Severe Battery Temp Problems = 4hrs to charge 2 batteries
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Never put lipo under 0 deg C, otherwise the battery will irreversibly damaged. Cooling to room temperature in the fridge is ok, but be careful no (outer most) cell be under 0 oC.
After I posted above, I searched some facts of LiPo on the net;
- 100% charge is danger because rising temperature causes battery "over 100%" charge state,
- natural discharge is faster in 40oC than 20oC, 20oC than 0oC (but monthly scale),
- degrading (yearly scale) is worse in 100% charge than 50%, 50% than 0%,
- the irreversible damage is shown under -20oC due to some chemical material freeze (but other paper says "space LiPo" could be kept under -70oC...?)
So the best way to keep battery is, 0% charge at 0oC degree; but very slow overdischarging occurs and battery may be damaged, so need to charge slightly to 0% once in few month. Many R/C shops cannot maintain like that, so 50% charge and keep under 20oC is the 2nd best way. In hotter region, keeping in vegetable partition in fridge (5-10 oC) is good way. And be careful avoiding dew when take out.
Back to the topic, battery damage will be occur when over 40oC AND 100%. Fully charged battery is not damaged when just after starting motors on 25oC, nor med in flight 50oC but 50%, you know. Just after landing and remaining battery 0% or 25%, rather safe even if you do "force charge" (power on then charge)... but should stop under 75%, then wait till battery becomes cooler. Instantly, obeying charger warning is safer.
I sometimes fly on morning, connect to charger (warning and doesn't start charging), leave and go to job, then charge automatically starts when cooled and fully charged when back home. And if, you're in hurry, force start charging is only the way - travel to seaside and shoot sunset scene is more precious than battery life.
- 100% charge is danger because rising temperature causes battery "over 100%" charge state,
- natural discharge is faster in 40oC than 20oC, 20oC than 0oC (but monthly scale),
- degrading (yearly scale) is worse in 100% charge than 50%, 50% than 0%,
- the irreversible damage is shown under -20oC due to some chemical material freeze (but other paper says "space LiPo" could be kept under -70oC...?)
So the best way to keep battery is, 0% charge at 0oC degree; but very slow overdischarging occurs and battery may be damaged, so need to charge slightly to 0% once in few month. Many R/C shops cannot maintain like that, so 50% charge and keep under 20oC is the 2nd best way. In hotter region, keeping in vegetable partition in fridge (5-10 oC) is good way. And be careful avoiding dew when take out.
Back to the topic, battery damage will be occur when over 40oC AND 100%. Fully charged battery is not damaged when just after starting motors on 25oC, nor med in flight 50oC but 50%, you know. Just after landing and remaining battery 0% or 25%, rather safe even if you do "force charge" (power on then charge)... but should stop under 75%, then wait till battery becomes cooler. Instantly, obeying charger warning is safer.
I sometimes fly on morning, connect to charger (warning and doesn't start charging), leave and go to job, then charge automatically starts when cooled and fully charged when back home. And if, you're in hurry, force start charging is only the way - travel to seaside and shoot sunset scene is more precious than battery life. 
I have 4 batteries. When I finish first one - it needs like 15 min to cool down. So 4 batteries means 1 hr flying - not a "perpetual" flying. Needs to cool down or couple more batteries
Happily Picking up my four extra intelligent batteries on Monday... Oh yea!!
It's going to be so sweet to actually be able to spend some quality time in the field, instead of these short flying durations. Can hardly wait...
Charging them all with one 100w charger will be my second hobby. Fun.
I need to get some number stickers for them. Keep them rotating on a regular basis.
RedHotPoker
It's going to be so sweet to actually be able to spend some quality time in the field, instead of these short flying durations. Can hardly wait...
Charging them all with one 100w charger will be my second hobby. Fun.
I need to get some number stickers for them. Keep them rotating on a regular basis.
RedHotPoker
DJI's battery tech seems a bit complex because they have (Apple-like) turned an ordinary LiPo into a 'black-box' (or white box) with their packaging. But here are some basics that informed me about their maintenance.
LiPo batteries use standard lithium-iron-phosphate (LiFePO4) chemistry: the Po just refers to packaging -- the chemistry is bundled into standardized flexible, foil-type (polymer laminate) cases that are 20% lighter than cylindrical or prismatic cells. Battery voltage in a single LiPo cell is around 1.8-2.0 V (discharged) to 3.6-3.8 V (charged) set by the LiFePO4 chemistry. The P3 batteries stack 4 of these in a box. DJI's packaging and constraining the LiPos adds a little bit of weight, but the moderate pressure on the stack of layers that compose the cell results in increased capacity retention, because the contact between the components is maximised and delamination and deformation (puffing) is prevented, which is associated with increase of cell impedance and degradation.
