Can I make my own battery?

[b.mavroeidis]

Hello everyone,
As I'm searching for a battery to power my electric go kart I came across a dilemma:
Should I use a some lead acid batteries to power my motor
or built my own battery using the following cells:
(Samsung INR21700-50E 5000mAh 10A )
The motor is going to be around 1.8 to 3 kW.

​

 

[karl]

Do you have the equipment to spot weld tabs to the batterys?
Have a plan to secure all the cells together?
Are you qualified to work with and understand the danger of lithium ion batteries?
Do you understand Ohms law and Kirchhoff's ?
Do you have a plan to charge it?

If you answered yes to all those questions, go for it!
I still would advise against it and suggest you find something off the shelf.

 

[b.mavroeidis]

I have the equipment for the welds and I'm planning to 3d-print all the necessary parts to secure the cells.
Also I'm planning to build a cooling system for the battery.
And yes I have a charger for them.
So my main concern is if they are going to perform well.
Will they last?
Because there are more expensive than lead acid batteries I will only be able to afford something like 20Ah ,will it be enough?

 

[karl]

something like 20Ah ,will it be enough?

At what voltage?

 

[b.mavroeidis]

48V

 

[karl]

Lets apply Ohm's law, you are familiar with it, right?

3000w @ 48v , we need to find how many amps that is.
P/E = I
So 3000w / 48v = 62.5 amps

Your theoretical battery can provide 20 amps for 1 hour.

20/62.5 = .32 of an hour = 19 minutes of runtime at full power,
not factoring in any losses in the wiring or controller.
Actual runtime will be less.

 

[b.mavroeidis]

Yes , lets say that with the losses the runtime will be around 15 minutes. What kind of range would that give me. A 3kw motor running full speed for 15 minutes with an approximate 150kg payload.

 

[karl]

What is the drag coefficient of the kart? What is the rolling resistance of the wheels?
What is the speed of travel? Is the ground flat and smooth? What is the ambient temperature
it will be operated in?

I am not an engineer, and I am got going to devote lots of time into this.
So maybe sit down and do some research, while waiting for someone with more
experience to chime in.

 

[ezcome-ezgo]

I have no experience with this whatsoever. However! I subscribe to Karl's Law that says: If the amount of resistance to an idea from Karl is inversely proportional to your knowledge of the subject, look for something else to do.

 

[b.mavroeidis]

What is the drag coefficient of the kart? What is the rolling resistance of the wheels?
What is the speed of travel? Is the ground flat and smooth? What is the ambient temperature
it will be operated in?

I am not an engineer, and I am got going to devote lots of time into this.
So maybe sit down and do some research, while waiting for someone with more
experience to chime in.

Who even calculates drag coefficient on a diy go-kart hahaha? Speed of travel would be in the 20-30 mph zone. Rolling resistance is yet unknown. Ground type will be flat and smooth most of the times. The ambient temperature varies. (Greece)
Thanks for the time you already devoted

 

[b.mavroeidis]

I have no experience with this whatsoever. However! I subscribe to Karl's Law that says: If the amount of resistance to an idea from Karl is inversely proportional to your knowledge of the subject, look for something else to do.

Haha alright , message received but we mostly do the projects to develop our engineering skills

 

[karl]

Who even calculates drag coefficient on a diy go-kart hahaha? Speed of travel would be in the 20-30 mph zone. Rolling resistance is yet unknown. Ground type will be flat and smooth most of the times. The ambient temperature varies. (Greece)
Thanks for the time you already devoted

Lol Im just messing with you. I have never built / had experience with electric karts so I would have to calculate the answer.
Somebody who has played with simular setups would be able to give a much better idea quicker based on the real world.
(like functional artist)

When you just said 20ah and did not give the voltage, ya kind of had me worried.
Just wondering if they still teach analog electronics and back of envelope calculations , or just go straight to
digital/ coding.

 

[b.mavroeidis]

Lol Im just messing with you. I have never built / had experience with electric karts so I would have to calculate the answer.
Somebody who has played with simular setups would be able to give a much better idea quicker based on the real world.
(like functional artist)

When you just said 20ah and did not give the voltage, ya kind of had me worried.
Just wondering if they still teach analog electronics and back of envelope calculations , or just go straight to
digital/ coding.

Haha I'm not that much of a noob I just have a second thread for the same subject and I mess up the info I've given in each thread. When I asked for the range I was expecting just a quick estimate based on results from similar projects on normal real-world senarios and not exact calculations.
Anyway its cool that you admit you do not have experience on the subject and I shall thank you for the time you already devoted (even to troll me haha).

 

[karl]

Good sport, and your very welcome to any of my limited repair man knowledge. I do want to build an electric lawn chair one day, ive stockpiled warranty 48v battery packs from cordless trimmers , blowers, saws , ect for the purpose. ( was told to throw in dumpster after waiting period) So many good 18650's.

Im sure your kart will turn out great and I encourage you to post some updates and pictures on the project!