Does protected cells require smart charger?

[mbuhboot]

Hi,

I am going to buy my second bike lamp based on cree/S4 leds. I am planning on using a deal extreme 3-cree led module (a reflector, regulator and 3 leds) and use Protected 18650 li ion cells to power it up.

From reading about protected cells it seems as if I don't have to use a smart charger to get them charge. I can simply plug them to a DC power supply with the right DC (4V?) and afte enough time (divide battery capacity by charger capacity?) disconnect them.

Are my assumption true or am I mistaken?

Are there any good sources for LiIon battery packs? I am also looking for a battery compartment that will let me insert either 18650 or CR123 to form a battery pack - but have found no source for it.

Any recommendations will help..

Moshe

 

[James S]

ALL liion cells require a "smart" charger, protected or not. I'm pretty sure that none of the protection circuits include a charging circuit, they just keep you from charging at too high a temperature and cut off the power if the drain becomes so high as to cause the battery to vent. They also cut off the battery below a certain voltage so that you dont run them below the floor level and cause them to die.

Though there are people here that do it You cannot charge a LiIon cell with just a regular DC power supply. Best case it will ruin the cells, worst case it will burn your house down.

Get a specific LiIon charger for these cells and you'll get long safe life out of them. they are not expensive.

 

[65535]

You technically could do that, some people only use a constant current constant voltage power supply to charge any rechargeable cells, as long as you set the output voltage lower than the maximum charge voltage there will be no problems with over charging. Some people swear by this method, and with a large enough power supply there is little limit to the amount of cells you can charge.


As for using a cheap wall wart supply, there is no way I would do that. The protection circuit built into those cells is to protect the cell from common accidents like over discharging and failed charging, it was never designed to control the charge like a charging circuit would, stick to a "smart" charger and don't get yourself or your property, worse yet your family hurt.

 

[johnnymceldoo]

How do you know what the final voltage should read on a charged cr123 or 18650? On one of my chargers a cr123 read 4.2 volts charged and on the other it charged all night but the green light never came on and the voltage read over 5 volts at which point I took the battery out.

 

[NotEnoughLight]

Johnny, with what I see with my cells, I would discourage using the cells again if you see a charge of over 4.2 volts. Mine showed 6 volts when charging but could not light up an LED using direct drive. Soon after resting the cell I got 2.75 volts. And the LED is perfectly functional. I'm sure someone knowledgeable will chip in with something more technical soon. Merry Christmas!

 

[mbuhboot]

Hi,

Sorry for the late reply. I activated the mail notification option but either it doesn't work or I have a false positive anti-spam case to check..

Anyway - I interested in building a 3.7 X n power pack (to get a 5A and more 3.7 power supply). To do so, I thought of connecting in parallel several 18650 batteries to form a battery pack.

Can I use a smart charger to charge this battery pack? I need a simple (read: cheap) but effective smart charger (that works on 220V as well as 110V AC) - any recommendations?

Should I buy a ready made power pack such as the one offered by websites like batteryspace or all-battery?

Are there any ready made battery compartments for 18650, 25500 or other LiIon batteries so I can insert several batteries in them and after use, can take them out easily and safely to be charged outside?


Moshe

 

[DM51]

You need a dedicated charger for Li-Ion cells. Do not use any other method of charging them unless it has been specifically designed for these cells.

Fully charged, a Li-Ion cell should read 4.2 volts. When it reads 3.5 volts, it is empty.

Over-charging them (above 4.2V) or draining them too low (below 3.5V) drastically shortens their cycle life and is dangerous – they become unstable and can spontaneously vent with flame.

 

[SilverFox]

Hello DM51,

You should also state that you are referring to resting open circuit voltages. You can actually draw a Li-Ion cell down to 2.5 volts under load, and as long as it springs back to 3.5 volts you are OK.

Tom

 

[mdocod]

From reading about protected cells it seems as if I don't have to use a smart charger to get them charge. I can simply plug them to a DC power supply with the right DC (4V?) and afte enough time (divide battery capacity by charger capacity?) disconnect them.

provided that your DC power supply has very accurate output controls AND most importantly allows you to set a maximum current then you CAN use this method as it will follow the rules of li-ion charging pretty well. See, the issue is that if you take a "dead" (<3.5V) cell and hit it with a DC power supply set to 4.20V, you are going to end up charging WAY TOO FAST for part of the charge. If you are dealing with 18650s and you can set your power supply not to hit the cell with any more than say 1-2 amp, than you should be ok. the charge rate will ramp down as it gets closer to full with this method and should work reasonably well. (If I remember the ideal charge rate is something like 0.7C for li-ion, so 1.5A would be a good maximum rate.)

 

[DM51]

You should also state that you are referring to resting open circuit voltages. You can actually draw a Li-Ion cell down to 2.5 volts under load, and as long as it springs back to 3.5 volts you are OK.

Tom

Thanks Tom, you are right. I was trying to keep my post as simple and clear as possible, as some of the previous posters raised quite a few issues, some of them rather alarming matters affecting safety.

However you are right, and I should have specified resting voltage.

To the previous posters: to measure the resting voltage of a Li-Ion cell, take it out of the flashlight and let it rest for 30 minutes, then test it with a digital multi-meter (DMM). This gives the cell time to recover to its resting state, when you can get a more accurate idea of its condition and state of charge.

Before attempting any unconventional ways of charging Li-Ion cells, you need to have a thorough and comprehensive understanding of these cells and the relevant safety considerations. As James_S, 65535 and mdocod have pointed out, it is possible to use other forms of DC power supply to charge Li-Ion cells, but it is extremely inadvisable unless you know exactly what you are doing.