My first go kart - electric conversion

[florin]

Few weeks ago I bought an old rusty racing go kart for $150.
It has a Honda GX140, Enginetics hydraulic brakes, a home-made seat and it doesn't work (engine is missing the pull starter, the carb is full of rust, the brake line is broken and the caliper is seized).

My plan was to convert it to electric power for my 8 years old son, so all I was interested in, was a strong chassis, good wheels and good steering.

I removed the brakes (the line was broken and the caliper was stuck) and the motor and I installed an Ametek 72V DC motor (I have few of them laying around), a 60 Amp key switch, a 30A fuse and two Lithium Polymer 22V 4Ah in series, for 44V, 4Ah (from my remote controlled airplanes).

The motor was attached to a piece of plywood using a U clamp and a bungee cord - works better than expected. This is just an initial set-up, to test gears and different motors. After choosing the optimum set-up, I'll build some better metal brackets.

The initial test was with a 12V Pb battery - the kart was moving too slow. I used then a 22V LiPo battery and the kart started to move faster. Now I am using 2x22V in series for 44V, 4Ah that gives a top speed of 15Km/h (about 10mph) and almost 1 Hr of driving. It is above my expectations. I was hoping for 15km/h, but I did not even dare to think of 1 hr driving per charge - for a 8 years old kid.

I was afraid the go kart won't start from a still position, but when the kid is turning the key, it starts really well. It does make a "bang" and probably it's stressing the chain/sproket/engine...but it is a test set up.

I ordered a speed controller from eBay for $35 and a hall effect sensor that will make a nice throttle device. I have to install a magnet on the throttle pedal that will generate a signal in the Hall Effect sensor that will transmit the signal to the speed controller. The hall effect sensor is replacing the potentiometer that comes with the speed controller. Well, I hope it will work, otherwise I have to find a way to move the potentiometer with the throttle pedal.

I purchased a relay ($4 for the relay and $4 for the socket and wires) that will be activated by a switch on the brake pedal. When the relay is not energized, it will provide power from the battery to the motor, but when the brake pedal gets pushed, the switch will activate the relay and the relay will cut the power from the battery and short the motor terminals for an electric brake. I tested the short terminals brake and it seems very strong. If it is too strong, I will add a resistor in series to lower the short current or even more resistors in different steps/ positions of the brake pedal.

Below are some pictures and videos of the go kart I bought and the first electric set-up (battery/motor, fuse and switch).

Video1

Video 2

Video 3

http://www.youtube.com/watch?v=Ovv6Vyd7wEY&feature=autoplay&list=ULvNeI2BF1lng&playnext=2

 

[souperman000]

a nice, clean conversion. I like it.

 

[landuse]

Well done. So many people seem to have a problem with electric, but you seem to know what you are doing

 

[j.concepcion54321]

Nice kart! How much power do you think all 72 of those volts would provide roughly? I'm looking for a motor for my chopper bike. Electric would be easy and that way the neighbors can't tell its motorized cause ill just pretend to pedal. Lol.

You said you had a few of those motors? Would you be able to sell one? Let me know. Or send me a PM if interested.

 

[ML-TOYS]

Thats nice, but being a service center for kids battery ride ons i have to put my input.

Any battery other than a SEALED lead acid battery is dangerous near flesh. Car and bike batteries can leak, spray and even explode spraying the driver with acid.
Lipo batteries can also explode.

This is the reason ALL scooters, kids and adult mobility scooters use sealed lead acid or gel batteries.

Like i said just my input but things for people to consider when safety is a factor.

 

[florin]

ML-TOYS, thanks for reminding me the potential danger. Indeed, Lipo batteries can catch fire in certain conditions like short circuit, overcharging, or mechanical damage. Overcharging cannot happen while driving and the effect of a short circuit should be handled by the fuse which is installed right at the battery terminal. Also I am using two LiPo bags to reduce the effects of a potential fire. I can install a metal box a well, to contain the potential fire

LiPo batteries need special handling, special charging algorithms and special storage and I think if you treat LiPos with respect, you are OK. I store LiPo batteries in ammunition cans and a metal safety box, I charge them at 1C only and always charge and use them in a safety bag, I discharge them 50% only. Yes, I do have a lot of "respect" for these batteres

Personally, I feel safer using LiPo (in a fire bag) under the steering wheel than a gas tank.

Here is a movie of an overcharging test for LiPo batteries without a safety bag and with a safety bag:

http://www.youtube.com/watch?v=d4lNx2Wn6Oc

 

[ML-TOYS]

That wasnt just towards your build, its safety info for everyone who is not aware.

 

[florin]

Nice kart! How much power do you think all 72 of those volts would provide roughly? I'm looking for a motor for my chopper bike. Electric would be easy and that way the neighbors can't tell its motorized cause ill just pretend to pedal. Lol.

You said you had a few of those motors? Would you be able to sell one? Let me know. Or send me a PM if interested.

