I just completed a light and I need help estimating possible run times please with it remaining on.
It uses a Cree T6 emitter with a 3-5volt input 700ma constant current driver.
The battery packs are wired up so that each pack can run off 3,6, or 9 batteries but voltage remains uniform. I appreciate your help to know what I might expect for runtimes in the following scenarios:
9 standard alkaline AA batteries running at 4.5 volts
9 Eneloop Ni-Mh (up to 2000mah) AA batteries running at 3.6 volts
9 Energizer lithium AA batteries running at 4.5 volts
I’m in the process of making a 2nd light as well. The difference will be that it will use a 1400ma driver instead. How would run times for this setup differ. Half as long?
9v alkiline 170mah 9 x 170= 1530 mah divide by 700 = about 2 hours That’s if it was using 9v should be about 3 times that at 3v.
Eneloop 3 in series to get 3.6v so 9 divided by 3 = 3 3 x 2000 mah = 6000 mah divide by 700 ma = about 8.57 hours
Lithium AA 3 in series to get 4.5v so 9 divided by 3 3 x 3000 mah = 9000 mah divide by 700 ma = about 12.85 hours or slightly more because of the extra voltage above vf.
for 1400 ma divide these estimates by 2.
This may not be a exact estimate, just a estimated run time, they are other losses and variables that would probably shorten these estimates.
I think it’s a tough thing to estimate, so you should probably just measure it.
Is the driver a linear buck driver, or is it a more efficient driver that acts like a transformer? That will have a huge difference, depending on the voltage you supply it. I’m guessing it’s a linear driver, so you do not want to feed it a voltage much higher than 3.5v or you’ll be completely wasting all the power above that. In that case, 3 Eneloops in series is your best bet.
Also, note that alkalines will not be 1.5v under load. They’ll sag easily, and voltage will continue to drop over the run-time.
NiMH are not 1.2v. They will be higher than that when fully charged, and drop towards that as they discharge. They are also affected by voltage sag, but not nearly as much as alkalines.
Similarly for lithium primaries, which will start at about 1.7v each.
There are a lot of variables for sure. Using the 9v with linear wont be very efficient if it even works, buck would be better. I wouldn’t have thought the 9v alkiline would sag to much if his running 9 of them in parallel, that’s only 78 ma each with 1400 ma 156 ma each. But I haven’t tested it. Which alkaline you use accounts for more variables and how many you use.
