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Dec 03, 2019, 09:24 PM
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Excellent testing Joe!!! The XPS packs will live their life in a heli unless I get another edf which I have been considering for a while. Had a BAE Hawk which I loved and the foam F/A 18 blue angel and viper were fun also! Damn now I want an EDF again.


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Dec 03, 2019, 10:20 PM
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Quote:
Originally Posted by sethmattox
Excellent testing Joe!!! The XPS packs will live their life in a heli unless I get another edf which I have been considering for a while. Had a BAE Hawk which I loved and the foam F/A 18 blue angel and viper were fun also! Damn now I want an EDF again.


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Well I will have a eflite 80mm havoc by the end of week. Merry Christmas


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Dec 04, 2019, 03:02 PM
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URUAV Lipo review


Forgive me if this has already been covered, but has anybody tested a URUAV 6S 6000 75C lipo here. I intend to use it in EDF twin 80mm aircraft. Thanks Steve F
Dec 04, 2019, 04:52 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by heliclown
Forgive me if this has already been covered, but has anybody tested a URUAV 6S 6000 75C lipo here. ...
Tested packs are listed in first posts of this thread.

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Vriendelijke groeten Ron
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Dec 05, 2019, 04:58 AM
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Thx Ron
Dec 07, 2019, 09:43 PM
aka JetMan Joe
MCSGUY's Avatar
Thread OP

Lipo Care Best Practices


The JJ604 provided translation of bzfrank's expert level Lithium Polymer Technology publication covers all major issues in the care and feeding of our lipo packs. The power point like format makes for a heavy (worthwhile) study and can be found at:
https://www.rcgroups.com/forums/show...nglish-version
This bullet point(ish) condensation incorporates a (very) small bit from my own studies and represents BEST CASE PRACTICES. Take what you can use and ignore the rest understanding the trade offs.

To Maximize Cycle Life and Performance:
1. Never fast charge cold packs, it causes permanent damage
*restrict charging temperature to between 70F/21C - 86F/30C degrees
*reduce charging rates to1C or less when near bottom of this temperature range (regardless of label specs)
*optimum charging temperature is > 77F/25C degrees
2. Never discharge at high amps when packs are at low temperature, it causes permanent damage
* optimum discharging temperature is > 77F/25C degrees
* real "C" maximum discharge levels should be avoided until pack temperature is > 86F/30C degrees
3. To enhance life even more, charge below 4.20v/cell and limit depth of discharge (DOD) as much as possible
* charging at 4.10v/cell doubles cycle life
* limiting DOD <70% doubles life
4. Maintain pack running temperature below ~131F/55C if you wish to avoid accelerating the aging process
5. Immediately charge a pack to 3.7v if any cell has been discharged to 3.0v (or near)

Storage Facts:
1. Regarding maximum cycle life there is little difference storing packs between 3.7v/cell - 3.9v/cell if kept within 32F/0C - 68F/20C degrees
2. Regarding reducing age related capacity reduction store at 3.7v-3.75v/cell and maintain temperature between 32F/0C - 68F/20C degrees
3. Long term storage above 77F/25C degrees accelerates aging which becomes more pronounced the higher the storage charge is
4. Storing packs at 3.7v-3.75v/cell avoids the possibility of thermal runaway due to accumulated effects of abuse and/or aging which produce dendrites (Dendrites: microscopic crystallized mineral treelike whiskers or protrusions responsible for non-crash related internal short circuits)
5. Always place packs in Lipo bags or other flame proof containers when not in use

Fun Facts:
1. To obtain accurate comparison data, IR must be measured at the same temperature (ideally ~72F/22C) AND at the same state of charge (SOC)
2. All other things being equal, the reason heavier packs typically generate higher real C output is because cells are constructed using thin layers, wrapped and stacked for maximum surface area. The greater the surface area the greater the output the greater the weight.
3. Some manufacturers indicate ~158F/70C to be the maximum temperature for their packs. However damage begins at any temperature over 140F/60C due to chemical decomposition forming harmful by products which adhere to the SEI layer.

