Advances in battery technology

[coops]

well.. so much written.. hope there is nobody upset about this..

Not at all Kraeuterbutter, its very good to have the information and thank you for taking the time & effort to answer my questions

From what you say, they do sound promising, but for me there's still a question about the lifetime: I'd say 3-4 years for Li-Po and 6 yrs for NiMH are both optimistic; 10 years or even 6+ for the A123 FePO4, we'll see! let's hope so - as you said, only about 1yr of consumer use so far. As I said, if they came with a guarantee...

building a charger by yourself (if you are good in electroncs) easier than building a nicd/nimh charger

hehe! I'm not good in electronics: though maybe I could grasp the theory given time, I'm not going to try to build my own charger right now! Its useful to know they're not that demanding to charge, though I'm still unclear how in practice one charges these series/parallel cellpacks i.e. all together, or each parallel group separately? If separately, are multiple chargers needed, and how would this affect charge time, which to me is an important advantage of these cells? (sorry! - crash course in electronics, I think I need!)

but there are problems:
do you get a package a non electrical person can implement immediatly in there bikes.. -> no

Yes, so its for the technically & electrically adventurous!

i see this cells for people who build there own bike or make a conversion, who can solder...

Yes, so as above! I might have a go one day...

Thanks again for all the information Kraeuterbutter, and your language skills really put me to shame so please don't ask to be excused!

 

[kraeuterbutter]

@flecc:
yes, speed is the key for success..
some people think: i don´t want to damage cells, i use a weaker iron -> and melt cells (Nimh, LiIon, ...)
key is: powerful iron, not more than 2sec. of soldering and its fine

in my experience there are some LiIon very sensitive on soldering..
the konion (Sony 18650V, Sony 18650VT) for example.. soldered to long and they make "pop" (a sound) and the cell has 0Volt and is gone...
(i think the intern temp-protection... it protects the cells for a termal runaway, but is irreversible.. so a safety-feature for emergency..)

nevertheless the konion are great cells... the only cell on the market which realy needs no balancing-unit.. even after 300cycles the cells are in balance (drift only 0,1% !!!)

for cell life in bike-situation:
i have to admite that i have not used cells in such "low-power"-applications like a ebike so far....
in my applications i empty my cells in times between 90seconds and 10min..
so the batts are stressed more, charged faster (chargetime for me between 15min and 45min)
so also on charging more stress to batts than they would see in a bike..

so my cyclelife and lifetime of cells is for sure shorter than it would be in a bike-application

 

[kraeuterbutter]

here a short overview about the M1 A123 Fepo4:
DeWalt 36V Technology (A123 Systems)

it shows a discharge-curve...
there you can see how constant the Fepo4 discharges compared to LiIon or Nimh
click to see PICTURE

if the currents are high enough (you will not see that in a e-bike) and the cells warm themselfs, the voltage even gets better during discharging !
something not seen before with nimh or Lipos


oh: and here you can see, how the cell performs at different loads (currents) and how the temperature rise is..
the cells are good for up to 70°C without any harm to the cells..
you would not see 70°C in a bike-application anyway..

here the graphics:

source: Elektromodellflug - BMZ 26650-X - LiPo-FePo4 im Test
grafic shows a single cell...
yellow line: 10seconds 12,5A (~3,1Volt), 5seconds 50A (~2,7Volt) ==> so average voltage: 3Volt
green line: 34,5A -> average voltage: 2,75Volt/cell

in bike you would use 3p or more in parallel ===> so load is much less, voltage even higher than here on the grafix.. (maybe 3,2-3,3volt ?!?)

 

[JohnInStockie]

3.6V Lithium polymer batteries

Hi All

Just saw these (see the chart) and wondered if I understand this correctly. Are these 3.6V (i.e. 3 x 1.2 V meaning you only need 1/3 the no of batteries? And the weigh a LOT less than NiMH!!! And look at those DD size ones, the capacity is ..

