Confused over battery runtime - LEDs in series

[xraymtb]

I'm in the process of building my first DIY bike light but am confused over the current usage of LEDs in series.

I get that running 3 XR-E's in series will need around 11.1v, but if I drive them at 700mA, will that use 700mA from the battery each hour or 2100mA each hour (3 x 700mA)?

 

[pe2er]

With LEDs in series, the current through each LED and through the battery is the same; 700mA.

 

[znomit]

With LEDs in series, the current through each LED and through the battery is the same; 700mA.

Depends on the driver. Generally the battery current will be higher or lower.

 

[yellow]

best to (roughly) calculate it:

current * voltage the led "need" / voltage the battery "has" = current draw at battery


example:
1st: 3 led in series, 700 mA current, 14.4 Volt pack
700 * (3*3.7) / 14.4 = 540 mA draw at batt

2nd: 3 led in parallel, 700 mA current (per led), 14.4 V pack
3*700 * 3.7 / 14.4 = 540 mA draw at batt



... You need the correct driver, of course

 

[znomit]

best to (roughly) calculate it:

:thumbsup:
And throw in 10-20% more for the driver.