# Electric Racing Kart



## Xph (Apr 1, 2009)

Time for me to decide how to spend this year's racing budget.

I currently enjoy racing a 125cc shifter kart at the local Kart track or auto crossing (parking lot) racing with the SCCA club in the area.. 

I have an extra Kart frame, and wanted to go about trying to Electrifying it to achieve similar performance to my current gas karts.

So some basic parameters, there are obvious size and weight constraints (which is why I am posting here as opposed to the car forums).

Fully loaded Kart and Driver should weigh no more than about 400lbs, the driver is half that; the kart frame and brakes weigh about 100lbs, so battery motor and controller need to come in about 100lbs.

Operational parameters, I have a dyno plot for a TAG series 125cc motor I use, it makes about 12ft lbs of torque... When I use that motor I run a gear ratio of 8:1 or so; so I am assuming I'd be looking for upwards of 100NM of torque at the wheel to have similar acceleration.

Further, the Kart speeds at the local track / autocross can reach about 80mph; the kart tire has a circumference of 34.2" which means I need about 2500 wheel RPM to make 80 mph

Run times: A typical Autocross run is no more than 90 seconds from start to finish, usually more in the 60 second range and about 1 mile in distance. The feature at the kart track is 8 laps of racing and maybe 1 or 2 laps of staging (the track is 6/10 of a mile per lap). 

So I am looking for Motor, Controller and Battery recommendations; As well as thoughts on how things will work given the rapid discharge times I am looking at.

For my general figuring, I was looking at the AGNI 95 series, which I could run at a 2:1 ratio, looks like that would give me about 100nm of torque at 400amps 72volts... A bit short of my goal but in the range... 

I am thinking that a battery "pack" system built from the Dewalt DC9360 or something similar would be in order, but my early calculations show I would need 6 to do my 90 sec Auto Cross run, and 40! to make it 10 minutes for a Kart feature (although those calculations may be way off, I am assuming 60% wide open throttle time, and used a 400amp number from the AGNI graph for max torque).

Your input is greatly appreciated.


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## Guest (Apr 2, 2009)

No way to do the motor and batteries and controller and cables @ 100 lbs. Like most EV's you will be heavier than normal but if you keep the weight low you could keep the cart under control. However you may want to look into lithium where weight is an issue. Since you only need enough for a few races then a couple nice small amp hour packs would do you good. 36 volts may do you just fine. 

Pete 

A cart sounds fun. : )


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## MalcolmB (Jun 10, 2008)

Nice project. If my back of an envelope sums are right I reckon it's just about doable, though it won't be cheap. You should check my numbers of course

The Agni 95 sounds perfect for this application, and it weighs around 10 kg.

You need to be able to do around 10 miles, right?

Based on a consumption of 200 Wh/mile, that would require a 2 kWh pack, say 72V x 30 Ah.

(2 kWh in 10 minutes means an average power output of 12 kW, which should be ample I think, though you would need to keep an eye on the motor temperature).

Assuming dewalt cells are 2 Ah (actually 2.3) that would mean a 24 series/15 parallel pack, so 360 cells, which is pretty close to your own figure of 400.

You could just about do it with LifeBatt cells, which are easier to package, but they would sag more with your current requirements.

360 A123 cells with interconnects and cables would weigh around 30 kg, so that leaves you with just enough for controller and contactors.

Obviously you would need to find someone to build the A123 pack with a good BMS.


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## Xph (Apr 1, 2009)

Well technically its 10 laps at .6 miles each, so only 6 miles not 10; Its just that with the motor sports application, I can only really guess how much power I will need (lots of corners and brake zones)... (http://www.badgerkartclub.com/tracklinemap.htm)

Thanks for the input guys, the budget I am shooting for is to try to make it cost about the same as a typical kart motor... which depending on the level of prep, and the exchange rate is somewhere between 2k and 5k although on the high side is fine for now.

Also I would likely start at the AutoCross, where its just a single 50-60 sec run; 3 in the morning and 3 in the afternoon, this would allow me to go smaller on the pack size (as long as it was easy enough to swap out packs), and to monitor motor temps / power consumption duing the build up; Also since its not wheel to wheel, its much safer if my performance is off.

So it sounds like A123 type packs are about all that is a given at this point. 

The AGNI motor might be the one, but I would really like to get an idea of what other options are out there; maybe something with a little higher perf. 

And then I have no idea on a controller to get... (only that I am probably DC... )
Renerative braking might make sense for the 10 min run, but I dont think I want to complicate my inital build with it... further I would be concerned about heat.


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## DavidDymaxion (Dec 1, 2008)

Unfortunately, regen is expensive to add later (you might have to replace both the motor and controller), so it is good to do it up front if you think you want it. Racing is a good application for regen, as you accelerate hard and then brake hard, are are rarely just cruising. There are Curtis sepex controllers that handle up to about 35 kW.

