toothbrush charger

[myp71]

I have a soniCare toothbrush, I need a charger for this.It is one of those put close to the base and it starts charging it has wire windings in the toothbrush and in the charger.So can I make one of these chargers for this system? I'm not to fond of 110v ac so I do not know if i can do this or not<p>Thanks in advance
Myp71 (CRUISER SOMEDAY)<p>[ September 02, 2003: Message edited by: my p71 ]</p>

[bodgy]

Well the answer is it is probably no more than a NiMH type charger, maybe with a few extra temp or voltage check circuitry - depends really how cheap or not that brand of electric toothbrush is.<p>However if you aren't happy playing with transformers or mains and especially if the charger is non isolated capacitive dropper type circuit, then you should steer clear.<p><wit mode on>
How about getting a lemon and an orange - sticking one electrode each into said fruit other electrode connect to your fillins (if any) bung toothbrush unit on fillings wait 3 days - hey presto toothbrush re-charged
<wit mode 0ff><p>Seriously how about a wind up charger - one ex stepper motor, one large or super cap one switchmode reg IC and winding handle. - It'd be different!<p>Colin<p>Hmm, maybe that should be my next submission to N&V a wind up toothbrush recharger and a toilet paper sheet counter - yes I do count the sheets, no one swindles me!<p>[ September 03, 2003: Message edited by: bodgy ]</p>

[haklesup]

That is an inductive coupled charging system. You basically have a primary coil in the base unit and the toothbrush has the secondary coil, the rectifier and charging circuits. When you put the toothbrush in the base unit the two coils are nested and they form a transformer.<p>What you need to do is recreate the primary coil of the transformer. Physically that should not be difficult. Just put a bunch or turns of magnet wire around a plastic cylindar that has an inside diameter approximately the same size as the toothbrush base. Then connect the two ends of the wire directly to 110V AC (you can put in an MOV and fuse if you want).<p>The unknown here is how many turns you need in the primary coil. It could be anywhere from a couple hundred to a few thousand. I have no idea how many turns there are in the secondary coil (in the toothbrush) but the turns ratio is probably what you would use for a 6V output.<p>If you want to experiment, start with about 200 turns of #28 to #22 gague wire around the form and see if that will put a charge into it. Increase the number of turns by 10% or so each time until the toothbrush feels warm when you charge it. At that point you probably have too many turns.

The more turns you put on the primary the higher the voltage at the output of the secondary. If you have way too many, you will burn out the toothbrush. Additional information can be gleaned buy comparing the AC current at the primary coil with and without the secondary inserted.<p>Chris

[Ron H]

That's backwards, Chris. More turns on the primary gives you LESS voltage on the secondary.

[josmith]

I just took a look at my sonicare charger. The coil surrounds the bottom 3/4 " of the body. I tried to measure the resistance but it measured overrange on the 2meg scale.<p>The button on the body glows soft green when charging so you might be able to use it as an indicator of proper voltage. Chances are that all of the charging circuitry is in the body and the charger base is just a coil.

[frhrwa]

Bodgy... I'm saving all your "quips and quotes", and inserting them into a ... Book of Bodgy... I think this will be a best seller.. may even get a movie made... keep it up, you keep it really interesting reading your notes... thanks..

[Carl Pugh]

In the interest of preventing smoke, it might be advisable to put a electric light bulb in series with the coil that you have wound. When the light bulb does not glow, it could be removed. Maybe use a 60 watt light bulb.

[haklesup]

Good call RonH. If I didn't do things backwards once in a while, how would I make all that cool smoke.<p>That actually makes the experiment easier because it is simpler to remove turns from a coil than it is to add them. Maybe you can find a spool of wire that is already approximately the right size and just unwind it until the charger works.<p>Try disassembling an open frame solenoid and use that coil. The kind they use on older washing machines would probably be about the right size. Maybe a large relay coil that you can remove the metal core from.<p>If your chosen coil has too few turns and thus induces too high of a voltage in the toothbrush, you can try inserting the brush less completely into the primary and thereby coupling the magnetic field less.<p>Joesmith comment that the resistance was greater than 2M indicates that the coil in the OEM unit is not just a plain coil (a transformer should be only a few ohms). They may have additional circuitry probably for safety measures or current limiting. My gut feeling is that it should work with just a plain coil. You may want to avoid leaving the brush in the charger after it is fully charged for a prolonged period until you know what is really in the base unit.<p>Chris

[Ron H]

"Joesmith comment that the resistance was greater than 2M indicates that the coil in the OEM unit is not just a plain coil (a transformer should be only a few ohms). They may have additional circuitry probably for safety measures or current limiting. My gut feeling is that it should work with just a plain coil. You may want to avoid leaving the brush in the charger after it is fully charged for a prolonged period until you know what is really in the base unit."<p>There may be a capacitor in series to prevent some idiot from burning out the coil by connecting it to a DC supply. A series capacitor could also be used to get more current through(and voltage across) the inductor, although fewer turns would seem to accomplish the same thing as far as the secondary is concerned. There may not even be enough room in that little base for a capacitor. Am I rambling?