How do the batteries discharge themselves?

[msinger]

Does the power light on the battery illuminate while performing the auto-discharge?

No.

 

[generaltso]

We really need to test this. I guess the best way would be to set two batteries' discharge timer to 1 day. Tap the button to check the charge on one of them every day. After 3 days, they should both have discharged to storage voltage. If the tapped one doesn't discharge, we know DJI was blowing smoke. If both have discharged, it's working perfectly. If neither has discharged, we have a problem.

I'll try this and see what happens.

I started this test on Wednesday at 8pm. Two batteries were both fully charged and set to discharge after 1 day. Tonight at 8pm, it will have been 3 days since then. The battery that I've been checking by hitting the button every day still shows a full charge, so no conclusive results yet.

 

[msinger]

generaltso, perhaps DJI support gave you the wrong information. P2 batteries also reset the elapsed days to auto discharge when the battery button is pressed.

 

[generaltso]

generaltso, perhaps DJI support gave you the wrong information. P2 batteries also reset the elapsed days to auto discharge when the battery button is pressed.

Quite possible. That's why I'm doing this test. I'll give it until Monday to be sure. If the untouched battery has discharged and the touched one hasn't by then, we'll know DJI gave me bogus info.

 

[dtokez]

Those "connecting points" are not accessible without tearing up the internal insulation used for the wiring to each of the cells. It's very tight in there. If you destroyed a battery you can likely trace the wires to the boards to figure out where those points are. But since balancing takes place internally through the integrated smarts onboard, I'm not sure why anyone would want access to those balance points.

If you look in the female connector on the battery you can see different pins, well they could be different pins. Of course the 2x male connections on the charger would bridge those pins. not sure if they were the pins that alokbhargava was talking about? Very curious about how these batteries work, anyone want to open one up lol. That is good news they have hopefully fixed the self discharge timer though!

 

[kupua]

I honestly don't really understand this Lipo Battery discharge... We, wither know it or not all use them and specify a discharge for storage. Most recent laptops or note books use Lipo's, and they say it's ok to be plugged in (hence fully charged) and they don't really say you have to discharge to a lower voltage? They are not recommending to discharge the some lower battery level after being fully charged. Many other items also use Lipos! My case and point, I don't know of any other Lipo battery manufactures that say they should be not be stored at 100% level?

Or could it be more a point of DJI, saying it as a way to hasten the battery refresh cycle?

 

[With The Birds]

I honestly don't really understand this Lipo Battery discharge... We, wither know it or not all use them and specify a discharge for storage. Most recent laptops or note books use Lipo's, and they say it's ok to be plugged in (hence fully charged) and they don't really say you have to discharge to a lower voltage? They are not recommending to discharge the some lower battery level after being fully charged. Many other items also use Lipos! My case and point, I don't know of any other Lipo battery manufactures that say they should be not be stored at 100% level?

Or could it be more a point of DJI, saying it as a way to hasten the battery refresh cycle?

This is not a DJI thing, it is a characteristic of LIPO chemisty. Store a LIPO at 100% SOC for three months and you can throw it in the bin, the increased internal cell resistance will make it next to useless as far as usable capacity goes.

The self discharge function is great, one less thing you have to worry about in battery management and people who dont understand the limitations of LIPO's still get good service life and performance.

Laptop batteries also last longer if they are kept at 50% charge and removed from the machine away from the heat when on mains power. Difference is the advantage isnt as pronounced because the current demand in use is nowhere near that of batteties in this application.

 

[John Locke]

I proposed 4 resistors, each 1/4 watt, thus totaling to 1 Watt against the total dissipation of 0.566 W

Quarter watt resistors won't work. If they are in series they will all have over a half watt going through them. Your resistors need to be half watt if they are in series. If you connected 4ea 1600 ohm in parallel, then 1/4 watt resistors would work ok and you'd have your 400 ohm resistance.

 

[alokbhargava]

Quarter watt resistors won't work. If they are in series they will all have over a half watt going through them. Your resistors need to be half watt if they are in series. If you connected 4ea 1600 ohm in parallel, then 1/4 watt resistors would work ok and you'd have your 400 ohm resistance.

My proposal is to connect 100 + 100 + 100 + 100 ohms in series

Current through each will be 37.3 mA

So wattage dissipation in each = 37.3*37.3 *100 = 139 mW, so a 250 mW rating for each resistor should be good enough. If the equivalent resistance remains the same, total dissipation remains the same and gets equally divided.

If you connect 4 resistors of 1600R is parallel,
dissipation in each will be = (37.3/4) * (37.3/4) *1600 = 139 mW. So both will result into same wattage ratings.

 

[With The Birds]

Quarter watt resistors won't work. If they are in series they will all have over a half watt going through them. Your resistors need to be half watt if they are in series. If you connected 4ea 1600 ohm in parallel, then 1/4 watt resistors would work ok and you'd have your 400 ohm resistance.

You cant cheat ohms law John, current is constant and dissipation of each resistor will be well under 1/5 watt per resister at full applied pack voltage.

