30 January, 2015

Rehabilitating one Metabo screwdriver with a Li-ion 4400 mAh 12.6V

Metabo BZ 12 SP with DIY Li-Ion Battery
As a gift, I was given an old screwdriver that was going to go to waste. It used the old Ni-MH battery technology or Ni-CD, and you know me ... I love those tools that works wirelessly, so I started to build for it a more economical, durable and powerful li-ion battery than the original, as there are no li-ion batteries for this screwdriver.
Note : Adapting these instructions you will be able to build batteries for any wireless device that you have at home and that, for its price or quality of their batteries, you are considering to throw away.
This requires using Li-ion batteries that allow discharge at 2C at least, or they could be damaged quickly. Lipo could be used but these have half life than other liIon chemistries. The Li-Mn (manganese) allow faster discharging without damage, but are quite expensive, and LiFePo, A123 manufacturer would be ideal, but pricy too.

I found a middle ground in Lico of  Boston Power-shaped like two 18650 united , but actually is a single battery, ovalish format, making better use of the space, and with very good capacity for cases where two batteries are used in parallel (such as laptop batteries), and they have a very good chemistry that is not damaged by 8Ah instantaneous demands such as a screwdriver, retaining its capacity better than others between uses:

See below Load controller chip
For its technical page, these batteries allow no problem loading and unloading of 1,5C , ie 6,6Ah instant, at discharge holds up well 2C (110W peak) .
Like all packs Li-Ion batteries in series, we have to charge cells equally, using load controller connected to all cells; I have used one for creating 12.6V or 16.8V batteries (3 or 4 cells in series), that you'll find at Aliexpress :

Left chip voltage regulators, central controller chip

In the B3- connector is shown "no use", but it could be used to make a 16,8V battery (it has 4 regulation chips)

However drill input must be connected directly to the positive and negative pole of the battery , since control gives only 4A, cutting and stopping off power to the drill every time you exceed it.The control however serve to charge them in a balanced way to last working many years (10 years or more).
Note: Once the connections are made, if the driver has no voltage at P1 and P2 , it is because you need to "activate" the controller applying voltage to P1 and P2 (respect the polarities indicated), although in this case it is not necessary; we are using it only to recharging.

In the next picture you can see the solder contacts drill, and the black cable is the charging cable connected to P1 and P2 from driver. I put the driver in this hole. To isolate the driver I used PVC tape to resist high temperatures, but it is valid also regular electrical tape.

Details of the battery connections in series. I put the batteries in that position, and then I stuck around with glue-heater,

To finish I placed a padded rubber to avoid damage for shocks (a Li-ion battery is dangerous crushed; is shorted internally) and I bound it with duct tape. You can see the charging cable taken from a charger:

And finally I connected a proper female connection to a 15V charger (no problem overcoming the voltage by some volts, the driver is responsible for balanced charging the cells up to 4,15V).

Testing the screwdriver, now it is stronger than with the original battery, this screwdriver is very useful with both speed and torque control in the head, GREAT!

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