LiFePo4, results so far

[Beeping-Sleauty]

Having purchased one of Pings' 'Duct-Tape' LiFePo4 batteries and had a month to give it a fair trial, i can give the following results.

the 36v 10ah battery is mounted on a Eco-brand Whirlwind, this is a 40kg steel framed bike, it is fitted with a 250w brushed hub, i weigh 12 st, local terrain is mixed, mainly flat, but with a couple of long steep hills & decscents.

after 25 charges, the battery has settled down and gives an average distance of 22.7 miles using pedelec mode only, interestingly, using throttle without pedelec produces 25.6 miles, although i am putting in a fair amount of effort.

climbing the steepest hill which i estimate to be a third of a mile, the speed stays constant at about 9mph with me pedalling comfortably.

highest speed pedalled on the flat, with no wind, returns 24.3 mph, highest downhill speed pedalled 29.2 mph. average speed 16.7 mph on the flat.

the battery stays strong right up to 21 miles and then dies quickly, but turning off the keyswitch for 3 minutes allows the cells to re-balance and produce almost another couple of miles.

have not suffered any cut-out, at any speed, or on any hill.

this is slightly better performance (8%) than a new SLA battery on the same bike.

overall, i am delighted with it,

Next week, weather permitting, i shall be trialling the battery on a Suzhou Bafang 250w brushless motor which is mounted in another steel framed PowerCruiser (35kgs) and hope to produce better results from that setup,

laters,
beeps

 

[JohnInStockie]

Sounds very promising Beeps, keep up the good work.

FYI it looks like the LiFePos of A123 are indeed finally getting some attention in bigger markets, had you seen this announcement?

John

 

[Haku]

A 40kb 'pushbike'? eesh! I find my bike that weighs in at around 22kg to be a pain whenever I have to carry it up/down steps, especially when I've got a few kg in the panniers.

From what I've heard of LiFePo4 batteries, they're less prone to bursting into flames if damaged/overcharged/shorted and can deliver a serious amount of amps so are ideal for high wattage motors.

I wonder how they compare to li-ion or li-poly type batteries in real-world tests/usage, anyone know ?

 

[Jeremy]

LiFePO4 is certainly a lot safer than any other current lithium technology, has a longer cycle life (over 2000 cycles are being quoted), seems capable of very high discharge rates in the right sort of packaging and has a relatively low self-discharge rate.

The downsides are that it's slightly heavier than some other lithium technologies for the same energy/power, plus a LiFePO4 battery needs a good battery management system to keep all the cells balanced and prevent over-discharge and over-charge.

Jeremy

 

[Tiberius]

Beeps, Jeremy,

What's the actual weight of these batteries? Could you post a link so I can get some details, please. I need to build a specially shaped battery pack for my current project.

Nick

 

[Beeping-Sleauty]

Battery weight

Beeps, Jeremy,

What's the actual weight of these batteries? Could you post a link so I can get some details, please. I need to build a specially shaped battery pack for my current project.

Nick

Hi Nick,

these batts weigh 3.6kgs naked or 4.3kgs in the battery case, SLA weigh 10.6kgs cased

mine is like this:

36V 10AH LiFePO4 Electric Scooter E Bike Li-Fe Battery! on eBay, also Parts Accessories, Scooters, Outdoor Sports, Sporting Goods (end time 18-Mar-08 17:36:02 GMT)

Slim Sized, 280x110x80 mm, 11x4.5x3 inch, <8 lbs - this will need extra packing / protection, especially underneath as these are soft cell protected only by duct tape,

LiPing store: eBay UK Shop - PingBattery: 36V LiFePO4 Batteries, 48V 24V Battery, Electric Bike Scooter

see some photos & a good ( if lengthy ) forum item here:

Endless-sphere.com &bull; View topic - Duct Tape E-Bay Lifepo4s???

email Li Ping (pingping227@hotmail.com) with the type of motor you are using and state this spec + size, if you need a different shape let him know, he will build one and list it on eBay, this is his normal practice, make sure you get a BMS ( battery management system ) that can handle the peak amps draw of your motor, 20 amps should be enough.

delivery is about 10 days, Li Ping will send you a tracking number, it will arrive EMS via Parcel Force, so make sure someone is in to sign for it.

ensure you have a fuse & a keyswitch in the circuit, if you have any problems please let me know.

good luck

speedy beeper

 

[frank9755]

Beeps, glad your battery is working well. None of my business, but I was wondering why you don't put your Suzhou Bafang and battery into a lighter bike?

