Electric toothbrush not working with other battery?

Thread Starter

Tom_37

Joined Sep 30, 2020
13
I have a Braun oral-b pro 2000 toothbrush and with the original battery it now only lasts about 1 minute. I replaced the original 3757 Ni-MH battery with an AA size Ni-MH (higher capacity) battery and the red “battery low” indicator blinking. I had put it on the charger and it charged the battery from 1.45 V to 1.52 V and the green charging light still blinking but it won’t charge any higher. When I want to turn it on it’s not working only the red light still blinking.

Finally, I put back the original battery to see if it went faulty during repair and it's working as intended. I also tried with a bench power supply and it won't work with any voltage only with the original battery. So how is this circuit checking the battery? What’s the trick?


braun_oral_b_2000.jpg
 

AlbertHall

Joined Jun 4, 2014
12,157
Welcome to AAC, @Tom_37
Charge the original battery and measure its voltage. I suspect it will read around 4V indicating that it is a lithium cell and so the toothbrush is not going to work on 1.5V.
 

Wolframore

Joined Jan 21, 2019
2,576
Found this instructional, might be helpful, it states that it needs a 1.2V NiMh, so I wonder if there's something wrong with your replacement battery. Do you have another you can try?

Verify that it's not shorting out the positive against the case of the battery, sometimes they are in a metal jacket which is ground, note that the top one is encased in a heat shrink type material.

https://toothbrushbattery.com/guides/braun-oral-b-professional-care-1000-battery-replacement/
 

Thread Starter

Tom_37

Joined Sep 30, 2020
13
Found this instructional, might be helpful, it states that it needs a 1.2V NiMh, so I wonder if there's something wrong with your replacement battery. Do you have another you can try?

Verify that it's not shorting out the positive against the case of the battery, sometimes they are in a metal jacket which is ground, note that the top one is encased in a heat shrink type material.

https://toothbrushbattery.com/guides/braun-oral-b-professional-care-1000-battery-replacement/
As a stated in my question I even connected a bench power supply and tried every voltage up to 2 Volts.
 

WBahn

Joined Mar 31, 2012
27,392
Charge up the original battery and see what the current draw is when the tooth brush is running off of it.

What voltage is the old battery charging to?

The toothbrush might have overvoltage protection and perhaps you have charged the replacement cell too high for it, although 1.45 V to 1.52 V doesn't sound excessive, plus your bench supply should be able to supply enough current at 1.3 V to work.

I'm assuming you are making sure that you have the polarity correct.
 

Thread Starter

Tom_37

Joined Sep 30, 2020
13
I found out what was the problem. The circuit needs to be "reset" by placing it on the charger everytime I replace the battery. Thats why it wasn not working with the power supply. Thanks for everyone who tried to help.
 
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