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Exploiting a Bosch GSB LiIon Battery

The Bosch GSB drills, Lawnmower and a few other appliances operate from 37V Lithium Ion batteries that are good for 15-20 Amp peaks - that's over 700 Watts.

The problem that they, and other appliance batteries, pose is how to make a socket/adapter or whatever to make a good attachment to them. I'm a big fan of ABS sheet to make things like this:

  • it's pretty tough (it is the stuff that is used for car bumbers)
  • it is easy to cut: aircraft shears, nibblers and even an office guillotine works up to ~1.5mm sheet. Hacksaw or fine blade power saw (jigsaw, sabresaw or rotary) for thicker sheet
  • it can be drilled, screwed into and even threaded
  • It can be heated and bent to shape
  • It can be solvent glued or heat welded to make strong joints

It is available in several colours and finishes: black 'pinseal' makes a good surface that won't show scratches too much, and 'Carbon Fibre' print looks very neat. I keep 1.5mm, 4mm and 6mm 'pinseal' and 4mm 'Carbon Fibre' to hand and save every off-cut! I buy my plastic from Bay Plastics They sell 2 and 3M sheets and they also fabricate quantities of product by machining, heat forming and welding. This is a lot cheaper than tooling for vacuum forming/injecting for small production runs - Highly Recommended

My prototype adapter to fit a battery to a Brompton luggage block: it used thick plywoood sandwiched between 4mm ABS sheets.

The channel that holds the battery in place is strips of 4mm ABS with screws and spacers. A switch is fitted on the top and I included a 37V output using Mini Sureseal plug.

Prototype adapterAdapter

The 'breakthrough' to making more of these was to replaced the 'screw and ABS strip' channel with a heat-formed channel that make a tighter, better dimensioned fitting with no screws.

I used 2 strips of mild steel to give me the former around which to bend the ABS. I used 2 metal strips to make them easier to remove after the ABS had cooled. I used a Hot Air gun (B&Q) and carefully tested the plasticity as I bathed the fold in hot air. You will see the surface change once it is pliable and then you roll the edge over the former. I used a piece of cloth to apply pressure until cool.

The picture (left)shows a simple unswitched battery shoe with a Deans connector output . I can then plug this into a WattsUp or similar and a switch. This goes against my 'standard' of Deans for Low voltage, so I made a Deans-to-Speakon adapter:

Bosch Battery

The 37V LiIon battery: inside is just a pack of cells and a thermal sensor that pushes the battery out if it gets too hot! I haven't made a pin to do this, but it would be a simple addition.

The 2.6A/hr pack weighs about 850 grammes and will do a full power burn (~15Amps) of the nano motor uphill for ~3-4minutes. Or 3-4 miles of buzzing around town without much pedalling.

The first step is to cut a piece of 4mm ABS the length of the battery slots and wide enough to allow for folding the sides in. Make it too big and then saw the edges to fit.

Use a battery to mark the position of the contacts. The contacts are cut from copper sheet made by cutting and flattening 15mm Copper pipe.

The screws that hold the contacts may be unneccesary as the contacts are held by the next layer that is folded up to insulate them

The contacts have been bent and fitted to slots cut into the 'shoe'

12AWG or similar copper wire (the 'earth' wire from mains 'twin and earth' is good) is usd for wiring.

The copper strips that fit inside the luggage block are cut from 'Proper Copper' draughtstrip. These are over-size along their width and then folded and slotted into the luggage block 'socket'.

The LEFT HAND contact (-ve) is wired to the LEFT HAND luggage block contact. The RIGHT HAND (+ve) wire is sleeved and solded to the switch. The switched wire is insulated and solded to the RIGHT HAND luggage block strip.

Two views of the 'socket' for the luggage block: it is made from 2 pieces of 6mm ABS glued together.

A 4mm piece that has a right angle fold that becomes to bottom of the adapter that also retains the battery pins.

A slot is cut for a small rocker switch from Maplin.

Slots are cut to retain the luggage block contacts.

The finished item. Self tapping screws from both sides holds the 'sandwich' together.

The luggage block contacts are held by their edge and I tapped a luggage block into place during assembly to hold them in the right position.

Finish off by sanding the edges and corners.