how to make a lithium battery for an electric bicycle

Electric bicycles use batteries made of lithium-ion batteries.
The most common one is a cylindrical cell called 18650 cells, which is named because it has a diameter of 18mm and a length of 65mm.
I will show you how to make your own DIY electric bike battery with these batteries, which is much less expensive than retail electric bike batteries.
This is actually very simple because when you buy more batteries, the price of these batteries will get better, I often buy a bunch of extra batteries and just make extra batteries locally for sale.
In this way, the battery I made for myself is finally free!
To make your own lithium battery for electric bikes, you need the following, and more details about each battery are included below: lithium 18650 batteryThe ion battery is 3.
7 V, you need to connect them in series to get the correct total voltage of the electric bike battery and connect them in parallel to increase the capacity.
There are many different units in the market, each with its own advantages and disadvantages.
I used the Panasonic 18. 0pf battery in this battery, which is 2.
Each 9AH, up to 10A can be provided continuously.
If you want more capacity, you can choose 3 Sanyo 18. 0ga batteries.
Each 5AH, 10A is also provided continuously.
However, if you don\'t need that much power, the most economical battery is the Samsung 26F battery, which is 2.
6AH, can provide about 5A continuous.
Samsung batteries are more suitable for electric bikes that don\'t need so many high-power batteries.
Most of my e-bikes use Samsung 26F batteries because I like to make packages with a larger capacity and use them on medium power e-bikes.
Keep in mind that since each unit can only provide a continuous of 5A, you may need to use more continuous units in parallel.
For example, in a 30 a continuous package, at least 6 units in parallel are required.
I get my cell from the AliExpress and payment to the supplier is escrow before you receive your goods and confirm that the goods are in compliance with the description.
I like it better than ebay because that way I know my money is safe and I can get it back if I have a problem with the seller.
But I only use reputable battery vendors, as linked above, so I haven\'t had a problem with the battery yet.
Battery Management System (BMS)
You need a BMS to monitor your battery during charging and discharging.
Basically, it protects cells from draining too far or overcharging.
You need to match two main factors when selecting BMS: voltage and current rate (
More important for discharge than charging current).
If you are building a 36 v battery, you need a 36 v BMS (
Or usually 10 s, which means 10 cells in series)
Match your battery.
The 48 V battery uses 13 s BMS and the 52 V battery uses 14 s BMS.
Just make sure that the BMS you choose is the same number of batteries you are building.
Remember to check the discharge current.
If you want your battery to be able to handle 20 a in a row, choose a BMS rated at least 20 a, and a higher BMS will give you a safe buffer better.
Spot welding you really need to use the spot welder to make lithium batteries from 18650 batteries.
Technically, it is possible to weld the battery together, but it will generate a lot of heat at the end of the battery, thus damaging the battery and preventing the battery from performing its full capacity.
I have a few different cheap spot welders.
Even with the price of the spot welder, the final cost of your DIY lithium battery may be lower than the retail electric bicycle battery.
Also, you can do some more batteries and sell them!
For the same reason as my cell, I got all my live welders from AliExpress-
Because I know I will get a good product or get my money back!
I like to use a rather simple spot welder without a manual probe, I sell it for about $150, but I also have good experience with 709 series welders and other people who have extra manual probes, even though they are a bit expensive.
A friend of mine wanted to make the battery himself but didn\'t want to invest in a spot welder.
He eventually bought one, made his battery and then sold the spot welders for more than he paid on ebay because they are very rare in the US.
Anything useful to you!
The Nickel Belt you will use the nickel band to connect your cells together.
Make sure you get a nickel strip of 100% instead of nickel plated steel, which is cheaper but more resistant.
Be careful, some suppliers are trying to sell the nickel-plated steel strip as a real 100% nickel strip because it is almost impossible.
To make sure you receive a true 100% nickel strip, you can use a spark test or a salt water test as described below.
You need some large diameter heat shrink tube to seal your battery.
I picked up about 110mm rolls of heat shrink tubes of different sizes from 10 m to 300mm.
Though if you don\'t make as many batteries as I do, you can get it in 1 m length.
The rest of the parts and tools you need are smaller and I introduced them in the following steps.
I want to put my battery down here. seat bag.
I also want the battery to be 36 v, which means I need 10 batteries in series.
This limits the multiple of my 10 cells.
To see how many cells I can put in that bag, I put it on a piece of paper and tracked the outline.
I then started placing cells on paper in the drawing until I couldn\'t hold them anymore.
It turns out I can get 30 there, but 40 will be too much.
So I chose the 30-cell battery, which means that the series battery for 36 V 8 and the parallel battery are 10 and 3 cores respectively. 7AH pack (2.
9AH × 3 cells per cell = 8. 7AH).
For a light folding bike, it would be a nice little package, which should be about 20 miles/hour, and a good package below 20 miles.
To roughly mark the location of the battery, I took a battery out of the paper at a time and drew a circle in its location.
This will help me with the wiring diagram for my next step.
Next, I colored 3 cells deeper in each group to distinguish the parallel groups.
The black circle represents the positive end of the cell, and the white circle represents the negative end of the cell.
