What 18650 batteries for your battery pack?

Electrically assisted bikes, trikes, etc.
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bikes4two
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What 18650 batteries for your battery pack?

Postby bikes4two » 3 Mar 2020, 12:37pm

So I'm currently at the research stage of converting the good lady's bike to an eBike (current favourite is one of the TSDZ2 mid-drive units) and have fallen upon the options for battery packs - so some questions if you'll indulge me please?

> Firstly, I have read posts on here saying about a UK battery pack builder and to 'PM' to ask for details - can I find who the poster was? Of course not, so if someone can point me in the right direction I'd be grateful
OK, so on to some points about the actual 18650 cells used in battery packs:
> From reading the specs on different 18650 cells, the storage capacities range from 2100mAh to 3500mAh. Prices vary of course so producers of battery packs have price points to meet.
> Assuming that the price is not an issue, what criteria other than capacity needs to be considered in a pack build? I mean, why go for 2500mAh cells when 3000mAh or 3500mAh are available?

I realise that the power draw of the motor and it's controller have a bearing on battery choice vs the CDR (Continuous Discharge Rate) of the 18650 cells, but what other parameters need to be considered?

And slightly off-topic, I'm not adverse to considering building my own battery pack, so any readers who have done, or have considered doing this, and can give me useful pointers and advice, I'd be very grateful.
Last edited by bikes4two on 3 Mar 2020, 5:19pm, edited 1 time in total.
Without my stoker, every trip would only be half a journey

rjb
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Re: What 18650 batteries for your battery pack?

Postby rjb » 3 Mar 2020, 12:58pm

Couple of guys I met locally are converting bromptons but they use off the shelf power tool batteries. https://www.nanoelectricbikes.co.uk/
It's the way I would go if fitting a conversion. :wink:
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

billym444
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Re: What 18650 batteries for your battery pack?

Postby billym444 » 3 Mar 2020, 1:14pm

i use several diffrent cells for diffrent motors, its always a trade of between cost mAh and draw.


depending on the P of the pack and budget, i tend to use samsung 35e for smaller motors, enough draw and lots of mAh without having a massive pack.

a 17.5ah softpack 10s5p is only 20 x 12 x 7cm
big Bafang fan lol

stodd
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Re: What 18650 batteries for your battery pack?

Postby stodd » 3 Mar 2020, 1:20pm

hmm - I made a post and it has disappeared, so repeating.

Another thing to consider on batteries is number of discharge cycles.

The reference you want is probably Jimmy at https://bga-reworking.co.uk/product-cat ... batteries/
I've never used him but everyone who has seems enthusiastic about his knowledge and willingness to help.

Ask at https://www.pedelecs.co.uk/forum/forums ... cussion.2/ for lots of people who know about batteries and battery building.

You probably have, but look at Woosh for buying kit (complete with appropriate battery). Again very helpful. http://wooshbikes.co.uk/

Powertool type batteries probably won't help with a kit such as TSDZ2; just for short range low power (and light) helper motors.

billym444
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Re: What 18650 batteries for your battery pack?

Postby billym444 » 3 Mar 2020, 4:56pm

i think I’ve just built battery 400, thought lost count. So i would hope i no a little by now.

Tend to stick with 35e for smaller motors, though i do keep Sanyo and LG for some rebuilds i do for a company. Slightly bigger motors i switch to 30Q. And for really big motors Sony 30 or 35a.

apart from a recent experimental build for someone, to 36v running as a 72v to run a 3000w motor, never had any problems stick with those cells. but the 2 x 36 running as a 72 failed and was having issues. in my defence i was asked to build like that, and even though i over specked the 36v packs, one drained quicker than the other.

but i would definitely look at Samsung 35e for a 250w motor, lots of ah in a small pack.
big Bafang fan lol

hemo
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Re: What 18650 batteries for your battery pack?

Postby hemo » 3 Mar 2020, 8:55pm

30Q suffers from self discharge and causes issues.
LG MJI, LG M36, Sam 29E are best cycle age life cells around, currently several cells are under 700 cycle age testing on ES and the three above all over 90% capacity retention after 700 full cycle testing using 2.5a charge and 1a discharge criteria using a 4 wire monitoring system. Lots of graphs and facts to digest.
Which cell to use though id dependant on current draw required and cells in P that can be accommodated.

billym444
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Re: What 18650 batteries for your battery pack?

Postby billym444 » 4 Mar 2020, 6:59pm

i do like 29E but a tad low on the A so not great for big motors unless using a high P. havnt had much of a problem with the 30Q. but i normally use the sony 30 and 35A for big motors
big Bafang fan lol

hemo
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Re: What 18650 batteries for your battery pack?

Postby hemo » 4 Mar 2020, 10:38pm

Selecting the cell for the current draw required is important, hard to beat 29E for low power 250w at a max 1.5C rate.
For low power use/current draw and cycle age life the 29E trounces the likes of Panny PF & Sanyo GA all day long , second in best in class only beaten by the LG pair of MJ1 & M36.

