New 14s battery pack, US18650VTC6 vs NCR18650GA

[flippy]

if you keep between the 4.1 and 3.something the 29E is basically indestructable. i capped my testing after 500 cycles as i needed to move the gear to a new place.
the GA's have notcable more dropoff in capacity while doing the same 500 cycles.

fun fact: the 29E6 and 29E7 are the same cell but the E7 is a very small chemistry change to increase lifespan.

 

[Pajda]

Unfortunately, I have realized that IEC DCIR data can be also interesting a little be late, started from cycle No 100. Have no initial data.

I thought so. That gives me a good feeling that I am not alone who sometimes forgets. This has happened to me many times and when one realizes it after several tens of cycles, one can only say: Shieeeeeeet!!!

 

[larsb]

won't go for a removable battery solution because i want a none-removable, sealed, an hidden system.

The **only** alternatives are an active pre-heating system, or moving to some other, much less energy-dense chemistry.

At cold enough temps, not a question of "reduced longevity", but discharge in effect just stops, and charging means the pack is instantly rendered useless, unrecoverable scrap.

Insulation will help a bit at marginal temps for a short rest time, but well below freezing for hours outdoors, only with active pre-heating.

Incorrect. Did 2 years of commuting on a mixed samsung 25R+18650GA pack. Subzero temps, everyday charging at below 10 deg C, rides in -15deg C, you name it.

 

[john61ct]

High rate charging in extreme cold does shorten lifespan, by a lot, there's no question about that.

Yes in your anecdotes that's not very cold, not enough to cause that total failure.

Actual numbers varies by battery model.

 

[larsb]

The **only** alternatives are an active pre-heating system, or moving to some other, much less energy-dense chemistry.

Nothing anecdotal about it. If above was true then it would be physically impossible to use that pack for so long, about 300-400 cycles to 4.2V

if i built 10 packs like that they’d function the same way since weakest battery of 200 sets the performance of the complete pack.

 

[john61ct]

Read my posts again, in detail, tired of repeating.

Post a link to the actual spec sheet for your cells.

 

[docware]

if you keep between the 4.1 and 3.something the 29E is basically indestructable.

Yes, 29E (both E6 and E7) have very small capacity/energy bellow 3,1 V. I wouldn´t go bellow 3,3 V (under load) to avoid entering critical 10% SOC.

 

[larsb]

Read my posts again, in detail, tired of repeating.

Post a link to the actual spec sheet for your cells.

I agree that too low temps are bad for the cells, that preheating is a good thing In these conditions. What i don’t agree with is the categorical statement that it is
mandatory in colder climates. The 300-400 cycles i got out of my pack in winter temps from -15 to plus 10 deg C proves this. Sure i’d gotten a longer use out of my pack with preheating but it did not die or stop me a single time.

-15deg C is a temp where most people don’t charge and don’t ride so i’m pretty sure my two winters of everyday riding (50km) were on the harsh side.

No need for a spec sheet, i’d think the samsung 25R and sanyo18650GA are pretty well known here. They are nothing special - and not the best for cycle life.

If someone wants to build heated packs:
I got this qoute from Keenovo on aliexpress back in the day: 2 silicon heater pads with thermostat at 15deg C for 80USD. I never bought or installed these..

 

[john61ct]

[ What i don’t agree with is the categorical statement that it is
mandatory in colder climates

Which I did not state.

Simply warning that it's not just a matter of lowering charge rates and reduced performance, but

that at "cold enough" cell temps they can be irrecoverably destroyed.

Many are not aware of these issues.

The actual temperature ranges, and how low a charge rate is safe, do very much vary with the specific chemistry involved.

The context of my original response was advocating for bringing the pack inside, rather than using active heating.

 

[larsb]

The **only** alternatives

I’d say that if one removes all other options, keeping **only** one then it’s the same as mandatory.

But heck, never mind. After all, i’m not a native english speaker so you’re probably right

 

[Pajda]

docwae I think it would be great if you can move your cycle life measurement results to the first post in new topic?

I will add general/well known comments to his results. At first, I can confirm that this results are in line with my measurements.

The first parameter which have a huge impact on cycle life is used average DoD window. This test setting 60-70% of average DoD window lies on the edge as we say in Czech "where the grain is separated from the chaff". It means that almost all cells on the market will "do the job" under this conditions. If you will go further down to 50% DoD, the difference between cells in capacity fade/DCIR rise almost disappear. But if you go to higher average DoD window, you will clearly see the huge diferences in both cycle life aspects between cells even in the same category. I am trying to say that you can operate for example LG M36 at 80% average DoD (and even 100% DoD is not an issue for this particular cell) and still expect better results than Sanyo GA operated at 60% average.

The second parameter which have a huge impact on cycle life is charge rate. For example 1A, which uses docware in his tests is equivalent to ca 0.3-0.4C charge rate and should be marked as very conservative (but it is close to the daily average for traction batteries). As I previously say that I do not like generalization, I can say that the Panasonic/Sanyo production line in 18650/21700 does have significant problem with CC continuous charge rate higher than 0.3C, where the LG chem equivalent production line does not show significant difference between 0.3C and 0.5C charge rate.