Each group will have 3 units connected in parallel (
The positive end is together, the negative end is together).
To determine the order of the cells, I simply started with the small end of the bag and named the first group of 3 cells \"Group 1 \".
Then I drew a line attached to the top (positive)
Of these cells, the cell group sitting next to them is negative.
That\'s why half of the cells are reversed so that the positive and negative of the adjacent group can be connected in series.
I then went on to say, make sure that each group of consecutive parallel cells is connected to the next parallel cell, from positive to negative, from negative to positive.
It is important to keep track of your connections when you draw them.
On the other side of the paper, I tracked the circles and colored them on the front of the paper --
So it\'s like a real
On one side of the paper there are positive cell ends and on the other side there is a life model of negative cell ends.
If the front and back sides of the two parallel groups are connected on one side of the paper, I make sure that they are not connected on the other side.
Otherwise, this will lead to a short period of time.
You really want to avoid this.
The short circuit of the battery will heat up quickly and will catch fire or explode.
The last connection is like this: 1-
Connect to itself1 to 2 only-2+ to 3-3+ to 4-4+ to 5-5+ to 6-6+ to 7-7+ to 8-8+ to 9-9+ to 10-
This step is very important!
You need to make sure that all the batteries you plan to use are the same voltage. They can be +/-
Hundreds of volts, but more than that, you will have quite a bit of current flowing through them when you connect them in parallel, trying to balance them.
If you get brand new batteries directly from the factory, they should be basically the same.
All my cells read 3.
63 V, except for a cell that reads 3. 59V.
This may still be a decent cell, but the fact that it has been self-released means to some extent that it is not as standard as other cells do, so I replaced it with another cell that is the same as the other cells.
I can also use this unit in other projects in the future, especially for low power projects --
I just don\'t want to risk putting a cell that might have a problem in a larger package with a bunch of perfect cells in it.
Now you are ready to start packing.
Depending on the size and shape of the package, you can start with welding or hot bonding.
The first parallel group in my bag is arranged in a triangle, so I first glue the cells together and then spot-weld them.
I placed about 6 or 8 spot welds on each battery of each nickel strip.
The nickel bar I use is 7mm wide, 0. 15mm thick.
I have at least 5 nickel bars connected in series to each group so there is a lot of material flowing through the current.
Some people connect all their batteries in parallel and connect them in series with a nickel strip, but that\'s a bad idea.
It causes all the current to try to squeeze through a thin piece of nickel.
For a series connection, it is better to stack many nickel bars together.
Think of it as a road.
A nickel bar is like a street in a lane, and five nickel bars stacked together are like a five-lane road --
The highway can handle more traffic.
The welding arm on my spot welding machine can only reach 2-
There are 3 cells in one package, so I only stick a few parallel groups on the package at a time, do the welding, and then stick more.
If you have a welder with a hand held probe, then you can stick the whole package together from the beginning and then weld it at once.
Continue to glue and weld your cells until you reach the last group.
In my case, I will put the entire package on my paper template after adding each parallel group to confirm that I maintain the shape I need.
It will be much easier if you use a square because the cells will naturally arrange and you don\'t have to go ahead and check to make sure your packaging is kept in the shape of the plan.
After I finished all the welding, I found that my battery did put in the bag, but it was very tight and I still needed to add some foam and heat shrinkage before I finished.
To illustrate this, I decided to rearrange my bag a little bit.
I took two batteries out of Group 9, which is the widest part of the battery near the back of the battery, and I moved them to the absolute back of the backpack where I still have more space.
On one side of the package, I can still weld these directly to the last set (group 10)
, But on the other side, I didn\'t have direct, so I used a small piece of thick wire to weld to the nickel that had been welded to the battery.
I like to prepare the connector before I add it to the battery.
In this way, I have less chance to shorten the packaging in the accident.
For the charging connector, I chose the RCA connector.
I use female on battery and male on charger.
To make the female end on the battery, I developed a clever trick to actually use a mono to RCA adapter because it gave me a female RCA connector with a large number of welded surfaces, and strong connectors.
I used 16 gw silicon wires in the charger connector and put the wires and connectors in a helping hand device, which made it easier to weld.
I start by soldering the positive line to the end of the Mono adapter and then covering it with heat shrinkage.
Next, I weld the negative wire to the long tube of the Mono adapter and cover the entire connector with a heat shrink.
I\'m sorry I forgot to take a photo of adding a discharge connector, but I just used the Anderson wire rod connector stuck at the end of the 12 KW grid.
Before connecting the BMS, I like to add my wires to the BMS.
There are 3 wires that need to be welded on the board: C-(
Charging negative), P-(
The packaging is negative for me. e.
Will exit the package and insert the negative wire of the controller)and B-(
The battery is negative. e.
The negative end of the first parallel group cell).
After checking, I welded all three wires to the board to make sure I cut the wires long enough.
I used the B-of the month-AWGs silicone wire-and P-connections.
Finally, I wrapped the entire BMS with pi high temperature non-conductive tape and then glued it to the package with a thin piece of foam heat.
