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Recycling Laptop Batteries
Recycling Laptop Batteries
As a way to save money on the overall cost of the project and have more energy storage capability aboard the TOP, used lithium ion batteries were selected. They come at a significant price reduction, of less than a dollar per battery, compared to over three dollars for a new 18650. Although many used batteries do not hold their original capacity, what is left is more than enough for this application. Additionally, the used batteries still have more energy density than tradition led acid batteries.
As a way to save money on the overall cost of the project and have more energy storage capability aboard the TOP, used lithium ion batteries were selected. They come at a significant price reduction, of less than a dollar per battery, compared to over three dollars for a new 18650. Although many used batteries do not hold their original capacity, what is left is more than enough for this application. Additionally, the used batteries still have more energy density than tradition led acid batteries.
In total around 30 used laptop batteries were broken down and tested to make up the batty bank. Most commonly there are six 18650 batteries inside one laptop battery. Normally one battery dies, rendering it unusable as a laptop battery, but that leaves five good lithium ion cells. Once the cells are removed from their casings and the metal strips connecting them are removed, they are ready for testing.
In total around 30 used laptop batteries were broken down and tested to make up the batty bank. Most commonly there are six 18650 batteries inside one laptop battery. Normally one battery dies, rendering it unusable as a laptop battery, but that leaves five good lithium ion cells. Once the cells are removed from their casings and the metal strips connecting them are removed, they are ready for testing.
Battery Testing
Battery Testing
With all the batteries cleared of their old circuitry, they need to be tested to ensure they still hold enough capacity to be viable for the project. The first step is to measure the voltage of each battery with a digital multimeter and record the value on the battery. With all the battery voltages measured, the batteries were sorted into groups based on their measured voltage. For example four volts and greater, or 4 - 3.5 volts and so on. For the project only batteries that measure 2.5 volts and greater were used for safety reasons.
With all the batteries cleared of their old circuitry, they need to be tested to ensure they still hold enough capacity to be viable for the project. The first step is to measure the voltage of each battery with a digital multimeter and record the value on the battery. With all the battery voltages measured, the batteries were sorted into groups based on their measured voltage. For example four volts and greater, or 4 - 3.5 volts and so on. For the project only batteries that measure 2.5 volts and greater were used for safety reasons.
From there each cell was charged completely to as close to 4.2 volts as possible, then discharged to 3.0 volts and recharged to 4.2 volts. This was performed over the course of many weeks using the OPUS BT -C3100. The charging and discharging cycle measures how much energy is stored by each cell when it recharges the second time. This gives an indication of how much storage capacity is left in the battery. From there each battery was grouped based on storage capacity and assembled into a bank using the VRUZEND battery bank kit.
From there each cell was charged completely to as close to 4.2 volts as possible, then discharged to 3.0 volts and recharged to 4.2 volts. This was performed over the course of many weeks using the OPUS BT -C3100. The charging and discharging cycle measures how much energy is stored by each cell when it recharges the second time. This gives an indication of how much storage capacity is left in the battery. From there each battery was grouped based on storage capacity and assembled into a bank using the VRUZEND battery bank kit.
Safety concerns
Safety concerns
Lithium ion batteries can be dangerous even when new, as they have a very high energy density. If shorted out they can catch fire or even blow up. It is not recommended that anyone implement used lithium ion cells into a project without a researching how to go about it safely. Used cells are even more dangerous as the remaining lifespan is unknown and potentially dangerous situations are more likely to occur the older they become.
Lithium ion batteries can be dangerous even when new, as they have a very high energy density. If shorted out they can catch fire or even blow up. It is not recommended that anyone implement used lithium ion cells into a project without a researching how to go about it safely. Used cells are even more dangerous as the remaining lifespan is unknown and potentially dangerous situations are more likely to occur the older they become.
Battery Management System
Battery Management System
The battery management system (BMS) is used to balance the voltages between the batteries connected in series. Without a BMS the voltage in a given battery can rise higher than the voltage across other batteries. These differences can cause premature degradation of an individual cell. If left unattended the premature aging can lead to cell failure and possibly a flammable situation.
The battery management system (BMS) is used to balance the voltages between the batteries connected in series. Without a BMS the voltage in a given battery can rise higher than the voltage across other batteries. These differences can cause premature degradation of an individual cell. If left unattended the premature aging can lead to cell failure and possibly a flammable situation.
Final Battery Specs
Final Battery Specs
The final battery bank holds over 130 amps with 72, 18650 lithium ion cells in total. Each cell is averaged to have 1.75 amp capacity, but this average is intentionally kept slightly lower. In total there are around 100 usable amps without causing any damage to the system. The maximum voltage of the battery is 12.6 volts. The lowest the voltage of the battery bank can be dropped to safely is right around 9 volts. The final configuration is a 3S24P, which indicates there are 24 cells in parallel and 3 sets of 24 parallel cells, are placed in series with one another. Heat shrink has been placed over the entire thing to ensure the battery terminals are covered.
The final battery bank holds over 130 amps with 72, 18650 lithium ion cells in total. Each cell is averaged to have 1.75 amp capacity, but this average is intentionally kept slightly lower. In total there are around 100 usable amps without causing any damage to the system. The maximum voltage of the battery is 12.6 volts. The lowest the voltage of the battery bank can be dropped to safely is right around 9 volts. The final configuration is a 3S24P, which indicates there are 24 cells in parallel and 3 sets of 24 parallel cells, are placed in series with one another. Heat shrink has been placed over the entire thing to ensure the battery terminals are covered.
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