Battery voltage

i just wanted to ask if i used a cr2 3v rechargeable batt. to power a laser, would the initial voltage be 3.6v
and with a 3.6v battery, would this voltage be 4.2v and if so how long does it stay there till as i heard that its supposed to drop reapidly to its normal voltage

except a cap and a resistor what other prtoention should be used if any

thanks

Use a proper current drivers. Rechargeable lithiums give around 4.1 volts when fresh out of the charger, running down to 3.5 along the way and 3.0 when depleted. See graph below for a typical curve (yours will be slightly above the black trace considering CR123's and driving 200 mA or so).

so if the current draw is around 350mah it should be around 3.7v

if i just want to use a cr123 batt what resistor should i use

3.7-2.7
1/0.3=3.33

or if its voltage is 4.2v and i use the same resistor it will draw
4.2-2.7
1.5/.0033=454ma

thats the only concern because with fully charged batteries it will be 454ma???

izzy007 said:

so if the current draw is around 350mah it should be around 3.7v

if i just want to use a cr123 batt what resistor should i use

3.7-2.7
1/0.3=3.33

or if its voltage is 4.2v and i use the same resistor it will draw
4.2-2.7
1.5/.0033=454ma

thats the only concern because with fully charged batteries it will be 454ma???

Click to expand...

What are you trying to power :-/. As Benm said, use a proper driver circuit. A current regulator really isn't that hard to make (or you could buy one from DDL or SenKat or someone... I think..) and will let you regulate the diode to full power instead of hoping you aren't overpowering it on a charged battery, only to see it fall in power as the battery drains.

The graph doesn't show the voltage at a certain current, its showing voltage over time based on current drawn. The point of it though is that if you're just sticking a resistor in with a li-ion batt, you gotta prepare for up to 4.2-4.3 volts of input on a full charge.

What type of laser are you trying to power anyway? Got some specs on the diode or whatever it is?

i dunno which diode it will be but most likely a 16x of 20x. i wanted to power of a single cr123 battery so i think the best idea would be to use the circuit of the flashlight and add a resistor in series until i can get around 300ma??
or can you give me a link to a good cheap driver on dx