# Low cost autocross conversion (VW rabbit)



## DavidDymaxion (Dec 1, 2008)

I found for $/kW, Headways were a great bargain, actually cheaper than CALB (which are better for $/Ahr). You'd also really be stressing a 100 Ahr CALB with a 1000A controller, the 8 Ahr "P" Headway cells are rated for much higher C rates. Since you don't commute very far, you don't need many Ahr, but still want high power for AX.

I got my headway cells from http://www.manzanitamicro.com/produ...page=flypage.tpl&product_id=61&category_id=29

Think about rapid recharging, too, between runs.

From what I've read, make sure your motor will clear the axle -- that could be a deciding factor.

FWIW, I plan to autocross my Porsche. It has a Kostov Sepex motor, a 1000A Kelly, and will have about 500 to 600 Headway cells. 

IT


dcdebolt said:


> Hello all, I've lurked here off and on for years and I've finally decided build an EV out of my old 1975 VW Rabbit.
> 
> I'd like to do this right the first time so as not to waste money, so any advice would be appreciated.
> 
> ...


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## drgrieve (Apr 14, 2011)

I agree with David. If you have the skills have a look at a high C rate battery.

Calb 100 ah, is good for 8C bursts. There are different headway the normal around 10C and the P I believe is 15C.

Then very popular at the moment is the A123 20 ah cells. Good for 20C and have excellent energy density as well. This would be my choice, but they are also the hardest to put together as there is no off the shelf designs.

As for motor pairing then either Kostov 220v with Soliton jr, or Warp 9 with Soliton 1 are good combinations depending on budget and desired weight.


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## Batterypoweredtoad (Feb 5, 2008)

A Kostov 220V with a Junior and a single 100 series string of A123 Batteries would be an absolute riot in that car. The car would weigh well under 1500lbs and have a Looooow center of gravity. You could make a rectangle pack that you put anywhere you want to balance the car or you could make a flat pack and put it under the car. The flat pack would be less than an inch thick and either pack would weigh about 100lbs.

Edit: You are really making me want to build a budget Miata Autocrosser.


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## Duncan (Dec 8, 2008)

Hi DcDeBolt

I don't think you will need a gearbox at all!
I suspect with a 9 inch motor and 1000 amps you will spin the front tires in top gear

Gear-changing may not be needed at all!

I would be keeping it light 
I have a 44s 2P 16Ah Headway pack
(I'm voltage limited because I am using an OpenRevolt)
The pack is only 50Kg

With your controller you could use a bit more from the battery - 100Kg of Headways can deliver over 200Hp (at the 10 second rate)

A123's should be even better


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## Coulomb (Apr 22, 2009)

dcdebolt said:


> To keep weight down, I was thinking of 45 of the CALB 100ah cells in series. Would numerous 600-800 amp bursts of power during an autocross run would be too much for 100 ah CALBs?


I would think so (i.e. I believe it would be too much current draw for the longevity of the pack). I think 6C should be limited to about 10 seconds, to accelerate to cruising speed and current. Then no more high C burts till the next set of lights. That doesn't sound to me what you would want for autocross.

But this is based on theory, not direct experience (at least, not much experience, and most of that on the bench).

The other thing to consider is that 600-800 amp bursts at the motor don't mean 600-800 amp bursts at the battery, if you are running at less than full motor voltage, due to less than full motor speed. Hopefully, the load from the dc/dc and/or heater would be fairly low during autocross, and can be neglected. So if you need extra motor current due to not having a gearbox, it won't cost you extra battery current (and without the losses in the gearbox, you will presumably be better off, apart from the extra motor heating that comes with direct drive).


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## Yabert (Feb 7, 2010)

Hi dcdebolt

Because higher torque is nice to not have to shift (espesially between 20 to 60 mph) I suggest to you 1000A controller and Warp 9.
This kind of systems can give you 70-80% more torque than a K9 powered by a 600A controller.

Power remain the same (because peak power will probably related to battery capability), but higher torque is an advantage.

For example, my 1800 lbs Smart Fortwo (with VW transmission) can adequately accelerate from 0 to 68 mph in third gear only with my 1000A controller.

