# Electric mini sprint dirt track race car build



## madderscience (Jun 28, 2008)

You can do a lot with very minimal or no BMS if you are paying very close attention to what the battery is doing and its overall health. This might be a viable approach in a competition/race car. I'd never recommend it for anything you drive daily though; look up some of my other BMS related posts for more long winded reasons why.

Keep in mind racing you will probably be using 3,4, or maybe as much as 10 times as much power as the same miles driving normally on the road. So I hope you are sizing the pack with that in mind. Remember on top gear when they drove the tesla roadster on the track and ran it out of juice after 30 or 40 miles then made a big fuss because it was supposed to have 200+ mile range? Same thing. (of course later they admitted that most of the supercars they drive under the same circumstances get 1 or 2 mpg under the same conditions...)

Some kind of indicator of problems would be very helpful if you are in competition, and you of course want it to be simple. All the production/3rd party BMSes I know of have this ability. 

At the barest minimum put a digital panel volt meter across every 12V series worth of cells (assuming you are running not too high a voltage) and mount them someplace you can see it. Its also very easy to build a simple voltage comparator circuit that will light an indicator if the voltage it is sampling goes above or below a threshold. One of these could be attached to every 12V as well along with the panel voltmeter. Instead (or in addition to) each one lighting an LED they can trigger a common warning indicator and/or throttle limiter via optocouplers to deal with the different potential of each sampling circuit (which I am assuming is powered by the bank it is monitoring)

Of course you can keep making things more sophisticated but eventually you have built your own full featured BMS.

Good luck.


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## Windydrew (Dec 18, 2015)

The tracks are 1/8th mile and 3 heat races are only 6 laps. It's the feature I might get in trouble over. It's 25 laps and full of cautions and restarts. I will only know how long the battery will last when I start racing this spring as I don't know how to predict how much power I will use. Once up to speed, there's probably not a lot of energy needed to keep it going but passing and turning happens often. I guess I'll find out in April. 

I'm going to use a Nissan leaf motor, getting a custom sprocket made soon.


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## TerryH (Jun 9, 2012)

Agree with Madderscience. In a race setting you can probably get away without a BMS. Technically you will become your own BMS. Different animal but I monitor my cells in the dragster manually and it works fine. I actually enjoy it. Good luck with your project. Sounds very cool!


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## Windydrew (Dec 18, 2015)

Thanks. I'm looking at getting battery plates made to make the volt battery more usable. My plan is to have steel plates laser cut and then have adapters made with either npt or an threads on them for the coolant connections. That way the modules could be reconfigured in any way needed. I'm planning on making 4 96v packs out of it. I will take the 2 24v sections and put them on the one remaining 48v section. That way they'd be more balanced in size and weight. I wonder if anyone would be interested in these plates and adapters to use these packs easier? I'll ask what it would cost to make more. Thanks, I'll keep updating when I know more.


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## piotrsko (Dec 9, 2007)

I myself would use the battery plates as-is. They are structural, probably stressed to 6 G for accidents, although IMHO way too many attach bolts. Quick change DIY mini packs.

Bms is your choice, I don't run one so far 2years sucessfully. No easy install using factory bms.

I would also use Chevy quick change harnesses. 1#10 bolt and good for (so far) 600 peak amps.

The entire pack is more or less rated equivalent to 2gallons of fuel. So if you can run the feature on 2 gallons, you're golden.

I haven't done this since ASCOT in smell-a closed so I am not sure how relevant I am any more.


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## Windydrew (Dec 18, 2015)

What do you mean by way to many attach bolts? I'm talking about the metal ends plates that hold the battery together with the 4 long bolts and the water connection fittings won't work so I'll have to have something custom made. I think you misunderstood me.


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## Windydrew (Dec 18, 2015)

Also, what is the chevy quick change harness? I'm using 2/0 cable for my car, there's no way to use the factory battery straps for my situation.


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## Windydrew (Dec 18, 2015)

piotrsko said:


> The entire pack is more or less rated equivalent to 2gallons of fuel. So if you can run the feature on 2 gallons, you're golden.


How did you figure that?


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## Yabert (Feb 7, 2010)

Windydrew said:


> My plan is to have steel plates laser cut and then have adapters made with either npt or an threads on them for the coolant connections.


I've done this with aluminum (post 298): http://www.diyelectriccar.com/forums/showthread.php/smart-fortwo-ev-high-power-version-51472p30.html
Be careful because the two plastic coolant exits of a battery module are not flat. There is always one side who protrude more than the other.
I think it can be easier to carefully weld connectors on the existing end plate.