John

 

[Ian]

There are indeed 3.6V, but it looks like the voltage rapidly falls to under 3V for most of the cycle, but only 2.3Ah capacity, so you'd still need a lot of them!

 

[JohnInStockie]

Ian I think your looking at the wrong ones, or I am reading the wrong ones. I saw 35Ah!!! And if you look at the ElectroChem batteries, those DD size ones are 30Ah !!!

 

[Ian]

Ian I think your looking at the wrong ones, or I am reading the wrong ones. I saw 35Ah!!! And if you look at the ElectroChem batteries, those DD size ones are 30Ah !!!

I was looking at the chart John, I've just looked at the link and yes it does state 35Ah for the DD size, but they are single use lithiums (not rechargable). In any case the max current is only 300mA. It's a pity but there are no magic batteries available so we'll just have to keep lugging the heavy ones about.

 

[JohnInStockie]

Say no more this is about the best I think

 

[flecc]

3.7 volts is the norm for the Lithium cells used in our bikes.

But the trouble with all lithium cells John, is that they don't like delivering large currents. What small cells do is meaningless in this context. Once these are upsized to the size of cells that we need in our bikes, the failure to deliver occurs, and that's why you see the complaints of cutting out on hills in this forum.

The technical problem is simple to understand. In a small cell, current hasn't very far to get out. In a large cell with the high density content necessary to give us the capacity, the current struggles to get out from the cells inner regions through that density. As a result, when under high load, the voltage drops to the danger level where the protection cut-out operates.
.

 

[kraeuterbutter]

@John:
your first link -> 300mA max. dischargecurrent.. for a bike you would need more like 30000mA max. dischargecurrent (or more)

your second link -> i doubt that this cells are high-current cells, they say something like "phonebatteries"

here a picture of high-current-lipo-cells which would be suitable for e-bike:

more here:    Elektromodellflug - KoKam - 20C Li-Pos im Test

the battery has 4800mAh, weights 116g/cell

green line shows you a continouse discharge with 48A current..
you see, the line stays pretty high
even at 76A continouse current it stays for long time over 3,4Volt (blue line)

and the yellow line shows you the peak-performance:
10seconds long 24A, 5seconds long 96A, this all time alternating..

the dotted lines show the temperature rise.. you see, it stays far away from 60°C all time (the manufactor allows up to 70°C)

so: a 10s Batterypack with 37Volt nominal would weight under 1.3kg
would have 4.8Ah
and be able to hold over 33Volt for a continouse 2500WATT of power !!

this battery will not see the problem flecc described ("complaints of cutting out on hills")
the measurements are not provided by Kokam but from an independent tester, which is very well known in the RC-hobby-community for testing all lipos around, so you can trust this values..

10s2p would be still under 3kg, and good for over 4000Watt continouse without a problem (peaks of over 6000Watt would also be no Problem)

last thing: this shown battery is a 20C cell !
meanwhile there is the new series H5 from Kokam which are rated for 30C currents !
so: 30% stronger, less heat, and "relativly safe" (people have reported of killing packs by shortening, currents over 300A and nevertheless no fire, no explosion..)
maybe the higher manganese in the cells..
(for that the cells fall in voltage more flat at the last 1/4 of discharge than other cells)

 

[flecc]

4.8 Ah isn't enough for our bike use though kraeuterbutter, we need more than double that at the minimum. The norm is now 10 Ah, with some moving to 12 to 14 Ah currently.
.

 

[kraeuterbutter]

well.. maybe not true for everyone..

some want light battery and are willing for that to charge every day
i just wanted to show, that also a small, light battery will not suffer power at all..
the bigger the battery, the more power it can deliver.. so "problems on hills because of weak battery" are none-existing
a 12Ah battery would rip your bike in two parts with 10kw poweroutput

and 10s2p would be over 9Ah which should give already some good distance to drive...

but, it should also be mentioned:
PRICE, price, price
a 36V 10s1p 4,0Ah Kokam will cost around 420 Euro
i think that is for most biker a NONO..