Gas usage is a good proxy for how much energy you'd need in batteries. I've heard various numbers, and it varies a bit depending on how the vehicle is driven, I'm sure. Anyway, I've heard numbers from 500 to 1000 pounds of lead batteries is equivalent to a gallon of gasoline, and about 1/3 of that in lithium.

My family has a racing kart that my kids run at autocross while I run the full size car. My son usually beats me, and that's with a single gear kart! The shifter karts usually take fast time of the day.

Our 2 stroke kart gulps gas, it'll use 1/2 gallon of fuel at an autocross! The 4 strokes use about 1/2 the fuel.

1/4 gallon * ~250 lbs lithium / gallon ~= 60 lbs of lithium batteries,
or about 400 A123 cells.


Xph said:


> Well technically its 10 laps at .6 miles each, so only 6 miles not 10; Its just that with the motor sports application, I can only really guess how much power I will need (lots of corners and brake zones)... (http://www.badgerkartclub.com/tracklinemap.htm)
> 
> Thanks for the input guys, the budget I am shooting for is to try to make it cost about the same as a typical kart motor... which depending on the level of prep, and the exchange rate is somewhere between 2k and 5k although on the high side is fine for now.
> 
> ...


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## Xph (Apr 1, 2009)

That seems fairly close; the key to autocross that makes it a good primer, is as long as you use "battery packs" then you only need the power for 1 run at a time.. The dewalt 10cell packs are about 2lbs each, so that would be 12lbs which will probably be plenty for the 1mile autocross run..

The kart race at 6 miles is a bit tougher, 40 packs would be 80lbs for a feature, but it could be considerably less wiht regen and depending on how much time is spent on the throttle.

My thought is I would pick a controller that could handle regen; but start without it and see where we end up with heat...

Honestly one of the biggest reasons for me to go electric is noise; its the one of the tougest ordianance restrictions to overcome; getting more and more restrictive over time as communites clamp down on sites and conditional use permits... I think EV has the potential to offer the same perf, for the same price, with the same or better reliability, and a fraction of the noise.

Given the relativley short duration of the "heats" or "runs" I am hoping swapping battery packs can solve the weight issues for this applicaiton.


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## MalcolmB (Jun 10, 2008)

Xph said:


> The dewalt 10cell packs are about 2lbs each, so that would be 12lbs which will probably be plenty for the 1mile autocross run.


Although the Dewalt cells are rated at 70A continuous, I think it will shorten their life considerably if you run them close to this level. Your battery packs will last longer if you carry a few more cells in parallel than you actually need, and the weight penalty would be small in relation to loaded kart weight. One idea might be to work out the maximum size of pack you need and then split that in two. You could then run with a half pack or full pack depending on the type of race, or you could be charging one half while racing with the other.

It sounds as if you might be thinking of using the Dewalt packs as they are? The packs are limited by the built-in BMS so they will only supply around 20A. Most people who use them for high-power applications open the packs, strip out the cells and rebuild them in the most suitable configuration, with a separate BMS. The cells can now be bought at around $7 each on eBay though.


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## Xph (Apr 1, 2009)

Thanks! (I didnt know the information re the 70A rating)

Regarding the stock packaging, I saw that today in some other reading, basically indicating that the controller in the pack is heavy and limits the output, as well as the internal connectors not really being ideal for high load....

So I will essentially need to make my own packs (probably with some heat syncs too) which also means I will need to figure out something for charging (I was hoping I could get away with retail for both of these)...

I got word back from the AGNI rep, who indicated that the motor would be good to 500A and even 600A for short periods. Given that, I would certainly want more than a 72v 20cell x3 config.. Maybe even something like a 20cell x 9 which would still only come in around 40lbs and also give me enough run time to get through all three morning runs before a recharge.

Even though if we use the larger pack, we are still looking good on weight for autocross (26lbs motor, 8 lbs controller and 40lbs batt, leaves room for some mounting brackes, wires, other misc and heat syncs)...

And for price, the AGNI guy recomended a Kelly KD72601, which together with the motor looks to be about 2k shipped. at 7$ a cell, the 180cell batt comes in at 1260$ and we just need some wiring, a few sensors, and BMS.. (well and now a charger) I think I should be ok in my original sub 5k budget, but it will be close..

At the moment, I am looking for input on the Kelly controller option... 

Also can I run the AGNI 95 at a higher votage using a different controller, the AGNI site only shows to 76v, but I understand efficienies go up at higher voltage, with all of the cells I am working with it would be easy to go to 144v.

And any recomendations on BMS since it appears I will now be building my own batteries / packs..


