Why would a toothbrush/toothbrush charger blow, running off an inverter?

davidpbo

davidpbo

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Tried to charge my electric toothbrush off a (cheap) inverter and it is now blown. (Braun Professional).

Anyone like to offer an opinion as to why that might be?

I had assumed they functioned as the primary of a transformer and were a wire coil.

No comments on the laziness of using an electric toothbrush. It does mean my teeth get cleaned better.
 
Cheap inverters produce a really ragged AC supply. Sounds like enough spikes to blow the diodes rectifying the AC to DC in your case.
 
Might have failed even on mains. We have an older Braun toothbrush on the boat and it has been fine for years using mains, Honda Eu and 2 cheap inverters. We also have a new one at home that's dud and failed after a few weeks just before leaving home.

My wife checked and found lots of reports regarding that model failing to charge after a short period. We'll be returning ours in October/November as it will still be under warranty when we get back to UK.

Try checking your model on Internet to see if there are lots of similar failures. Can't remember the model for our failed toothbrush.
 
RAI said:
Cheap inverters produce a really ragged AC supply. Sounds like enough spikes to blow the diodes rectifying the AC to DC in your case.
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Any rectification would be in toothbrush not the base. I presume they work with the base being the primary of a transformer and the toothbrush having the secondary coil in its base. I would have thought any spikes would having been smoothed out to some extent by the inefficiencies of the coupling.

I note that there are issues of reliability with these chargers.
 
We have had the same experience this summer. Fitted a Maplins 300w inverter last winter to charge the mains equipment on board with mixed success. Camera batteries and razor ok but blown 2 brand new Boots electric toothbrushes. Noticed also it runs an electric alarm clock but does not keep good time - therefore pretty useless. I will think about a pure sine wave inverter to replace it.
 
Yep, I've blown a Braun one too, suspected the inverter, this tends to support that. I use a Ring 50 quid one now, but always connect a heavier load to it before a light load gets connected. Can't remember what the other thing that it fried was, possibly a 'phone chager, but it was simultaneous.
 
We have had a few blow in the last three years and all at home. I have heard that Braun chargers are not all that good - the price on ebay seems to confirm that they are sought after.
 
We have blown two Braun toothbrush chargers with our inverter, we are now very careful only to use shore power or the gen. set. All other gear phones, cameras, laptops seem OK.
 
pteron said:
Is it the charger base or the toothbrush that's blowing?
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I am presuming charger base. Toothbrush still working but now run out of juice. Charger base open circuit across plug pins unless someone tells me to the contrary I am assuming it is a coil forming the primary of as transformer, the secondary being in the base of the toothbrush. That being the case it is interesting that they appear to be unreliable unless it is a statistics thing - people only comment/post if it breaks.
 
davidpbo said:
I am presuming charger base. Toothbrush still working but now run out of juice. Charger base open circuit across plug pins unless someone tells me to the contrary I am assuming it is a coil forming the primary of as transformer, the secondary being in the base of the toothbrush. That being the case it is interesting that they appear to be unreliable unless it is a statistics thing - people only comment/post if it breaks.
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That surprises me too. I suspect that the primary is overheating and melting a turn due to the harmonics in the mains from the cheap inverters. I wonder if anyone has disassembled one?
 
Done a little bit of investigating - the operating frequency is around 20kHz, so there will be a switching converter in the base. I bet the harmonics from the cheap inverter are interacting with the switcher and causing it to malfunction.

If this is so, then I suspect that those chargers that are blowing on the standard mains are doing so because of noise on the mains. A bit more filtering on the input would fix that.
 
pteron said:
Done a little bit of investigating - the operating frequency is around 20kHz, so there will be a switching converter in the base. I bet the harmonics from the cheap inverter are interacting with the switcher and causing it to malfunction.

If this is so, then I suspect that those chargers that are blowing on the standard mains are doing so because of noise on the mains. A bit more filtering on the input would fix that.
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Surprised at that. I would have thought poor magnetic coupling between base and brush would have meant that mains frequency would have been used.
 
Ia there any simple way to check the raggedness of the output. I have a 1000w chinese new this year and it seems happier and creates less heat than the 300w one I use for the laptop(compaq 4 pin plug for PSU).?
 
paulclan said:
Ia there any simple way to check the raggedness of the output. I have a 1000w chinese new this year and it seems happier and creates less heat than the 300w one I use for the laptop(compaq 4 pin plug for PSU).?
Click to expand...

An oscilloscope or a spectrum analyser.... but unless you are familiar with working with mains can I suggest you don't?

What's the spec on the device?
 
davidpbo said:
Surprised at that. I would have thought poor magnetic coupling between base and brush would have meant that mains frequency would have been used.
Click to expand...

The power available in the magnetic field is proportional to frequency and coil area - so you can have big coils and low frequency or small coils and higher frequency. They chose the latter to get it to fit into the base of the toothbrush!
 
In my case, it was the charger/base. When we got home I had a spare base unit, and the tbrush worked as well as expected after being 'flat' for two weeks.
 
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