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## Windydrew (Dec 18, 2015)

The adapters I would have made would account for the difference, I will use extra long all thread and use the extra to mount the water fittings. I've got a guy lined up to laser cut the plates once I give him my design. I have to pull the plates off the longest cause it'll have to be used as 2 96v packs. So once I do that, I'll have the design figured out and then work on the water fittings. Almost have my garage cleaned out, might me done today. I'll get pics of my setup when finished. Thanks


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## madderscience (Jun 28, 2008)

on the gallons of fuel equivalent, you can estimate needed battery size from fuel consumption by making a comparison of the relative efficiency of a gas engine vs. electric motor (we usually use 4x better for electric motor) , and knowing gas contains 33.2kwh of energy per gallon. This assumes of course no weight chassis efficiency difference between the electric and gas versions of the vehcile.

If your race car needs 1 full gallon to do 25 1/8 mile laps, or about 4 miles under race conditions, then:

33.2kwh/gal * 1gal / 4 == 8.3kwh

So you should be able to do the race easily on a full 16kwh Volt pack, 3/4 of a pack will be pushing it, and you WILL run out if you use a 1/2 pack.

I think the 2 gallon equivalent comment comes from the relative efficiency of a volt. It can go about 35-45 miles on a charge (using about 12kwh, which works out to somewhere around 20-25mpg equivalent)

This math assumes regular gasoline and efficiency of the race engine similar to that of regular cars. If you are running ethanol it is LESS energy dense than gasoline but I don't know the numbers, and race engines may also be less energy efficient (or more, I don't know) that a gas engine used on the road, so all things to look into. Still for ballpark numbers I don't think I'm far off.

It just occurs to me you might have an ace in the hole if you are using an AC drivetrain -- you can figure at least 10% maybe 20% recovery of energy due to regenm assumming you are braking hard going into the corners. If its all throttle work and no brakes it won't give you anything.


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## Windydrew (Dec 18, 2015)

So if I can normally make it through the entire night with about 8 gallons of methanol, what would I need for a battery?


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## samwichse (Jan 28, 2012)

8.3kwh/gal or 66.4 kwh for 8 gallons worth according to the above.

Way too much for the size of car you're running.

Maybe you could do two swappable packs and charge one while you're using the other and trade between events?


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## Windydrew (Dec 18, 2015)

Well, for now I'm going to do my best to make this pack work for now. Might have to get a big 110v charger and plug it in right after each race.


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## Windydrew (Dec 18, 2015)

I'm hoping with the pmac motor, it'll be a little more efficient making good power. I guess I'll know soon enough. Merry Christmas if I don't get another chance.


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## Glocker40 (Dec 20, 2015)

Your project sounds cool ! I too wish to use the Volt batteries for my MX Bike buggy I'm building. It's also nice to hear the gas-electric comparisons in simple terms and the different ways to monitor the battery. Do you have photos of your motor?


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## Windydrew (Dec 18, 2015)

The motor is in the machine shop right now getting a custom hub made for a sprocket. Once it's out, I'm going to be mounting the motor first. It weighs a lot, about 126 lbs. I'm hoping to get rid of all the extra brackets and just use a couple bolts front and back to shave a little weight off of it. I'm working on the design for the battery plates to save as much weight as possible on those mounts as well. I'll use the car frame as structure for the batteries since it's a tube frame and doesn't twist much. Should be interesting once I start making progress soon. Keep watching! Thanks


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## madderscience (Jun 28, 2008)

Hmm,

well according to here:

https://en.wikipedia.org/wiki/Energy_density

Methanol has HALF the energy density of gasoline. So that means if you use 8 gallons of it in a night at the track, that would work out to roughly 32 kwh, or two full charges of your volt pack. If that is broken up into four races using roughly half a charge each and with enough time in between to charge, it might be doable.

Another way to estimate how much energy you need (there are many)

How long can you sustain 100hp continuous on a 16kwh battery pack? (Totally arbitrary hp number of course, and power use won't be constant on a race track, but its a way to look at it.

100hp * 746w/hp == 75kw. If you did that for an hour you would need 75kwh. So assuming you want to use no more than 12kwh from your 16kwh volt pack, that means you can sustain 75kw for 12/75 hours, or just about 10 minutes. This does not consider the C rating of the battery or any other kind of overheating or other such issues. Its just a simple mathematical estimate based on capacity of the battery to put out so much power for so long. 

Going back to that 4 mile race (25 1/8 mile laps) if you were driving a regular full sized car like grandma going to church, you would have to be averaging 24mph to need all that 10 minutes to do 4 miles. In reality a full sized regular car would only need 3 or 4hp to do that. So 100hp continuous for the same distance hould allow for pretty spirited driving.