 

[john61ct]

Wow that level of real-life detail in longevity rating would be of **huge** benefit to the community!

 

[Altair]

The information given here by the experts is practically priceless for users who are not very knowledgeable (most of us) in the fine details of performance vs longevity, for our expensive batteries.
A big ThankYou to you guys, for taking the time to post the results of you extensive tests and your actual experience in operating the batteries. Your efforts are greatly appreciated!

 

[flippy]

docwae I think it would be great if you can move your cycle life measurement results to the first post in new topic?

I will add general/well known comments to his results. At first, I can confirm that this results are in line with my measurements.

The first parameter which have a huge impact on cycle life is used average DoD window. This test setting 60-70% of average DoD window lies on the edge as we say in Czech "where the grain is separated from the chaff". It means that almost all cells on the market will "do the job" under this conditions. If you will go further down to 50% DoD, the difference between cells in capacity fade/DCIR rise almost disappear. But if you go to higher average DoD window, you will clearly see the huge diferences in both cycle life aspects between cells even in the same category. I am trying to say that you can operate for example LG M36 at 80% average DoD (and even 100% DoD is not an issue for this particular cell) and still expect better results than Sanyo GA operated at 60% average.

The second parameter which have a huge impact on cycle life is charge rate. For example 1A, which uses docware in his tests is equivalent to ca 0.3-0.4C charge rate and should be marked as very conservative (but it is close to the daily average for traction batteries). As I previously say that I do not like generalization, I can say that the Panasonic/Sanyo production line in 18650/21700 does have significant problem with CC continuous charge rate higher than 0.3C, where the LG chem equivalent production line does not show significant difference between 0.3C and 0.5C charge rate.

when i get into my new workshop i plan to run a specific test with different DoD's on the 29E and see what happens when you go to town on the ampsin order to kill it as fast as possible but reduce DoD.

if you want to tag-team our efforts here as running 500+ cycles takes a long time it might speed things up a bit.

 

[docware]

Well Pajda, if you will continue with such commentary, then it´s worth to move to a new topic. 8)

 

[larsb]

While we’re on the cold battery subject: is there an 18650 battery that has better performance and life length at low temps? I do a fair bit of cold riding and even with preheating i can only heat half my trips in the winter.

 

[john61ct]

LTO is the way to go, not sure what cylinder sizes it comes in.

But terrible density. . .

 

[larsb]

Yep.. too terrible. If i had car-like space then maybe.

 

[flippy]

While we’re on the cold battery subject: is there an 18650 battery that has better performance and life length at low temps? I do a fair bit of cold riding and even with preheating i can only heat half my trips in the winter.

insulation and keep the heater on. once the pack is up to temp it does not take much to keep it there. if you lose too much then it just means your pack is too small.

 

[john61ct]

Pretty sure all LI chemistries other than LTO are similarly endangered by charging in low temps.

Winston Chung claims Yttrium doping gives his LFP prismatics a much lower range, but I've never seen third-party testing confirm whether that's true or not.

 

[john61ct]

For really cold weather, need a well-insulated tightly sealed box with silicon heating pads powered off the pack itself.

Note only **charging** "too fast" in temps "too cold" will actually destroy the pack.

With discharging, you're just getting much lower performance, it isn't dangerous.

 

[larsb]

I drive 25km each way to work, don’t have access to a charger/outlet at work so the way home is with a cold pack. Cannot bring the pack inside as it’s too large.

I could build a heater circuit and run it from the pack itself but it would need a timer (or a phone app and remote controlled switch.)

Too complicated so a cold resistant chemistry would be a good option.

 

[john61ct]

Well within 5-10 years it's possible radical new chemistries may actually enter the market.

Meantime we need to adapt what we have

 

[flippy]

I drive 25km each way to work, don’t have access to a charger/outlet at work so the way home is with a cold pack. Cannot bring the pack inside as it’s too large.
I could build a heater circuit and run it from the pack itself but it would need a timer (or a phone app and remote controlled switch.)
Too complicated so a cold resistant chemistry would be a good option.

you only need a switch to turn the heater on in witer and a temp based switch to keep the pack heated all day. just keeping it around 10~15c is plenty.
example: https://www.aliexpress.com/item/1977398631.html

just glue these to the same metal sheet you slap the heater panel on to distrubute the heat. use a LOW POWER heater strip. 5W max for bike batteries.

 

[docware]

This car seat heating pad is giving 22W at 12 V. Put on the blanket, thermocouple inserted between heating pad and blanket is showing after few minutes 30 – 40 °C depending on the thermocouple position at ambient temp 25 °C. Dimensions of heated part 28 x 44 cm. No problem to bend in radius 2 - 3 cm.

https://www.aliexpress.com/item/32729791102.html?spm=a2g0s.9042311.0.0.44a74c4dJVSX6V