As battery, A123 AMP20 are the best at this moment, but you will need some skills to build a pack. If not the case, Headway 38120HP can do the job.
I talk here of 48 to 64 cells in serie capable of 1000A burst.... it's a 150-200 lbs battery pack. Higher voltage and less amps capability (240v (75s) 700-800A) can be good too, but it's related to controller voltage.


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## dcdebolt (Feb 21, 2009)

Yabert said:


> Because higher torque is nice to not have to shift (espesially between 20 to 60 mph) I suggest to you 1000A controller and Warp 9.
> This kind of systems can give you 70-80% more torque than a K9 powered by a 600A controller.


Thanks for the response Yabert and everyone else. What I'd like to see is the power curve of a Kostov 9 at 600 amps. I guess the motor is so new that it seems like there's little real world data on it and the graph's on Kostov's site make no sense to me. Any help here is appreciated. 

Is it true that a Warp 9 may not spin as high of an RPM as a Kostov 9 because of the voltage difference? And shouldn't I consider this as a factor for an autocross car? 

Keep in mind that I have to retain the transmission for this, as direct drive won't really work for this front wheel drive car (Unless I modify the transmission?). And I'm not sure it will handle over 175 foot pounds of torque for very long. I'd like to spread the power out over the rpm range as much as I can without hurting the bottom line: fastest laps possible.

As a side note on batteries, the higher-torque Warp 9 with lower voltage appeals to me because it seems less complex to have a lower voltage battery pack. With A123s or Headways I'd like to parallel 2-3 cells to take advantage of the natural cell balancing that seems to go on between parallel cells. 

I'd like to go without a BMS if possible. I've been reading Jack Rickard's posts about the dangers and complexities of a BMS. The idea of a BMS now scares me. But he seems to focus on prismatic cells. With the smaller cells, I hope that regular battery monitoring and fully enclosing them in lexan or aluminum boxes with good connections would prevent a fire from overcharging, right? I don't want to burn my garage/house down. That's priority #1. 

Thanks!

PS, I've decided to buy 16-32 grey market A123 20ah pouch cells to test on my 48v electric CB160 motorcycle project. if I'm comfortable with them I will buy more for the rabbit.


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## Batterypoweredtoad (Feb 5, 2008)

The Kostov K9 220V produces slightly more torque per amp than the Warp 9. IIRC the K9 is ~130 ft lbs at 500 amps while the Warp 9 is ~120 ft lbs at 500 amps. The Kostov on the other hand requires more volts per RPM. The Kostov is a really nice fit for the Junior because you can use more of the voltage capacity of the controller with its 220V rating (likely conservative). The Warp 9 fits the Soliton 1 better because it can likely handle the 1000 amps better because of its larger mass, and is already maxed at 190V (very solid limit) by either controller. I personally like the K9 220V Soliton Jr combo for your setup with the single 100 series string of A123 batteries. It should put out around 156 ft lbs of torque and at 220V similar horsepower. That string should match a K9 220V about perfectly with the sag taking you from 320-330V nominal to around 210-220V at 600 amps. Add another string and you would be able to maintain around 260V at 600 amps. That would be really nice if you really wanted to push the little K9 220V.


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## dcdebolt (Feb 21, 2009)

Batterypoweredtoad said:


> The Kostov K9 220V produces slightly more torque per amp than the Warp 9. IIRC the K9 is ~130 ft lbs at 500 amps while the Warp 9 is ~120 ft lbs at 500 amps. The Kostov on the other hand requires more volts per RPM. The Kostov is a really nice fit for the Junior because you can use more of the voltage capacity of the controller with its 220V rating (likely conservative). The Warp 9 fits the Soliton 1 better because it can likely handle the 1000 amps better because of its larger mass, and is already maxed at 190V (very solid limit) by either controller. I personally like the K9 220V Soliton Jr combo for your setup with the single 100 series string of A123 batteries. It should put out around 156 ft lbs of torque and at 220V similar horsepower. That string should match a K9 220V about perfectly with the sag taking you from 320-330V nominal to around 210-220V at 600 amps. Add another string and you would be able to maintain around 260V at 600 amps. That would be really nice if you really wanted to push the little K9 220V.



