Fastest climber?

[NRG]

Pricing is a bit of a mine field. We believe a target UK retail price of sub £20 per Ah, or sub 60p per Wh is fair....

Yes that is fair probably more than fair TBH, so good on you.

EF, yes, agreed VAT and duty will raise the price but this will be offset to some extent by bulk purchase. I was comparing the retail price from Hobbycity of some 5Ah packs I've just bought so yes, they come in at $2 / Ah per cell so a 37v 10ah pack works out to be $200 plus shipping and VAT or approx £180 delivered retail. Trade will of course be less than this and the BMS and case can't cost that much trade so a retail price of <£300 is IMHO about right and about what the market can just about bare... The high cost of replacement batteries is what will kill any long term interest in E-Bikes if customers are faced with the prospect of a new battery that costs 50~70% of a new bike every few years.

I agree about the dangers of Lipo but as you know on ES and in my own experience with careful voltage and charge management the early horror stories of a few years ago have largely disappeared and life cycles are well past 200.

I know you have these new Prismatic cells for sale and I'm certainly interested to see how they work out, maybe on my next battery refresh I'll drop you a PM.

 

[emissions-free]

For sure a small BMS that can do 20A contant output isn't so expensive but when you start looking at something that can handle 60 or 80A constant they don't come in cheap. Likewise with the case. If you go with 1 of the standard types you see around they're not expensive but it does all add up by the time you've added all the small parts, shipping, VAT, Duty and some profit.

It is pretty hard to compete with the likes of Hobbycity which have a massive turnover and really do keep their prices low from what I've seen. The li po does look really good but I can't see it ever being mainstream with the safety concerns there are not to mention the hassles with breaking down packs to charge etc. For the interested enthusiast sure but for the average commuter, I don't think so. I think it's great that there is the choice.

A 36V 15Ah (generally tested to more like 16Ah, nominal 39.6V) set of the 15Ah A123 cells made into a pack with a reasonable BMS is gonna be roughly somewhere in the region of 350-400GBP including air freight to UK. Not the cheapest option but these aren't 2C cells

 

[NRG]

I hear you about the safety concerns but I believe Wisper is about to go mainstream with this chemistry so I think its coming of age....also the Cells from HobbyCity aren't 2C either However, that's not relevant with UK legal E-Bikes as we don't need to pull more than 2/3C...

 

[flecc]

I hear you about the safety concerns but I believe Wisper is about to go mainstream with this chemistry so I think its coming of age....

If the li-po being referred to here is lithium polymer, I don't understand the discussion. Wisper are just one of the many e-bike companies who have been using it for two and more years in complete safety, while Panasonic have been using it for five years on e-bikes.

Actually polymer is more a construction than a chemistry.
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[Straylight]

Thanks Flecc, I was getting confused as well

 

[NRG]

Ah, thanks for the correction Flecc, I thought they, like other suppliers, where using Lithium Ion rigid case batteries not the 'soft cased' Lithium Polymer...

 

[flecc]

Ah, thanks for the correction Flecc, I thought they, like other suppliers, where using Lithium Ion rigid case batteries not the 'soft cased' Lithium Polymer...

Polymer is very much mainstream now, used by Panasonic in nearly 20 makes, plus Gazelle, Yamaha, Giant, eZee, Wisper, Powacycle, Powabyke and many more.

NiMh is now a rarity, LiFePO4 is barely starting to appear in production bikes, and the SCiB type (which isn't really suited to e-bikes) is only on one make.
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[emissions-free]

The lithium polymer that is used in RC applications that NRG and myself are referring to is not the same as what is used in these e bike batteries.

I think the main reason lifepo4 hasn't been accepted by the bike manufacturers is that lithium polymer is cheaper per w/hr, generally has higher energy density and lasts long enough for the warranty

 

[flecc]

The lithium polymer that is used in RC applications that NRG and myself are referring to is not the same as what is used in these e bike batteries.

Do you mean the RC based ones use the lithium iron phosphate chemistry in a polymer construction?

I think the main reason lifepo4 hasn't been accepted by the bike manufacturers is that lithium polymer is cheaper per w/hr, generally has higher energy density and lasts long enough for the warranty

I rather doubt this. Some leading companies have been testing LiFePO4 in conjunction with their battery manufacturers for a long time now, but they haven't been able to achieve the necessary reliability in mass production circumstances in compact forms. LiFePO4 is possible of course, but with adequate reliability and high enough discharge rates they are bulky, necessitating either smaller capacity or even larger battery installations, both a backward step.

eZee have been experimenting with LiFePO4 since late 2006 and are just at the point of limited introduction with smaller capacity, while Wisper and their battery supplier AE agreed not long ago that the technology was not quite ready yet.
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[emissions-free]

Well I think it will not be long before LiFePO4 has been accepted by even the most demading buyers. It already has been as it will be fitted into production cars soon. LiFePO4 doesn't have to be bulky and can sustain high discharge rates.

