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Looking for the 'best' cell for a project.
#1
Hi,

I'm planning on building a battery bank that would act as a power source for my equipment where I work.

When I get in to the nitty gritty I plan to make a thread here to help check my thinking an ensure I don't make any cockups.

For now, I am trying to find the 'best' cell for my needs.

My two primary concerns are size and weight, so this counts out LFP for me - even though its life cycle is better. 

I was initially looking at the Samsung INR18650-35E - this would be in a 7s17p setup. However upon reading its spec I am concerned with it's cycle life and I am wondering if there is a better cell to choose.
What has turned me off of the Samsung specifically is that their spec sheet has the capacity ≥2010mAh or 60% of capacity after 500 cycles at 3500mA, charged at 1024mA or 0.3C.

I had thought the 35E chemistry (which I believe is LiNiMnCoO2) should be better than this. 

I understand that cycle life is highly dependant on depth of discharge as well as speed of charge, but the figures for the Samsung seemed lower than other cells, but the specs are not always easy to find, and the included graphs not always easy to read. 

I am essentially after a cell that has a good density over 3000mAh, with the ability to supply continuous current of about 80A in a 7s17p set up that I can charge in 2-3 hours.

I will end up poring over specs, but I was hoping you fine folks here ma be able to give me a little direction!

cheers,


I thought I would post an example of the difference I am seeing incase I am reading specs incorrectly:

Samsung 35E Specs - Page 8: 

charge current 1,020mA
discharge current 3,400mA
500cycles
Capacity ≥ 2,010mAh (60% of Standard Capacity)

Sanyo/Panasonic NCR18650GA - Page 7:
Graph appears to show:
charge current 1,650mA
discharge current 6,000mA.
500cycles.
Capacity ≥ 2,200mAh 

These Sanyo also has a slightly higher max cont discharge of 10A vs 8A.
Essentially the Sanyo seems to be a better cell in every way I can find, and it is only marginally more expensive to purchase.
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#2
Wrong section. Battery Project Builds is for actual projects being worked on and showing the progress, not for asking questions. Questions go in the other sections.
Moved.
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#3
(06-08-2020, 12:34 PM)Korishan Wrote: Wrong section. Battery Project Builds is for actual projects being worked on and showing the progress, not for asking questions. Questions go in the other sections.
Moved.

Apologies, thanks for moving.
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#4
The lg M26 series of cells would work if you can use 7s20p setup. used the cells that I have tested are testing 2550 - 2750 at 1000 mAh discharge. Most have been LGGBM261865, the datasheet https://www.batteryspace.com/prod-specs/11609.pdf, Not sure why it is not in the database yet. the cells have come from ninebot scooters, and electric bikes. Not sure where you are located. but batteryclearinghouse, and batteryhookup are where I have purchased good cells.
LG M26 7s20p would have 200A continuous discharge, 50A charge, 52AH
3500mAh Samsung 35E 7s17p continuous discharge 136A, charge 34A, 59.5AH
NCR18650GA Panasonic/Sanyo 7s17p 3300mAh, max continuous? discharge 170A, charge 28.475A, 56.1AH
There are many Recyclers that resell good cells in the US, and a few scattered worldwide. hope this helps
later floyd
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#5
Hey, thanks for the reply. I'm actually in the UK and will be buying the cells new - not exactly the ethos of this forum I know but I do not need to save the money on the cells.
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#6
If you haven't yet check out the cell database located at top of the page. searched 3000mAh, form factor 18650 https://secondlifestorage.com/celldataba...00&fsort=1
New cells are great, no guessing if they have been abused or how many cycles they have on them.
hope this helps.
Later floyd
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#7
super, thanks.

I really wish there was some kind of standard test definition for these cells. It's damn near impossible to compare them.

I was just looking at the Panasonic NCR18650B and thought "Wow, only down to 3000mah after 300 cycles, thats even better than the NCR18650GA"

But then the testing conditions are totally different. The GA is discharged at 6A where the B is 3.2 and the GA charged at 1.65A whilst the B is at 975mA.

At a guess, these cells are probably very similar... and all the spec sheets tell me is that if you treat it softly it will last longer, which is a given.


It's kinda why I was hoping someone might have a good idea of what the 'best' cells are to pick from.
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#8
(06-08-2020, 10:38 PM)Shorty Wrote: super, thanks.

I really wish there was some kind of standard test definition for these cells. It's damn near impossible to compare them

..............It's kinda why I was hoping someone might have a good idea of what the 'best' cells are to pick from..............
True but you also have to think about what the cells are used for. What did the manufacturer and the consumer come up with and the cost factor.
When you are a laptop manufacturer like IBM, Dell, HP and you buy millions of these cells 10th of pennies count so the manufacturer will tailor the batteries to the consumer. I want a laptop pack that will last at least 6hrs what can you do for me. I want a medical pack that charges quick and last for 24 hrs.
I want a cell that charges super fast and can give up gobs of amps for my power-tool and be able to charge in 1/2 hour. etc..................

