One 14500 Li-ion runs my old cordless shaver?

[cenz]

Hi all,

I have a old National Cordless Shaver (from 1970, pics below), 3.0V DC power input, motor is ES-565, does anyone know whether can use one 14500 li-ion to power it ? safe?

thanks

 

[Illum]

14500s are 4.2V hot off the charger and is considered dead at 3.8V which is still much too high for the shaver...unless you can build a buck circuit that regulates it to ~3V and within dimensions of an AA battery. Look for 3.3V for closest output and should it becomes necessary you could drop a resistor in the outputing bias for 3V at a desired current level.

A simple LM317 linear regulator can be configured into a voltage regulator but at high current loads it could wreak thermal havoc inside a plastic shell and may not be easily installed within the battery holder.

I have built a Max756 3.3V boost circuit that can be fitted into my minimag along with an AA battery for the nite-ize 3LED dropin...its not too difficult provided its a 8-DIP for smaller and requires only an inductor [optional for buck...I think :thinking: ] and a couple caps

As far as I can think of a max604 IC from maxim should do you fine provided your not drawing above 500ma

 

[Fallingwater]

is considered dead at 3.8V

A resting voltage of 3.8V means the cell is at 40% capacity or thereabouts. Not full, but certainly not dead.

Assuming the connection is cells-switch-motor with no circuitry inbetween, driving that shaver with a LiIon would overdrive the motor. Whether it'd survive this treatment depends entirely on the motor in question (some appliances have underdriven motors by design).

You could reconfigure the battery bay for a parallel connection and use two LiFePO4 14500 cells. This would give you relatively safe voltage (fully charged 3.6, operating voltage around 3.3, discharged 3, IIRC) and the ability to use rechargeables without the voltage drop of NiMH cells.

You'd need a charger capable of taking LiFePO4 though.

 

[SilverFox]

Hello Cenz,

In general, 1 Li-Ion cell will replace 3 NiMh or NiCd or Alkaline cells. Since your shaver only has 2 cells, it would be over driven by a single Li-Ion cell.

Tom

 

[cenz]

A resting voltage of 3.8V means the cell is at 40% capacity or thereabouts. Not full, but certainly not dead.

Assuming the connection is cells-switch-motor with no circuitry inbetween, driving that shaver with a LiIon would overdrive the motor. Whether it'd survive this treatment depends entirely on the motor in question (some appliances have underdriven motors by design).

You could reconfigure the battery bay for a parallel connection and use two LiFePO4 14500 cells. This would give you relatively safe voltage (fully charged 3.6, operating voltage around 3.3, discharged 3, IIRC) and the ability to use rechargeables without the voltage drop of NiMH cells.

You'd need a charger capable of taking LiFePO4 though.

Two LiFePO4 14500 in parallel is good idea, and I need to modify the cell ways...

Thanks ALL!

 

[Mr Happy]

I'm not quite sure what advantage you would get from changing the battery supply? It seems like it should give several uses from one charge on a pair of NiMH cells as pictured, and since they are rechargeable it need not be a big bother cost wise?

If performance or run time seems excessively poor, it may be that the gearing and bearings just need some cleaning and lubrication. It should certainly run as well on a pair of rechargeable batteries as it ever did on a pair of alkaline or zinc chloride batteries.

 

[Fallingwater]

Two LiFePO4 14500 in parallel is good idea, and I need to modify the cell ways

Note that the motor is still likely to be a bit overdriven (though a lot less than with a LiIon cell).
Also, never put in parallel two cells with different charge levels; if unsure, just use one.

I'm not quite sure what advantage you would get from changing the battery supply?

The way I see it, being that the shaver is old and most likely has a direct connection from the battery to the motor, using NiMH would make it go slower than on alkalines due to the lower voltage (I don't think a shaver draws enough current to slump the voltage of primary cells much).
A pair of LiFe cells would be the best of both worlds, as they'd get you a slightly faster motor and the ability to recharge them.

If performance or run time seems excessively poor, it may be that the gearing and bearings just need some cleaning and lubrication

That is, of course, always a wise thing to do to old equipment. Cenz, I recommend you do that in any case.

 

[Mr Happy]

using NiMH would make it go slower than on alkalines due to the lower voltage

This is an oft-repeated fallacy. The truth is that alkalines only have a higher voltage than NiMH when they are brand new. If you look at a discharge curve the voltage drops very steeply once you start using them, such that after about 10% of their life the voltage of alkalines has fallen to NiMH levels and is still falling. This is why Maglites only look super bright for the first few minutes of running on a set of alkalines and then become much less impressive.

Additionally, electric motors are one of the heaviest loads on a battery, usually more so than lights. In the old days, the "super heavy duty" zinc chloride cells were specially developed for motorized devices like shavers.

 

[Fallingwater]

This is an oft-repeated fallacy. The truth is that alkalines only have a higher voltage than NiMH when they are brand new. If you look at a discharge curve the voltage drops very steeply once you start using them, such that after about 10% of their life the voltage of alkalines has fallen to NiMH levels and is still falling.

I'm very aware with this behaviour, but what you say depends a lot on the load. I'm assuming the shaver would draw a lot less current than an incandescent bulb or high-flux LED. This is why I said that I don't think it'd make the voltage slump much.

Additionally, electric motors are one of the heaviest loads on a battery, usually more so than lights. In the old days, the "super heavy duty" zinc chloride cells were specially developed for motorized devices like shavers.

Electric motors CAN be a huge load, but I don't think small ones in shavers are. I say this because I have a small rechargeable shaver that'll run for ages on two NiCD AAs.
Then again, his is 1970 technology, so it might be a lot less efficient. I probably just don't know enough about shavers in general.

If what you say is true, though, my original idea of using LiFe cells to have a higher, more constant speed makes even more sense.