# LiFePO4 powered mini buggy



## electron bom (Dec 4, 2014)

Upon somewhat completing a recent rebuild of my kart, I decided the next project would be to get it registered for street use. I would like to use it to commute to work and school. As its a bit lower than most normal road-going vehicles, I wonder what the probability is that a preoccupied (read 'texting') SUV driver will not see me, run me over and squish my various and sundry internal organs out into the road. In my mind, the potential joy of driving this ridiculous thing on the street is worth the risk.

Here is some of the damage that prompted the rebuild, the motor overheated due to operator error 











During the rebuild I also increased pack voltage. A side to side comparison of battery trays is an appropriate illustration of how a 16S pack differs dimensionally from a 24S pack of CALB CA100 cells.










Here are a few pics of how the kart is currently setup.


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## Duncan (Dec 8, 2008)

Hi Electron

IMHO you will be "visible" because you are different
Just In Case - you could add a pair of flags a couple of feet higher
Two flags because one is dorky!
Choose something radical for the flags - your favorite sport team or the Jolly Roger - not just a boring red triangle

Keep a good eye open in front of you - the biggest problem you are likely to have is somebody pulling out on you because they haven't "seen" it as a car


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## electron bom (Dec 4, 2014)

Flags! I never thought of that, thanks for the idea 

Here is a video of an acceleration run. Vehicle weight (w/o me) is 600lbs, 180 of which are the prismatic cells. I think it would be neat to build a super lightweight pack and do a back to back comparison. I can only grin foolishly at the thought of how it could behave should it weigh 450lbs being powered by a 30lb lipo pack 

http://www.dailymotion.com/video/x2o87bl_27-6-kw-acceleration-test


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## Jayls5 (Apr 1, 2012)

I have a bunch of questions for you:

Is that a ME1003 I'm spotting? Top speed? That's around 8 kWh, right? Expected range? Curb weight?

What kind of user error are you talking about that trashed your old motor? How hard did you push it? Thanks.


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## electron bom (Dec 4, 2014)

Jayls5 said:


> Is that a ME1003 I'm spotting?


It sure is!



Jayls5 said:


> Top speed?


In the video I'm seeing my speedo just barely touch 45mph. On paper it should do 43.5mph. My registered speed indicates that the ME1003 is spinning only slightly faster than 3000rpm.



Jayls5 said:


> That's around 8 kWh, right?


At 76.8V nominal the pack is 7.68kWh, then again CALB underrates these cells and they claim their 100AH CAs will actually perform like 110AH cells at 0.3C 



Jayls5 said:


> Expected range?


I can't say for sure, but since the rebuild I've only reached 8.5% DOD. That level of power consumption propelled me ~3.75mi over rolling hills with lots of acceleration, its kind of addicting. Extrapolate that out to a max of 80% DOD and I get 35ish miles of range on hilly roads fantasizing that I'm a Formula driver  (ie: not commuting-to-work levels of throttle input). Further maths reveal that these numbers suggest I'm doing 174.08wh/mile and while my figures are only as accurate as my e-xpert pro's margin for error is wide, I can't help but notice that my mini buggy is 12.5% more efficient than a Tesla model S at similar speeds Ok, so the Tesla is doing well over 60mph by the time I hit 40mph, I guess its apples to peanut butter sandwiches, but whatever...


Jayls5 said:


> Curb weight?


 600lbs without me.



Jayls5 said:


> What kind of user error are you talking about that trashed your old motor? How hard did you push it? Thanks.


Over the winter I had it out in the snow almost every time the roads became covered (WRC fantasy). One day it snowed a little more than usual (~6") and I continually became stuck while my front fender had a plow effect on the snow in front of me. I can't say definitively what current over time did the motor in since the reason I fried it was that I wasn't paying attention in the first place. I did notice my e-xpert registering 340 amps immediately preceeding a particular smell, my controller was set to limit current to 260 . My best estimation is that I was feeding the ME1003 between 260-340 amps for about 3ish minutes. I really wish I had a data log to share with you, but like I said, I was being an idiot.


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## dougingraham (Jul 26, 2011)

electron bom said:


> Here is a video of an acceleration run. Vehicle weight (w/o me) is 600lbs, 180 of which are the prismatic cells. I think it would be neat to build a super lightweight pack and do a back to back comparison. I can only grin foolishly at the thought of how it could behave should it weigh 450lbs being powered by a 30lb lipo pack


A known to work pack is the ones John Metric has made and sells via his Ampahaulic.com web site. They are 6S 4.5 AH packs that can do 450 amps (100C) for for brief periods. I bought one of these for testing and so far it is my benchmark. You would need three of them in series. They weigh 700gms so three would be 2.1 kg (4.62 lbs). An 18S pack would have a peak voltage of 75.6 volts with a nominal voltage of 66.6 volts. This is 0.3 kwh so with your 174 wh/mile this pack would only power you for about 1.7 miles. Make it 6 packs instead for a 4.2 kg (9.24 lbs) pack that could take you 3.4 miles. If your motor controller can handle it go to 4 packs in series for a total of 100.8 volts (88.8 volts nominal) and then parallel that for a total of 8 packs. Should have a range of 4.5 miles at a weight of 5.6 kg (12.32 lbs). This would drop your 600 lbs down to 432. Should boost your range as well a little. This would be pretty reasonable if you can live with the range. These packs cost $120 each which is quite a bit less than the best rated RC hobby packs that can do the High C rates.

