Braun electric toothbrush charging

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.)

Reply to
pedro
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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.

--
Bob Milutinovic 
Cognicom
Reply to
Bob Milutinovic

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.

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 ....

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.

Reply to
pedro

With an OralB charger base,DVM Fluke 77 and 1mH small choke near the spigot of the base , measured 0.45V ac, HF not mains frequency but Fluke still registered something

Reply to
N_Cook

I would check the coil in the hand piece. Either try a different base or open by twisting. The hand piece coil is accessible. I fixed one that had opened and needed resoldering.

Reply to
John Keiser

The old ones (no idea what model #) have a simple charging circuit of a diode and a coil in the bottom of the handle, and 2 Ni-Cd batteries. I can't get that size battery anymore, so I rigged two larger cells outside and taped to the handle. It has worked for some time. I used to replace the cells every 2-3 years when the wouldn't hold charge anymore.

Jon

Reply to
Jon Elson

Making sure we are using the same terms here: 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.

Reply to
pedro

I use both Braun and Sonicare toothbrushes. (I like variety.) The Brauns charge fine on the Sonicare base (though they just "sit there", without even a nub to hold them in place).

I have a few extra Sonicare chargers. I will gladly send one to any US resident who needs one, for the cost of postage, plus 50 cents handling.

Reply to
William Sommerwerck

Right you are; it was the previous generation which I had, in which the base was barely more than a small plastic disc and a nub-encrusted protrusion with which the brush docked.

This morning I had a look at my daughter's newer unit, which has a slightly wedge-shaped oval as the docking point, and that seems to have considerably more bulk to the base unit - about an inch tall - which may likely house additional electronics.

I still contend though that because of the relatively low price of these units, it's not worth pursuing repair for any reason other than personal satisfaction.

--
Bob Milutinovic 
Cognicom
Reply to
Bob Milutinovic

I goofed somewhat. I have a couple of spare Braun chargers, as well. The offer stands.

Reply to
William Sommerwerck

The offer is appreciated but as I'm "down under" and it would require an adaptor to connect to our AU/NZ outlet, it's probably easier to bite the bullet and purchase the replacement from the Braun guys.

Reply to
pedro

The one we have is like this (but with Oz-pins of course ...):

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Sorry about the URL mess.

That's the current Plan A. $34 plus $10 shipping from east coast, or $39.95 ex the one local source.

Then I can do a Jeff Liebermann learn-by-destroying job on the existing wall unit. Wedging a couple of flat-blades into the current one showed what appeared to be the end of a pcb and clear silicon bog filling the entire enclosure. There's something in there warranting a pcb, and enquiring minds (this one at least) feel a need to know.

Reply to
pedro

Well that's an entirely different kettle of fish; the ones I've seen have the male mating on the base.

This is my daughter's charging base looks like; mine was similar but much thinner -

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Indeed, indeed. But just as I discovered when going through a similar procedure with a top-of-the-range Philips shaver in which the batteries had leaked (gotta love the old NiCd technology!), you'll likely find that the sum of the parts is worth a tenth of what they want for it.

--
Bob Milutinovic 
Cognicom
Reply to
Bob Milutinovic

But all the people who test-shaved the guineapigs have to get paid too.

--

beslutning at undlade det.
Reply to
Leif Neland

The techo guy at the authorised Braun service centre tested my charger and confirmed it was dead as, so I purchased a replacement. He also asserted that they do not contain any smarts, and operate at line frequency.

For the benefit of others who may find themselves in this position, the charger coil is driven at 72kHz unloaded, and this rises to 76kHz when charging the toothbrush. So much for line frequency!

When I get a round tuit I may attack the dead unit with the trusty Dremel to see what exactly is inside.

Thanks for all comments/suggestions.

Reply to
pedro

SWMBO's previous one(s) were like that style.

If they can sell it in Oz for $34 then its probably $2 tops to the Chinese factory. That may buy all the parts (labour being inconsequential there, a bowl of rice per week) in their market but isn't going to dent the parts list here.

Opening is for learning only. Not sure what I will find - electronics failed or the coil O/C.

Reply to
pedro

I have has some degree of luck with opening some sealed power supplies by p utting them in the vise sort of crooked and slowly cranking the vise. Most of the time they'll eventually "pop" and crack open along the sealed halves . Be careful with this as they sometimes pop with a lot of force. I've neve r tried this on a toothbrush base though. I'm sure they must be sealed a lo t better than a power supply. But if you're "learning by destroying" then y ou have nothing to lose. Lenny

Reply to
captainvideo462009

See this EEVBLOG for insides of Braun toothbrushes. It is not line frequency.

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Chris

Reply to
Chris Jones

In case you hadn't noticed (in the post you replied to... ), I had advised that very fact.

The one David is checking out is quite a different model, and in my case the charger was u/s which made the initial determination of frequency impossible.

Reply to
pedro

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