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Old 11-07-2007, 03:55 PM #1
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Default 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


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Old 11-07-2007, 10:10 PM #2
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Default Re: Battery voltage

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).
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Battery voltage-discharge20curve.jpg  
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Old 11-08-2007, 02:39 PM #3
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Default Re: Battery voltage

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???
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Old 11-08-2007, 02:48 PM #4
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Default Re: Battery voltage

Quote:
Originally Posted by izzy007
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???
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?
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Old 11-09-2007, 04:09 PM #5
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Default Re: Battery voltage

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
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