What resistor between WXOS and 2x RCR123?

HenryE

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Mar 8, 2005
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157
I want to use rechargeable cells with this WXOS (5.91V-6.39V) star, and would really like it to last longer than a flashbulb.

Assuming the rechargeables come off the charger at 4V or more, what value resistor should be in series with that emitter? Or, am I better off just burning primary cells...?

Thanks
 

jmw19

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Jan 26, 2006
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State College, PA
I used the calculator here with source voltage of 8.4V, led Vf of 5.91V, and drive current of 700 mA.
It recommends a 3.9 ohm, 2W resistor. If you're comfortable overdriving the Luxeon, calculating for 7.4V (where the RCRs will spend most of their time), gives a 2.2 ohm, 2W resistor.

Good heatsinking should decrease the risk of burning these out - you'll want to sink the resistor as well, as 2 watts is a good bit of power to dissipate.

Best,
Jon.
 

HenryE

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Joined
Mar 8, 2005
Messages
157
Great. I think 3 ohms should be ok with good heatsinking. I plan to mill an aluminum interface between the star and the housing.

THANKS!!!!
 
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