And that would be a heck of a ride!


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## electron bom (Dec 4, 2014)

Thank you for the link, I will definitely look into his kit. I previously considered a 4S4P pack utilizing the lipo cells below for a 32lb pack capable of 800A continuous. I hesitate because it seems the general consensus among the RC enthusiasts is that the claimed discharge rates are somewhat optimistic...


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## dougingraham (Jul 26, 2011)

electron bom said:


> Thank you for the link, I will definitely look into his kit. I previously considered a 4S4P pack utilizing the lipo cells below for a 32lb pack capable of 800A continuous. I hesitate because it seems the general consensus among the RC enthusiasts is that the claimed discharge rates are somewhat optimistic...


The first problem with the RC packs is the wire is 10 gauge and 10 gauge wire has a fusing current of 333 amps. The ampahaulic packs have 8 gauge (472 amp fusing current) and John tells me he can get them made with 6 gauge (668 amp fusing current). You can use the RC packs but you need to parallel a lot more of them. From Hobby King it looks like anything above about 3 ah on the high C rate packs comes with 10 gauge. You do have to be careful to not to get 12 gauge. I have been looking at the 65C/130C packs and if you believe those ratings on a 3.3 AH pack they are talking 215 amps continuous and a burst rating of 429 amps. Clearly 429 exceeds 333 so the 10 gauge wire will most likely fail before you reach that current. The second big problem is the connectors. Most of these high C rate packs come with 5.5mm bullet style connectors. These are actually pretty good but they start to heat at 100 amps. At some point the solder will melt and the wires will pull out of the solder cup. The next reasonable size of Bullet connector is the 8mm ones. They are probably good for 200 amps continuous but can do more for a while.

If you want to try to use the HK packs for drag racing you will want the High C packs and really only run them at about half of their continuous C rating. That way you can use the 5.5 mm bullet connectors and the wire and battery will not suffer. That battery you have a link to (8AH at 25C) I would run at 12.5C which is 100 amps tops. This would keep the wires and connectors happy. But you need 4P like you mentioned to keep the currents in check with your setup. A 4P pack of these would limit the current to under 100 amps per pack. 4P is 32 AH. I think the 4S4P arrangement would work for you. 924 gm per pack means 14.78 kg (32.5 lbs). Voltage would be a nominal 74 volts and it would store 2.37 kwh.

But my impression is that you are not drag racing so you need more than just 15 seconds worth of power. So 100C discharge rates are not necessary for your application.

Best Wishes!


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## electron bom (Dec 4, 2014)

Thanks much for the break down! I dare not feed the me1003 more than 400A peak, my controller will allow 450A and is capped at 80VDC.


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## Jayls5 (Apr 1, 2012)

electron bom said:


> It sure is!
> 
> 
> In the video I'm seeing my speedo just barely touch 45mph. On paper it should do 43.5mph. My registered speed indicates that the ME1003 is spinning only slightly faster than 3000rpm.
> ...


Awesome! What does your voltage sag look like at max output? I'm running 74v nominal with the same motor, but I think I have enough LIPO cells at this point (90AH) to not have any significant sag while cruising at high speed. I'm load testing the last shipment of cells that came in to finish filling this thing up:

















I'm not sure if you have been following my build thread, but I'm air cooling my ME1003 with an 8" automotive fan bolted to the back of it. If you're trying to get a little more power out of yours, it might be something to look into. The fan only pulls 80-100w. The fan was super cheap on ebay, and I have an extra plastic baffle to mount it on if you're looking for one.



electron bom said:


> I can't say for sure, but since the rebuild I've only reached 8.5% DOD. That level of power consumption propelled me ~3.75mi over rolling hills with lots of acceleration, its kind of addicting. Extrapolate that out to a max of 80% DOD and I get 35ish miles of range on hilly roads fantasizing that I'm a Formula driver  (ie: not commuting-to-work levels of throttle input). Further maths reveal that these numbers suggest I'm doing 174.08wh/mile and while my figures are only as accurate as my e-xpert pro's margin for error is wide, I can't help but notice that my mini buggy is 12.5% more efficient than a Tesla model S at similar speeds Ok, so the Tesla is doing well over 60mph by the time I hit 40mph, I guess its apples to peanut butter sandwiches, but whatever...
> 
> 600lbs without me.


I somehow missed the video from earlier. Looks quick!

I would be stoked if I got your range after finishing things up on mine, but I have about 400 pounds worth of extra vehicle even though my total pack weight is only 105 pounds. 



electron bom said:


> Over the winter I had it out in the snow almost every time the roads became covered (WRC fantasy). One day it snowed a little more than usual (~6") and I continually became stuck while my front fender had a plow effect on the snow in front of me. I can't say definitively what current over time did the motor in since the reason I fried it was that I wasn't paying attention in the first place. I did notice my e-xpert registering 340 amps immediately preceeding a particular smell, my controller was set to limit current to 260 . My best estimation is that I was feeding the ME1003 between 260-340 amps for about 3ish minutes. I really wish I had a data log to share with you, but like I said, I was being an idiot.


