Electronics > Beginners

Conversion of a beard trimmer from nimh to Li-ion

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PointyOintment:

--- Quote from: Hero999 on August 24, 2018, 09:15:45 am ---
--- Quote from: BradC on August 24, 2018, 05:13:14 am ---The motors in that test are the cheapest of the cheap with bent metal brushes. They'll last a lot longer with some suppression caps on them to reduce the brush arcing. There are always more expensive variants available with carbon block brushes that last considerably (like several orders of magnitude) longer, but you get what you pay for. They also handle more voltage a bit more gracefully.

I'd be super surprised if the motor in that beard trimmer didn't have carbon brushes and some form of suppression.

--- End quote ---
Metal brushes aren't used to save money, but are better suited to lower voltages. Carbon brushes on a 3V motor would result in inferior efficiency to metal brushes.

--- End quote ---

Is there a way to tell what brush material a motor has without opening it (assuming you can't peek inside through a vent hole, and don't have an X-ray machine)?

james_s:

--- Quote from: PointyOintment on August 25, 2018, 01:08:55 pm ---Is there a way to tell what brush material a motor has without opening it (assuming you can't peek inside through a vent hole, and don't have an X-ray machine)?

--- End quote ---

If there's a part number on it you might be able to find a datasheet.

downloaders:
I don't actually understand everything you guys are saying but regarding the "An 18650 and it's chemically similar cousins are nominally 3.6 volts over almost the whole discharge curve" I don't understand where the data for this comes from. I use 18650 and Lipo's a lot and with this little motor I guess the 18650 will be at least at 3.8V for quite some time. The AAA were 900mah and lasted maybe an hour, a 3000mah 18650 will last maybe 2.5hours and I guess for close to being empty it will output >3v.

james_s:

--- Quote from: downloaders on August 29, 2018, 03:56:41 pm ---I don't actually understand everything you guys are saying but regarding the "An 18650 and it's chemically similar cousins are nominally 3.6 volts over almost the whole discharge curve" I don't understand where the data for this comes from.

--- End quote ---

https://batteryuniversity.com/learn/article/lithium_based_batteries

Again, "18650" is not a battery chemistry, it is a physical for factor, 18mm diameter, 65mm long. Multiple battery types are made in the 18650 size.

downloaders:
So the step down module came, and guess what? I does not work. I should have measured the current. The module goes up to 500ma and When measured, the motor needs max 1.5A when i hold it down a bit like when cutting beard.

I couldn't find any step down module that could turn a 4.2 - 3.5V to 3V with 1.5A or more.

Does anybody know one that I could use, or some other way to bring the voltage down to 3v from 4.2 - 3.5V?

Thanks!!

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