Converting a screwdriver to Li-ion without BMS

Many craftsmen have a cordless screwdriver in their service. Over time, the battery degrades and holds a charge less and less. Battery wear greatly affects battery life. Constant recharging doesn't help. In this situation, “repacking” the battery with the same elements helps. The most commonly used elements in screwdriver batteries are the “SC” size type. But the most valuable thing a master has is repairing things with his own hands.

Let's remake a screwdriver with a 14.4 volt battery. Screwdrivers often use a motor for a wide range of supply voltage. So in this case, you can use only three Li-ion cells of the 18650 format. I will not use control boards. The discharge of elements will be visible in operation. As soon as the self-tapping screw does not tighten, for example, it’s time to put it on charge.

Converting a screwdriver to Li-ion without a BMS board

First, let's disassemble our battery. There are 12 elements inside it. 10 pieces in one row and 2 in the second row. A contact group is welded to the second row of elements.We leave a couple of elements with a contact group, and dispose of the rest.

Now you need to solder the wires for further work. The contacts turned out to be made of a material that cannot be tinned, so we soldered the wires to the elements. Minus to the body of the element, and plus directly to the positive patch. The old elements act as a support and do not participate in the work.

I will use lithium-ion batteries of the 18650 format. The elements are used. High-current elements are needed for modification. I “changed” my elements into heat-shrink from Sanyo, the old one was pretty shabby. I checked the residual capacity Imax.

We connect the batteries in series and solder the head elements. The battery is almost ready.

Now let's ensure comfortable charging. You need to install a four-pin connector. I used a connector from an old motherboard for the number of pins I needed. I took the mating part from an old computer power supply.

Cut a hole for the connector. Fill the connector with epoxy glue or super glue with soda. We also solder the wires.

Solder the wires to the elements. Wire from the first contact of the connector to the battery positive. A wire from the second contact of the connector to the plus of the second element, which is also the minus of the first element, and so on. Since I will be charging with a “smart” charger, I need to make a balancing wire.

As a connector for connecting to the charger, I will use the wire from the computer's power supply. The wire through which the floppy drive was powered. We cut off all the keys from the connector and it fits perfectly into the charger. It unsolders easily. Red wire to the first contact of the battery connector. Black wire to the second pin of the battery connector, etc.

We connect to the charger and do not forget about the power wires. Our wiring is a balancing one. We set the balance on the charger and wait for a full charge.

In this simple way you can modify a shooter battery for your home.

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