 

[olof Ekbergh]

I honestly don't really understand this Lipo Battery discharge... We, wither know it or not all use them and specify a discharge for storage. Most recent laptops or note books use Lipo's, and they say it's ok to be plugged in (hence fully charged) and they don't really say you have to discharge to a lower voltage? They are not recommending to discharge the some lower battery level after being fully charged. Many other items also use Lipos! My case and point, I don't know of any other Lipo battery manufactures that say they should be not be stored at 100% level?

Or could it be more a point of DJI, saying it as a way to hasten the battery refresh cycle?

Well Lipo batteries like Apple uses are the ideal MBP batteries as you charge them every night and then use them up every day. This is the perfect way to use Lipos. Have you noticed people who keep their MBPs on chargers all the time and rarely discharge them get the shortest lifo out of batteries.

Apple also builds their own batteries to fit into unconventional spaces, very clever, and Lipos are perfect for this as they do not have to be cylindrical. They are thin layers of Polymer and chemicals that can be made almost any shape, very thin if need be.

 

[generaltso]

We really need to test this. I guess the best way would be to set two batteries' discharge timer to 1 day. Tap the button to check the charge on one of them every day. After 3 days, they should both have discharged to storage voltage. If the tapped one doesn't discharge, we know DJI was blowing smoke. If both have discharged, it's working perfectly. If neither has discharged, we have a problem.

I'll try this and see what happens.

Well, I've completed the test and have conclusive results. DJI support is full of crap. The battery that I tapped every day is still fully charged. The untouched battery discharged properly. So this behavior did NOT change with the 1.6 firmware update. Bummer.

 

[msinger]

I guess it's still working as designed then.

 

[generaltso]

I guess it's still working as designed then.

Yup, for better or worse, it's still working as it always has. It would be nice to be able to check and see if the battery has discharged without actually preventing it from discharging. Oh well.

 

[John Locke]

Well Lipo batteries like Apple uses are the ideal MBP batteries as you charge them every night and then use them up every day. This is the perfect way to use Lipos. Have you noticed people who keep their MBPs on chargers all the time and rarely discharge them get the shortest lifo out of batteries.

Apple also builds their own batteries to fit into unconventional spaces, very clever, and Lipos are perfect for this as they do not have to be cylindrical. They are thin layers of Polymer and chemicals that can be made almost any shape, very thin if need be.

I think most phone and computer batteries are lithium ion, better suited for mild current draw and also ok leaving fully charged while being plugged in. Lithium polymer batteries don't like to be left sitting fully charged, as the technology is different. Lithium polymer is designed for high current drain, more amps than lithium ion.

 

[With The Birds]

I think most phone and computer batteries are lithium ion, better suited for mild current draw and also ok leaving fully charged while being plugged in. Lithium polymer batteries don't like to be left sitting fully charged, as the technology is different. Lithium polymer is designed for high current drain, more amps than lithium ion.

What we call Lipo here is still a lithium ion cell. The distinction seems to be more marketing department lingo and spin than from the R&D area. Same base tech but in a solid package they call it a li ion and in the rc model pouch format for the cells we get the generic li poly name.

The observed life differnece is application based, as you have pointed out the high current demand ages cells faster, it also caused cell voltages to drop faster under load making them unusable earlier.

 

[olof Ekbergh]

I think most phone and computer batteries are lithium ion, better suited for mild current draw and also ok leaving fully charged while being plugged in. Lithium polymer batteries don't like to be left sitting fully charged, as the technology is different. Lithium polymer is designed for high current drain, more amps than lithium ion.

Apple actually do use Lipo batteries in the MBP lineup. It was controversial back in 2009. But now many other Laptop manufacturers are using Lipos as well.

You may remember the many instances of expanding batteries and battery fires a few years ago.

Lithium Polymer is a type of Lithium Ion battery, it uses a thin Polymer sheet between layers, and can have many different shapes.

Here is a link about it: Hot news - LiPol Battery Co., Ltd.

 

[J.James]

From what I could tell from a battery that went bad that I disected. The self discharge circuit seems to use the same resisters that are on the smart board that also have some thing to do with cell the balancing. So it prob would have them on the board any way and dji just some how figured out a way to use the same resisters that would burn off any over charge in any of the cells if its ballancing at the end of a charge and able to use them to send power to them when it needs to do the self discharge.

 

[Mike T.]

Because I want to check the charge.

Why is the battery programmed to reset the auto-discharge timer? What purpose does this serve?

Maybe so the battery won't start the discharging process mid flight.

 

[Vertigo]

This is not a DJI thing, it is a characteristic of LIPO chemisty. Store a LIPO at 100% SOC for three months and you can throw it in the bin, the increased internal cell resistance will make it next to useless as far as usable capacity goes.

What you say is mostly true, but its not nearly as bad as that though, much depending on storage temperature. Ive seen some test of this, and when they store lipo's around 20C and you store them for a full year, fully charged, you will lose something like 30% of their capacity. Going by memory, but thats the ballpark. If you store them much warmer, it will be worse, above 35C or so IIRC, they would be all but dead after 6 months, if you keep them cool, the capacity loss will be pretty limited.

Mind you, those tests where run with normal lipo's, not high voltage like the P3. And those might be more susceptible.