Nick, FYI, with mine, Ping just quoted a price, which worked out at about £155 delivered for the same spec and shape as Beeps' one, without going via eBay and having someone bid me up.

Frank

 

[Beeping-Sleauty]

got carried away..... electrically

Beeps, glad your battery is working well. None of my business, but I was wondering why you don't put your Suzhou Bafang and battery into a lighter bike?

Frank

Frank,

it didn't start out that way, i needed a 2nd bike for my partner, i picked up the Powercruiser cheap and having learnt a little from my Whirlwind, decided first to upgrade the gearing, this worked well and meant i spent more time on it, which then meant i found myself short of range due to the SLAs, so i upgraded to LiFePo4, and found myself cycling further, but still a bit frustrated by the drag and the rather limp brushed hub motor, i then decided on a new brushless hub, hence the Suzhou Bafang.... at the moment i don't mind the extra weight of the bike and find it really does build up good momentum, plus it feels extremely solid to ride, although chunky & rather oversprung, it's a joy on bad roads, reminds me of a large armchair.

i still ride my non-elecric Marin MTB and this weighs 26kgs with all the clobber on-board so i am quite used to pulling a lump around

eventually i can see me stripping these upgrades onto a suitable high spec lightweight frame, it's a bit of an on-going process, sort of 'creational creep' if you like.

beeps

 

[Tiberius]

What's the basic building block inside these batteries?

Would it be possible to take them apart and re-arrange into a different shape?

Nick

 

[Footie]

From what I can tell the battery packs are made up of what's called "prismatic cells". Skilfully soldered together and running/charging through a special BMS. Link below to endless sphere forum showing a pack undone.

Endless-sphere.com &bull; View topic - Duct Tape E-Bay Lifepo4s???

The only down side I have read about them is they seem to struggle at high voltage (72v+) and high amperage drain (30 amp+) (mainly US users having problems) they seem to burn out or fry the BMS. Lower voltage and amps seem fine. Scroll down a bit, on the link above, to see a burned out BMS unit after a 36 amp hill-climb.

I think you need to know what you’re doing to take them apart. If you’re after a special lay out it may be worth emailing Ping. He's very helpful and seems very happy to make to order.
.

 

[Tiberius]

Interesting pics, thanks Footie.

So its not like juggling cylindrical batteries around, which can create all sorts of shapes. Looking at the website, there aren't direct links between V and Ah and any particular dimension, so it seems different internal arrangements can be had from the factory.

The higher the voltage the more difficult the task of the BMS, so that could be the reason there.

Nick

 

[Jeremy]

Nick,

The basic cells in one of these packs are 3.2V 5Ah units. They are joined together in a series/parallel arrangement to create a pack with the right overall capacity.

I split my 36V 10Ah pack in half, to rearrange the cells in a better format for my under seat pack. They are connected together with small printed circuit sections, with slots cut in them for the tabs. Each battery tab (which is a very fragile looking foil strip) comes up through the slot in the PCB and is bent over and soldered on top. The strips of black neoprene support the small PCBs and provide some strain relief for the battery tabs.

I found the tabs straightforward enough to unsolder, but it does require some dexterity, a good soldering iron and a solder sucker. I only split my pack down the middle, so that I could rearrange the two halves facing each other, but can't see why, with a little patience, you couldn't take the whole pack apart and re-build it.

Here are some pictures of my pack:

Jeremy

 

[frank9755]

I think I recall Jeremy reconfigured his battery, and put it in a very smart black box. It can be done if you are confident you know what you are doing. I guess it is not too hard as you are just reconnecting it as it was.