The foam provides a small amount of impact protection, and the tape and foam together ensure that if the contraction breaks on the plate, there will be no short-circuit cells between the bottom of the plate and the battery.
Next, I welded all the small wires (10 in all)for the BMS.
Each is marked 1 to 10 so you know where to weld each.
Please note that I weld them on the Nickel Plate between the batteries, not on the batteries.
This helps to drain as much heat as possible from the cells
You don\'t want to heat the cells themselves if you can avoid it.
No matter where I let the wire go through the battery, especially the end of the battery with exposed nickel bars, I use non-conductive glue to bring the manufacturing barrier just in case.
After the battery connection was completed, I added the main charging and discharging wires. The P-
Package of extinguished discharge joint of BMS, B-
Is connected to the negative end of the first cell group.
The thick red line is welded to the positive end of cell group 10 and is connected with P-
Wire to discharge connector.
Again, I am trying to do all the welding between the batteries on the nickel tape to avoid heating the battery itself.
Some battery manufacturers have skipped this step, but I think it\'s important.
I surround my cells with thin foam layers and give them more filling and protection.
I usually use a 2mm thin foam, but on this package I decided to use a thinner 1mm thick foam as it already fits perfectly.
I cut the foam into an approximate shape of the package, making the foam a bit long around so that it ends up being two layers thick in the corner --
Areas most likely to be pushed to st and affected.
I sealed the foam with the same heat-resistant tape
It is not necessarily beautiful.
It\'s time to finish your battery with some professional heat shrinkage.
Most thermal contractions shrink to about 50% of the normal diameter, about 10% of the length, so keep this in mind when adjusting the appropriate size of the thermal shrink for the battery.
The way I use to calculate the correct size is to measure the perimeter of the package, no matter which direction I\'m going around it, and then use this number to calculate the size heat shrink tube I need, it will eventually be anything between that number and that number twice, and the sweet spot is in.
It is quite simple in practice.
For example, the first heat shrink tube I used circled the package I made in a long direction.
I measured the bag and found that the circumference of the shape is about 42 cm.
The heat shrink tube is usually measured with a diameter, but a really large heat shrink tube like this is usually measured with half a circle, because it is flat and not as round as a small heat shrink tube of a wire.
So if the circumference of my bag is 42 cm and the heat shrink is reduced to half of it, that means I need a heat shrink part with a half circumference between 21 and 42 cm (
While it is best to stay away from the extremes of this range so that the heat shrinkage is not too tight or too loose.
I ended up making this product with a heat reduction rate of 26 cm.
For any heat shrinkage that slides on the side of the package, which means that it extends 90 degrees in the direction of the battery, I cut it to 11 cm wide.
This 11 cm has proven to be a magical number that has enough prominent parts on the top and bottom of the cell to wrap them, but not too much, because you will get the extra floppy material cut off
You should use a heat gun on the heat shrink tube, but be sure not to turn it up, otherwise you can actually burn or melt the Heat Shrink tube.
My hot gun is very powerful, so I often use my wife\'s hair dryer on high places, which is very effective for heat shrink tubes!
After your first heat shrink tube, you may want to add the second one that covers the end of the package in another direction.
For my bag, the circumference of the widest part is about 35 cm, so I used a 190mm heat shrink in this part.
I wanted to make sure that it was easy to remove the battery from the bag even if it was very tightly installed, so I added this handle to the bag.
I put some 1 \"nylon straps around my backpack to form a circle and added a little extra so I could put a few fingers on my hands.
I marked the overlap and got it to my sewing machine.
I bought a cool newbie sewing machine and it turns out to be very handy
I use it for a variety of projects I don\'t expect
Like in the battery building!
I am still a beginner in sewing machines, but I think the stitching works well and feels safe.
I place the coil around the battery and stick it hot on three sides in the proper position to form a handle on the back end of the battery.
I should have added a heat shrink tube to the loop before I sew, but I forgot, so I had to come up with a good way to cover the small end of the package.
I tried using a small piece of heat shrink tube for the first time, but since it is wedge-shaped and just slides off the package when shrinking, it doesn\'t stay in place and eventually falls off the tip
Instead, I had to cheat a bit.
I developed this method when I wanted to shrink the heat to a wedge shape but couldn\'t get it to stay on its own.
First of all, I cut a heat shrink tube of the right size to cover the small end of the package and extend almost all the way to the large end of the package.
Then I stick it to the distance so it doesn\'t slide down.
I then slide a heat shrink tube on it and heat it in place.
When the piece is reduced, it locks the heat-shrinking piece below and holds it firmly in place.
Finally, I applied the heat to the tip of the battery, and the heat shrink I originally cut was placed there, sealed the end of the battery and covered the nylon belt at the tip, and keep in place due to the heat shrinkage above.
This is everything!
I tested if the battery was right and the battery slipped into the bag comfortably.
The small doors at the back cover the connectors, allowing me to reach them without removing the battery every time.
I hope you find this helpful and feel free to ask any questions in the comments below!
If you want to write an article in more detail, how do I create one
To post here, I also made a video on youtube where the whole process was shown with batteries of different shapes.