If I want to charge up an electric toothbrush (in the UK) which is 110 volts (as the toothbrush is from the States) then I would presume I would require a step down transformer.
Does using a transformer to charge up a 110volt toothbrush from a
240volt electricity supply use more electricity than charging up a similar toothbrush which is from the UK and is therefore designed for a 240volts electricity supply and therefore does not require a transformer?Thanks!
Well yes, as the transformer is not 100% efficient and some losses occur as heat and sound (humming). But the actual ammount of loss is minute.
AWEM
Check the instructions. Many "personal grooming" items will accept all common international voltages, as by their nature, you may wish to travel with them.
Yes, it would use a little more. If the transformer is large, it may use a lot more. However, a toothbrush charger should take almost no power from the supply in the scheme of things. The best transformer type for this application is a BS3535 shaver adapter socket, which you can permanently install in your bathroom.
Christian.
Cheers guys, thanks for the info!
Much appreciated...
Any transformer will have some degree of inefficiency, manifest in the fact that they get warm. Depending on the transformer you might be looking at 90% efficiency, implying that might use 10% or so more electricity. So a continuous nominal 6 watt load at 10 p a kilowat might cost 3 or 4 pence a month more to run via a step down transformer.
So the answer to your unasked question is that if you already have an appropriately sized transformer, its not worth replacing the toothbrush!
In practice a shaver socket will use the same transformer to isolate 240 v that it uses to provide 120 volt, and so there is probably sod all difference in running cost.
Andy (awaiting flames for dodgy maths!)
Most toothbrush points have a transformer anyway as the Law says Thou Shalt Not Have 240v floating around in bathrooms (unless its - er - floating (with respect to earth)).
Iron losses (those present whenever the transformer is live due to magnetic hysteresis and eddy currents) on small transformers can be remarkably high. Many years ago I used to test large electrical machinery and sometimes found the small transformer for the control electronics had more losses than the rest of the stuff put together. It largely depends on how well the iron core of the transformer is designed and constructed. As a rule transformers are best switched off if not actually in use. If they need to be on a lot they should be designed with this in mind. Doing it properly is expensive.
The following may be interesting especially the bits about losses.
Edgar
Doing it properly is expensive.
Hence cheap power supplies ( wall warts) from China are usually very lossy.
Dave
Is it a Braun with the contactless charger? If so, I have a spare one as I have replaced the head but I still use the older charger which was wall mounted.
A series capacitor is also an option, but it must be calculated correctly. The cap will be lossless.
NT
Only if it is a perfect capacitor. They're rather rare.
Regards JonH
Chargers with a wide ranging voltage input such as 100-240V should be operated from the 120V output of shaver sockets. This is because the off-load output of a bathroom isolating transformer is permitted to be as much as 270V, which is likely to exceed the voltage rating of the charger, and chargers don't draw enough load to bring it back within range.
Interesting point. Is an isolation transformer of the shaver type less efficient at 110v than 230?
at 50Hz the losses will be so tiny it will not be possible to tell the difference in power consumption between the charger with and without the cap.That is near enough to perfect as makes no real world difference.
FWIW a capacitor is smaller, lighter, cheaper, more efficient and more reliable than a transformer in this app. And if youre lucky it may fit inside the mains plug.
NT
Yes, but only by the sqrt(sod_all)
In that sort of application, magnetic losses will dominate over losses in the windings -- and they're constant. There's the usual I^2R loss to think about and that'll go up for 110V kit, but not so you'd notice.
Indeed. Pay bugger all for wallwart, and three times over the savings in electricity if you leave it plugged in indefinitely.
No REASON for it to be so inefficient other than cost, pure and simple.
Sadly it doesn't isolate you from shocks like a transformer...
No different really.
Indeed so, as little iron in the core as you can get away with!!!
DAve
I always wondered if one could improve the cost of charger transformers by using transformer and C in series, C drops the V to the tf, limits i, and resonates (with low q due to tf's R) at 150Hz, enabling much less iron to be used, and far fewer turns, both of which reduce transformer cost. The downside is the cost of the C, which may be more than the iron and winding time saved. Note there is a double saving on winding time: less turns and thicker wire, the latter permits higher winding speeds.
NT
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