# electric toothbrush contactless charger magnetic core geometry.(ETCCMCG)

Y

#### Yzordderrex

Jan 1, 1970
0
Greetings,

Does anybody know what the geometry of the core is in a electric
toothbrush charger? I have an electric toothbrush that charges when

I would like to use a similar design for charging handheld radios for
our troops. There are problems with salt water getting into battery
packs and corroding contacts and so on.

I am mulling over running a MHZ or better sinewaves through the
interface. I was thinking probably a sheilded ferrite half cup on
each side of the interface should do it. I was wondering what effect
the gap would have .

regards,
Bob
N9NEO
Just say NEO!

J

#### Joerg

Jan 1, 1970
0
Yzordderrex said:
Greetings,

Does anybody know what the geometry of the core is in a electric
toothbrush charger? I have an electric toothbrush that charges when

AFAIR around 3/4" long and 1/3" diameter. You can open the charger and
look. Unplug it from the wall outlet first

I would like to use a similar design for charging handheld radios for
our troops. There are problems with salt water getting into battery
packs and corroding contacts and so on.

I am mulling over running a MHZ or better sinewaves through the
interface. I was thinking probably a sheilded ferrite half cup on
each side of the interface should do it. I was wondering what effect
the gap would have .

They usually run around 60kHz. One has to mind regulatory hurdles for
other frequencies. 1MHz would be a big no-no, results in egg in the face
at the EMC lab.

The gap increases leakage inductance which can be (partially)
circumvented by a series resonant design.

T

#### TT_Man

Jan 1, 1970
0
Does anybody know what the geometry of the core is in a electric
toothbrush charger? I have an electric toothbrush that charges when

I would like to use a similar design for charging handheld radios for
our troops. There are problems with salt water getting into battery
packs and corroding contacts and so on.

I am mulling over running a MHZ or better sinewaves through the
interface. I was thinking probably a sheilded ferrite half cup on
each side of the interface should do it. I was wondering what effect
the gap would have .

regards,
Bob
N9NEO
Just say NEO!
The base has a ferrite pin that couples the coil in the base to the coil in
the handset. Can't remember the frequency, but it wasn't high. What was high
was the voltage - +/- 100 or 200Volts AC. That surprised me, but it is
probably obvious to those who know about these things....

J

#### Joerg

Jan 1, 1970
0
TT_Man said:
The base has a ferrite pin that couples the coil in the base to the coil in
the handset. Can't remember the frequency, but it wasn't high. What was high
was the voltage - +/- 100 or 200Volts AC. That surprised me, but it is
probably obvious to those who know about these things....

Else they'd need a transformer. That might result in the cost to rise
five cents which in turn could lead to hissy fits in the board room.

T

#### TT_Man

Jan 1, 1970
0
Else they'd need a transformer. That might result in the cost to rise five
cents which in turn could lead to hissy fits in the board room.

The whole thing is already a transformer...... why not use a lower secondary
voltage? just less turns, thicker wire..... there is probably a good reason
why it's such a high voltage. But I can't think what. Even the follow on
electronics would be tricky at that high voltage. Seemed to be some sort of
buck converter. It was totally potted in rubber gunge and I destroyed much
of what was there but I did see the very narrow pwm pulses.

J

#### Joerg

Jan 1, 1970
0
TT_Man said:
The whole thing is already a transformer...... why not use a lower secondary
voltage? just less turns, thicker wire..... there is probably a good reason
why it's such a high voltage. But I can't think what. Even the follow on
electronics would be tricky at that high voltage. Seemed to be some sort of
buck converter. It was totally potted in rubber gunge and I destroyed much
of what was there but I did see the very narrow pwm pulses.

The tooth brush side is usually low voltage. At least it was in mine
because it had to charge up two NiCd batteries. Plus that saves turns,
meaning copper, meaning $$P #### petrus bitbyter Jan 1, 1970 0 Joerg said: The tooth brush side is usually low voltage. At least it was in mine because it had to charge up two NiCd batteries. Plus that saves turns, meaning copper, meaning$$\$

I opened up some of them too and what I saw make me guess they're doing some
kind of trickle charging. So by current limiting. Which should not be too
difficult as the "tranformer" coils are very loosely coupled. Don't put the
thing on a metal surface while charging as most of the energy will get lost
by warming up the metal.

petrus bitbyter

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