The cell you are looking for needs to fit your needs. You mentioned powering your equipment at work. How long does this "power bank" need to last.
How much amperage demand will you need consistent or in spurts. How fast do you want to be able to recharge this "power bank".
Once some of these variable are know then you can decide on the cell chemistry.
You wrote" I am essentially after a cell that has a good density over 3000mAh, with the ability to supply continuous current of about 80A in a 7s17p set up that I can charge in 2-3 hours." That basically restricts you to an IMR and INR chemistry you may get away with NCA but they may not like the fast charge.

There are so many different cell manufactures with a multitude of part numbers out there and all of them with different C/D characteristics so yea it can and will be confusing.

Wolf
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#9
Also keep in mind that at a continuous discharge of 80 amps your cells need to be able to provide almost 5amps. The amp load isn't spread across all the cells but from the parallel group. So it is 80 amps divided by 17. It isn't unheard of but you'll be looking for cells that are rated for at least 2c discharge so you aren't pushing the limits of the cell.
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#10
Wolf -

Yea I had guessed the different test methods were likely to show their major customers exactly how they perform for the specific products, still - new and nascent businesses must run into this problem a fair amount, especially if they are figuring it out for themselves! (Not that this is currently a business for me)

I didn't want to flood my initial post with info so didn't go into too much specifics, but to answer your questions:

Quote:How long does this "power bank" need to last.

This will vary depending on my set up. I work in Film and TV, so my set up is dynamic. I would expect a demanding set up to drain a 1.5kwh battery pack in 2-3 hours. The 80A load is mostly over-provisioning on my part. However the idea behind the '80a' figure is that this would be the upper limit the system is capable of if you had a demanding system. If, for example, if you wanted to feed a Mac Pro and some other AC equipment via an inverter this could easily suck down 60a, add in a few 12v items and you would be getting near the 80A figure. But this 'high load' would only be used a few times a day when the system is stressed... Sorry, I guess the answer is "it's complicated"

But the idea is that the batteries would be hot-swappable, so someone with an exceptionally high power demand could have several of these batteries - or build a larger one. The eventual plan behind this is to offer this system to others in my industry as a kind of 'modular' power system. But different batteries might choose different chemistry. 

Quote:How much amperage demand will you need consistent or in spurts. How fast do you want to be able to recharge this "power bank".

In terms of 'spurts' - the inrush/surge of a connected inverter would be the highest 'peak' (do manufacturers like Victron publish these specs?). The use of the 'high power' equipment like a Mac Pro happens in maybe 30 minute periods between 5-8 times a day (processing footage) when the CPU/GPUs are stressed. 

I am aiming for a 30amp 'fast charge' for use during the day and 'hot-swapping' and a much slower overnight charge to prolong cell life. 

This is the charger I have in mind for this: https://tbs-electronics.com/product/omni...a-12v-24v/ which has three separate fully programmable outputs.

I am also wondering if it's possible to use a Solar Charge Controller to program a charge 'profile' and then supply this via a AC-DC power supply instead of PV voltage. I have asked this question elsewhere and directly to Victron but can't find any info on anyone doing this. 

I'm doing my best to avoid the Chinese chargers, reliability and quality are two strong concerns. Although there are doubtless Chinese companies that produce good electronics, thse chargers are not common and taking a 'punt' on something from AliExpress is not something I really fancy doing. (I may yet buy a 30a 29.4v Li-Ion charger to test, but its not what I'm 'speccing' for at the moment)

Quote:Once some of these variable are know then you can decide on the cell chemistry.
Thanks a lot for helping me narrow it down!



Quote:gpn:
Also keep in mind that at a continuous discharge of 80 amps your cells need to be able to provide almost 5amps. The amp load isn't spread across all the cells but from the parallel group. So it is 80 amps divided by 17. It isn't unheard of but you'll be looking for cells that are rated for at least 2c discharge so you aren't pushing the limits of the cell.

Thanks yes I am keeping an eye on this, as above the 80a is unlikely to be fully utilised, but I am trying to spec for it. 

I am using an excellent little app for Android called 'Battery Pack Calculator' (link) which is super useful to quickly gauge metrics like discharge rate and capacity for various cells, as well as being able to add your own. It's also very helpful to me to solidify the relationships between 'series', 'parallel', mAh, max drain etc as you can adjust these things quickly without having to be sure you did the math right. (I have an understanding of all these things, but its easy to screw up a sum here or there and base other things off of a mistake)
^bit of a plug for it, as it has been so useful for me^
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