduction gearbox and motor with model S one. One would need to find a way to mount suitable rear shocks.
Roadsters rear track is 1499mm and MS's rear track is 1699mm so some addition cutting or/and shorter suspension arms would be necessary.
Original PEM would also go away, one would need to fit new PEM/motor liquid cooling into Roadsters liquid cooling circuits.
And mount smaller wheels
JRP3
Hyperactive Member
So how about raising the level and providing all the needed dimensions? Track width is only one of the concerns, Model S motor/inverter diameter and length being two of the main ones, along with the gear drive dimensions, as well as available space in the Roadster body.
This aftermarket buy a Model S drive unit and do major changes to make it transplantable into a Roadster sounds like it would be as expensive as the original Roadster.
If the induction motor core of a Model S is same size as the Roadsters or a bit less, the cost effective way to go would be for Tesla to mount the more compact PEM components along with motor cooling pump, etc. in the same rectangular PEM housing and either refurbish the existing motor casing to take the S motor and cooling, or create a new one that fits in space where old motor housing sits. Not suggesting this would not add another 10 or 15K to the upgrade price, but good bang for the buck, since combination of bigger battery, better PEM and liquid cooled higher output motor could make the 0 - 60 time even better than 3.7 for Sport.
If the induction motor core of a Model S is same size as the Roadsters or a bit less, the cost effective way to go would be for Tesla to mount the more compact PEM components along with motor cooling pump, etc. in the same rectangular PEM housing and either refurbish the existing motor casing to take the S motor and cooling, or create a new one that fits in space where old motor housing sits. Not suggesting this would not add another 10 or 15K to the upgrade price, but good bang for the buck, since combination of bigger battery, better PEM and liquid cooled higher output motor could make the 0 - 60 time even better than 3.7 for Sport.
JRP3
Hyperactive Member
I just can't see Tesla putting any engineering time into something like that for a low volume discontinued vehicle. The pack upgrade is relatively easy and straightforward, as well as being very good press for the company.
Those dimensions are different enough that whole rear assembly would need to be replaced with MS's one. Motor diameter, gear radius etc are not important in such scenario as long as there is enough space in general. As one would also remove Roadster's PEM, space should not be a problem. For exact dimensions where to cut, drill into roadster frame would need to put one next to the other. As track is 20cm wider this is excellent opportunity to fit a really fat rear tires, like 425
With a bit shorter custom arms and different ET those could be reduced somewhere around more civil ones like 325. Still fat but superb grip.
The real problem is control and electrical compatibility - getting Roadsters computer to talk to MS's PEM. Could even be impossible.
Replacing just the motor and keeping Roadsters PEM is useless, nothing to gain.
Replacing Motor and PEM while keeping roadsters rear subassembly is impossible - no room.
One would still need to limit MS's PEM from drawing to much current. Roadster Sport draws up to 215kW, MS60 draws up to 225kW and MS85 up to
MS60 battery voltage is 350V, so at 225kW it draws 640A or 3,7C
Roadster battery voltage is 370V, so at 215kW it draws 580A or 4,1C.
I'd expect MS60 PEM to throw errors if it sees 370V and one would need to use MS85 PEM that is used to seeing up to 400V.
Mount this into a roadster with a new "400mile" battery and fly...
JRP3
Hyperactive Member
Well yeah, that was my point. There might not be enough room for the entire assembly but if the bare motor/inverter/gearbox fits a custom assembly could be built.
Since the Roadster PEM is above the motor I don't see how that would provide extra space for the S inverter which is bolted beside the motor.
As for voltage, reprogramming the S inverter would be the best way, if you could. At some point the S programming will make int out into the wild.
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