Boxster 986 conversion design

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ReneS
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Boxster 986 conversion design

Post by ReneS » Mon, 16 May 2016, 23:10

I am at the design stage as i would like to have all the parts sourced and on the bench before i start pulling apart the car ( too much fun to drive). I want to keep this conversion down to the minimum time frame possible.
The brief
build a car that can be driven as daily driver but has some get up and go in it as well. Use all the existing dash instruments and keep as much of the original systems as possible the idea is to make it hard to pick this is a converted car.   needs to be road registered
Car: 1997 Porsche Boxster 986 manual 5 speed
Motor: Emrax 268 low voltage AC, This is a light weight high power motor that is very short at 90mm allows me to fit more batteries in the engine bay.
Controller: emdrive500 this is the recommended controller for this motor in low voltage and is reasonably priced.
Batteries: Lifepo4 30ah pouch in a 180AH 121.8 Volt pack this is the max for the motor controller configuration. and keep the car at or near the original weight
Charger: yet to be decided
DC/DC converter: Iota 55ah
Any feedback would be greatly appreciated

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Adverse Effects
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Boxster 986 conversion design

Post by Adverse Effects » Tue, 17 May 2016, 01:24

depends on the Lifepo4 model as to the C rating you can pull out of them but that seems a little light on the amps for a low voltage system

also

Continuous motor power
depends on the motor RPM
2000 - 4000
40Kw . 75Kw

Peak motor power few seconds at hot star
160Kw @ 1000Amps

that would cook that battery pack

dont sound like much fun
Last edited by Adverse Effects on Mon, 16 May 2016, 15:34, edited 1 time in total.

ReneS
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Boxster 986 conversion design

Post by ReneS » Tue, 17 May 2016, 02:52

HI
thanks for the reply
i didn't consider the continuous discharge rate in my calculations

the battery packs have a 3C continuous discharge and a 8C max but the controller has a max of only 660Ah with a continuous of around 416Ah this means the batteries should be good but i may add another parallel battery per cell for safety.
I wont be getting the max out of the motor with the controller but i am going by the notion that it is probably better for the motor if i say below the max. down the track i may change or add a controller for more power but if my numbers are right i still should get around 333NM and 107kw peak.

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Richo
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Boxster 986 conversion design

Post by Richo » Wed, 18 May 2016, 20:59

Looking at the specs of the 986 it did 150kW 239Nm.

The ERMax-228 (100kW) has a peak of 240Nm.
The ERMax-268 (200kW) has a peak of 500Nm.

I think the main issue is the ICE reaches peak at 6,000RPM.
This is past the recommended max of the ERMax motors.

I'd think the ERMax-228 would feel better than the original ICE in terms of performance.
The ERMax-268 would be like a worked turbo version.
Assuming you could get a controller and batteries to feed it.

I'd want to check that the gearbox is suitable for 2x the torque.
Or get a 6spd off a turbo'ed variant as a future mod.
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

ReneS
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Boxster 986 conversion design

Post by ReneS » Wed, 18 May 2016, 21:31

thanks for the feed back its great to look at things from a different angle.
.
I see your point and agonized over motors for hours if not days.
AC or DC big or small, the whole ev specs to ICE specs seems a bit black magic to me so i have erred on bigger is better if i can get away with the 228 i would but i don't want to under spec either.

i chose a low voltage option and because of this the controller will not supply the full amps required for the max performance the motors can give at LV. this meant going for the bigger motor with less amps but more power than the smaller 228.

if i am right i should get a bit more than the 228s max performance at less amps with the 268. the 228 is far cheaper so would be have been great but to get full performance out of it i would need 2 controllers ( this may be a future option).

gearbox is a factor i didn't consider and will have to keep in mind. Having the larger motor will hopefully give me scope to de tune the controller to a point where i get my hoon fix and don't break anything.

thanks again for the input this way i can build a better machine
cheers



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Richo
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Boxster 986 conversion design

Post by Richo » Thu, 19 May 2016, 20:25

Yep if it fits and you can afford it go with the 268.
So the 500A controller with 268 should get you the same 240Nm as the original ICE.

Another thing I notice that 130V gets you to 4000RPM but you need 240V to get to 5000RPM Image
The numbers don't quite add up from their spec sheet.
If the KV rating was 4000/130=30.7 then 240V should get you 7300RPM.

At least one day you could upgrade the controller and gearbox to get blistering performance!
1000A 3-phase controllers are still a bit pricey Image

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Richo
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Boxster 986 conversion design

Post by Richo » Thu, 19 May 2016, 20:39

180Ah x 3C = 540A.
Yep that should be ok for most batteries.
22kWh x 3C -> 66kW
22kWh x 5C -> 110kW
22kWh x 10C -> 220kW

I don't see the datasheet for the emdrive500.
But looking at the 400 I see a few issues to consider.
The peak current is for only under 100V.
The maximum battery voltage is 125V (registers as a fault?!?).
Using LiFePO4 at charge of 3.6 is 34 cells or 108.8V nominal.
And a charge of 122.4V.

Under full load of the cells might only be ~95V this only gets you to ~2900RPM.
The peak of the ICE was ~6,000RPM

Not too sure what you can so about this bar using a different controller and higher voltage with slightly lower Ah per battery.
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ReneS
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Boxster 986 conversion design

Post by ReneS » Thu, 19 May 2016, 23:00



emDrive_500_datasheet_V2_0.pdf

this is the Emdrive 500 data sheet, i think its been designed for the LV Emrax but it defiantly doesn't give it full amps.

this are great feed back and thanks for taking an interest. i will have to check with both Emrax and Emdrive about how the combo will work together.
cheers Rene

ReneS
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Boxster 986 conversion design

Post by ReneS » Sat, 18 Jun 2016, 03:17

Change of plans
After much considerations and deliberations I have decided to go the more trodden path of a HPEVS twin 35s instead of the Emrax.
the low max RPM and the lack of any real EV conversion info about the Emrax made it a bad choice for a first timer like me.

currently collecting all the parts needed for my build.
Cheers
Rene










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