so ive been reading up on cells amp discharge ect. but cant figure out why you need to use flat top batterys. why do you not use button top. is there a reason? i ask because button top seem to have higher capacitys and are often cheaper.
18650 cell question
- Thread starter billym1967
- Start date
Not heard of that before, makes no difference to cell performance , doesn’t sound right to me. Ease of spot welding I can envisage a difference I guess....
You may already have noted in your reading but there tends to be a trade off between capacity and discharge rates. So those high capacity cells might not have discharge rate suitable for Ebikes
Have a look at the cell specs for the Samsung 30q . They could be currently considered a “gold” standard /cell of choice
Are the button top cells you talk of 10000mAh Ultrafires by any chance? You need to be very specific when discussing 18650 cells, since there's a lot of crap out there.
so what ive read and i could be wrong. discharge rates and how high they are is to do with not over heating the battery. if you do a 10s5p battery using cheaper cells say 3.7v 2500ma 5a discharge cells. use a 20a bms board.
you get a max 42v battery 12.5 with a max discharge of 20a . now my bafang 250 is max 15a so would a battery made at the spec ive said be ok, or would i get overheating problems. and would it matter if the battery's were button top or flat top. someone on here told me more is better, but how much more is better.
just what im reading it seems that anything over 5a discharge should be ok for a 250w motor
you get a max 42v battery 12.5 with a max discharge of 20a . now my bafang 250 is max 15a so would a battery made at the spec ive said be ok, or would i get overheating problems. and would it matter if the battery's were button top or flat top. someone on here told me more is better, but how much more is better.
just what im reading it seems that anything over 5a discharge should be ok for a 250w motor
dont really have any particular button top in mind its more a curiosity question. wasnt really looking at big mAh
Button top 18650 cells have built in LVC protection circuit and normally used for torches etc.
Button top same spec cells as flats are usually more expensive 0.50 - 1.25 euros more per cell on Nkon, protected cells even more so which are no use for multi cell builds.
Less area to weld on pos end and protrudes a bit higher.
Mooch on e-cigs does a lot of testing on all types of cells and notes after taking cells to their CDR (continuous discharge rate) and above cells show a distinctive loss of capacity and voltage drop in single cell use.
Overheating will induce higher IR it's affect is shown up as voltage sag and capcity loss = cell life shortened.
Using higher CDR cells will offer better life than lower ones if a decent cell is used.
Lots to browse and refer to in link below.
https://www.e-cigarette-forum.com/blog-entry/list-of-battery-tests.7436/
Any 18650 cell over 3500mah is a fake crap cell, like wise any over 30/35a CDR.
Even the VTC5/6 30/35a cells it appears suffer at the high end of it's CDR, but remember all these tests are for single cell use. For our needs we parallel 2- 6 together for most of our needs so any very good cell at 10a CDR or above is ideal.
Less area to weld on pos end and protrudes a bit higher.
Mooch on e-cigs does a lot of testing on all types of cells and notes after taking cells to their CDR (continuous discharge rate) and above cells show a distinctive loss of capacity and voltage drop in single cell use.
Overheating will induce higher IR it's affect is shown up as voltage sag and capcity loss = cell life shortened.
Using higher CDR cells will offer better life than lower ones if a decent cell is used.
Lots to browse and refer to in link below.
https://www.e-cigarette-forum.com/blog-entry/list-of-battery-tests.7436/
Any 18650 cell over 3500mah is a fake crap cell, like wise any over 30/35a CDR.
Even the VTC5/6 30/35a cells it appears suffer at the high end of it's CDR, but remember all these tests are for single cell use. For our needs we parallel 2- 6 together for most of our needs so any very good cell at 10a CDR or above is ideal.
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thanks Nealh. so if you go for low A discharge cells, even though they may do the job the battery life will be reduced due to them having to work a lot harder. so if the cells are quite cheep it still may be worth while.
A 5 A discharge capable cell will be at 0.6C and a 15 Ah capable cell will be at 0.2C. Look at those discharge tables again and you will see why a 15 A discharge Samsung 30Q is the cats pyjamas for a 5P10S battery 
and only 190 € for the cells!
You only need a 12.5 Ah battery? Get the Samsung 25R - 20 A discharge and 140 €.
and only 190 € for the cells!You only need a 12.5 Ah battery? Get the Samsung 25R - 20 A discharge and 140 €.
Cheap cells are never worth while! Unless you are building a massively parallel battery say 10P10S. Then you have to carry it around (twice the weight, twice the volume), that works in a car but not on a bike.
HE2's are a very good match to the 25R and currently at a good price from Nkon, though they are older stock from 2016.
HG2 are on par with 30Q and for a bit more cap GA & MJ1.
Sometimes there is too much choice !!!
HG2 are on par with 30Q and for a bit more cap GA & MJ1.
