Advances in battery technology

[kraeuterbutter]

some updates for the A123 Fepo4-cells..
(mine are running still great, power as on first day)

here a guy makes some cycle-tests with the cells..

test one: A123: long term (after 1,000 CYCLES done, 2nd cell over 500 cycles at higher A) - RC Groups
1050 cycles done

(after 400cycles 6% capacity loose, no loose on punsh/voltage
then another 250cycles (were the cells were charged to 4,3Volt/cell instead of the allowed 3,6V/cells for test reason - no problems, many lipos would have failed or even burned)
...
and after 1050cycles in sum capacity is down to about 70% of original 100% value
and voltage under load has also started at about cycle 1000 to become lower (so inner resistance startet to rise after about 1000cycles)

the test was done with much more stress to the cells as they would see in a bike
(charged in 20min or less all time during test, discharged in less than 10min all the time down to 2,5V/cell )

so: you would not charge your pack in 20min in a bike
and you would not discharge it in less than 10min
nevertheless the cells survived over 1000cycles at this circumstances..

he is now doing a test with higher charge current (charing at 5C, so fully charged after around 12min and discharging at 10C (so emptied from full to empty within 6min)

he as already 512cycles so far
capacity went down from 100% to 84%

[kraeuterbutter]

and a example from the real world:
bike with A123

Gary Goodrum (Ggoodrum) from www tppacks com (he normaly sells thunderpower lipoly-batteries)

has done a e-bike conversion with A123-Fepo4-round cells..
he uses 16s6p A123 Fepo4 Pack for his e-bike

the cells weight 6816gramm
capacity: 13.8Ah
possible Amps of the pack: 540A peaks and 300A continous
possible poweroutput: 20000Watt peaks and 12000Watt continouse
(so, no bike would be a problem for that pack)

The bike has a 2500W brushless hub motor on the front wheel and uses a 48V controller. Using a 16s a123 setup matches the discharge profile for a 48V SLA configuration pretty close, which is why he uses one of the chargers typically used in this application.
He weights 250pounds, and the bike goes up any good size hill, accelerating while doing it !

Yesterday he went on a ride for about 10 miles, roundtrip, and it was very hilly. He had a WattsUp hooked up in the bike which reported that he hit a max of 2475W and used 6433 mAh, or about half the capacity. That says his 13.8Ah should be good for about 20 miles, maybe a bit more with flatter course, and/or some "collective management".

he will post pics and maybe even video next days..

2475Watt sounds like a lot for a ebike.. at least: its like nothing for the 7kg battery-pack, because they are able to be emptied within 3min putting 12000Watt out if neccessary

[JohnInStockie]

Sorry maybe I am missing something here. I have an NiMH battery, 24V 6.5Ah. It can power a 186W motor for roughly an hour, cover approx 17 miles with me on it (weighing 16.5 stone) and my kit (another 20 lbs).

NimH batteries seem to be pretty resourceful, generally.

The only thing I can see as a difference is the charge time, and isnt that down to the type of batteries being used, not really the technology?

I am a simple man, and dont understand many things in this world, but as I cant have anything more powerful than a 250W continuous motor in the UK, I dont understand where there are any leaps here. If this mean I can recell my 24V Nimh D cell battery and get 13.8Ah or even 20 Ah, then thats fantastic. Does it mean that?

One thing though, my battery weighs only 4.5 kilos, not 7 kilo's like that one.

John

[Ian]

I think John, from reading between the lines that the battery pack in question is 48V so it will store twice the energy of a 24 pack with the same Ah rating.
I agree with you about NiMh though, not the lightest but they are proven and reliable.

Before I spend a lot on newer battery types I'm going to want a watertight guarantee that it will last. So far my own experience of lithium, and that of at least one other member of this forum is not promising.

[allotmenteer]

Originally Posted by Ian

I agree with you about NiMh though, not the lightest but they are proven and reliable.

Before I spend a lot on newer battery types I'm going to want a watertight guarantee that it will last. So far my own experience of lithium, and that of at least one other member of this forum is not promising.

I'll second that! On my 14.89 mile commute yesterday my 6.8 Ah li-ion gave up the ghost at the 7 mile mark. Just as well I had the 8 Ah powacycle Nimh battery in my pannier! I find that the 8 Ah Nimh has so much more usuable capacity than my li-ion. The li-ion gets chemically exhausted very easily whereas the Nimh just goes on and on.
I'll not be buying any kind of lithium battery again, at least not until I hear of more positive experiences with them from forum members.

