Battery charge checker

parkgt · Sep 28, 2019

What is needed is chargers that charge to 60% as an option.

parkgt · Sep 28, 2019

DanMan32 said:
There has been incidents where it was suspected that starting out at a significantly less than 100% has caused a miscalculated SoC where late in flight % suddenly drops.
It was like the AC starts out "OK, I have 60%" but later says "oh crap, I thought I had 30% left but voltage tells me I only have 10%. Time to land NOW!"

I guess then that I have been lucky. Maybe the Smart batteries are not that smart after all. Seems that checking voltage would would be another way to ascertain SOC.

DanMan32 · Sep 28, 2019

Voltage is part of the equation. However voltage alone can be misleading. When power draw increases, internal resistance in the battery can drop. For example, at idle, my M2 shows 4.30v at near 100%. But if I take off, voltage drops to 4.00v if I recall but still shows about the same %. Granted that's one of my older batteries.
The batteries have a Texas Instruments chip designed to manage multi-cell LiPos. TI have refined the algorithm in later versions of said chip, and OEMs like DJI can customize the programming.

GadgetGuy · Sep 29, 2019

DanMan32 said:
There has been incidents where it was suspected that starting out at a significantly less than 100% has caused a miscalculated SoC where late in flight % suddenly drops.
It was like the AC starts out "OK, I have 60%" but later says "oh crap, I thought I had 30% left but voltage tells me I only have 10%. Time to land NOW!"

The bigger issue is unbalanced cells where one cell may be significantly lower than the others. The 100% charge rebalances all cells. During auto discharge to storage mode, the cells are not properly balanced. Flying on them in this state could lead to a battery shutoff in flight, or at a minimum, a forced landing whenever any one cell drops below 3.0V under load, which can easily happen during rapid ascension immediately after launch at temperatures below 70°F. Been there. Done that. Almost got killed! Best avoided.

Skywalker · Sep 29, 2019

CanadaDrone said:
(don't fly if it's below 20C).

I thought you could fly at lower temperatures if you gave the battery a chance to warm up prior to racing off. I was lookin forward to some snow videos.

Thomas B · Sep 29, 2019

Itsabirdy said:
I thought you could fly at lower temperatures if you gave the battery a chance to warm up prior to racing off. I was lookin forward to some snow videos.

@Itsabirdy ... You can fly, per DJI manuals at temps from 32 degrees F to 104 degrees F.
I rarely see the former, and avoid flying above 100 degrees F.

rangemaster728 · Sep 29, 2019

Thomas B said:
@Itsabirdy ... You can fly, per DJI manuals at temps from 32 degrees F to 104 degrees F.
I rarely see the former, and avoid flying above 100 degrees F.

Or spend the extra dollars and buy Mavic 2 Enterprise batteries; they are good down to -10°C (14°F)...self-heating.

ff22 · Sep 29, 2019

Itsabirdy said:
I thought you could fly at lower temperatures if you gave the battery a chance to warm up prior to racing off. I was lookin forward to some snow videos.

You can or, at least, I did:

Since the snow did not yield underfoot - that means it was very refrozen, it was definitely below freezing (here that would be 32F)

CanadaDrone · Oct 2, 2019

Itsabirdy said:
I thought you could fly at lower temperatures if you gave the battery a chance to warm up prior to racing off. I was lookin forward to some snow videos.

Correct - the battery itself should be at least 20C though. You can check this before you take off and also monitor it during the flight. Sorry if I was not clear.

DanMan32 · Oct 2, 2019

Requiring 20C (around 70F) seems rather high, especially just to start out. Many of you have started your flights way below that. It will quickly warm up though.

CanadaDrone · Oct 2, 2019

DanMan32 said:
Requiring 20C (around 70F) seems rather high, especially just to start out. Many of you have started your flights way below that. It will quickly warm up though.

It's easy to get the batteries to 20C (68F) no matter how cold it is outside - put them near your car heat vents or in a pocket close to your body for a while before flight. The 20C recommendation comes from DJI. Battery temperature is one of the easiest things to control and keep an eye on, and also one of the most important things. Once the drone is running, the temperature shouldn't drop unless it's way too cold out.

DJI has rated the Mavic 2 down to -10C but I personally would not fly in temperatures that cold, though I do realize some people fly in much colder weather than that. Far too many things that can go wrong for my liking.

DanMan32 · Oct 2, 2019

Putting them in your pockets in dead of winter won't likely get them to 70F. 40F when it is 0F outside maybe, and is perfectly fine. You may be confusing 20C with -20C. I believe -20C is the minimum recommended by DJI.

CanadaDrone · Oct 2, 2019

DanMan32 said:
Putting them in your pockets in dead of winter won't likely get them to 70F. 40F when it is 0F outside maybe, and is perfectly fine. You may be confusing 20C with -20C. I believe -20C is the minimum recommended by DJI.

If they are against your body, they stay quite warm - your body is almost 20C warmer than the batteries need to be. Inside a coat or something on an interior pocket and that would be plenty, or what a lot of guys do is keep them in their warm car until they are ready for use. This is exactly what I did in Iceland and I did not have a problem keeping my batteries at 20C. In terms of ambient temperature, the minimum for the Mavic 2 is -10C, as per DJI literature (this is in addition to the +20C minimum battery temperature).

I can guarantee you that DJI does not recommend you start with a battery temperature of -20C - if you could even get a battery to operate with an internal temperature that low I would be surprised. Their exact wording is, before use:

"Pre-heat your battery to 20°C(68°F) when the (ambient) temperature is lower than 10°C(50°F)"

Some drones like the Inspire and M2 Enterprise series have battery heating functions, but the consumer versions of the Mavic do not.

Battery temperature is also important for charging - Mavic batteries will not even quick charge unless they are in an ideal range (22-28C) and it's dangerous to charge them outside of a 5C-40C operating range.