I can accommodate complete beginners as well as those with experience of DIY Lithium batteries and LEDs. You will build your own USB Powerbank from reclaimed 18650 cells that you can recharge with a USB phone charger. Charge mobile phones and power LED lighting in the field!
Laptop batteries, medical devices, modern power tools, cordless home appliances and more recently vaping devices contain 4.2V Lithium Cells. These are often of a particular size: approximately 18mm wide by 65mm long, thus the name 18650.
There are lots of 18650s out there as well as many other form factors of reclaimable and useful rechargeable Lithium cells. Lithium cells are much longer lasting than traditional Lead-Acid cells and often outlive the cheap disposable devices they are inside. Lithium battery packs sometimes get thrown away if one cell in a pack dies, as the whole pack may become useless even though the rest of the cells are fine.
If you bring any of these lithium battery packs or cells, we can test to see if any of the cells can be reclaimed. If you don’t have these, I will provide you with 4 x 18650 cells reclaimed from portable medical devices.
How to safely handle and store 18650 lithium cells and batteries in general. I will talk about how Lithium Battery protection circuits work and why they are necessary. We will discuss the dangers of Lithium Batteries.
We then move on to testing some 18650 Lithium cells and cracking open a few of the old battery packs you bring. Learn to use testers and multimeters. We will discuss what the numbers actually mean.
Using a Kweld Mini Spot Welder and Nickel strip, we will weld 18650 cells together into a battery using a 3D printed holder. We will then solder wires from the battery to activate a 5V USB Powerbank module that includes protection circuitry. The completed battery pack is then tested and wrapped in heat shrink plastic to protect it. Or it can be installed into the enclosure of your choice…
Testing reclaimed cells
1. Reclaimed cells are ideally of the same make and of a similar capacity. The better the consistency of the batteries is, the better the performance of the battery pack.
2. Shorting (over-current) and over-charging Lithium Batteries can result in toxic smoke, fire and explosion due to thermal runaway. Battery packs over 96 Wh are subject to restrictions in transport. The packs we will build are about 30 Wh.
3. All 18650 lithium cells must have circular separators between the terminals and heatshrink over the casing to avoid shorting. You must not take the heatshrink and separator off without replacing them. Try to test the reclaimed cells in their original packaging.
4. All lithium cells not in batteries are to be stored upright in a fire-proof but not sealed metal box. Any unused or defective cells must be given back to us for safe storage.
5. All the DIY lithium battery packs we make will incorporate a protection circuit and will have covered terminals.
We will be doing 3 Tests on each cell:
1. Internal Series Resistance is under 75 mΩ for a low-current pack or less for higher current packs. Higher ISR means more heat!
2. Capacity more than 80% of original capacity.
3. We must check that the Cell does not Self-discharge. All the supplied batteries should be ≈4 V. If they are much less, we will get you another.
Preparation before building battery
Top up your cells in the chargers. Trim the sharp edges from your nickel strip. Put your cells into the 3D printed holders. Carefully sand off any nickel burrs.
3 Checks before connecting any cells:
1. Voltage is no more than 0.05 V difference. This is important as high current can flow!
2. Internal Series Resistance is no more than 30 mΩ difference.
3. Capacity difference lower than 50 mAh.
If you DIY lithium batteries, you must have a BMS or they are not safe. A BMS will monitor the voltage of each parallel group of cells in a series pack. It will disconnect the negative electrode of the battery if any parallel group goes above ≈4.25 V or under ≈2.75 V for Lithium Ion and above ≈3.7 V or under ≈3 V for LiFePO4. This depends on BMS settings.
Common BMS wiring instructions (check manufacturers instructions):
1. Connect the BMS B- to the battery pack negative electrode.
2. Make sure the voltage sensing wires are disconnected from the BMS side.
3. Solder the sensing wires to the parallel groups of cells: Start with the black wire to the battery pack negative electrode then connect the 2nd wire to the 1st parallel group positive pole, the 3rd wire to the 2nd parallel group positive pole and so on. The final wire should attach to the battery positive electrode.
4. After attaching all the sensing wires, don’t plug into the BMS straight away. Double-check the wiring is correct as you can easily destroy your BMS.
5. Plug the sensing wires into the BMS.
6. If you have a common port BMS, connect load- and charge- to P-.
7. If you have a separate port BMS, connect charge- to C-, connect load- to P-.
8. Measure the total voltage of the pack and the output voltage of the BMS. If the voltage is the same, it means the wiring is correct.
9. Some BMS require a charge current to activate them.
Risk: Sparks from Kweld poor contact, wrong settings or poor quality nickel strip
Expulsion from the spot welding process can be dangerous because the shower of sparks represents pieces of molten metal flying out from the joint, potentially causing eye injuries. The Kweld is a mini spot welder and expulsions are not large enough to damage the skin.
Control: Safety glasses mandated during Kweld use. Full training given to each operator. To Do: Records kept of training.
Risk: EMF from Kweld
A very strong electromagnetic field is created between the arms of a spot welder when the current flows while making welds. A spot welder should not be operated by someone with an implanted medical device, such as a heart pacemaker.
To Do: Records kept of confirmation of fitness.
Risk: Burns from Soldering iron or heat gun
There is a risk of minor burns from these devices.
Control: First aid kit with Burn Gel dressings. Heat used under supervision by Green Dragon staff only. Fire Extinguisher visible and accessible.
Risk: 18650 Lithium Batteries
Shorting (over-current) and over-charging Lithium Batteries can result in toxic smoke, fire and explosion.
Control: All 18650 lithium cells to have circular separators between the terminals and heat-shrink over the casing to avoid shorting.
Control: All lithium cells not in batteries to be stored upright in a fire-proof but not sealed metal box.
Control: All battery packs to incorporate a protection circuit and to have covered terminals.