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## Xph (Apr 1, 2009)

What about using Capacitors to help even out the peak loads to the battery pack for longer life... Or is this too outside the norm / requires an EE Major and custom circuitry


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## MalcolmB (Jun 10, 2008)

For battery packs, you might be interested in this thread: http://www.diyelectriccar.com/forums/showthread.php/a123-batteries-built-into-modules-3-29007.html

The Agni/Kelly combination has been used a few times by Jozzer, who's converted a few motorbikes and is building a race bike for the electric TT race. He reckons the motor runs very cool, because it's so efficient.

Just a note on pack voltage, DeWalt are being optimistic calling a 10-cell pack 36V. Lithium phosphate cells are usually considered to have a nominal voltage of 3V, so 72V would be 24 cells.

I think the Agni 95 can be run to 84V, but you should definitely check that with Agni.

Re: Capacitors – I'd put that under the heading of running before you can walk, besides which karts are pretty small vehicles, so you'd want to be very careful where you put your hands and feet if you have live capacitors on board 

Malcolm


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## JohninCR (May 6, 2008)

You may want to reconsider the multiple pack approach. A123's recommended fast charge current is a 4c, so it takes only 15 minutes, and normal recommended charge takes only 45 minutes. Of course you'll need a charger and BMS capable of that, but it's cheaper than the multiple packs of batteries. 

Cheaper, lighter, and smaller would be a pack made of the Lipo cells the RC guys use, and the way they use theirs is quite similar. You won't get the same cycle life, and the batteries are more dangerous, but in terms of performance the LiFePo4's can't keep up. It's a cheaper way in + greater performance to weight ratio + can even be charged in only 5-10min. That's what everyone will go to anyway, at least until the safer chemistry batteries catch up to the Lipo's.

John


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## Xph (Apr 1, 2009)

Thanks for all of the great feedback... It would seem that I can start ordering parts, and that my goals and assumptions seem resonable. I should be close to my weight goal, and within my budget, I will have to see how the acutal performance pans out.. The big variable seems to be the battery and BCM... and it seems that this is the likely the reason you dont see more Electric Karts at the track or Kits for sale...

So I will need to be prepaired to break out the spot welder, soldering iron, and spend some time researching the latest BCM electrical diagrams to get something just right for my purposes...

http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=1061

Is looking like a decent place to start shopping. but I will still need some BCM, they offer a DIY kit, but it seems a little short of my needs and a bit expensive

Also looks like I am going to need a bunch of these cells if I want to get to 72v @500A... The issue I see with these is that most are rated for a 30A draw, and they start to get very expensive when you go up to the 50 or 100A... and even at 50A I am still going to need 200 to build a 74v 500A batt... 6K$ for a 74v 500A 50AH batt @ 50lbs and thats without a BCM... I am guessing unless there is a way to raise the Discharge raiting (eg using ultracapacitors http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=26_62_64&products_id=126)... these are not going to be practical for my inital build out.

But even if I could integrate some ultracapacitors, I think I am going to need to go befriend a local Electrical Engineer or two to get some custom BCM technology to keep my kart from catching fire or worse.

I guess one of my goals wich seems out of reach at the moment, was to stick with off the shelf, just a parts list, wiring diagram and a few mounting brackets... this would have allowed me to prototype a system others could go out and buy to race with me... The only real chance I see of this would be to go back to using heavy Optima syle batteries, but these just arent safe in a karting applicaiton, they are way to heavy. I suppose I could go back to the Dwalt packs, and just limit the discharge to something around 20A per pack using the built in BCM, this would just cap me to around 100A draw with my smaller pack size and I would be under powering the motor.


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## Xph (Apr 1, 2009)

Hmm I have to say something like this looks intreguing... 

http://www.xheli.com/20c11-1v2200mah-lipo-battery.html

its a 20C 11.1v 2200mAh LiPo 6.4oz pack for 30$...

So 70 of those would net me a 2100$ 77.7v 22AH pack... which I could discharge at up to 400A

That should power me through 3 runs of autocross with Ah to spare and what I speculate would be about half the power I would need for a Kart race.

And it would only weigh in at 28lbs + wiring and mounting brackets.

As for battery cycles... If I raced every weekend for a summer for a year, maybe 30 events say... and throw in a practice day every week, so make that 60 days, maybe 3 power cycles a day.. The battery pack should easly out last the life of the Kart. 

However, I would still suspect I would need some BCM's for a 70 pack battery, not to mention they are designed to be charged individually, and I wouldnt want to buy 70 chargers...


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## SMEECH68 (Jun 24, 2009)

We are also building a Electric Race Kart for Badger.
We started with a Hasse chassis and I am using a Briggs ETEK motor with 4 12/20 sealed AGM batteries (48 volt system to start) and a Alltraxx controller.
I would like to talk to you about your kart and share idea's as well as race & practice at Badger.