Solid-Electrolyte Interphase (SEI) layer:
* a necessary ~0.00004"/.001mm thick layer which forms on the Anode during the first charge cycle (or after a few break in cycles with lower quality products)
* it acts as an "interface" between the electrolyte and the electrodes
* in it's best condition it allows free rein flow of ions between the Anode and Cathode during charging or discharging.
* battery performance is highly dependent on it's condition
* as a cell ages or sustains damage the SEI thickens increasing resistance (~IR) and reduces capacity

Thermal Runaway:
1. Plating is a form of Dendrite that can develop when excessive quantities of Li+ ions are pressed into the Anode during charging, influenced by:
* over voltage
* excessive charging current
* low cell temperature during charging
* old/mistreated (over heated, over amped) cells having a thickened SEI layer
* imperfections due to lower quality Anode material

2. Dendrites cause internal "Micro Shorts" which bridge the separator between the Anode and Cathode and grow over time into "Macro Shorts". Macro shorts damage electrode separation and breakdown the SEI layer which generates extra heat, furthering the vicious cycle which increases plating. At some point (called "onset") this damage begins to "self heat". When self heating increases to a 10C/Minute rate and reaches ~150C combustion begins. This process can take minutes or hours and is only evidenced by difficult to detect, minute increases in self discharging (see Storage Facts, #5). To protect against this possibility store packs empty (3.7v-3.75v/cell) and cool (< 68F/20C)

3. The Cathode (+ electrode) determines the other portion of a cell's power equation and is made using Cobalt or lower cost Magnesium which provides ~65% the Wh/Kg as Cobalt. The Li+ ion exchange during discharge mechanically stresses the Cathode. The higher the current the higher the stress. Too high discharge rates, especially at low temperatures causes cracks in the cathode material. High temp and voltage above 4.1v cause the electrolyte to disintegrate (oxidize) and migrate by products through the cell to the anode which increases SEI thickness (~IR) and costs lithium (capacity). These reactions generate gases which can lead to irreversible "puffing" through overload or fully charged storage. Younger cells are more resilient to this process then aged/abused or high cycle cells. Puffing due to over discharging causes copper dendrites which lead to fire risk during charging. Irreversible (room temperature) Puffing can be indicative of SEI disintegration which can lead to thermal runaway.

Joe
Last edited by MCSGUY; Jan 28, 2020 at 03:38 PM.
Dec 07, 2019, 10:58 PM
Registered User
Note my POV is LI battery tech in general, not just the propulsion context.

Quote:
Originally Posted by MCSGUY
1. Never fast charge cold packs, it causes permanent damage
*restrict charging temperature to between 70F/21C - 86F/30C degrees
*reduce charging rates to1C or less when near bottom of this temperature range (regardless of label specs)
*optimum charging temperature is > 77F/25C degrees
Millions of people are charging in cold weather every day.

To me, 1C is higher (faster) than I'd ever go, even above 80F.

0.4C is maximum for maximizing longevity, for use cases where discharge rates hardly ever go over 1C, only using 80% of capacity, thus 5000+ cycles & decades' longevity is a reasonable expectation.

Of course each LI chemistry and even model battery will have its minimum "no charging anywhere near this temp or instant scrap" spec.

In truth you usually can charge at a **very** low C-rate around 0C, say under 0.1C

But in general, being conservative I'd start pre-warming when below 5C, if going over 0.1C

10 should be fine for 0.2-3C

Faster charging than 0.4C, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30 first to maximize longevity.

Of course in many contexts people just take the hit losing some life cycles, if they're even aware of the issue.
Dec 08, 2019, 02:05 AM
Registered User
OK, so store batteries empty and cold, but charge them warm... Who really preheats all their lipos before charging, every time? I store mine in the unheated garage, and try to bring in the ones I want to use the night before, to get them to at least room temp. But it’s not always 100%...

Interesting read, but I feel a bit like compromises have to be made living in the real world and not a theoretical one. Which is not to say I ignore safety. On the contrary. But some concessions to convenience are surely unavoidable..
Dec 08, 2019, 02:21 AM
aka JetMan Joe
MCSGUY's Avatar
Thread OP
Quote:
Originally Posted by Herrsavage
........
Interesting read, but I feel a bit like compromises have to be made living in the real world and not a theoretical one. Which is not to say I ignore safety. On the contrary. But some concessions to convenience are surely unavoidable..
I have to agree. I don’t intend to stop overcharging, pushing the C limits or getting anal about DOD. However I was pretty blind to the impact of fast charging cold packs. That’s one practice I can strike from my list. Don’t know if I’ll go so far as to buy a Lipo heater but after spending the better part of 2 days studying Frank’s (and some other) work l’m seriously considering it.

The other thing I might adopt is bringing my packs down from 3.8 something to 3.7 something. That’s almost a freebie as far as inconvenience.

I won’t adopt everything but I really like having a better understanding of the chemistry behind it all. Almost 40% of my annual RC $$ go towards Lipo’s so I appreciate JJ’s efforts.

Joe
Last edited by MCSGUY; Dec 08, 2019 at 02:44 AM.
Dec 08, 2019, 02:36 AM
Registered User
Yes, that was my take too. I will set my dischargers to 3.75 down from 3.8.

I only ever (balance) charge at 1C, except Graphenes very occasionally maybe up to 2C. But OK, not now if they’re cold.


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