Downboy Current Question

[smitty244]

Hi all, I know this may be a silly question but forgive my ignorance /ubbthreads/images/graemlins/wink.gif. I'm thinking of driving a Lux V (T bin) with 2x18500 LiIon cells (7.2 volts average, 1400mAh). I know with the BadBoy regulators the current goes up as the voltage goes down to keep the constant current. Is it the opposite with DownBoy? Do current demands go down as the voltage goes up? Essentially I'm would like to know if the 1400mAh LiIon is going to act like a badboy and have more than the 700mA from the Lux being drawn from it or less (so I can try to predict runtime). Thanks!

 

[Billson]

With a BB, current draw from the battery will increase when the voltage sags but the the current into the lux is kept constant.

DB will keep the current constant as long as the voltage from the batteries is above the Lux V's vf. When the voltage from the batteries fall below the lux's vf, the converter goes into direct drive.

 

[smitty244]

So the current draw with a downboy from the batteries stays the same? If I'm using batteries with a capacity of 1400mAh and a downboy set to 700mA then I can expect a current draw of 700mA from my batteries constantly then?

 

[Billson]

Constant current converters regulate output current so if we say DB700, it means the board is sending 700ma to the led and not the current it's drawing from the battery. The current drawn from the batteries will depend on the remaining charge left in the battery. When a load is applied to the battery, the voltage will sag. As voltage sags, the board has to draw more current to maintain regulation.

Maybe one of our electronics expert can answer your question on how to maintain curent draw from the batteries. It's beyond my ability to explain or figure out. /ubbthreads/images/graemlins/icon3.gif /ubbthreads/images/graemlins/confused.gif