Drop me a email to: [email protected]
Thank you, David Smith


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## nepore (Jul 24, 2009)

I think is expensive, but is a really nice project


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## neanderthal (Jul 24, 2008)

I dont know about using the kelly Every time I see a test on one the actual output is 1/2 to 1/3 of what it is rated for


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## AmpEater (Mar 10, 2008)

neanderthal said:


> I dont know about using the kelly Every time I see a test on one the actual output is 1/2 to 1/3 of what it is rated for


I had a Kelly in my custom 3 wheel kart. The 500A version seemed, at least measured by my "butt dyno", to be comparable to the 400A curtis I was running before. But it weighed half as much and was less than half the size. In my application I had no manual brakes, and relied entirely on the regen function, which was suprisingly strong but limited to my batteries capacity to accept charge current. I imagine something like A123 cells could actually lock the rear wheel up if set to full regen. (As a side note, this was an experimental vehicle, I'd never reccomend relying solely on regen for safe stopping, too many things can go wrong that would mean the loss of brakes).

As far as I know, there really isn't any other option for regen controllers out there right now. For something like a go kart of bike where space is at a premium there aren't any controllers as compact as a kelly, either.

You're right on track for your project, the Agni is an excellent motor choice, and A123s are perfect for this sort of project. You could build a smaller pack now without spending too much $$ that could still deliver massive current, and upgrade in the future for longer run times (perhaps buld the packs in a modular fashion, 1x pack for sprints and 2x or 3x for longer races)

It will be a blast


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## blank_rv-6a (Aug 17, 2009)

Cool to see you guy's having crazy thoughts like me about Karts. Just a off the wall comment or two on regen braking. I haven't done all the calcs but some run front brakes and I think if you replaced the calipers with the rc motors plus have a maxwell ultra capacitor or two you could have a cool extra brake power with added power boost out of the corner. I just joined the site so I need to poke around more but it just seems to me we need to scale up the RC stuff to the kart realm. Perm Magnet sure saves some watts from the power pack. On short duration like 10 to 15 minutes I would think it would fall into the RC mode and a Hacker Brushless A200 weighs only 6lbs for 13hp....Sweet Now to go lurk some more.


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## AmpEater (Mar 10, 2008)

blank_rv-6a said:


> Cool to see you guy's having crazy thoughts like me about Karts. Just a off the wall comment or two on regen braking. I haven't done all the calcs but some run front brakes and I think if you replaced the calipers with the rc motors plus have a maxwell ultra capacitor or two you could have a cool extra brake power with added power boost out of the corner. I just joined the site so I need to poke around more but it just seems to me we need to scale up the RC stuff to the kart realm. Perm Magnet sure saves some watts from the power pack. On short duration like 10 to 15 minutes I would think it would fall into the RC mode and a Hacker Brushless A200 weighs only 6lbs for 13hp....Sweet Now to go lurk some more.


I looked up the A200....it's rated at 15000 watts, which is more like 20hp 

Now I get why the ebike guys are using them! That power/weight is just nutty


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## NickRummy (Aug 17, 2009)

I have no experience in the EV world yet but I have a LOT of experience in the RC world. I've run A123 cells and lithium cells with brushed and brushless motors. I've used the following site many times and have zero complaints. My only concern might be shipping costs. I've had numerous high voltage/current packs from them without any problems. 

If you want a beefier pack here is a 6S (22.2V nominal / 25.2V peak) 5000mah 30C pack for $100 with a 40C for 10 second burst. It weighs 789g. 

It can be charged at 2C also (10a)

3 of those $100 packs in series would peak charge to 75.6V and capable of 100A cont. and 200A burst for 10 seconds. If you take that set of 3 and parallel 3 sets to make it 3S3P you would be up to a pack that would peak charge to 75.6V and capable of 300A con. and 600A burst for 10 seconds. IT would weight about 7,101g (15.7lbs) and would cost $900 plus shipping.

If you want to up the voltage and capacity a bit you could go to a 4S4P setup which would be 88.8V nominal and peak to 100.8V, would be 20AH and be able to deliver 400A continuous and 800A burst for 10 seconds. It would cost $1600 and weigh 12,624g (27.83lbs)

I ran the older version of the pack above that was 20C in an RC truck I built. I bought this pack to replace a 6S A123 pack I was using. The new lipo pack had so much more current available it was unreal....










The motor that lasted for months on the 6S A123 didn't last but a run or two on the 6S lipo....


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## RollingTripod (Jan 2, 2010)

Hey Xph,
I like your project and how you are attacking it, you've given me lots of inspiration for a similar project of my own.
I, like you, am thirsty for more power ... I found this company who manufacture motors for electric drag bikes  and thought you might be interested 
http://www.evparts.com/prod-MT5610.htm
40hp peak at only 20kg
this may be too heavy for your project but they do smaller....
I hope the project is going well!


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