Lifepo4

[coops]

Just came across a long thread on Yesa LiFePO4 batteries, the same make as those on ebay.

Haven't read it fully yet, just sharing the information .

A 24V 10Ah is 230 x 85 x 65mm and weighs 3kg, so the 36V 10Ah 'Ezee size' one should be around 4.5kg? 3A Charger weighs about 500g.

Also, this is from the Yesa ebay Q&A:

Q: how much for a 48v battery and charger. thanks. 01-Sep-07

A: 48V 10AH LiMn2O4 , USD500, 48V 15AH LiMn2O4 USD540. 48V 15AH LIFePO4 USD680, we do suggest people choose LiMn2O4 pack when under 15AH. Cheaper but also good as LiFePO4. LiMn2O4 is not suitable for pack above 15AH .

and

the LiFePo4 battery is newly developed project in our company , we are trying to develop some more yet.

[flecc]

That doesn't sound good when a manufacturer of lithium iron phosphate recommends stick with Li-ion manganese under 15 Ah.

And as they say they're just as good, does that mean LiFePO4 are just as bad (same thing) and also cut out due to poor current delivery?

Makes one wonder.
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[coops]

I should have added the other part of the Q&A, for completeness:

Q: hi whats the diference between limn204 and lifepo4 thanx 01-Sep-07

A: In Generally , LiFePO4 is better but more expansive than LiMn2O4. LiFePo4 cell is 3.2V , LiMn2O4 is 3.7V . And LiMn2O4 can only be made for Pack under 15AH yet. But LiFePo4 has no limit.

So it sounds like they're saying LiFe is better, but not so much better its worth spending more for than LiMn, for 15Ah or less...?

The ebay page also says 70% of the weight of NiMH, which I don't see as correct if 36V 10Ah weighs 4.5kg?

[HarryB]

Originally Posted by HarryB

Ian,

They do a version that is 350x85x65mm so I suppose it is not impossible to get one to fit. You are right though the import duty and VAT make it questionable adding about £52 I think.

Having checked out the ezee case I don't think the 350mm battery will fit anyway. Does anybody have the internal dimensions of the ezee case?

[coops]

I don't Harry, though someone who has opened their case may know .

To be honest though, I can't see that performance would be (much) different from the existing Li ezee batteries, and at 4.5kg its quite heavy and not as cost-effective or reliable as NiMH, which weighs only fractionally more.

Another quote from the manufacturer in an email reply to an enquiry about discharge rate and voltage sag for a 24V 10Ah battery:

The 10AH pack for your 250W motor is enough.

The standard discharge rate is 1C = 10A

You test 22.5V at 15A is normal.

But we do not suggest to have too high rate discharge , since that may reduce the lifecycles.

We can make 12V pack, but 12V pack is not so popular , we have 24V, 36V, 48V pack .

The capacity can be 10AH , 12AH, 20AH .

So its a battery rated for low power use: 'standard' discharge meets less than 2/3 of e.g. a Torq's peak power output, and only half that for an f-series bike.

I wonder if other LiFe batteries are any better (why does it seem that powertools use decent quality Lithium batteries, but they're not available for ebikes??), but at the sorts of prices & weights these ones are, it just really doesn't seem worth paying any more for them than NiMH, especially given the uncertainty about performance & lifetime.

[flecc]

I think it's mainly price Stuart. Although iron is the theoretically best cathode material of all the elements, it's proved very difficult to construct a reliable high current delivery example.

Hence it mainly appearing in small moderate current delivery batteries, the Sunrunner low powered bike being a good example. I think it will be some while before they are good enough for the more powerful e-bike motors within a useful weight and size.

Where performance of lithium batteries is concerned, cobalt gives the best delivery and capacity combination, also much better than manganese, just a pity about the fire risks that come with low manufacturing standards.
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[aaannndddyyy]

While I was looking for more info on the lifepo4 I came across another new battery coming out soon the liFeBATT LiFeBATT LifePO4
And a forum discussing these two battery types (V is for Voltage)
LifeBatt, Real Calculations and Costs | V is for Voltage Community

[Jeremy]

The "Killacycle" electric bike has been running A123 (M1) cells (which are the LiFePO4 ones in DeWalt power tool packs) for some time now, at very, very high discharge rates and is reputed to have not yet blown a single cell.

Last time I checked Killacycle was drawing around 1800 A at about 370V from about 1200 cells (I think they've since added more cells to increase this a bit, in order to hit sub-8 sec standing quarters). Some simple math seems to show that this bike is drawing about 180A (peak) from each cell, so it's clear that these cells do have a pretty good high current capacity (although obviously their capacity will be significantly hit by such high discharge rates).

The major problem seems to be one of supply. A123 do not sell cells, as I understand it, to anyone except a select group of big companies (like DeWalt). The result is that smaller companies, such as those in the ebike world, can't get a look in. Those that do sell A123 packs are apparently ripping them from cordless tool packs, which is not exactly cost effective.

I've no doubt that the Chinese will soon be producing cloned cells that are reliable, but at the moment there does seem to be a big question mark over the quality of some cells/packs sold via Ebay and the like.

I'm running a small SLA pack at the moment, and was thinking about buying some NiMH cells and making a replacement. Having looked into various cell types in depth over the past couple of weeks I'm very much inclined to try and get hold of some LiFePO4 cells of decent quality, as all the indications are that this technology has the best mix of life, capacity and weight at the moment.

One our research programmes has been running extended life tests on several different Li technologies and this also tends to show that LiFePO4 may well be the best available technology at the moment.

Jeremy

[Ian]

Originally Posted by HarryB

Having checked out the ezee case I don't think the 350mm battery will fit anyway. Does anybody have the internal dimensions of the ezee case?

You are right Harry, the 350mm height will not fit. The Ezee case will just take a 5 high stack of D cells, approx 310mm, there is slightly more height at reduced width but a full 350mm is only available over an area of about 50 x 50, and only then if the XLR connector and fuseholder are removed. So unless the cell pack has an offset conical top ti will not fit. Seems I was over optimistic with my earlier hasty measurement.

A Flecc style extension to the case could always be made, but given the high cost and 6kg weight is it worth it.

[flecc]

There's no doubting the potential of lithium iron as Jeremy has said, but it's only available at an unacceptable cost to most at the moment.

The main concern I have with using continuous high discharges on them is how that will affect their life, even a three year life at those high prices being inadequate.

For me the best all round option when cost is factored in is still NiMh, even after their recent price increases. Once good ones are cheap enough, I'll switch to LiFePO4 instantly.
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