On Fri, 13 Dec 2013 22:15:19 +1100, "Bob Milutinovic"
wrote:

"pedro" wrote in message
.. .
The Braun Triumph 3738 toothbrush and 3731 charger use an inductive
coupling arrangement to charge the toothbrush battery. Right now
SWMBO's unit isn't charging and I'm tasked with fixing it. Does
anyone know if this operates at line frequency or something higher?
(That will help sensing the field from the charging base to verify it
is operational before I disassemble the toothbrush itself.)

It's an air-cored transformer in its simplest form, with absolutely no
"smarts" in the base unit - meaning you'll have 50Hz emanating from the
base.

Whereas with most battery-powered devices you expect the charge to gradually
diminish, with these units the base unit usually fails long before the
battery starts deteriorating. Almost invariably, the coil in the base goes
open-circuit.

Good luck in getting the base open (my one attempt revealed liberal use of
epoxy), and when (or rather, if) you do, good luck in re-winding the coil.
Given the time of year, you might just want to kill the proverbial pair of
birds by buying her a new one - it'll be far less hassle.

Making sure we are using the same terms he Wall unit = the flat
plug-into-the-outlet piece. Base is the coil assembly that the
toothbrush sits atop to be charged. Toothbrush = obvious.

I have a "search coil" of ~130 turns of 0.7mm wire on a bobbin.
Bobbin ID is 15mm and coil OD is 31mm.

Test #1: With the coil (unterminated) connected to the 15MHz CRO,
absolutely zilch on max sensitivity when the coil is sitting flat atop
the energised base. Definite flatliner.

Test#2: Fed an AC current of 1A through the coil and brought the
toothbrush right up to sitting on the bobbin. No interest whatsoever
on the battery status/charge LCD. I have forgotten all my inductor
stuff way back, but if the factory base has an input (label) of 2W
then this may well have had a comparable field give or take the odd
order of magnitude.

Just to be sure we are talking about the same product. The previous
generation product had a base-cum-storage-tower construction and the
base had a keyed spigot for locating the toothbrush with the charge
LED outwards. The one we have has an egg-shaped hole through the base
with a matching shape on the bottom of the toothbrush. The video of
battery replacement (link in my reply to Andy) shows the toothbrush
under discussion.