Shaver sockets and toothbrushes

[Scott]

I see my shaver socket is marked 'Shavers only' and the new ones have symbols for shaver and toothbrush. According to the manufacturer, there has been a design change. From what I read, the older ones are designed for intermittent use only (mains shavers not rechargeable equipment). I think I'll replace mine for peace of mind.

However, I just wondered how serious an issue this is. I am sure most people think an electric toothbrush (or indeed a rechargeable shaver) can be used from a shaver point. Is there a safety implication or is it just a question of buzzing noise and reduced lifetime?

[harry]

Ones intended for bathrooms (ie most) have a transformer that isolates the shave from the mains. Some are 110V too. The transformer is what limits the current it can take.

[Michael Chare]

But are they not all suitable for continuous use at UK mains voltage?

[Scott]

I know that but I am asking if it is suitable for continuous use as the suggestion it that it is not. I suspect a toothbrush draws far less current than a shaver anyway.

[newshound]

This thread came up a while ago, and I worried about it for a little while (I have a toothbrush and a water pick plugged into my "shaver" socket, there is no sign of overheating).

I'd guess (since rechargeable shavers have been around for a long time now) that modern sockets are designed for continuous use whatever they are labelled. I think "shaver" is used here as a generic term for "legal bathroom appliance".

No buzzing from mine, though whether this means SMS or a well designed transformer I have no idea.

[Brian Gaff]

I've never had an issue with the old ones to be honest, but I do notice there seem to be three different pin arrangements on shavers these days, all seem to plug into the sockets. I do not think the current on charge is going to be that much anyway, maybe there were some only just good enough ones made, I do not know but the last time I had the bathroom done, I had all electrics removed and charge up stuff via a plug in adaptor elsewhere in any case. Who would need to charge things up in the bathroom? Shavers particularly, these days will not operate while on charge which I find really irritating but this is the way the designers have gone, moving the charger into the plug and only having a low voltage cable to the shaver. Brian

[Theo]

In the interests of science I just measured it (Oral B toothbrush using USB wireless charger):

Charger without toothbrush attached: 50mW Charger with toothbrush: 720mW

I don't think we're going to blow any fuses.

Theo

[Theo]

I suspect by 'continuous use' means that the socket is rated at 1A/230V, but the transformer is thermally sized for something less. Eventually it'll cook. So if you were to draw that constantly, it would fail. However an ancient shaver might draw 230W for 5 mins a day (or 230W on startup, if not when running), and that's an acceptable duty cycle.

As the numbers I posted upthread show, toothbrushes and other rechargeable bathroom equipment take insignificant power so I can't see why there would be a problem running this continually.

I suppose another reason for 'non-continuous' would be the socket isn't rated for the plug to be constantly inserted, but that's a pretty dumb design.

Theo

[Scott]

Ah but, when the toothbrush is fully charged does consumption fall to

50mW? Is not the issue that the current is then continuous when the transformer is only for intermittent use? The manufacturers tell me the design has changed though not giving any details.

[Dave Plowman (News)]

It would be a very poor transformer indeed if it couldn't be run 24/7 at well under its rated load. Assuming it doesn't cook.

[tabbypurr]

that may be true in fantasy land

a dumb design is not the issue there

[Theo]

I didn't have a suitable fully charged toothbrush at the time of measurement, but I assume the toothbrush shuts off eventually (the LED stops flashing). I suspect some current is still taken just by inductive losses into whatever metal there is.

(I had a play - placing a piece of metal the shape of a drinks bottle cap over the plastic peg on the charger got the power up to about 500mW, so there's no fancy communication to the charger. This charger is however a $4 Aliexpress version, since Oral B don't offer a USB charger)

All this in the level of leakage current as far as the transformer is concerned, it'll neither notice nor care that you're taking less than a watt.

Theo

[polygonum_on_google]

I was lucky enough to need to buy after the change (at least, for MK). So both of ours are toothbrush-compatible.

I too find it difficult to believe there is a serious danger but it does seem that there really was a change and not just to the symbols.

[harry]

All devices containing a coil can be rated for continuous use or intermittant use. It depends on how easily the heating looses can be dissipated. So they can be "uprated" for a limited time. The more you uprate them, the shorter the time is.

They just work out how long it takes to clean your teeth/shave etc.

You only need continuously rated devices for continuous use. Otherwise they can be made cheaper and smaller.

[Scott]

Is the small current for a charger enough to qualify as a load for the purposes of continuous use?