Hi, my name is Kevin, but you can call me Roofus, and I’m a member of Workshop 88. Right now I work as a Service Technician in a tool rental business. I often find my self peeking at the insides of tools the average person wouldn’t venture into. My job has given me a firm belief that the only thing keeping everyone else from fixing what breaks is the fear that you’ll make it worse! So I’m doing this series Here Inside, to show people, that it’s okay to peek inside, and you never know if you can fix it, until you try.
I own an old Braun Oral B electric toothbrush. It was a gift, and I consider it a luxury I wouldn’t own otherwise, but I have grown accustomed to it. Recently it’s decided to show it’s age by slowly charging less and less. So, like any good maker who doesn’t like buy new things, I found the seal at the bottom and cracked it open.
Inside it’s pretty much just an on /off switch, the battery, which takes up the bulk of the internals, and a small charging circuit, which is the circuit board you see. Connected to the board at the very bottom is the induction coil, it’s used for the toothbrush’s contact less charging system.
It looked like the upper seal had failed and allowed water to seep in, there were small bits of corrosion on the motor and on the spring keeping the battery and coil in place at the bottom. First thing I did was check to see if the induction coil was still working by popping it on the charger and seeing if I started to get a decent current from it. And turns out, that’s where my problem was. Either the induction charger for the toothbrush, or the charging circuit itself were bad. Since the induction charger really needs to maintain it’s factory watertight seal to remain safe (it runs on household 110v), I decided not to venture into it. But I was interested in the coil and battery, and decided to have a look.
The coil, as you can see, is pretty tightly wound. So tight, in fact, that the photo I took makes it look almost like a solid metal ring. The entire thing is made from a very very thin wire you see sticking up in the photo, that wire is one of two leads that connect to the charging circuit.
The battery is actually made up of two individual cells. The cells are tied in series, and wrapped together, which is a pretty common practice.
Speaking of common, both cells were in fact a pretty standard 1.2v Ni-Cad cells. Which I just so happen to have on hand…
Well, not quite the same form factor, but readily available, and the exact same voltage. I just slapped them into a battery enclosure I had lying around, and voila, a working electric toothbrush. I left the old battery out and routed the wires through a freshly drilled hole in the bottom. It’s a little bit a of a kludge, but It works!