Series vs Series/Parallel question

[JB01245]

I am wanting to build a 4 HBLED light. Been playing around at the bench. If I wire the 4 LEDs in series, then I can run them off a 14.8V battery. If I run 2 LEDs in series and then 1 in parallel off of each of the "in series" LEDs, then I can run it off a 7.4V battery.

I have used the LED PRO calculator for estimating run time on the "in series" configuration, but I am unsure what to do to estimate run time on the "series/parallel" configuration. I am wanting to use a constant current driver set up for 700ma.

Can someone please help explain the difference in run time of an "in series" configuration versus a "series/parallel" configuration, if any?

 

[TigerhawkT3]

A parallel connection will have no increase in voltage, but you'll increase runtime/current. For example, 2AA NiMH in series is 2.4V and 2.5Ah (approximately). The same 2AA NiMH in parallel would be 1.2V and 5Ah.

I hope that helped.

 

[JB01245]

Thanks for the quick reply TigerhawkT3. So I guess if I using LED Pro calculator to figure run times on a 4 HBLED "series/parallel" configuration, then I need to double the Vf and double the LED current? I figured I was going to get half of the run time, just couldn't figure out how I was powering them with only 7.4 volts. Thanks again from a newbie.

 

[Curious_character]

Any time you connect two LEDs in parallel, or two series strings in parallel, the one with lower voltage will hog the current. Then, as it gets hotter, its voltage will drop, causing it to hog even more. LED current is an exponential function of voltage, so it takes very little mismatch to start the hogging process going.

c_c