 

[flecc]

That is a bit expensive, but not impossible. The BionX replacement lithium ion battery is 900 dollars in the USA, so 420 euros isn't so bad.
.

 

[coops]

These high capacity ready-made packs of lithium, e.g. nanophosphate you can get for ebikes, are they large cells arranged only in series do you think & so prone to the same problem supplying high current, or could they be a series/parallel arrangement?

Is it right then, that the only Lithium arrangement likely to work in ebikes is a series/parallel arrangement, but that charging would be made difficult?

Stuart.

 

[kraeuterbutter]

charging is not more difficult on a 10s2p pack than on a 10s1p

the electronics (Balancer, Equalizer, or other names how it is called, electronics to ensure no cells is over charged and/or overdischarged, so single cell-monitoring)

needs only to see the s-cells..

the single cells have to be paralleled at first, and after that connected in series..
so:

paralleling 3 single 4000mAh cells will give you a block with 12000mAh
the charger/equ/bal sees when connected only one single cell with 12000mah

all 3 cells have same voltage anyway because they are paralleled
for the user handling is absolut same

its even so, that you sometimes buy packs which are shrinked and you don´t know how many cells are paralleled inside

 

[coops]

Thanks kb

its even so, that you sometimes buy packs which are shrinked and you don´t know how many cells are paralleled inside

And would you just charge it like it was a series then i.e. plug in charger & go, thats it? Or still need monitoring of single cells?

Stuart.

 

[flecc]

Thats done by the equaliser/balance electronics that kraeuterbutter refers to Stuart. Obviously those are essential, it's not just a case of soldering cells in a series/parallel formation. It's the sort of electronics on cells and overall that are in the eZee battery seen here, but with balancing circuitry as well to ensure the parallel cells get evenly charged.

kraeuterbutter has previously illustrated some of the separate charge and balance modules he uses.
.

 

[coops]

I thought kb might be referring to one of these "ready made" Li packs some ebike dealers sell?:

These high capacity ready-made packs of lithium, e.g. nanophosphate you can get for ebikes, are they large cells arranged only in series do you think & so prone to the same problem supplying high current, or could they be a series/parallel arrangement?

 

[kraeuterbutter]

if it is 10s2p (so 20cells)
or 10s1p (so 10cells)

is unimportant for balancing..

(you connect first the cells in parallel, and than you would connect this
ten 1s2p packs in series)

the cells which are parallel are never unbalanced.. they are equalizing - if you want to say that - all time, 24h a day by themself because they are connected
so: a single cell-monitoring of each cell in a parallel-pack would not help anything

let asume you have 2000mah cells..
connected parallel --> 4000mah
when now one 2000mah fails, it will kill the other 2000mah which is in this parallel-pack as well

so they will fail always together.
the balancer sees anyway only a 4000mAh cell that fails...

on the other hand: when you have a single 4000mah instead of the 2 2000mah-cells in parallel
when this cell fails the same happens

defacto: i have several packs with paralleled cells and can not say that they life shorter or longer than non-paralleled cells..

for balancing:
it should be done always for safety reason (if something is wrong, the balancer can reduce chargecurrent of charger or in extrem cases stop charging-prozess)
but it is not realy always needed..
i for myself - charging my cells most time outdoor at the flyingfield so no risk for any goods or life in case of fire -
charge the cells on the field with 10A current within 30min full often without balancer
even after 50cycles i have not seen any significant drifting
so: balancing/equalizing is good for safety reasons, BUT: its not the case that you risk you damage your battery when you do it without

i do it every 10th charging-process.. and works great..
when batts get old and cells start to drift more, the balancer tells me that (i see, that he has do do more work) and when this happens i use it always.. but then the end of batterylife is not far anyway
on new, good cells the balancer has nothing to do

 

[JohnInStockie]

These do look interesting here. If they were to do 'what they say on the tin' then they would provide 25Ah @ 25.9V in 7 cells weighing on 4.5 Kg which is the same as my Twists 6.5Ah Nimh battery.

Dont know the price though.

Comments anyone?


John