What type of potentiometer do I need? What resitance?

[Wolfgang Kuehne]

Hi,

I had an old useless shaver so decided to do some trick with it. The battery within the shaver was over (it could not be recharged anymore). Moreover it was a battery which can not be removed. So I decided to change the circuit and leave the battery out of the game. I connected the adapter of the shaver directly to its motor. However, this time the device did not have enough power to move the blades. Why?
So I took the adapter out of the game and decided to use an iPhone charger instead.

Currently the device takes its electricity from the iPhone charger, over a usb cable, who's cables are directly connected to the motor. At the moment the blades move with a very high speed, which I consider that will damage the device pretty soon. As well the motor turn that fast, that I can not keep it in my hand due to the vibrations.

I thought it would be OK to put a potentiometer to the whole setup to be able to control the speed of motor, but I have no idea what type of potentiometer to use, and what range of resistance.

In case of need provide the following details:

Not used parts:
The original adapter:
AC-DC
AC: 220V - 240V - 50Hz
DC: 3V 700MA

Battery withing the device:
It is AA, 1.2 volts, 1000mah

=======================================================

The setup as it is now:
According to the info here: https://discussions.apple.com/docs/DOC-3511

The iPhone charger has: 5 volts 1.0 amps 5 Watts



What should be the range of the potentiometer? Please help!


Thanks in advance,
Best,
Wolfgang

 

[PA4TIM]

That will not work.. The original is 3V, but that was for charging the battery. The battery probably is 2.7V and can deliver more as 700 mA. Did you used the right polairity ?
You need to limmit the voltage, not the current. If you use a resistor and the motor needs between 700 and 1000 mA and drop the voltage to 2,7V. That is 2.3V x 1000 mA = 2,3W . 2,7/1A = 2.7 Ohm.
So a 2,7 Ohm, 3W potentiometer will do the trick. That is if 1000 mA is right. You should know the current draw it did on the battery. To mucht current can kill the motor, to much volt wil cause to much current. So that is why bringing the voltage down is better. The easy way is to connect 3 or 4 diodes in series. Each one will give a 0-6 to 1V drop depending on the current. So begin with 4 and if it is going to slow use 4. Use 2A diodes to be save. As a test you van use 1N4004 but they are limmited to 1A. Better use a 3V adapter that can deliver about 1.5A or more.

 

[tpetar]

Hi everyone,

I'm not sure for iPhone adapter safety, maybe you just have lucky see these unlucky situations :

Everything you wanted to know about charging your iPhone or iPad
http://www.dailymail.co.uk/news/article-2406185/Fake-Apple-Cheap-phone-chargers-burn-house.html
**broken link removed**
http://mobile.slashdot.org/story/13...dies-apple-warns-against-counterfeit-chargers
**broken link removed**



For replacing adapter use adequate adapter with original voltage range. Adapter current capabilities can be as original or higher.

Motor run faster because you supply 5V instead 3V.


Best regards,
Peter

 

[Wolfgang Kuehne]

That will not work.. The original is 3V, but that was for charging the battery. The battery probably is 2.7V and can deliver more as 700 mA. Did you used the right polairity ?
You need to limmit the voltage, not the current. If you use a resistor and the motor needs between 700 and 1000 mA and drop the voltage to 2,7V. That is 2.3V x 1000 mA = 2,3W . 2,7/1A = 2.7 Ohm.
So a 2,7 Ohm, 3W potentiometer will do the trick. That is if 1000 mA is right. You should know the current draw it did on the battery. To mucht current can kill the motor, to much volt wil cause to much current. So that is why bringing the voltage down is better. The easy way is to connect 3 or 4 diodes in series. Each one will give a 0-6 to 1V drop depending on the current. So begin with 4 and if it is going to slow use 4. Use 2A diodes to be save. As a test you van use 1N4004 but they are limmited to 1A. Better use a 3V adapter that can deliver about 1.5A or more.

Yes, I used the right polarity... I tried it without the blades (which makes the device lighter) and the motor was turning fine, but with the blades on, while the adapter was directly connected to the motor, they would not move.

I checked the battery again. It is AA, 1.2 volts, 1000mah. There are some other stuff written in Chinese but I can not understand them.
(first row smth in Chinese): 100mA (smth in Chinese) 16 (smth in Chinese)
(second ros smth in Chinese): 1000mA (smth in Chinese) 1.2 (smth in Chinese)

Does this (updated) info about battery change the solution that you provided. Or should I stick to the same one from before.

Thanks

 

[PA4TIM]

Is there just 1 AA battery inside ? Then take an AA cell and connect it as test. Then you can measure the current it needs. In that case build or buy something that makes 1,5V. Look for a DC-DC converter. They are cheap on ebay.