## Help with small battery selection?

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I am trying to battery power a small device at about 50% duty cycle that draws about 60mA @ 3V (+AVR).

I am looking for the smallest battery options that would give me at least a few hours. I was hoping to be able to use some type of coin battery but those don't seem to handle near enough current. Any suggestions?

Thanks.

I had used the 3.6V 60mAh Ni-cd battery. The price of it is cheap. I just used it as a temporary power when the supply power was off. A diode should be added in the circuit if you need the 3V power.

Nobody can go back and start a new beginning, but anyone can start today and make a new ending.

But a 60mAh battery is only going to last one hour at 60mA current draw (in fact it's unlikely it'll hold the full rated charge so expect less - maybe 50 minutes?). If you have a draw of 60mA and want a "few hours" (I'll take that as 3?) then 60mA*3 = 180mAh - but make that 200mAh to be on the safe side.

True. I was also factoring in that the device is not running continuous but pulsing.

I came across the LIR2450 and LIR2477 as possible solutions. Their sustainable discharge abilities are a little unclear to me if anyone can help out (not familiar with "C" as a measurement).

Okay I think I understand but if someone could confirm.

A 1C charge/discharge on a 1000 milliamphour battery is 1000 milliamps or 1 amp?

yes

Thank you. Does anyone have experience with charging these batteries? I am looking at USB using a max1551.

That chip charges at 280mA. Can your battery handle that?

No, it cannot. But couldn't I use a current limiting resistor on the charge pin?

It charges 280mA using a DC source or 100mA using USB. 100mA is the Max Charge rate for the cell, but if I am reading correctly it should be charged at 50mA.

I was also looking at the MAX1811 and MAX1555 (variation of MAX 1551). I requested a few samples to experiment with, but I definitely don't want batteries exploding so I am trying to figure it all out as best I can. I've never used anything other than standard alkaline cells or a wall wart for my projects so far, let alone USB charging.

You should select a battery charger IC with which you can program the charge current with a resistor.

You could also look at the offerings of Microchip and Linear Technology.

And limiting the current with a resistor is not going to work, the charger will raise the voltage to compensate until it maxes out. You will also mess up the charging process because the charger switches over to voltage mode when the cell reaches 4.100 or 4.200V. That threshold is important and that precise, Li-Ion batteries do not like the slightest overvoltage.

Great info, thank you I'll look into your suggestions.

"Dare to be naïve." - Buckminster Fuller

A larger selection:
http://www.powerstream.com/licoin.htm
Off their home page are some thin rectangular cells that may work.

"Dare to be naïve." - Buckminster Fuller

Testing with a LIR2450 and with your help, I think I found a few good charging solutions:

LTC4054L
LTC4062L