Neverthless I wouldn't attempt it. I asked Ping for the shape I wanted (long and thin) and he made it in that shape. Given the size of the cells, there are only a limited number of possible shapes.

PS - I recalled right - Jeremy's post above came while I was typing this!

 

[Tiberius]

Nick,

The basic cells in one of these packs are 3.2V 5Ah units. They are joined together in a series/parallel arrangement to create a pack with the right overall capacity.

Thanks. I was trying to puzzle it out from the pics on endless sphere. So it looks like the cells are paralleled up to make 5, 10, 15 or 20 Ah x 3.2 V and then these are connected up in series to make the final voltage. The BMS then connects to each 3.2 V step. Is that right?

Nick

 

[Jeremy]

That's right, Nick.

My 36V 10Ah pack is made up from twelve pairs of cells. Each of those small connection PCBs connect four tabs, two from one pair of cells and two from the adjacent pair. The sense wires for the BMS come from each sub-pack interconnection.

A 20Ah pack is made up with four cells per sub-pack, I believe.

If you were looking to make a custom pack, then it would seem best to go for the highest capacity one you can. With care, I think you could use something like a Dremel to cut through the interconnect PCBs, unsolder the sense wires and separate the pack into individual sub-packs of cells.

Jeremy

 

[Tiberius]

Hi Jeremy,

My current (sic) thinking is that I might start at 48 V and try to keep the option to go to 72 V. I keep coming back to the thinking that more volts, less current is good.*

So maybe I could go for 24 V 10 Ah, and I could probably get those in suitable shapes for assembly into 48 or 72 V without dismantling them.

Nick

*at least in the overall system, if not in each battery pack

 

[Beeping-Sleauty]

wow...

late news coming thru... don'cha just love tickertape.

in the still, clear morning sun, i decided to trial the LiFePo4 battery on my 35kg steel framed bike, this is fitted with the Suzhou Bafang 250w brushless hub.

almost entirely flat new cycle path around the military base, finished with the grey gravel, all painted up & signposted, and very nice it is too, about 4 miles circumference. but not a smooth ride, the gravel is quite large grit.

i went around the base 4 times, just started on my fifth loop and battery cut-out at 17.2 miles, this is un-pedalled, throttle only distance at 14mph.

turned the bike around & switching the battery off/on gave me enough juice to get about 2 miles home. (pedalling for the first time today)

this is an excellent result, i want to know right from the start how much the battery can do by itself, then its easier to work out what i am putting in.

beeps grins

 

[Tiberius]

Hi guys,

I was just crunching the numbers on these Ping LiFePo4 batteries and measuring up the (no longer working) Li-Ion battery off the bike. For the same voltage and capacity (36 V, 10 Ah) they come out at about the same weight - both about 75 to 80% the weight of NiMH.

But interestingly, the volume is different. The Ping battery is nearly 2.5 litres, but I estimate the eZee Li-Ion is just under 2 litres, allowing for the case size.

Nick

 

[Jeremy]

That figures, Nick. LiPo capacity is a little greater than LiFePo4 for the same volume. LiFePo4 wins out (for the time being) by having a longer cycle life and being a safer technology, even though it has less capacity for a given size. The major difference is the 3.2V per cell rather than 3.7V per cell for LiPo.

Jeremy

 

[kraeuterbutter]

for weight:
36V and 10Ah -> it says 3,5kg / 7,72lb

is that with balancer-unit or without ?

for Lipos:
with Thunderpower Prolites you get a pack with
37Volt and 18Ah weighting also only 3,5kg
but lifetime is maybe not as long as with Fepo4

for lifetime:
there are Lithium Mangan-cells in metal-can (like the A123-cells) with hold very long in my rc-modell-applications (~250-300cycles are very good possible)

there are also Lithium Mangan-cells in foil, with the same fire-proof-features
and less weight (because of the foil)
BUT: lifetime in my rc-modell-applications is limited to 100-150cycles

is this the same case with the Fepo4 ?
do the Fepo4 in Metal-can (A123) hold longer than this here in foil ?
are there any experiences or articles ?