Give New Life to Your Drill
Introduction: Give New Life to Your Drill
Like a good maker I would never leave an old quality battery drill in the trash can. So when I found it I decided it was time to improve my refurbishing skills with last (at least for me) technology.
The main purpose of this instructable is not to explain all the steps needed to complete the project, but actually I feel that I will better help if I succeed in convincing you that it's not difficult at all, and a project like this makes sense. Other makers (many of them, really) wrote very good instructables explaining every step. I red some ibles, and I referred particularly to this (which I suggest you to read too):
DIY Professional 18650 Battery Pack
But there are many others, like:
DIY 4S Lithium Battery Pack With BMS
Lithium DRILL Battery 18650
How to Make a 18650 Li-ion Battery Pack!
Step 1: Remove Old Cells
Opening the battery pack should not be too hard, just try not to brake the enclosure, as you will try to assemble it again with new cells inside.
Mine is a Ni-Mh 18V battery pack. That cell technology is now outdated, like Ni-Cd batteries, and now some types of Lithium cell have been improved. They have a power density much higher, and they last longer if you have some caution in charging and discharging them.
Step 2:
The Lithium Ions cells have a nominal voltage of 3.7 Volt (with a maximum voltage of 4.2V), so I decided to buy on eBay 10 Li-Ion cells, and make a more powerful renewed battery pack. Indeed doubling the number of cells needed for the right voltage (5cells x 3.7V = 18.5V) will double the autonomy. It also double the electrical power, but the motor would probably not adsorb so much.
There are many different qualities and sizes of Li-Ion cells, I opted for the 18650 since it's cheaper and easy to find, although I decided not to buy the cheapest batteries, in my opinion around 4-5$ each for 2800 mAh cells is a good price to try.
I bought batteries from this seller and I'm very satisfied. All cells were exactly at the same voltage (3.81V if I remember right) when they arrived from China, so they had probably been grouped together with some care, and they were ready to be assembled in a single battery.
Step 3: The BMS
Since Li-Ion cells have to be charged under some conditions, you cannot charge them directly with a PSU, but you need to connect a circuit which take care of it. This circuit is the BMS (Battery Management System), and you have to buy one according to the number of batteries in series. 267
I used 5 groups of batteries in series, each group is made by two batteries connected in parallel (plus to plus, and minus to minus), and my battery pack will be named "5S2P". I looked for a 5S Li-Ion BMS.
As you can see you have a wide choice of shapes, dimensions, and amperage (which depends by the number of parallel cells). The more power you need the higher will be the cost. I paid my BMS (the blue one) around 10$.
Step 4: BMS Connections
Here you can see the schematic I followed for my BMS, but I connected groups of two batteries like the second image. You see that each board has different positions where to solder the wires coming from each cell. Just follow the diagram relative to your BMS, or the labels on the board (voltage starting from zero and ending with full voltage, with a number of steps equal to the number of batteries in series).
BMS needs to know the voltage of each cell, to equalize the voltage, this is the reason why you need all those wires. Look the first schematic, note that internal wires are thinner, but power wires have to be thicker, this is because the power will pass through them, so remember to use a good section copper wire.
Step 5: An Open-source BMS
If you're a real bad-ass maker, you'll probably want to build your own BMS, and this instructable is for you:
Open-source 3/4/5S Lithium BMS
(thanks <PERSON> from Netherlands)
Step 6: Fitting Everything
Just make some try to fit everything inside the case. I still had some space free... I could had added a voltage regulator or a 5V USB plug... so to use the battery as power supply... You can let loose your creativity here! 267