LiFePO4 chemistry and the pouches were largely developed by Sony, and are comparatively robust to fires (a big problem with telephones and laptops in the 1990s), take about 2000 cycles with 10 year shelf life and operate in the -30 °C to 60 °C range. LiPo cells are affected by the same problems as other lithium-ion cells: overcharge, over-discharge, over-temperature, short circuit, crush and nail penetration can cause pouch rupturing, the electrolyte leaking, and fire. DJI's integrated circuitry in the P3 & P2 batteries control these problems at the charge/discharge terminals:
(1) lock out the upper/ lower end of the temperature range to 0℃-40℃
(2) prevent charge currents of 8 amps or more, because you don't want to push a battery over the edge and catch it on fire.
(3) balance charging/discharging and current limiting (voltage is always regulated, but current can vary and determines how fast chemical reactions occur at the cathode)
(4) recommend charge and discharge the battery completely once every 20 charge/discharge cycles, discharging the battery until there is less than 8% power or until it can no longer be turned on, then recharge it to the maximum capacity (cleans up the cathodes of the cells)
(5) the on/off switch is probably just there to save power (LED, trickle current). I can't see how it would otherwise affect charging, but the trickle loss might help you push discharge down to <8%.
My Phantom 3 Pro is on order from DJI, so I haven't gotten the batteries to experiment. But I have a regulated power supply and the 3 battery strips (from eBay) set up in a rack with a 12v fan blowing on them that I will use whenever the P3 arrives. To imitate the 100w charger (~6A @ 17V) I would add 6 A per pack (6-12-18 for 1-2-3 packs) at a regulated 17vdc. Buy a 300w inverter and you can plug to your car (unfortunately 4 cell LiPos put you over the car's 12V system)
LiPo batteries use standard lithium-iron-phosphate (LiFePO4) chemistry: the Po just refers to packaging -- the chemistry is bundled into standardized flexible, foil-type (polymer laminate) cases that are 20% lighter than cylindrical or prismatic cells. Battery voltage in a single LiPo cell is around 1.8-2.0 V (discharged) to 3.6-3.8 V (charged) set by the LiFePO4 chemistry. The P3 batteries stack 4 of these in a box. DJI's packaging and constraining the LiPos adds a little bit of weight, but the moderate pressure on the stack of layers that compose the cell results in increased capacity retention, because the contact between the components is maximised and delamination and deformation (puffing) is prevented, which is associated with increase of cell impedance and degradation.
LiFePO4 chemistry and the pouches were largely developed by Sony, and are comparatively robust to fires (a big problem with telephones and laptops in the 1990s), take about 2000 cycles with 10 year shelf life and operate in the -30 °C to 60 °C range. LiPo cells are affected by the same problems as other lithium-ion cells: overcharge, over-discharge, over-temperature, short circuit, crush and nail penetration can cause pouch rupturing, the electrolyte leaking, and fire. DJI's integrated circuitry in the P3 & P2 batteries control these problems at the charge/discharge terminals:
(1) lock out the upper/ lower end of the temperature range to 0℃-40℃
(2) prevent charge currents of 8 amps or more, because you don't want to push a battery over the edge and catch it on fire.
(3) balance charging/discharging and current limiting (voltage is always regulated, but current can vary and determines how fast chemical reactions occur at the cathode)
(4) recommend charge and discharge the battery completely once every 20 charge/discharge cycles, discharging the battery until there is less than 8% power or until it can no longer be turned on, then recharge it to the maximum capacity (cleans up the cathodes of the cells)
(5) the on/off switch is probably just there to save power (LED, trickle current). I can't see how it would otherwise affect charging, but the trickle loss might help you push discharge down to <8%.
My Phantom 3 Pro is on order from DJI, so I haven't gotten the batteries to experiment. But I have a regulated power supply and the 3 battery strips (from eBay) set up in a rack with a 12v fan blowing on them that I will use whenever the P3 arrives. To imitate the 100w charger (~6A @ 17V) I would add 6 A per pack (6-12-18 for 1-2-3 packs) at a regulated 17vdc. Buy a 300w inverter and you can plug to your car (unfortunately 4 cell LiPos put you over the car's 12V system)
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I bought one of those electric coolers that run on 12V. In the heat of a Florida summer day, the cooler won't keep drinks cool enough for my taste, but it does seem to work well for cooling off my P3's batteries between flights.
-- Roger
-- Roger
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