Well, all I can say is that if the 44V 4Ah battery lasts for 1 hr, it means I used 4 X 44 = 174 Wh, so the motor put 174W while using my batery. Again, this is what I fed into the motor, but this motor can deliver a lot more power if you feed higher voltage.

Sorry, I cannot sell them, i used to sell those and I kept few for myself, same brand, just different voltages.

I also liked the idea of quiet electric kart.

 

[florin]

That wasnt just towards your build, its safety info for everyone who is not aware.

Yes, I understood that, but I included references to my set up and to my handling/charging/storage conditions for everybody to understand the implications of using LiPos.

Thanks again.

 

[florin]

Some progress : I replaced the plywood with metal brackets (Home Depot shelf supports). I still have to trim them as they are a bit too long.

I got all the electronics in the mail today: speed controller, the hall effect sensor, and the voltage regulator to build the throttle.

I also got the 40A relay from Princess Auto for the electric brake.

All I need now is few free hours

 

[landuse]

Clever use of shelving brackets

 

[florin]

Thanks landuse.

More progress was made, I connected the speed control to the motor and using the potentiometer, I could change the motor RPM. Then, I replaced the potentiometer with a hall effect sensor that cost a couple of bucks and now I can change the speed by moving a small magnet closer or further from the hall effect sensor.

All I have to do now, is to install the sensor on the frame and attach the magnet to a rod that is being moved by the throttle pedal. A push-rod system.

I'll post some pictures when I am done with the electric throttle.

 

[florin]

Here my new thread about building a cheap and reliable electric throttle: http://www.diygokarts.com/vb/showthread.php?t=18963

 

[robotmickey]

Hey! Cool kart. Someone asked earlier maybe, but what is the max output of that motor with all 72V and all the amps it will handle?

 

[florin]

Thanks, there is no label on the motor and I don't think there is any way to find it through a calculation.

 

[augidog]

great info, great project, and from this forum-user's perspective, great posts!

i'm embarking on a smaller electric project, for a DIY legal electric-assisted bicycle...i want to change an older system from 2-speed on/off to variable speed, and your theory is exactly what i've been looking for.

thanks, florin, nicely done.

 

[florin]

Thanks augidog. I hope to improve the design (the electronics), so please check this thread again in the future.

 

[Skalabala]

174W = 15km/h for an hour!!! Insane!! If you do 3+3 for 66V and 8ah then you are in business with a really small amount of batteries! How big are these batteries? Will 6 of them size up to one car battery in physical size? Imagine 20 of these batteries! You have something special going on here florin!

 

[florin]

The LiPo batteries are very different than lead acid batteries and they need a special charger that can charge this type of battery. LiPos are very light, store a high amount of energy, can be discharged at a high rate (a very common discharge rate is 30 times the capacity, which means if the battery is 4Ah, it can be safely discharged at 4Ah x 30 = 120Ah) and recharged in 1 hour. Newer generation of LiPos cand go even beyond these usual numbers.

A 12V lead acid battery has 6 cells of 2v connected in series, to make 12V. So each cell is 2V. In LiPo batteries each cell is 3.7V and you can buy them in any configuration you want: 1 cell, 2 cells, 3 cells, 4cells, 5 cells and 6 cells

If you buy a 2 cell LiPo, you have a 7.4 volt battery.
If you buy a 3 cell LiPo, you have a 11.1 volt battery...

The most popular LiPO cell capacity ranges from 100mAh up to 6000mAh (6Ah)

I used two batteries each having 6cells and 4000mAh which means each one is 22.2V. My total voltage for 2 batteries connected in series was 2 x 22.2V = 44.4V.

Each of my batteries is : 148x52x41mm (6 inch x 2 inch x 1.6 inch) and weights 590g (1.3 lb)

Here is a link with the details of these batteries:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7638

My batteries are 6S / 6 Cell / 22.2v, 4000mAh with a discharge rate of 20C Constant and 30C Burst.

This translates into:
6s = the battery has 6 cells in series
22v = 6 cells x 3.7 = 22V
C = 4000mAh - battery capacity
Continuous discharge rate C20 = 4000 x 20 = 80000mAh = 80 Ah
Burst discharge rate C30 = 4000 x 30 = 120000mAh = 120Ah

Here is a list of various LiPo that can be bought. This is the place I ususally by the LiPO batteries for my remote controlled airplanes:

http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=235

And this is a list of battery chargers:

http://www.hobbyking.com/hobbyking/store/__216__408__Battery_Chargers_Acc_-Battery_Chargers.html

 

[Skalabala]

Thanks for the info
But that is 3min 80ah and 2min 120ah
Anyway I am waiting for a price on these
http://skyhobby.en.alibaba.com/product/335318517-212908119/Tmetic10000mAh_22_2v_5C_lipo_battery.html
eight of them should be good for a tire smoker