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.

Thanks for the quick reply, Bob. I realised it was an air-cored
transformer, but I allowed for the possibility that they were
operating at a higher frequency to get decent coupling efficiency. I
was still out looking for an AM portable to check if there was any
50Hz field around the base unit.

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.

Given the 2W nameplate rating, that's a pretty high Zin - about 300K
if resistive. Some coil, so presumably a blocking cap to help keep
the current half-decent. There goes the prospect of measuring for an
O/C coil without cracking the case ....

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.

This one has the cord end of the wall unit seemingly retained in the
case with visible barbs on opposite sides of the case. They resist
decent efforts to depress them though.

If there is bugger-all of consequence in that wall unit, the only
reason for the size is as a handle for the tri-lobe tool moulded
thereon which undoes the toothbrush base.