Success with first electric go kart project (pics)

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garolittle

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Oct 27, 2017
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I am currently modifying a Drifter go kart by replacing the existing 24 V lead acid (14 amp hour) battery with a home made 24 V (7 series 2 parallel) 18650 battery pack. The batteries were purchased from ******* and arrived in perfect condition as usual. The 7S2P Pack is intentionally small so I can learn the basic issues of electric go karts.
The only change I am making is swapping out the battery. All other connections to the original charge controller (30 amp max) remain unchanged (throttle, charger, breaks, etc).
Everything worked well. It took a while to solder the XT60 connectors (I am new at this) but the motor runs well using the existing controller. I conducted several test runs with the go kart on the work bench and all worked well. The wires, BMS, and battery all remained cool during several tests. I will conduct a road test tommorow by reassembling the rest of the go kart and taking it for a slow and short ride. This is a very small project that I am using to learn the basics.
This hobby regarding electric powered stuff is awesome. I just need more time and money to keep it going. ?
 

DarkRaven

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You can't use the existing lead acid charger and you should look into the power draw from the electric motor / motor controller. With only 2p you might be overloading your cells.
 

garolittle

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Oct 27, 2017
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DarkRaven said:
You can't use the existing lead acid charger and you should look into the power draw from the electric motor / motor controller. With only 2p you might be overloading your cells.

Thanks. I will do that. I appreciate the feedback. I only charged it up to about 26Volts but you are correct that it may be too much power for the cells.
 

daromer

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Depending on size of motor and type of cells 2p sounds way to small in my ears too.

Pictures!
 

garolittle

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Oct 27, 2017
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Thanks for the feedback. I will find the correct charger soon. The battery is wrapped in kapton tape and the battery box is just cardboard with some electrical tape. You can not see it from the photos but I re-installed the motor/charge control cover so the chain would not be exposed. This is all very temporary since I will likely upgrade to a 36v motor/controller with a 10s/4P battery pack (and a much better battery case). Thanks again for all the feedback. This forum is awesome.

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DarkRaven

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Definitely looks well suited for a lithium conversion but you should check the specs of the motor asap and compare these to the specs of the cells you have used.
 

garolittle

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Oct 27, 2017
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Thanks. I researched the motor and it is 24V 250W with 10 tooth sprocket. My battery pack is 7S so my nominal battery voltage is 25.9V. The Amp Hours of my battery pack is 7.0 so the capacity is half of the original lead acid batteries. This becomes noticeable when I drive the Go Kart (I weigh 150 pounds) instead of my son (80 pounds). I could add more 18650 batteries but I want to save them for the upgrade to a 36v motor/charge controller. It has been a great experience and I am eager to learn more. :)
 

daromer

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10A easy. Ie 5A per cell. Unless you got high current cells you definitely need to add more cells because otherwise you will kill your cells :)
 

DarkRaven

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Yes exactly, you need more cells. Or high drain cells. Or both :)

You can see the effects already, you say the lower capacity becomes noticeable when you drive the kart. It has nothing to do directly with the capacity, but with the voltage drop under load. You're giving your cells a hard time and they simply can hold the voltage up. I guess you have been using new 3500mAh cells then? The high capacity cells aren't suited for high currents usually, you would achieve better results with cells suitable for the task at hand. For example, high drain cells with 2500mAh will probably give you a better performance although the capacity goes down from 7Ah to 5Ah.

Without knowing what cells you have exactly I guess something like 5p would be much more fitting. If you want high capacity and high discharge, more or less, then look at the LG HG2 cells. 3000mAh cells with 20A continuous discharge, they would be very well suited for the job.
You can either add more cells or switch to high drain cells. Or do both, a higher number of high drain cells will obviously be beneficial as well. RC LiPos would also work very well.
 

garolittle

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Oct 27, 2017
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Excellent information. I am learning more each day and I appreciate the advice. I amusingnew LG MJ1 3500 mAh 18650 battery cells connected with pure nickel strips. I used a spot welder for the nickel strips and 40/60 Rosin/Lead solder for the wire connections. I will purchase the lowercapacity/higherdiscardbatteries as recommended. I know this is a very small project but it is fascinating to know that I am driving a go kartusing electrons instead of gas power.
 

