# Inverters for Toothbrushes?



## peejay (May 10, 2005)

We've just bought a Braun rechargeable toothbrush and I was thinking of using it in the van and recharging it on the move between stoppovers with our cokecan inverter as we tend not to use hook up.

Now I do remember a while back that the general concensus was that inverters can sometimes fry toothbrushes.

Technology has probably moved on a bit since I last read about this and my new Braun has a Ni-Mh battery which is possibly different to the older types. (?).

So can I or can't I :?: 

Pete

ps, tried doing a search but there is a problem with the word 'toothbrush' in the search engine.


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## olley (May 1, 2005)

Hi Pete I think it was said that they only work on pure sine wave, not modified, something to do with the built-in-charger being electronic.

Olley


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## Spacerunner (Mar 18, 2006)

I have been using a cheap 150watt inverter to charge an electric toothbrush for eighteen months with no problem.

Toothbrush is a Braun with two of us using it, lasts about ten days between charges.


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## GerryD (Sep 20, 2007)

We certainly charge our Braun with a standard 150W inverter.
Gerry


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## DABurleigh (May 9, 2005)

Pete,

The risk only applies to inductively charged toothbushes (which I should imagine should be all of them).

Modified sine wave inverters generally can have problems with inductive loads - motor windings, some lighting, etc., but this doesn't mean they WILL have problems. Devil in design detail jobbie.

The only issue with toothbrush chargers is simply that this is the ONLY piece of equipment I have ever come across which has been BROKEN by use of a modified sine wave inverter.

So it is simply a matter of rolling the dice and hoping for the best, or not .....

Dave


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## Spacerunner (Mar 18, 2006)

DABurleigh said:


> Pete,
> 
> So it is simply a matter of rolling the dice and hoping for the best, or not .....
> 
> Dave


 nfire: ...or..... \/


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## peejay (May 10, 2005)

So, do I or don't I :?: 

Nah, think I'll give it a miss, maybe risk it after its had a bit of use.

Thanks gents.

Pete


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## pippin (Nov 15, 2007)

The silly thing is that a toothbrush charger requires only 2W at 240V AC which is a minuscule 8mA.

Even at 12V that is only 170mA (still only 2W!) - so using an inverter designed to supply up to (say) 150W is serious overkill.

It would probably be better/safer if the inverter were to be running a more substantial load as well as the toothbrush charger.


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## SidT (May 9, 2005)

Pete said.......

_Now I do remember a while back that the general concensus was that inverters can sometimes fry toothbrushes_

Hi Pete. I remember the original post as quite a few members said that they had fried their toothbrushes using cheap inverters, so we have never used it.
Cheers Sid


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## sallytrafic (Jan 17, 2006)

The *'why'* is quite interesting

A sine wave consists of just one frequency (the fundamental) in the case of the mains, 50Hz.

Non-sinewave waveforms contains frequencies at harmonics of the fundamental 50Hz. So 100Hz 150Hz etc.

A transformer is designed to work at an optimum frequency. The lower the frequency the less efficient. If you apply a frequency higher than it was designed for it will get hot.

The further the output of an inverter is from a sine wave the more harmonics it contains and the more that windings in motors, transformers etc will overheat.

A toothbrush holder is one half of a transformer the other half being in the handle of the toothbrush.


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## Spacerunner (Mar 18, 2006)

Frank

What exactly does that mean in 'wooden buckets and homespun' terms. :?


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## sallytrafic (Jan 17, 2006)

nothing


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## Spacerunner (Mar 18, 2006)

:lol: :lol:


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## peejay (May 10, 2005)

Thanks Frank, I was thinking of unscrewing mine and having a look inside but you've scared me now :lol: :lol: 

Pete


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## pippin (Nov 15, 2007)

Well, I know all about wooden buckets so perhaps I will dismantle my old charger and have a sniff around with the oscilloscope to see what the waveform looks like from my coke-can inverter.


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## sallytrafic (Jan 17, 2006)

Spacerunner said:


> Frank
> 
> What exactly does that mean in 'wooden buckets and homespun' terms. :?


I did once provide an easier answer >here (MHF thread)<

....although in detail there are two slight mistakes - well points we could argue about.

and pippin you will find the waveform will vary depending on the load (size and its power factor.)


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## pippin (Nov 15, 2007)

Yup Frank, that's why I am going to do some sniffing with different load levels and perhaps check the effectiveness of a resistive (lamp) load in conjunction with the charger.

Watch this space!


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