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Hello all,

I'm considering a lotus elise or exige conversion (S2)

  • My mechanical knowledge is minimal but I'm eager :rolleyes:
  • Hoping for a range of 75 miles
  • Performance: 0-60 <5secs, top speed 100mph
  • Money :20k for conversion
Car weight ~2057 lb with ICE. Engine is about 140kW

I see it's been done before a few times

1998 elise
http://www.evalbum.com/1454
Detroit auto
http://www.youtube.com/watch?v=uex5XDUUsDY&feature=related
Rev Elise
http://robotics.ee.uwa.edu.au/theses/2009-REV-Lotus-Drive-Ho.pdf

I have read through the wiki's and am suffering from information overload!

Questions:

  1. Is this something that can be done on that budget?
  2. Is this something that can be done by a virgin EV builder?
  3. Can you recommend some Motor/BMS/Batteries combinations that I can research further
Thanks

Lotutty
 

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Hello all,

I'm considering a lotus elise or exige conversion (S2)

  • My mechanical knowledge is minimal but I'm eager :rolleyes:
  • Hoping for a range of 75 miles
  • Performance: 0-60 <5secs, top speed 100mph
  • Money :20k for conversion
Car weight ~2057 lb with ICE. Engine is about 140kW

I see it's been done before a few times

1998 elise
http://www.evalbum.com/1454
Detroit auto
http://www.youtube.com/watch?v=uex5XDUUsDY&feature=related
Rev Elise
http://robotics.ee.uwa.edu.au/theses/2009-REV-Lotus-Drive-Ho.pdf

I have read through the wiki's and am suffering from information overload!
An Elise would make a wonderful conversion.

Questions:

  1. Is this something that can be done on that budget?
  2. Is this something that can be done by a virgin EV builder?
  3. Can you recommend some Motor/BMS/Batteries combinations that I can research further
Thanks

Lotutty
1. Yes
2. Maybe, depending on your level of mechanical/electronics knowledge or capacity to learn quickly
3. Yes

I would recommend a China Aviation pack, perhaps 300V of 100 AH cells, no BMS(don't discharge the pack more than 80%, don't charge to more than 99%), Netgain 9" HV series wound DC motor, Soliton 1 controller, and Zivan NG3 charger programmed for your pack. Limit your battery pack current to 400A(assuming 100AH batteries), turn the motor current to 1000A, and set the motor voltage limit to 192V.

Such a car would likely weigh about 250 lbs more than stock, do 0-60 mph in under 6 seconds, exceed 120 mph top speed, get 100 miles range at 60 mph to 80% discharge, and cost about $20,000 without upgrading it to have the addition of a BMS and better charger. This budget would leave no room for expensive errors, and obviously, would not include the cost of the donor vehicle, would be if everything was purchased new, and assumes you do all of your own fabrication or have free/cheap help for things like motor mounts, battery boxes, adapter plates, couplers, ect. If you find some of the major components used, your cost could be cut dramatically.

If you absolutely want a decent BMS, then swap out the Zivan charger for a Manzanita Micro PFC20 with its integrated BMS for LiFePO4 batteries, and add about $2500-3000 to your cost, and about 25% to your usable range per charge(due to being able to discharge 100% with the addition of a BMS).

If you want AC motor(s) and regenerative braking, you're going to have to compromise on at least one of the 3 criteria mentioned that have nothing to do with your level of skill.
 

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Netgain 9" HV series wound DC motor, Soliton 1 controller, and Zivan NG3 charger programmed for your pack. Limit your battery pack current to 400A(assuming 100AH batteries), turn the motor current to 1000A, and set the motor voltage limit to 192V.
As far as I know, there is no WarP9 high voltage version, only a high voltage version of the WarP11, 11" motor with max 288V. The max voltage for the WarP9 is 170V, with 156V recommended.

(due to being able to discharge 100% with the addition of a BMS)
I don't see why you think a bms permits you to discharge the cells 100%. You can do that with or without a bms, but it will greatly shorten the cycle life of the cells.

I think the difficulty in this conversion is the fact that such a high acceleration rate will require high battery pack voltage AND high battery power to handle the large currents required for such acceleration. I think that would require something like a series-parallel pack of Headway cells, as prismatic cells (Thundersky, CALB) would have to be large capacity (Ah) to handle such currents due to their spec of max current about 3C to 4C. The car likely wouldn't have enough room for enough of these to get the higher voltage required. I would guess you could get less than 7 sec 0-60 with just a WarP9, Zilla 1k or Soliton1, and 156V pack of 200Ah TS cells (if there is space for 46 them), with battery current limit set to 800 (4C). A battery current limit of 400A would greatly limit performance.

You can use this spreadsheet to estimate 0 to 60 time (zip file at bottom of post):
http://www.diyelectriccar.com/forums/showthread.php/dc-motor-charts-ev-performance-spreadsheet-41565.html

This pack would significantly exceed your range requirement, somewhere in excess of 100 mile range I would guess.
 

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Hello all,

I'm considering a lotus elise or exige conversion (S2)

  • Hoping for a range of 75 miles
  • Performance: 0-60 <5secs, top speed 100mph
  • Money :20k for conversion
these goals are somewhat mutually exclusive.... pick two out of the three and I think you can do it, excluding the cost of the donor car. For monster acceleration, the least expensive solution may be tandem 9" DC, which will enable you to stick down around 144v or 156v battery pack so you COULD use prismatic cells. But, if you go with 100ah cells for space, you really shouldn't pull more than 400 or 500 amps for very long. To get your range you may need 160ah. I'd guess even a modest controller pushing through a peak of 500 amps at 144v to a twin 9" DC would yield very fun accel, but maybe not sub-5 sec. If you are willing to compromise performance to save weight and cost you could step down to a twin 8" motor at 120v and have a blast.