I have stacks of these prismatic cells sat here:
A123Systems :: Products

They will do approximately 15-20C constant with even higher peaks and weigh only 467g for a 3.3V nominal 20Ah cell. Size 7mm *165mm * 227mm. Also come in 15Ah version with 400g, 6.8mm * 150mm * 210mm. Claimed cycle life of something like 7000 cycles and 10-15 years in automotive application.

 

[flecc]

Yes, they are certainly advancing and are nearly at the point of more widespread acceptance, one e-bike manufacturer dipped their toe in the water last year and now eZee have an option arriving.

E-bike makers are being extra careful ever since the debacles of the earlier lithium variants, the fires in cobalt cathode batteries, the current delivery failures of manganese cathode ones and the short lived premature failures of so many.

One can hardly blame them for being cautious, since those events proved very expensive. In the case of eZee, they tipped them from the top of the market to near the bottom and cost them well over 1000 free replacement batteries.
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[brucehawsker]

We, after careful thought, are sticking with Li-Ion. Our latest is 37V 17.4Ah and here is a photo. Huge current dumping capbility. Heat sink in a probust Al casing.

 

[flecc]

We, after careful thought, are sticking with Li-Ion. Our latest is 37V 17.4Ah and here is a photo. Huge current dumping capbility. Heat sink in a probust Al casing.

Wow! A mighty meaty monster!

Sounds like a good choice, but I imagine it's fairly heavy, though not as much as the twin batteries some companies and individuals use to gain capacity.
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[Wisper Bikes]

Max power

I am certainly still learning about batteries, we have for the last 4 weeks been testing a 37V 17.5A Panasonic celled power pack in NZ, to my astonishment is it being out performed on range and power by our current 36V 14A Li Po battery.

Does anyone know why this should be the case?

On top of this;

The Panasonic has looses 25% of it's power after 500 cycles and then goes into free fall loosing another 20% in the next 50 charges. Where as the Li Po lasts for nearly twice as long loosing 25% after a massive 900 full cycles and the next 20% after another 600.

I was looking forward to advertising a new 600Wh battery but it seems we can save our money and stick to what we have!

All the best

David

 

[flecc]

I am certainly still learning about batteries, we have for the last 4 weeks been testing a 37V 17.5A Panasonic celled power pack in NZ, to my astonishment is it being out performed on range and power by our current 36V 14A Li Po battery.

Does anyone know why this should be the case?

Very high densities within cells that are necessary to increase capacity can result in reductions in discharge rate due to raised internal resistance. Fine on a lower powered motor where the additional capacity is translated into extra range but not with a powerful motor which can be starved of adequate current.

The cell chemical stresses that result from a powerful motor draining a battery that's unable to deliver adequately shorten the cell life.

Those account for the two phenomena you've seen and highlight the importance of correctly matching a battery and it's capabilities to the motor power intended.
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[Wisper Bikes]

Electric Guru

It's like consulting a oracle!

Flecc you should set up in Tibet, dress in yellow robes and have people walk up mountains for days on end to ask a single question!

Many thanks, I was disbelieving the results!

Kindest regards

David

 

[brucehawsker]

I agree 100% with Flecc. The issue is current dumping capability. Out new battery can chuck out current like there is no tomorrow. This is to do with the physical geometry of the internal design - how much conductive stripping is used and how configured and how big the heat sinking. Our beast works not because only of the number of cells. Also Lion seems to work better han LiPO at the high end....

 

[Wisper Bikes]

Dump

Are you using a 250W motor? If so what does the motor need to have dumped from the battery to run at it's highest efficiency? There is only so much a 250W motor needs to maximise range and power.

I would be interested to learn what technology you are using and what the battery chemistry is. We have found a battery of exactly the same size as the one you are talking about very disappointing compared to the 14A Li Po we are currently using. Flecc has explained why the 17.5A batteries are not as good as the slightly smaller ones on 250W electric bikes. It would be interesting to hear if you have managed to overcome these problems.

If you are using Panasonic cells you may need to reconsider.

All the best

David

PS we have used both Li Po an Li Ion over the last 5 years, the difference in life and reliability is massively in favour of Li Po in our experience.

 

[flecc]

The latest generation of hard case li-ions can produce very high discharge rates, certainly if cell densities are not too high.

Of four lithium types used on my eZee bikes, original 10 Ah li-ion, new generation 10 Ah li-ion (never introduced for sale to customers) and new generation 10 Ah and 14 Ah li-poly, the "never introduced" li-ion that I've run during testing for over two years now, comfortably out performed the others. However, the downside is that at 342 charges it's almost at the end of it's life, probably explaining why eZee didn't introduce it.
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[eddieo]

BUT if the battery is £300 what do you think then.......