Lithium may be light, but a light, flat battery is not much good to anybody.

[kraeuterbutter]

i see your arguments..

i read in this forum two things:
1.) Lipos do not have the power of NiMh.. with a NimH/Nicd you have more power at 30-40A load in your bike

2.) lipos are dying very fast


This two statements made me to jump into the forum.
i have not much experiences with e-bikes (driven 3 for testing but don´t own one by myself yet)

but i have a lot of experiences with batteries..
Nicd, NiMh, Liion, LiPoly, LiMn and Fepo4
some of them also in competition-situations

the thing is: the cells you get sold in the bike-stores are very weak cells..
1C or 2C cells only ! (1C means: discharge is allowed to be as high as capacity, 2C means: dischargecurrent is allowed to be 2times as high as capacity: 2C 8Ah battery --> dischargecurrent should not be higher than 16A)

for that you can bring this LiPos or LiIons even in a (weak 500Watt) e-bike to the limits and shorten livetime of the pack..

i was using 2C Lipos 5-6years ago.. they were very fragile.. often they were dead after 30-50cycles !

the Point is for the A123 Fepo4
that are 20C cells.. (can put out 20times of amper then there capacity-rating)
yes, that is power (several 1000Watt) you don´t need in a e-bike
but for that: in a e-bike the batts are not at all stressed..
(so you can expect more than 1000cycles with them)

the other point is:
Calender Life-time (i don´t mean cycles here):
normal lipos and many LiIon do degenerate after 2-4 years.. so: damaged/dead after 2-4years because of a intern chemical reaction..
NiMh do hold longer.. there the mark is around 6years..
newer, higher-capacity NiMh are unfortunatly more fragile (they answer too deep discharge much more with damage than the older, not that high capacity-nimh did)

the A123 is rated for over 10years, so far over the battery-life-expectancy of Lipos and also over NiMh

and for cycle-life:
over the last 3-4 years our internet-community has tested several doozends of different lipos for lifetime..
resüme is (we stress the batts much more than it will happen in a ebike)
so far we had never a battery that made so many cycles at such cicumstances like the Fepo4
cheap china-lipos often fail after 50cycles
good and expensive lipos hold around 100-150cycles
Kokam LIpos there are many with holded even over 200cycles at same conditions
than there are the Konion, LiIon-round-cells on Lithium-Mangan-basis which managed to get 250-300cycles at same condition (they are also the only cells on the market sofar, which realy don´t needs any balancer unit and are very safe (no fire, no termal runaway))
and then there are the A123 that showed a battery-life of over 800cycles at same conditions (and over 1000cycles at little lower discharge-currents)
for Nimh: they loose after around 50-100cycles at such circumstances power/punsh and single cells in the pack start to fail after 200cycles
no pack reached ever more than 300cycles (many fail before they reach 100cycles)

this cells were all tested at much higher currents than you will see in a e-bike..
so in a e-bike they will live longer because less stressed..

A123: they have a very high Power-density
(count with around 1800Watt continouse power/kg for A123 Fepo4
compared to around 150-250Watt/kg of the best Lipos you get for your bikes (2C Lipos).. many bike-lipos even don´t manage to reach that)

downside of A123: energy-density
its not close to that what we are used to get with Lipos..
A123 have a energydensity more comparable to NiMh than to Lipos

[kraeuterbutter]

@John in stocky:

Sorry maybe I am missing something here. I have an NiMH battery, 24V 6.5Ah.
NimH batteries seem to be pretty resourceful, generally.

.....If this mean I can recell my 24V Nimh D cell battery and get 13.8Ah or even 20 Ah, then thats fantastic. Does it mean that?


....


One thing though, my battery weighs only 4.5 kilos, not 7 kilo's like that one.

well: your 4.5kg battery replaced by A123 would mean:
8 A123 Fepo in series (would result in ~27Volt noload and 24Volt under load-voltage)
and the cells paralleled 7times..
the cells will weight then 3,9kg (+ 600g casing we are at 4,5kg)

so: better voltage than your 24Volt-pack (which will under load be only around 22Volt i guess)

and not 6,4Ah but 16,1Ah
unlike Lipos you can empty the A123 pretty far without damage..
emptying this pack down to 16-20Volt would be ok
when you charge immediatly after you have emptied them even a empty-voltage of 8Volt on that cells would not do much harm to them !!!
but its of no point, because when the pack would go under 20Volt there is barley 1% capacity left..

