E-Kart

Hi ES,
Have learned a lot from the forums over the last year, I had a project that never really went any further than planning and some motors.
Now I have gotten wiser, and found out what I’m really getting into, so I’m going to start of my EV carrier with a E-kart.
I found a cheap 48v - 7.5kw motor from a “kewet” electric car. It was 70 usd. And seems to be made the old-school “heavy is better” way, ill post some photos asap.
The kart will be a rolling chassis that I’m looking for second hand, should be no more than 100usd.
The batteries is where I don’t know for sure. I was thinking that a 15p13s 18650 pack with Samsung INR18650-25R should do the trick. I have designed a case that allows for cooling of all that cells, I don’t know is this is necessary but the batteries are the most expensive thing for the project, so I would really like to keep them as cool as possible.



Ill update when I have more to show

Cheers Toby

15P on the battery looks good, it's 10A continuous per cell to give you the ~150A/7.5kW to the motor. You shouldn't have any trouble with motor or battery peaking 2-3x that.

Are you planning to race this or just blast about the yard with it? It's a big difference in endurance requirements.

Its just for the back yard, and parking lot fun time, maybe i i can fit some large tyres on the frame it will go on some gravel as well.

Yes the battery should be safe at almost any level of draw from the motor, they can deliver 100 amps burst for 1 second, thats 1500 amps burst at 54v max charge, = A LOT of power.. which is why i would like to have alle the cells actively cooled

Cheers

10A continuous puts a 25R at about 60°C (starting at room temp.) which is rather warm, but manageable.

The 100A pulse (<1sec) rating I think of as more like a short-circuit current rating. It's unlikely to be useful as cell voltage is probably not going to be much better than 2V.

If you can get the Samsung 30Q for a similar price to the 25R it's worth going for as the spec is equivalent but you get an extra 500mAh.

A useful chart for comparing lots of 18650's at a glance is "Mooch's battery chart" (just google image search for it).

Well.. You will never get 100A / cell out of them when built into a pack,..even with the best interconnects.
Even at a fraction of that ..say 20 amps...you will have 5 mins run time at best and a working voltage of about 30v !..and a hot pack that is going to lose capacity very quickly
But , its unlikely you will use the kart like that,..much more random bursts of power.
However, it would be much better to use decent 30-40C RC lipo, ...less stress, less heat, less cost, and simpler to build the pack.

Where are you located at? If you're in the southeast USA, I know where theres a couple frames/chassis cheap...

I made my own e-kart earlier this year. it only goes 25mph, but it gets there instantly... pulls over 300a from a start.

Im located in Denmark, but thanks for the tip

I know that i will never see og use 100 amp /cell, and 20 amp /cell is twice the current of the motor, which is most likely only needed at startup.

I dont really want to use RC lipos, my dad have a lot of RC cars, and the batteries die of a a rather alarming and random pace, and this is using good celles from different name brands..

But what would you suggest for a lipo?

The good thing with 18650 is that i all ready know my way around them and have made a few pack, and i like the formfactor

But im open for ideers !

MrDude_1 said:

Where are you located at? If you're in the southeast USA, I know where theres a couple frames/chassis cheap...

I made my own e-kart earlier this year. it only goes 25mph, but it gets there instantly... pulls over 300a from a start.

Click to expand...

I am in Central Florida. How Southeast are these Karts?

drewjet said:

MrDude_1 said:

Where are you located at? If you're in the southeast USA, I know where theres a couple frames/chassis cheap...

I made my own e-kart earlier this year. it only goes 25mph, but it gets there instantly... pulls over 300a from a start.

Click to expand...

I am in Central Florida. How Southeast are these Karts?

Click to expand...

Charleston, SC

tobiasstaermose said:

Im located in Denmark, but thanks for the tip

I know that i will never see og use 100 amp /cell, and 20 amp /cell is twice the current of the motor, which is most likely only needed at startup.

I dont really want to use RC lipos, my dad have a lot of RC cars, and the batteries die of a a rather alarming and random pace, and this is using good celles from different name brands..

But what would you suggest for a lipo?

The good thing with 18650 is that i all ready know my way around them and have made a few pack, and i like the formfactor

But im open for ideers !

Click to expand...

I needed LARGE lipo so that the kids could run it until they got bored... so I used Nissan leaf modules. Each module is 2s2p for ~64ah... I have 4 stacked making a 8cell battery.

What you need to understand about RC lipo is that "typical RC use" is horrible abuse to the pack. they charge them to the max, they discharge them to the max, they pull large C rates out of them, and then they recharge them at high C rates.
You take that same RC lipo stacked in parallel for Ekart or Ebike size, and it sees tiny C rates in comparison. You charge it to 4.15 and stop at 3.6 and it will only lose a tiny bit of capacity, but gain years of life. finally charge it at a 1C rate (or less) and it will work for a long time.
I have thousands of miles on my RC lipo.. and I always charge at just over 1C..

I have had a look around and it seems that for the capacity i want, and the current draw i need, the lipos seems to be just as, if not more costly than a costume build 18650 pack, i could be wrong.

I'm looking at 18650 cells from nkon:

3000mah x 195 cells (4.2v) = 2.457kwh
2500mah x 195 cells (4.2v) = 2.047kwh

The cells i'm looking at are:

Samsung 25R 200 cells = 560 euros (2.80 euros/cell) = 0.274 euro/wh
Samsung 30Q 200 cells = 760 euros (3.80 euros/cell) = 0.310 euro/wh
LG HG-2 200 cells = 850 euros (4.25 euros/cell) = 0.346 euro/wh
LG HE-4 200 cells = 548 euros (2.74 euros/cell) = 0.268 euro/wh
I dont know of any other cells that will work with this type of capacity/amp rating.

The 25R and (HE-4) does look like a good battery for this project, (the 25R is ratet better at the Mooch testing that the HE-4) Especially when I'm a student that does not really make the big bucks yet.

Any better ideas for my battery?

Photos of the motor:
Battle weight of 31kg









Cheers

Well well well..

Got my hands on 2 LG chem 10s2p 30ah packs from user Monstarr.

These should do the job, and at way under the price of a 13s15p 18650 pack, and probably ALOT safer







Now the hunt begins for a suitable controller and some form of battery cell monitor system, any suggestions, preferably in the EU?

Cheers Toby