How big is the methanol fuel cell on one of these cars, and how long will it last (time, and distance) under race conditions?


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## Windydrew (Dec 18, 2015)

I was told 3 to 4 gallons can get a car through a 35 lap feature.


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## Windydrew (Dec 18, 2015)

I ordered the volt lear charger for 350 shipped with all the connectors attached with a decent amount of wire so now all I need is the can controller. Getting closer. Going to try and mount the batteries by this weekend.


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## madderscience (Jun 28, 2008)

3 to 4 gallons of methanol for 35 laps. Now we are getting somewhere. That's 1/10 of a gallon per lap.

3.5 gallons (taking the average of 3 and 4) * 16kwh/gal == 56kwh for the night. 56kwh / 35 laps = 1.6kwh worth of methanol per lap.

If the electric motor is 4x more efficient than the race prepared gas engine (this is still an open question) as previously posited, then 1.6kwh / 4 == 0.4kwh per lap, or only 14kwh for 35 laps running on electric. 

That would suggest you might be able to make the whole race on a 90% or so discharge, but more likely you would want to recharge (or swap) once during the night, if you have a full sized volt pack. You would not even need to get a full recharge.

If you know average lap speed, then with that and fuel consumption per lap and your estimate of engine efficiency, you can compute horsepower requirement and use that number in my prior post where I figured run time based on continuous horsepower usage.

There are several different approaches for estimating presented now. You should have a pretty good picture of what it is going to take to power the car I hope. Good luck.


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## Windydrew (Dec 18, 2015)

Thanks, that does give me a good idea of what I can run. That makes me more confident that this will work.


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## jwiger (Oct 18, 2014)

Windydrew said:


> I ordered the volt lear charger for 350 shipped with all the connectors attached with a decent amount of wire so now all I need is the can controller...
> 
> 
> > Will you be running the charger off chassis? No sense in carrying that extra weight around the race.
> ...


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## Windydrew (Dec 18, 2015)

Yes, running the charger off board.


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## Karter2 (Nov 17, 2011)

Interesting project, especially as you have chosen the less common AC drive.
Any specific reasons to go with the Leaf motor rather than the proven DC options ?


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## Windydrew (Dec 18, 2015)

Karter2 said:


> Interesting project, especially as you have chosen the less common AC drive.
> Any specific reasons to go with the Leaf motor rather than the proven DC options ?


Price, efficiency, and recycling used parts all went info my decision. I prefer ac for regenerative braking. I won't be using it on this car but I plan on building multiple conversions with the leaf motor so I wanted to try it with a simple car like this. I have less than 2000 in the controller and motor, so it's much cheaper than comparable dx motors. And it's water cooled so I plan on running it at 200% power (160kw) to see how it handles it. I only need 150 hp or so but I want to show the competition that electrics are here to stay and are affordable. And these motors are everywhere since there isn't a market for them yet. Leafs are mostly still under warranty and the motors aren't a common failure part. So I prefer to use then rather than get destroyed.


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## Karter2 (Nov 17, 2011)

Ahh !
You are fortunate to have such availability of cheap Leaf components.
We rarely see a Leaf on the street here, let alone in a dismantlers 
Is adapting the Leaf hardware to run independent of its mother car, difficult, or are you using a 3rd party controller/inverter ?
Good luck with this, I am following with enthusiasm !


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## Windydrew (Dec 18, 2015)

Karter2 said:


> Ahh !
> You are fortunate to have such availability of cheap Leaf components.
> We rarely see a Leaf on the street here, let alone in a dismantlers
> Is adapting the Leaf hardware to run independent of its mother car, difficult, or are you using a 3rd party controller/inverter ?
> Good luck with this, I am following with enthusiasm !


Sorry I didn't respond right away. I've been busy building a solar hot water collector to get my heat bill down some. Fun fun. 
Ok, I will be receiving the 200kw motor controller next week some time. I'm looking forward to testing it, but the guy that designed it bought a leaf motor and already got the thing programed for me. Water cooled, customizable, ac motor controller for $1300 is an amazing price. He was able to build a conversion board to run th factory leaf resolver on the default encoder signal that he designed his program around so it's now ready to run almost any 3 phase motor you could find! Pics to follow soon.


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## Karter2 (Nov 17, 2011)

Ah ! Ok, is that controller from one of the contributors here ?.
...eldis, ? MPaulholmes ? ..


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## Windydrew (Dec 18, 2015)

Karter2 said:


> Ah ! Ok, is that controller from one of the contributors here ?.
> ...eldis, ? MPaulholmes ? ..