Hmm... I run around 300A motor setting on my Alltrax, but I never did continuous runs that long. Plus, I had my fan going. Maybe that kept it alive. Are you temp monitoring your motor? If so, where did you mount your thermocouple?


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## electron bom (Dec 4, 2014)

I have seen your thread I didn't recognize your SN at first, but I have thoroughly enjoyed following your progress. Your buggy build is VERY intriguing and inspires me to work harder on my own

I can't yet say what I'm getting for voltage sag with the new pack. I've been so busy with work and school that I've only driven the buggy once since conducting the rebuild. I'm looking forward to playing with it some over the weekend, but I'm still trying to come up with a solution to enable data-logging capability while I'm driving on the street. My laptop is a bit cumbersome and the buggy is pressed for space. That being said, I would really like to get some data points in the context of street driving. 

The question is, how to get my setup in the video below into my buggy?
http://www.dailymotion.com/video/x2...ushes-e-xpert-pro-alltrax-controller-pro_auto

I do have a thermocouple that came with the mychron, its not installed yet as I haven't decided where it would be best placed. 










I have been considering a puller fan, but I want to mount my thermocouple first to determine net effectiveness of the increased airflow. I noticed that you mounted yours to the motor case and are measuring motor case temperature as a derivative of magnet temps? I have been kicking around the idea of mounting mine just inside the vents concentrically around one of the vent screws.


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## electron bom (Dec 4, 2014)

I just found this on evwest for $389, wow its gorgeous albeit a bit decadent for a minibuggy like mine...


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## Jayls5 (Apr 1, 2012)

electron bom said:


> I have been considering a puller fan, but I want to mount my thermocouple first to determine net effectiveness of the increased airflow. I noticed that you mounted yours to the motor case and are measuring motor case temperature as a derivative of magnet temps? I have been kicking around the idea of mounting mine just inside the vents concentrically around one of the vent screws.


I think you mean "pusher" fan. If you're going through the back, the internal mechanical fan's airflow flows towards the shaft. If you put a puller fan on the back, it would be fighting the stock airflow direction.

Grab this fan: LINK. Just undo the retaining nut, flip the blades around, then reverse the polarity to make it a pusher. You can either make your own baffle, or I can hook you up with my extra one for a small fee .

It will be a tight squeeze, but I think there's room based on the last video you sent.

I haven't actually mounted my thermocouple yet, which is why I was wondering if you found a good spot. In my build thread, I referenced max case temperatures straight from email advice from Motenergy. I would rather have it close to the important bits though so there's less of a delay.


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## electron bom (Dec 4, 2014)

I was thinking more along the lines of a lightweight blade system akin to a vertical wind turbine. Ideally I'd mount it on the shaft and it would rotate at shaft rpm acting as a 'helper' fan, for lack of a better term. Planning my thermocouple placement around this type of fan design is difficult as there is no outstanding solution. Honestly your setup makes more sense, but I like the idea of minimizing parasitic current drains. Here is a pic of what inspired my idea.


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## electron bom (Dec 4, 2014)

^ cant beat that price though! (just clicked your link)


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## Jayls5 (Apr 1, 2012)

electron bom said:


> ^ cant beat that price though! (just clicked your link)


Haha, I thought you'd like that.

You can either D/C-D/C converter, run a large low voltage battery, or get a 100w flexible solar panel: Link

I personally just made a 30A 14.8v LIPO pack to run the rest of the car. Easy and only weighed 6 pounds.


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## Yabert (Feb 7, 2010)

Hey, I like your buggy!
What do you need to be registered? Fender? Roof? Flasher? Also, do you wear an helmet?


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## electron bom (Dec 4, 2014)

Did a few runs last night, at 370amp draw I'm seeing a sag to 68V. If time permits, I'll conduct a load test of my new cells this weekend. 

I'm running my speedometer, headlights and tail light off a HK 4S lipo, its the best solution imho. I suppose a 100w fan wouldn't be too much to ask of it as well. I could just wire another 4S in parallel which should more than compensate for the extra load. 

In my ******* state, you can drive golf carts (Low speed vehicles) on streets with less than 35mph limit, the golf cart however must be restricted to 29mph top speed, go figure... You must also have flashers (front/rear) side mirrors, head/tail lights, DOT windshield with wiper, safety restraint and reflective markers on all four corners of the body. I'm mostly there, but its hard to find a certified inspector who isn't insane. The last quote I received from an authorized inspector was $600!!!! At that price point, it may just be cheaper to register it as a custom built road car.


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## electron bom (Dec 4, 2014)

Thermocouple and fan upcoming, then I think its ready for its first auto-x.
Here is a video of my first test pushing it to the limits on the local 'proving grounds' =D

http://www.dailymotion.com/video/x2oy0bs_electric-kart-time-attack_auto


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