Battery Chemistry Choice for Occaisonal Ebiker

tongxinpete

Pedelecer
Aug 8, 2011
96
6
Telford, Shrops
I am only now an occasional rider thanks to other commitments. I remember researching Li-ion calendar life vs Li Po4 - At the time you needed to be on the bike 4 days a week to use up the 2000 cycles in 10 yr calendar life of LiPo4, & 3 days a week over 5 yrs for the 800 cycles of Li- ion
Apart from the difficulties associated with lithium it would seem a poor choice for anyone only using the bike now and again at weekends.
I built a pack from LiPo4 pouch cells, fine when working but BMS signal wires vibrate off, pouch cells fail etc. I am honestly thinking of going back to the heavy but reliable SLA I originally used for years, as kept charged & keeping a second charger at my usual destination they served me well.
I did come across this possibility http://www.neucell.net/applications.asp They claim 500 cycles @ 80% D.O.D (same as SLA) but are half the weight of 3 x 12 Ah SLA bricks, claim to be about 60 to 70% price of Li ion (actually the price per cycle works out the same - about 12p) The killer is no doubt the shipping cost of a 6Kg batt. There was once mooted a Chengzhu to Poland express goods train, taking 5 days per 1 way journey. Not sure if this ever happened - if so ideal for many things - not least Li batts / cells. When I last spoke with Neucell they could not supply the charger. I did find a Chinese ebay supplier that could set his chargers to suit Ni Zn - he knew the cut off voltage saying this chemistry was known in China - after SLA's were 'officially' banned there, at least on new ebikes - rather than home conversions. Any thoughts ?
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
3,094
929
Basildon
Normal Li-ion ebike batteries are so cheap and light now, I can't see a case for anything else. LiFePO4 is double the weight of Li-ion, but lasts four times as long. If long life is your prime requirement, that could still be a good choice, but nothing spoils a bicycle more than weight.

You have to remember that you can only use half the capacity of lead batteries, so 12Ah is actually 6Ah and you get half the range that you'd get with Li-ion. That 6Ah will cost you £75. You can now get reasonable 10Ah Li-ion packs for around £150, so not a massive cost difference, but a truly massive weight saving.
 
  • Agree
Reactions: Nealh

sjpt

Esteemed Pedelecer
Jun 8, 2018
640
235
LiFePO4 is double the weight of Li-ion, but lasts four times as long.
Does LiFePO4 also have a greater tolerance to the typical misuse of a casual user: such as leaving fully charged for quite a time, or leaving it to drop to a low voltage by not charging at all for a long time (say over winter)?
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
3,094
929
Basildon
Does LiFePO4 also have a greater tolerance to the typical misuse of a casual user: such as leaving fully charged for quite a time, or leaving it to drop to a low voltage by not charging at all for a long time (say over winter)?
I guess so. I've had a couple for about 8 years that I use for testing motors and controllers. I have left them untouched for two years at a time. I can't remember ever charging them except for when I first got them, when I did a capacity test. They still work fine now.

It's great that they're so reliable, but I wouldn't want to fit them to my bike because modern alternatives are so much more convenient and lighter.
 

tongxinpete

Pedelecer
Aug 8, 2011
96
6
Telford, Shrops
I built a batt from LiFePo4 pouch cells from BMSbattery some years ago - using their BMS. It is Ok when working, but I lost one cell due to 'puffing' - I could never work out why. I replaced this with a similar cell from AliExpress (cost £15 with shipping, replacement single cell from BMSbatt unaffordable) - again worked well for a time - but now I am experiencing cut off when climbing a hill (So if 15A is drawn for 2 mins) - If I unplug the controller feed & refit, it clears until the next time. My van went off road, I needed an alternative - this is what I found. I just feel it is like trying to run a taxi service with a 1903 DeDion. I do have a vruzend kit somewhere - but not just now time to pursue the hobby. I really need more reliability. I feel the motors & controllers now a mature technology - or 'done deal' - not so batts. Re the weight, I weigh 200 Lb, bike with hub motor 40 Lb - so the weight of batts is a relatively small part of total, when it comes to hill climb calcs.

I did get an interesting reply from Zinc Five, the patent holders of the Ni Zn improvements. They say they are a year away from having 'light traction batts' available in warehouses for the general public - aiming at golf cart owners, disabled scooters, ebikes, & RV lesuire. They did say they expect a life of 1K +cycles @ 60% D.O.D & 1.5C. Weight is half that of SLA & they have a true 1C rating. They will series charge with no individual cell voltage runaway.
HV cut off important, along with a max time on charge in case this point is never reached. Temp probe in batts ideal. these best in charger. Charge at 0.5 to 1C Also LV cut off during discharge required- this (customisable) we have already in motor controllers. Clearly if this is true the Zinc Five batt a better bet than the Chinese one.
 

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