Sometimes there is too much choice !!!
so great info, "A 5 A discharge capable cell will be at 0.6C and a 15 Ah capable cell will be at 0.2C" so what does that mean for the battery, will the 5A cell not run properly or does it just mean a shorter battery life.
so going further. when you buy a ready made 13A battery in a case. its quite large and heavy. now the first one i built using 40 Sony cells 11.6A is a lot smaller and lighter. so i was looking at some cells 3.7v 3000Mah 5A. so going of the 140 ero samsung cells about £123, that would be 50 cells im guessing. so these cells i was looking at if i built a 10s6p so 30A discharge would cost around £90, would still not be worth the saving as the battery performance would be very poor and life would be so much shorter.
what i'm stuggerling with is most of my 250w kits have an amp out put of around 15 so why the need for so much over power so to speak. is it just so the battery doesnt need to work as hard, so it lasts longer.
please do think i'm being thick, as i'm trying to learn and understand. but surely anything at 10s5p with a cell discharge of 5A and above should run a 250w system.
or am i being thick lol
or am i being thick lol
Two words: "battery sag". The more Amps you ask from the battery (and the cells inside) the shorter its life, on the ride and over the long term. Asking a 5 A cell to provide 3.75 A constantly is going to wear it down much faster than asking it to provide 1 A or 20% of its rated constant discharge. 5 A is assistance level 3 of 5 on my controller, sometimes I need assistance level 5 over several km...
Battery sag made me drop 18650 celled batteries and go to LiPo because I live in the foothills of one of Europe's major mountain ranges, as simple as that. Now I have +50 A constant discharge and see battery sag at less than 0.6v on most hills, often 0.3v-0.4v at assistance level 5!
Now that there are affordable spot welders I would probably choose to make my own battery. I probably wouldn't use 18650 but rather 20700 cells and I wouldn't try to economise by buying low A discharge cells. Batteries cutting out on the last hill before home drive me nuts...
15 A discharge cells exist now, why not use them? They are not much more expensive BUT the performance difference is huge if you compare performance/price rather than price alone.
You want a light tiny battery? Get 20 A discharge cells and use them 3P10S.
3 x 20 = 60 A discharge
5 x 5 = 25 A discharge
The math is super simple...
Battery sag made me drop 18650 celled batteries and go to LiPo because I live in the foothills of one of Europe's major mountain ranges, as simple as that. Now I have +50 A constant discharge and see battery sag at less than 0.6v on most hills, often 0.3v-0.4v at assistance level 5!
Now that there are affordable spot welders I would probably choose to make my own battery. I probably wouldn't use 18650 but rather 20700 cells and I wouldn't try to economise by buying low A discharge cells. Batteries cutting out on the last hill before home drive me nuts...
15 A discharge cells exist now, why not use them? They are not much more expensive BUT the performance difference is huge if you compare performance/price rather than price alone.
You want a light tiny battery? Get 20 A discharge cells and use them 3P10S.
3 x 20 = 60 A discharge
5 x 5 = 25 A discharge
The math is super simple...
Motor rating is secondary, what really matters is the controller peak amps and the cells CDR and how many parallel.
great answers, so the bigger the Distage the less the stress is on the battery and full out put so the battery will live a lot longer. So my Sony 10A cells will be working a harder, but still an improvement on 5A cells. so in the long run cheep cells may work and seem a bargin, but youll have to replace the battery a lot more often.
so if i wanted to build a big battery for a 36v bafang mid drive say 10s8p. what cell A should i be looking for and what BMS board
so if i wanted to build a big battery for a 36v bafang mid drive say 10s8p. what cell A should i be looking for and what BMS board
D
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As a general rule, whatever the maximum continuous discharge rate of the cell is, you divide it by two for ebike applications, so a 10A cell would be 5A, which means that you need at least 3P for a 15A controller. For a 5A cell, you need 6P. Looking at it the other way round, for a 15A controller, and a 4P battery, you need cells with a maximimum continuous discharge rate of at least 7.5A. That's the minimum. The more the better, but as you've seen, capacity is normally less on the very high discharge rate cells.
An 80 cell battery is very heavy. You need to think about how you're going to install it on a bicycle because it can spoil the ride completely or even make the bike unrideable. Do you really need that much capacity? Panasonic GA cells would give you 28AH.
An 80 cell battery is very heavy. You need to think about how you're going to install it on a bicycle because it can spoil the ride completely or even make the bike unrideable. Do you really need that much capacity? Panasonic GA cells would give you 28AH.
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great answer, so my sony 4p is fine as there 10A so giving me 20A total. so enought.
so if i want to build an 8p then anything above 5 should be of as 8 x 5 is 40 and still gives me 20 but better to go higher maybe 7.5A or above.
i was looking at these cells,
https://www.ebay.co.uk/itm/Li-ion-3-7V-3000mAh-High-Power-18650-Battery-8pcs-YCDC-For-Strong-beam-Torch/332420095032?_trkparms=pageci:bb001247-2aa3-11e8-a6fe-74dbd18036af|parentrq:38fa0c121620abda5821dc97fff9f036|iid:1&_trksid=p2481888.c100675.m4236
my thinking was build a 10s8p so the vauts should be 42v would give me an 18A battery so 650w hours and the A distage of what your saying would be 20A so enough for my bafang 250w mid drive. and with a bit of discount probably £125 for the cells so quite cheep.
or passably a waste of money
https://www.ebay.co.uk/itm/Li-ion-3-7V-3000mAh-High-Power-18650-Battery-8pcs-YCDC-For-Strong-beam-Torch/332420095032?_trkparms=pageci:bb001247-2aa3-11e8-a6fe-74dbd18036af|parentrq:38fa0c121620abda5821dc97fff9f036|iid:1&_trksid=p2481888.c100675.m4236
my thinking was build a 10s8p so the vauts should be 42v would give me an 18A battery so 650w hours and the A distage of what your saying would be 20A so enough for my bafang 250w mid drive. and with a bit of discount probably £125 for the cells so quite cheep.
or passably a waste of money