Step forward cordless tool specialists; battery and electronics experts I have a question

[Crazy Harry]

My elderly neighbour asked if I could help him. He has an old battery chainsaw made by ‘Garden Gear’. He has the saw body; two batteries but can’t find the charger – he did have some stuff nicked so it may be long gone. Replacing the saw and batteries is financially out of the question.
I couldn’t find a replacement charger for sale – I looked and looked for weeks online. In the end I did find a charger with the same profile as the batteries – as it happens an old Matika style I think so I guess that design was bought out by Garden Gear and manufactured by them for a few more years.

All good so far but the batteries we’ve got have two connections the charger has three. They don’t charge in it. I assume the third connection is for charge monitoring and if it can’t ‘see’ the battery it won’t charge.

Firstly; does anyone have an old Garden Gear charger they want to sell? – the new chargers are a different design as they too have changed their design.

Failing that; can one of you advise if or how I can modify the charger. When I ‘worked’ we occasionally build electronic control systems but I was trained in ‘systems electronics’ I can design units by assembling predesigned subsystems; etch boards and assemble them but my knowledge of component electronics stops with identification sadly. I’m happy to open up the charger and take pictures.

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[ph001]

The third pin would usually connect to an ntc thermistor in the battery. Try fitting a 10k between that pin and negative on the charger. You might find it springs into life.

It is a little unusual that the charger can deal with so many different voltage batteries though. Makes me wonder if the third pin is used to identify the battery type?? I would make up three wires with small crock clips each end so you can connect up the battery and measure the voltage.

[Crazy Harry]

The third pin would usually connect to an ntc thermistor in the battery. Try fitting a 10k between that pin and negative on the charger. You might find it springs into life.

It is a little unusual that the charger can deal with so many different voltage batteries though. Makes me wonder if the third pin is used to identify the battery type?? I would make up three wires with small crock clips each end so you can connect up the battery and measure the voltage.

Thanks for getting me going - I have a go in the week and post back how its going

[Conrod]

As the manufacturing date on the battery is 2007, and if they've been left discharged for a long time, in my experience even if you found a suitable charger the chances of those NiCd/NiMH batteries still being able to hold a charge would be minimal.

An alternative is to ditch the batteries and convert the chainsaw from cordless to corded using an old 18v laptop power adapter. You could then run a longer output cable from the adapter output to the chainsaw and solder the far end to directly to the current internal battery connections. OK, the downside is that it would now have a power cord, but it's a low voltage one (so no fatal shocks if you cut through it) and the chainsaw would be lighter without the weight of the battery.

[ph001]

Agree on the likelihood of 14 year old nicads not being very good. Most laptop chargers are only about 90w or so at best though so unless all you want to cut is cheese, you might struggle a little!

[Conrod]

Good point - the torque requirements of a chainsaw are likely to be on the high side!

[Chippie]

That’s the problem with cordless tools, with the cost of replacing the batteries you may as well buy a new tool complete with batteries and charger with 12 months warranty