How does my Sonicare charge?

I put my Sonicare toothbrush into its little charging station, and after an hour or so it’s charged. Since this isn’t like a Palm Pilot docking station (the brush just sits there, not locked into place), maybe some part of the brush touches the charger and maybe it doesn’t. The whole thing looks hap-hazard to me, but it works. I assume some kind of magnetic charging is going on, but how does the electricity get into the brush? It must move through the air (even if that’s 1/10 of an inch).

There is a coil of wire in the charging station and another coil of wire at the bottom of the Sonicare toothbrush. The power is transferred through magnetic induction just like a transformer.

There are two AA-size Ni-cad batteries right above that coil of wire which get charged when you leave it in the base. The A/C from the coil gets rectified to charge the batteries. There is a small circuit board underneath the on/off button that drives another coil right underneath the toothbrush. Notice that the bottom of the removable toothbrush has a pair of magnets that respond to this upper coil.

Why do I know this? A couple weeks a ago my wife went on a trip and took the Sonicare handle with her. So I found the old one in the back of the drawer. But the NiCad batteries were dead and would not hold a charge. So I carefully cut the handle open, disconnected the NiCad batteries and wired up a pair of external flashlight batteries. I was ugly but it worked.

I may or may not be ugly, but I meant to say “It was ugly but it worked.” :rolleyes:

I have one of these, and I am almost certain that the transfer of power from the sealed base to the sealed brush/battery/handle uses induction rather than conduction. If I am correct, there would be a coil against the inside surfaces of the two plastic parts that meet at the inside bottom of the base.

By continually changing the polarity of the current in the ‘driver’ coil (located in the base that plugs into the wall), a current would be induced in the ‘receiver’ coil in the brush/battery/handle. This current would charge the battery in the sealed handle.

I could be wrong, but I see no reason why charging would have to be any more complicated or sophisticated than this.

It uses an “air core” transformer.

The toothbrush and base have transformer coils in them.

These coils only need be close enough together that the magnetic fields of the base coils intersect the coils in the toothbrush. Obviously, they will try to place them in such a way as to maximize the field overlap.

Look up how any transformer works, it is just the same. The only thing that is unusual is that the two halves of the transformer are in their own case.

if you look at:

you will see the two coils side by side in one case. With the toothbrush, imagine a coil in each case, but when the toothbrush is put in the charger, it brings the coils as close to the pictured arrangement as possible.

You loose some efficiency, but it isn’t really a big deal.

Should the toothbrush be kept on the charging base when not in use, or should it be left off of the charging base until it runs down?

Well…Rufus, as Red Green says “If women don’t find you handsome, they should at least find you handy.”

I called customer service they said to leave the brush on the charging base between uses.IIRC,the owners manual is fuzzy about,or doesn’t mention,this.

Sometimes you can restore “dead” nicad batteries. After long use their chemicals are distributed wrong, and they can only hold a small amount of energy. To partially fix this, totally discharge the batteries by running the device for a few hours, then recharge them normally. If it works partially, repeat the process a couple of times. If it doesn’t work, well, the aged batteries were already destined for the wastecan.

RL, oral hygiene is important and all, but isn’t that alot of trouble to go to just to brush your teeth? :smiley:

The magnetic fields intersect! That’s what I wanted to know. Thanks, scotth.


Did you check that they are actually Ni-Cads? I’m just wondering if they’ve started using better batteries (Lithium-Ion maybe?), like in notebook computers, that don’t have some of the charge-related problems attributed to Ni-Cad’s. I wouldn’t surprise me to hear that they’re still using the less-expensive Ni-Cad’s and maybe even depending on long-term battery failure to generate replacement business down the line. On another tack, maybe there are more environmentally-friendly technologies that are being employed.

Doubt it. Definitely not Li-Ion, they’re still too expensive. I’ve seen NiMh batteries in some better portable CD players, but I doubt you’d find them in a toothbrush.

BTW, it’s been my eperience that appliances that continually charge their batteries (like cordless phones, or power toothbrushes), or at least the batteries inside them, have a much shorter life span. IMO it’s better to keep it out of the charger until it starts to run down. The charging circuits in these things typically aren’t very smart, and continue to charge the battery even after it’s fully charged. It’s much easier on the battery if you wait until then to recharge it.