Intro: Free Lithium Ion Battery Pack
In this instructable I show step by step how to make a lithium Ion battery Pack for free out of garbage laptop batteries. Lithium ion batteries are very powerful and lightweight. They are very expensive if bought new. They can be used to power so many thing from electric bicycles to full electric cars. I will be using mine to hold electricity generated by my homemade wind turbine.
The below video shows the battery pack in action.
I was lucky to find two 6 cell laptop batteries for free. If you can't find free or cheap laptop batteries they can be ordered off of e bay for very cheap.
I will go over how to check the cells and charge them using transformers that are lying around the house. Then I go over how to build a battery pack with the voltage and amps required for your application.
Step 1: Tools/materials You Will Need
Here are some tools/materials you will need. I found everything already at my house and the batteries for free.
Transformers (I used 12V 1A and a low amp transformer)
Multi meter (to measure cell voltage and charging amps)
small wires (I used 22g)
Thicker wires for 10A or more
soldering iron and solder
A fuse (I used a 10A car fuse)
connectors (I used a solder less breadboard for now)
flat head strong screwdriver (to open laptop batteries)
scissors (to cut apart battery connections)
Alligator clips (to connect to transformers for charging)
Step 2: Opening the Laptop Batteries and Getting the Cells Out
First you need to open the plastic battery case. Use a strong flat head screw driver and put it into the joint between the two halves of the case. It is easiest to start at the corners. Rotate the screwdriver to pop the case apart. Continues around the joint until the top cover can be removed.
Now carefully bend the case so the battery joints opens up. Now get strong scissors between the batteries and cut the metal connecting them. Pull the other batteries out and cut the metal between the cells so they can be separated.
Step 3: Check the Voltage and Charge the Batteries
Check the voltage of each battery. I like to write the first voltage down on the cell as well as the year and battery number. If I get a low voltage cell I may have problems with it in the future and want to record it.
A voltage over 3 is good and can be charged normally. To charge I connect 3 of these batteries in series and charged them with a 12V 1A transformer I had lying around the house. Connecting them with alligator clips works well. It is important to connect the transformer for a few seconds and read the current. Charging should be done under .8C for 18650 cells. .8C is .8 times the amp hours. My Cells were 2000mah so maximum charge current would be 1.6 amps. When charging you need to measure the voltage on a regular basis (every 10 on 20 minutes until you know how long it takes with your transformer). Each cell should only go up to 4V or maximum 4.2 volts. Over charging the cells could damage them or even cause them to explode. If you cannot monitor the batteries you will have to buy an automatic lithium ion charger. While charging, each cell voltage should be measured when it is not connected to the charger
If the voltage is below 3 then charging needs to be done slowly. I would suggest using less than 100ma until the voltage is over 3 volts. I used some walkie-talkies that were made to charge rechargeable AAA batteries. I connected across 3 batteries to get an open voltage of about 6. I connected this to one lithium cell and got a nice current of 33ma. Always check the current before charging. I use this charger to also balance individual cells in the pack.
Step 4: Connecting the Batteries to Form a Battery Pack
I needed a battery to replace an old lead acid battery I used in my shop. I made a 100wah battery using 12 lithium cells form 2 laptop batteries. This battery is 12v when fully charged and 9V when empty. It can run at about 8 amps at 1C.
Any multiply of 4volts can be made using lithium cells. Connect them in series for more voltage and in parallel for more amps. With my 12 cells I could get a maximum of 24amps at 4volts (12 cells in parallel) or 48 volts at 2 amps (12 cells in series). You can connect the cell to suit the application you need them for.
This step is dangerous because you can accidentally connect the batteries and short them out. If this happens the battery will get very hot and could catch fire. It is important that you never connect the + and - of the same battery with out a load. Also connecting batteries in series and connecting the ends will short all the batteries.
first decide how many cell you want in parallel and series. I will have 4 groups of 3 cells in series each will be 12 volts. I will then connect these four groups in parallel. In short we call this a 3s4p.
First I cut the metal tabs so they were not to long. I sanded the top surface with 220 grit sand paper to get ready for soldering. Now put the first set of batteries together and tape them with electrical tape. Now solder short pieces of wire to the ends. I am making a 3 cell series battery pack so the first and last battery have + in the same direction. The middle battery is upside-down. When soldering lithium cells it is important that it is not too hot and for too long. I like bending the metal tab up and soldering onto it so the battery does get too hot. I start by soldering a long wire to the negative of the first battery. Then I solder a short wire to connect the + of the first to the - of the second. The I connect the + of the second to the - of the third/last battery. The possible terminal of the last battery gets a long wire. I like using black for the first negative long wire and red for the long positive wire. It is important to tape the long wire down onto the middle of the pack so they do not pull on the battery.
Step 5: Connecting the Packs Together
There are many ways to connect the pack. I will be charging each pack individually because I only have the 12v 1A transformer for now. Because of this I will connect the pacts together so they are easily disconnected for charging.
All I had was a solderless breadboard so I used that to connect the packs in parallel. I took 2 sets of 4 header pins and soldered a thicker wire across the 4 pins of each. I then soldered a 10 amp car fuse to the positive wire in order to prevent shorts in the battery pack or too much current from being drawn.
Step 6: Charging the Battery Pack
The battery pack can be charged all at once if you have the right charger. It is important to balance the cells during charging. During charging the cells should be checked and the low voltage cells should be charged extra. All the cells should receive the same charge if they are the same type but small differences in the cells might cause uneven charging.
For my battery pack I charged each 12V pack individually using my 12V and 1A transformer. I disconnected the battery leads of one pack from the breadboard and connected them to the transformer. I charged all 4 battery packs to ensure they all have the same voltage. During charging I also checked each cell to make sure they had the same voltage. If one cell was significantly lower I used my walkie-talkie charger to increase the voltage so the voltage for all cells were the same.
Step 7: Running the Battery
It is important to test run the battery pack. Only when you discharge the pack will you find if any cells are damaged.
I connected a car radiator fan motor to the pack. I measured a healthy 4.1 amps and 11.5 volts. The voltage dropped from an open voltage of 11.9V to 11.5V running voltage. The motor was pulling about 47 watts from the battery. It was running at .5C. I should be able to run the motor for about 2 hours.
I started by running the motor for 5 minutes and then measuring the battery voltage. It dropped to 11.76. The motor got hot so I stopped the test. I is useful to run the battery pack until it is empty and record the watt hours.
12 volts is useful the power many things used in cars. You can also use a car inverter with the battery pack to power household AC appliances.
the last picture shows the packs connected in series to get 24 volts.