so to summ it up:
at same weight you would get 16,1Ah instead of only 6,4Ah
at better voltage and Power (7000Watt continouse poweroutput would not stress that battery )
(with the lipos you get int he bike-shops you have to fear to stress the pack to much when going up a steep, long hill - fear to damage the battery
==> not with the A123...)

and battery-life is for sure also greater than on your NiMh..
when you realy get 1hour drivetime with your NiMh (so only low discharge-currents) you can be expecting to get FAR over THOUSAND !!!! cycles with a A123-battery! (we have now some selfmade tests with over 1000cycles but on much higher loads..
when we can trust the claims of A123-Systems on a low load like on your bike it should be even several thousands of cycles !!)

very good thing on the A123 is that also when getting older and after many cycles there is only a slow loose of capacity.. (we measured 6% after 400cycles)
and inner restistance is unlike other batteries (Nimh, Lipos) barley increasing at all !!!
the first 100-200cycles the battery even becomes better and better !

at halfe discharged and 35°C cell-temperature we measured ~9mOhm of inner restistance
this value stayed at this low value for the first 500cycles !
which other battery do you know which can do that ?!?

what does that mean in reality:
when you drive your bike lets say 200days a year, every time empying the battery completley,
you will see after 2 years about 6% less possible distance to go (so instead of maybe 20km only 19km
but SAME power as on the beginning !!
here they are differnet to most NiMh and Lipos i have tested..
none of them would show after 400cycles same inner restistance !

[JohnInStockie]

@ kraeuterbutter

OK, so let me get this right in my mind. If A123 re-cell my NiMh battery with 8 A123 Fepo in series.....

1) It will be the same weight.
2) It will work the same as a Normal NiMh
3) I will get many many more charge cycles.
4) I will get 16.1Ah (instead of 6.5Ah)
5) It will not damage my controller or my motor??
6) I can use my current charger??

Is that what you are saying? If yes then I obviously have one other question, How Much?

John

[kraeuterbutter]

ad 1)
not neccessaraley.. you can make a Fepo4-pack with 6,9Ah with lot less than 4,5kg as well and still more power

ad 2)
what do you mean by that ?

ad 3)
yes, for sure

ad 4)
depends on how many cells you combine

ad 5)
the battery will not function as a natural limit like some week batteries do..
that said:
if you short your motor and it pulls 500Amps !
the battery will deliver that 500A (only going down with voltagae to about 19-20Volt)

a full charged 8s Fepo4 will be at 28,8Volt
a full charged 20cell NiMh (24Volt nominal) will be at 28Volt fresh from charger
(depending on peak-level)
so: motor will not be damaged, and controller.. depends on your controller but most likely: no, will not be damaged

6) of course not

how much:
when you make a pack by yourself:

8s3p with 6,9Ah, more power and around 1,7kg bare-cellweight: ~240$-260$

8s7p with 16,1Ah, more power and around 3,9kg bare-cellweight: ~600$

or a light-weight setup for short distances:
7s2p and slightly less voltage than 24Volt Nicd
(but still ~21Volt at 30A)
with 4,6Ah and only 990g bare-cellweight would be around 140-150US$

this 1kg light pack would still be capable to put out around 1000Watt continousely and over 2000Watt for short

[coops]

@ JohnInStockie

Hi John I think what kraeuterbutter means to say in answer to (6) is that, since a A123/FePO4 battery is a type of lithium battery, they need a different charger from a NiMH battery - at least I think that's it?!

@ Kraeuterbutter

Thanks for the update on these new batteries: they do sound promising.

I'm definitely interested if they give some weight, power, charge speed and lifetime advantages over current Li and NiMH in ebike use, with no apparent disadvantages except cost.

Some questions if I may: 10 years life is claimed, but what is currently the longest term use (in time, not cycles) at rates similar to ebikes e.g. 20A max and 36-48V? Also, from your experience, how technically difficult and dangerous is it to try to make an A123/FePO4 cellpack and use it (i.e. should it be made professionally)? and lastly, how quickly could one charge a cellpack like this for ebike use e.g. around 36-48V 10-15Ah min, (1) for best lifetime (2) in case speed-charge is needed and how portable would the charger be (could it be carried on a bike?)?

Apologies if any of this information has been posted elsewhere, I did not find these specifics .

Thanks,

Stuart.