If acceleration is you priority you may want to step up to headways so you could use a zilla 2k controller and jam thru 2000 amps, but that drives the cost of the battery pack and controller WAY up.
 

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As far as I know, there is no WarP9 high voltage version, only a high voltage version of the WarP11, 11" motor with max 288V. The max voltage for the WarP9 is 170V, with 156V recommended.
Netgain has a new 9" HV model good for 192V. It is offered as part of the prize package for Jack Rickard's contest. It is very new, and may not yet be officially for sale. But it exists and has been developed by Netgain.

I don't see why you think a bms permits you to discharge the cells 100%. You can do that with or without a bms, but it will greatly shorten the cycle life of the cells.
LiFePO4 can handle full discharges and have high cycle life; what is tricky about them is that without a BMS that actively manages them upon discharge, they become unbalanced towards the end of their discharge cycle, and the weaker cells will start to die out prematurely. A BMS that mitigates this effect could allow them to be deep discharged.

That being said, an 80% discharge cycle with a 'limp mode' built in when it reaches 20% SoC would still give sufficient range, for less money, than paying for a BMS, a BMS which may not even do what you need it to.

I think the difficulty in this conversion is the fact that such a high acceleration rate will require high battery pack voltage AND high battery power to handle the large currents required for such acceleration. I think that would require something like a series-parallel pack of Headway cells, as prismatic cells (Thundersky, CALB) would have to be large capacity (Ah) to handle such currents due to their spec of max current about 3C to 4C.
4C is plenty, if the goal is 0-60 mph in 6 seconds in what would be a 2300 lb car. The controller can limit the current draw from the pack, and counting battery voltage sag at 400A draw, there would easily be 100 kW electrical available with such a pack. With 1000A max at the motor, provided until the battery cannot deliver enough power to extend that 1000A to the high voltage end of the motor's curve, it also prevents too much current from going to the motor at high voltage. Such a pack might only allow 450A @ 192V at the motor electrically.

This would still be enough power for the desired acceleration, given numerous conversions with weight around 2300-2400 lbs, with similar power at their disposal(eg. Blue Meanie, John Wayland's Datsun 1200 that does 0-60 mph in 5.5 seconds with a 168V/1000A ADC 9"/Zilla setup in a 2400 lb package, where the battery pack sags to ~130V @ 1000A, and would have much less upper RPM power than this hypothetical LiFePO4 Elise, although the 1000A torque on Blue Meanie would be extended further down the motor's RPM range). The key to getting this acceleration is the 1000A at the motor; I do believe the Soliton can keep an absolute limit on battery current, yet allow the user to set a higher motor current limit, like the zilla, and that would be key to getting the desired acceleration with a low power, low current LiFePO4 pack.

The headway cells or A123s or other high power variants would probably prove much too expensive for his cost goal.

Jack Rickard's electric Porsche Speedster, with only a ~25 kWh CALB pack, can still do 0-60 mph in 7 seconds(pack probably makes a little less than 100 kW). An Elise with a more powerful pack that is 30 kWh nominal, more powerful and higher torque drive system, and similar weight would probably fair much better.

While my proposed setup wouldn't give sub-5-sec 0-60, in would be close, probably somewhere in the 5 sec range.

The car likely wouldn't have enough room for enough of these to get the higher voltage required. I would guess you could get less than 7 sec 0-60 with just a WarP9, Zilla 1k or Soliton1, and 156V pack of 200Ah TS cells (if there is space for 46 them), with battery current limit set to 800 (4C). A battery current limit of 400A would greatly limit performance.
The car may or may not have enough room. The converter will have to determine that. Judging from the conversions I've seen, it probably will have enough, but the builder will have to figure that out before coming to a conclusion on what he wanted.

It matters not whether you have a pack that can dish out 400A or 800A, if they both weigh the same, both have the same power per unit of weight, but one has twice the nominal voltage, when using a Zilla. You can independently set the battery current limit from the motor current limit, and set a max motor voltage that is less than the pack's nominal voltage.

If he were using an upgraded Curtis, a ReVolt, or DCP Raptor, he'd need a larger AH pack to get the motor current needed. Not so with a Zilla.

With a Zilla, if two packs are capable of 100 kW to the motor, they will give roughly the same performance, but with one exception: the higher voltage pack would allow a higher motor voltage limit, increasing top speed and upper RPM acceleration. While peak power basically doesn't change, the higher voltage setup gives you more total area under the torque versus RPM curve.

That being said, 156V would easily get an Elise to 100 mph, if not 110. After that, it would run out of upper RPM power. Further, a higher max motor voltage lowers current draw at speed, allowing the motor to maintain a high speed for a longer duration before it overheats(given that a series DC motor's continous power is rated based on its continuous current, and its max continuous horsepower increases correspondingly with the motor's max voltage at that current draw, subtracting new losses that form due to things like higher RPM operation).

If a BMS is wanted, it would be cheaper for a 156V pack than a 300V one though.

I was making a suggestion that would help maximize top end performance, as well as allowing good acceleration.

This pack would significantly exceed your range requirement, somewhere in excess of 100 mile range I would guess.
Maybe. The Elise is very light, but its aerodynamics leave a bit to be desired. I made the assumption that it would need about 220 Wh/mile to maintain 60 mph based on some back of the envelope calculations. It has a drag area of 0.65 m^2 with the top on, and assumed was sticky tires with a Crr of 0.012. Discharge to 80%, account for a very tiny Peukert's effect in LiFePO4(next to non existent), and you get 100 miles range on a 300V/100AH LiFePO4 pack at a steady 60 mph.

If he drives very carefully and at lower speeds, and/or uses some very LRR tires in exchange for losing some handling, he might get 150 miles with such a pack to 80% DoD.
 
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