Thanks. I'm very curious to know if the K9 could safely spin to a higher RPM than the Warp 9 as I'd love to be able to keep the car in second gear when negotiating an autocross course. The gas motor of course would do 60 mph at 7000 rpm in second and 55 mph at 6500 rpm. I'd like to be able to spin up to about 6,000 rpm very briefly for the one straightaway that is usually part of the De Anza course. Could that be done safely with the K9?


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## Batterypoweredtoad (Feb 5, 2008)

dcdebolt said:


> Thanks. I'm very curious to know if the K9 could safely spin to a higher RPM than the Warp 9 as I'd love to be able to keep the car in second gear when negotiating an autocross course. The gas motor of course would do 60 mph at 7000 rpm in second and 55 mph at 6500 rpm. I'd like to be able to spin up to about 6,000 rpm very briefly for the one straightaway that is usually part of the De Anza course. Could that be done safely with the K9?


I don't know if the Kostov will spin higher than the Warp, but this link claims "over 6500 rpm as nominal" for the Kostov: http://kostov-motors.com/tractionmo...dc)/seriesdcmotorsforelectricvehicles/k9220v/ . I am really not sure how much voltage it would take to make any power up there though.

This chart: http://kostov-motors.com/files/productattachments/6ff70418861d3230f01fc0340802fb1f_S220E01.pdf is where I am getting the info I am using.


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## dcdebolt (Feb 21, 2009)

Batterypoweredtoad said:


> I personally like the K9 220V Soliton Jr combo for your setup with the single 100 series string of A123 batteries. It should put out around 156 ft lbs of torque and at 220V similar horsepower.


How do you calculate these power figures based on the graph you linked to?


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## Otmar (Dec 4, 2008)

Many people seem to think that higher torque is a good thing in a conversion. I don't agree. 

It is true that for a given input power higher torque means lower RPM, I believe that in a system with a shifting transmission lower torque and higher RPM is generally more desirable than the inverse. 

Your Rabbit transaxle likes what, 120 ft lbs? Ask Bill Dube' how hard it is to make a Rabbit transaxle take high torque. (I have a great picture somewhere of him holding the gears that were ejected on the drag strip, and that was only 600 Amps). If you increase the HP with higher RPM (for short amounts of time) and run in third instead of fourth I believe the chances of grenading your transaxle are lower. 

Automotive transmissions were not made for the high torque of series motors, it's better to minimize that and optimize for high RPM horsepower. Besides, high RPM motors for getting higher HP are theoretically lighter.


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## Yabert (Feb 7, 2010)

I'm forced to agree with Batterypoweredtoad and Otmar... your transmission will prefer the lower torque of the K9. I also really like the 99 lbs kostov motor, but higher voltage is a bit more trouble.

If you think than your tran can take the torque, performance will be similar for similar battery pack power capability. Let say:

K9 at 600A = 150 lbs-ft x 7.75 (second gear) = 1162 lbs-ft at wheels. From your numbers, 6500 rpm = 55 mph
W9 at 1000A = 240 lbs-ft x 4.95 (third gear) = 1188 lbs-ft at wheels. Convert from your number 5000 rpm = 66 mph
I base the ratios on my 02A VW transmission...

And you can use a bms to simplify your charge. You just need to use a simple and well build bms. I used Mini bms and it work perfectly.

Oh! and just like that, did you to peek at used forklift motor? Save money on motor and put more on battery!


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## Batterypoweredtoad (Feb 5, 2008)

Yabert makes a great point-power is power is power. If you are feeding 150hp from your batteries into your motor you are getting 150hp(minus losses) out of your motor. It doesn't really matter what motor you are using for that math. The difference is at what rpm's you get that power, and you have a transmission so you can pick whatever gear works best for your motor. 

The motor chart: pick a point on any of the curves and go straight left or straight down to get the corresponding values. All points on a vertical line happen at the same time. Ex-at the "S2-60min"(60 minute rating) dotted line you get: 

n(rpm)=6800 
U(voltage)=212 
cursive n(efficiency)=86% 
I(amps)=180 
P(power)=32kw 
then go straight down to the horizontal axis and you get: 44Nm (Torque) 

To estimate torque at 600 amps I took the Nm value from that chart at 500 amps, converted it to ft lbs, and then multiplied it by 1.2 (600/500).


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