Yes, I believe it's Paul. His website is PaulandSabrina


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## Windydrew (Dec 18, 2015)

So had made some progress on my race car in the last week. Machine shop got my custom splined sprocket for the leaf motor done. Also Paul got my motor controller finished up and shipped. Looks great and can't wait to get it running. Now my last piece of the puzzle is the charger. Was going to use the volt lear charger, but when I went to place my order on evtv after talking with Jack, he removed the CAN controller because I ticked him off somehow. Now I'm stuck with a 3.3kw aluminum paper weight. If anyone can help me out to either get Jack to change his mind or come up with another solution, I'd pay good money for a solution. Thanks


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## dedlast (Aug 17, 2013)

I'm curious about your splined sprocket, if you don't mind answering a couple questions. How are you clamping or holding it onto the shaft? Also, who did you have make it and how did they make it?

Thanks,
B


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## Windydrew (Dec 18, 2015)

dedlast said:


> I'm curious about your splined sprocket, if you don't mind answering a couple questions. How are you clamping or holding it onto the shaft? Also, who did you have make it and how did they make it?
> 
> Thanks,
> B


Local machine shop called Finn-Kool. 
So I bought a bunch of clutches from a few different vehicles, I think I ended up with a 95 geo tracker clutch. Machined down the center until it was round. Then cut down a cbr 600 sprocket to fit over the clutch hub. Then welded the two together. I'm going to be drilling and tapping a set screw to the o ring groove in the leaf shaft. I'll be taking pictures soon once I get ready to mount the motor up.


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## dedlast (Aug 17, 2013)

Just to make sure I'm not getting my hopes up too far, do the splines in the Tracker clutch match the splines on the Leaf motor? How tight do they fit (if they do)? 

Thanks, again.
B


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## Windydrew (Dec 18, 2015)

dedlast said:


> Just to make sure I'm not getting my hopes up too far, do the splines in the Tracker clutch match the splines on the Leaf motor? How tight do they fit (if they do)?
> 
> Thanks, again.
> B


It's 7/8ths 20t. It fits the leaf a little loose, but when they were machining it, they added a collar to it to make it tighter fitting and adding at screws to keep it engaged. I believe the clearance was less than 20 thousandths.


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## dedlast (Aug 17, 2013)

Veerryy interesting. Thanks, that's a good find and should be a good starting point, just like you did with it. 
Let's see, 7/8 is 0.875. I measured 21.5 mm on my Leaf spindle which is 0.8465. The difference I get in those numbers is 0.0285. The Leaf could be a bit more than that, but I don't think by much, maybe as much as ~0.086. It should be pretty easy to clamp that down to a usable number.

B


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## Windydrew (Dec 18, 2015)

Got my battery plates and motor mount laser cut at the local fab shop. Haven't found anyone to build my coolant adapters yet, but I'm working on that now. I'll post pics when I get the battery plates and motor mount attached.

Also bought 8 48v hp server power supplies for charging at the track. 24kw total power but Ill probably turn them way down. Getting closer!


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## dedlast (Aug 17, 2013)

Windydrew said:


> It's 7/8ths 20t. It fits the leaf a little loose, but when they were machining it, they added a collar to it to make it tighter fitting and adding at screws to keep it engaged. I believe the clearance was less than 20 thousandths.


Drew, 
Any chance you have pictures or more info on what you had done? I picked up an Exidy '95 Geo Tracker clutch disk for $30 delivered (it was actually cheaper than driving to the pick and pull). I tore it apart and machined the center hub down a bit to make it more usable but I still need to figure out how to get it clamped down to the motor shaft.

Bill


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## Duncan (Dec 8, 2008)

Hi dedlast

Why do you need to "get it clamped down"
Both the Leaf and the Geo use the male and female bits with sliding clearance as does every manual car on the road
There is also a similar sliding clearance spline on most driveshafts

So why do you want to clamp it down??


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## dedlast (Aug 17, 2013)

"So why do you want to clamp it down??"

Because I am choosing to keep the clutch. Why? Because I want to.  
I think I need to solidly mount the flywheel to the motor so it doesn't "dissolve" the spline over time.

Bill


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## Windydrew (Dec 18, 2015)

I doubt what I did will work if you plan on using the clutch, which I even question why you would want to. I made a sprocket for chain drive, I doubt anything else would work besides the leaf gearbox in your case buthe even then the leaf doesn't use a clutch.


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## Windydrew (Dec 18, 2015)

So time for an update. Electric sprint car frame has been sold and a Pulse Autocyle has been purchased. I'll start a new thread for the build but it's already mostly complete, a few parts away from running. Restoration will follow this winter.


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