DarkRaven

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Asy you are keen on learning stuff, here is some more for you to digest :)

When getting new cells you should always take the time to check the datasheet. It will always tell you something useful.
In case of the MJ1, the max discharge is 10A so you are running your cells right at the limit, probably even a bit beyond. And while you can do it this doesn't mean you should do it. It impacts the life expectancy of the cell and also the performance, as you have seen.
Since you've already started with the MJ1, stick with the MJ1, but double the amount of cells and go for 7s4p. Or even bigger, as much as the available space allows. You will also see that doubling the cells will give your actually more than double the runtime because the useable capacity increases with lower load. Also, the max energy per cell will increase because the average voltage will be higher with lower load.

Also, LG specifies resting time for the cells after charging (10 minutes) and after a high load discharge (20 minutes). So don't charge the cells right after using them and don't use them in the kart right after charging them
 

garolittle

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Oct 27, 2017
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Thanks DarkRaven. I will increase the battery pack size to 4P or maybe 5P in the near future. It should not be too difficult since I have a spot welder and can just add more cells to the current configuration (see pic). I will also order some Samsung INR18650-25R 2500 mAh 18650 battery cells for future projects. They can discharge at 20A and have a C Rate of ove 8.0. Thanks for the advice.

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DarkRaven

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Samsungs INR18650-25 cells are very popular for power tools and such. Very good and reliable cell, good choice!
 

garolittle

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So I just added more capacity to the battery. I now have a 7S4P configuration (and as everyone predicted) the resulting power increase was noticeable. I can easily make it up my driveway and I managed my first official drift on a nearby vacant road. The experience has been great and I am enjoying the learning process. I will soon upgrade to a 48v motor/charge controller and a new battery pack (probably 14S/8P) using the higher discharge Samsung 18650 cells. I really appreciate everyones feedback and I look forward to posting results of the upgrade.
 

Geek

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That contraption looks like fun. 48v motor should really spice things up for you. :)
 

garolittle

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So before I upgrade to the 48 volt motor/controller, I increased the size of the existing battery pack to 7S7P. The increase in power was very noticeable and I learned a few more things. I added a small volt meter so I can ensure I do not drop below a certain power level. Thanks again fo all of the advice so far. I will post pictures of the upcoming 48 volt motor installation.

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DarkRaven

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You can't do that endlessly though, at some point more cells in parallel won't give you more power and just increase the runtime :)
By the way, you were a bit generous on the main positive connection (and I guess on the main negative one as well). You can do it like that and go all the way down the length of the battery, but you don't need to. It has no beneficial effect. The cells are already connected, you are just providing a bigger connection between the terminals of the cells and it doesn't effect the way current flows through the main wire.
 

garolittle

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Oct 27, 2017
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Thanks DarkRaven. I thought I had to run the wire down the length of the positive and negative terminal parallel cells but I guess I was wrong. I appreciate the information since I am learning as I go. This is a fun project
 

garolittle

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Oct 27, 2017
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So I gave into the temptation for more power. :) I will soon replace thecomponents on the electric go cart referenced above with the following set up:

  • 48V 1000 Watt BrushedMotor with rated current of 26.7 amps
  • 48V charge controller
  • 14S9P batteriesusing Samsung INR18650-25R 2500 mAh 18650 cells (connected with spot welder using pure nickel strips)
I added a 35 amp fuse (rated for up to 58 volts) and I hope to hook everything up to the go kart this weekend. Thanks to those on this forum who have provided advice to me. I really appreciate it. Here are a few photos of the newbattery pack I createdand the motor/charge controller that I will soon install.

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