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bikes4two
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Re: What 18650 batteries for your battery pack?

Postby bikes4two » 5 Mar 2020, 12:37pm

Thank you to all who have replied so far - I'm learning a lot and each posting prompts me to delve further into the subject.

The term 'smaller motors' or 'low power motors' - can someone give me a general idea of what (watt :-) ) is meant here? Are we talking of 500w or less or 250w only.

As said up thread, my mid-motor of choice is likely to be the TSDZ2 (36v/250w or 36v/350w flavour) and my battery choice will be based around that motor size.

I note that BGA Reworking (aka eBikebatteries.co.uk) build using mainly 2900mAh - why is that do you think - is it just working to a price point or some other factor such as charge/discharge cycles?
temp.jpg
Without my stoker, every trip would only be half a journey

stodd
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Re: What 18650 batteries for your battery pack?

Postby stodd » 5 Mar 2020, 1:05pm

The TSDZ2 can probably draw 600w or even more peak in either the 250w or 350w versions. The nominal rating is for continuous use over a period of hours.

Looking at https://www.ebikes.ca/tools/simulator.html does not have the TSDZ2, but the BBS02 is shown as max output 500w for battery draw over 700w. I suspect if you hit a hill you could have a continuous draw for several minutes of well over 400w, depending partly on the controller and how you ride.

Not quite sure what the other posters meant by 'big'. I'd say the TSDZ2 is at the high end of the 'standard legal' motors, but not in the same class as the (absurd) 1000w direct drive motors. 'small' probably refers to lightweight Brompton assist or similar booster motors.

hemo
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Re: What 18650 batteries for your battery pack?

Postby hemo » 5 Mar 2020, 11:51pm

The 2900 Sanyo/Panny cells are used in ready built batteries to a price point as they are a good price and Jimmy doesn't mess about with cells, he buys job lots or 10k,20 & 30k batches of cells.
If you have a battery case and go for a re-cell you can choose other better cells if you know what you want.

There are lightweight hub motors 250w rated and marked from Bafang or Aikema on the open market that can produce up to 42nm of torque these are comparable to 80nm mid drives for power, these small hubs weigh in at 1.2kg - 1.7kg for front or rear cassette hubs.
For a really compact build Keyde have a rear small 2.1kg cassette hub with 35nm torque with inner controller & speed sensor amd led/lcd for £270 all in, ideal for a light rider.

All 250w motors are the same as 350w motors the only real difference is how many amps/current your controller applies.
All 250w will and can produce up to 3 or 4 X there nominal output for short bursts, if enough current/amps is supplied by the controller and the battery if it is capable of delivering those bursts without causing cell damage.
With batteries the devil is in the detail of the cells used and knowing which are the better cells as not all cells even with the same current rating are equal over their life span.

robjordan
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Re: What 18650 batteries for your battery pack?

Postby robjordan » 6 May 2020, 11:06am

This site from Denmark is one of my favourites. He carries out comprehensive testing of batteries, as well as chargers, multimeters, etc. No adverts, no Patreon, pure nerdiness. Hope you enjoy!
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

freeflow
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Re: What 18650 batteries for your battery pack?

Postby freeflow » 6 May 2020, 1:51pm

Google for Torchy the battery boy. His website has lots of excellent info on Lithium batteries. He also has an eBay presence for the sake of batteries, bike lights etc.

hemo
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Location: West Sussex

Re: What 18650 batteries for your battery pack?

Postby hemo » 6 May 2020, 7:53pm

The ES thread on age testing cells has ended for now as 6 out of the 10 cells have reached the 700 cycle testing, Autumn might see more age cycle testing using different cell and types.
Eleven high end cells were used, ten were 18650 charged at 2.5a and discharged at 1a continuous and one a 21700 cell was charged at 3.75a and discharged at 1.5a, it impressively was one of the best performers.
These were voluntary independent tests carried out by an ES member using figures that even manufacturer don't use or release to the public, certainly no one else has published figures like these.
A few produce cell data pertaining to capacity and discharge time over a few cycles ( probably < 10) but not over a cells practical life time.

% wise at 700 cycles or there final testing figure, these were the capacity retention results.
LG MJ1 & M36 700 cycles/94%.
Sam 50E (21700) 600 cycles/ 94.5%.
LG HG2 600 cycles/92.5%.
Sam 29E 700 cycles/90.5.%.
Sam 35E 600 cycles/ 88%.
Sony VTC6 700 cycles/86.5%.
Sam 30Q 700 cycles/84.5%.
Sanyo GA 700 cycles/84%.
Panasonic PF 700 cycles/< 80% ( the graph stopped at 80% so looks like the line trajectory it dipped down to about 76%).