Can someone please explain LiPo battery voltage!

I have recently purchased and built a DJI F450. Everything seems to be going ok apart from the LiPo batteries, and in particular the low voltage settings on my Naza Lite flight controller.


I’ve watched endless YouTube clips trying to understand the whole low voltage thing, but I just don’t get it. One thing everyone seems to agree on is that you should not let a battery lose any more than 80% of its charge.


I have two batteries; a 4 cell 14.8v and a 3 cell 11.1v.


Now, I’m no mathematician, but 20% of 14.8v is 2.96v. So why when people enter the first level voltage protection, are they putting in figures like 14.1v or 14.2v??


Likewise with he 3 cell. Why are people entering first level protection at 10.5v when even 30% of 11.1v is 3.33v??


I’m clearly missing something here, and it’s probably going to be something embarrassingly simple. But I just don’t know what it is, and it’s doing my head in! (not to mention probably wrecking my batteries and flight times)

Batteries are confusing. First, for Lipos, each cell has a nominal voltage of 3.7 and a max of 4.2 (fully charged). Multiplying the nominal voltage by the cell count is what gives you the voltage ratings you see on batteries. You're obviously going to operate above and below the nominal voltage based on the charge level of the battery. Technically, nominal voltage isn't even a rating, but a naming convention. Also, voltage will not go down linearly at all. It will actually drop somewhat quickly and then plateau for awhile in the operating range, then it will drop again quickly (you don't want to get to this point).

The actual capacity of the battery is the mAh rating. When people talk about % of charge, they're usually talking the capacity number (mAh). The low voltage warning numbers people recommend, as far as I've seen, are based on testing how much capacity in mAh is put back into the battery when charging from certain resting voltage numbers. There are several different "charts" I've seen around that show people's test data indicating which voltages they've found correspond to what percentage of charge for the packs they tested.

In this case, I'd just play it safe and stick with what is tried and true and generally recommended by others. I've played with changing the low voltage warning before and have had a copter fall (luckily only 2-3 feet off the ground) because the ESC's will actually cut-off when a certain voltage is hit - and like I said above, it drops fast after it gets out of the plateau range.

Cheers mm

That makes things a little clearer.

I have ordered a low voltage alarm to fix to the quad, so that will hopefully negate the need to guff around with Naza'a low voltage settings anyway. I just hope I haven't stuffed up either of my batteries in the mean time.

No problem! That's a good plan.

The battery alarm is working a treat! I got about 15 mins out of my 3 cell, 3000mAh over the weekend in pretty windy conditions.

I just need to get the wobble sorted now.

Awesome! 15 minutes?? Nicee! What is the wobble issue?

Yep 15 minutes. I think it was about that anyway. I recorded the flight with my GoPro and that was about 16 minutes, so I'm guessing it was in the air for about 15; could have been a little less.

I've posted a video on another thread re the wobble issue (http://quadcopterforum.com/threads/vibrations-wobble.3294/)

For anyone interested, on top of mm's informative post, I have also found a really good link explaning just about everything Lipo.

http://www.rchelicopterfun.com/rc-lipo-batteries.html