Toothbrush

[dewaltdisney]

I have a cheaper end Braun electric toothbrush. It needs recharging every two weeks which is okay if inconvenient at times. One thing that has always puzzled me is the charger as there are no visible contacts on the base or in the port in the brush. There is a smooth plastic male connector that you put the toothbrush on. Can anyone explain how the electric charge passes?

Thanks

DWD

[Argyll]

Magic

[dewaltdisney]

It does seem like that, I just cannot see how plastic to plastic makes a contact? Is it swirling magnetic fields?

DWD

[Rorschach]

Inductive charging, same as some mobile phones use these days. Inefficient for anything other than small electrical devices.

[dewaltdisney]

My guess apparently was nearly right it is caused by alternate magnetic fields in a process called inductive charging. I should have looked on YouTube in the first place

DWD

[ericmark]

It seems Nikola Tesla did experiments with this he liked AC but others liked DC, the whole advantage/disadvantage with AC is the inductive linking, this is how a transformer works, there is a trade off, the higher the frequency the smaller the transformer can be, but also the higher the losses are when transporting over long distances, so theroy is the longer the distance the lower the frequency, but USA use 60 Hz and we use 50 Hz, so it seems UK is larger than USA? Think in USA it was local hubs, where in UK we designed the national grid when local hubs were still DC.

As to tooth brush the frequency is important, as switch mode power supplies have for years turned AC to DC then back to AC at a high frequency then transform it down, in case of tooth brush and rechargeable torches it turns it back to DC in the torch or tooth brush.

This process means with have loads of devices where electronics connect directly to the mains, years ago it would be transformed first, and the transformer would remove any spikes on the supply before they reached the electronics, so today we fit surge protection devices, I have one in my consumer unit, you can also get them built into sockets and extension leads, and also in the devices themselves, but only in the consumer unit can they really connect to earth, as else where it could trip the RCD, early desk top computers had this problem, they all had a small leakage due to the built in surge protection.

We tend to test the installation leakage with an insulation tester that uses 500 volt DC, the fact it is DC means there is no capacitive or inductive linking, so it does not show the back ground leakage, which should not exceed 1/3 of the RCD rating, to measure this we need to have the AC supply energised and measure the difference between line and neutral current, lucky the clamp on ammeter

Clamp-meter-small.jpg (55.86 KiB) Viewed 332 times

can do this with ease, but my old one to left went down to 0.01 amp, so needed new one to right which goes to 0.001 amp to measure that 9 mA allowed with a 30 mA RCD, only had it a year, before that is was a trust to the Lord thing, I had no idea how close to the wind I was sailing.

So we have War of the currents in USA where they decided if AC or DC was best, and we used their experience when we decided, same with colour TV we saw their error, and used the RR moto of take a proven design and improve on it, so our colour TV better than theirs. But with jet planes it was the reverse, they learnt from our errors with square windows.