battery developments

[Deleted member 128]

I came across this interesting article today, it talks about some of the design trade-offs with lithium-ion batteries and some of their failure mechanisms:

What's Wrong With Lithium-Ion Batteries? (Made By Monkeys)

And this talks about developments in electric vehicle batteries:
Battery Makers Ratchet Up for New Electric Vehicle Effort - 9/3/2007 - Design News

Enjoy
John

 

[flecc]

Thanks for these links electrifly.

That first one makes lots of sense. Although it's primarily about smaller units, it's refreshing to read an article that gives no credence to the constant hype about lithium technology.

I regard all statements about Li-ion performance in our bikes with scepticism and wait for the results before reaching a final conclusion. To date none of the promises have been realised.
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[Brangdon]

This article is quite interesting too: battery_level_monitor_tech_improvements. Bikes will switch off if they think the battery is getting too low, and they tend to be conservative about how they estimate that. A more accurate and confident reading should translate into higher effective capacity even if the underlying chemistry isn't changed.

 

[flecc]

This article is quite interesting too: battery_level_monitor_tech_improvements. Bikes will switch off if they think the battery is getting too low, and they tend to be conservative about how they estimate that. A more accurate and confident reading should translate into higher effective capacity even if the underlying chemistry isn't changed.

While that's true for the gadget batteries mentioned, it won't help on e-bikes with their huge variations in demand, quite unlike most gadget behaviour. The problem is that they already cannot use the available charge due to the cell resistance when the charge drops, so attempting an extension will gain nothing.

I've experimented on this with one of my bikes, the Quando derived Q bike. Run on level ground with ever smaller throttle openings as the charge declines, usage can continue to a point where it's impossible to determine if the motor is actually still contributing power, though still with the cutout not operating. Making an increased demand at any of the later stages of charge results in instant cutout due to the inability of the cells to deliver due to the internal resistance, so any extension attempt cannot realise anything useful.

However, at any stage the battery is still good for the bike's LED lighting for hours, illustrating how with gadgets low consumption levels, the technique is useful, but not for higher current demands.

 

[Ian]

There is also the well known Lithium issue of drastic reduction in cycle life with repeated use of of the full capacity, probably the biggest bone of contention with bike owners.

 

[flecc]

There is also the well known Lithium issue of drastic reduction in cycle life with repeated use of of the full capacity, probably the biggest bone of contention with bike owners.

Good point Ian, using them to very empty could reduce the life to just a few months.
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[Deleted member 128]

variations of lithium battery performance

It would be really interesting to see how the performance of Lithium batteries varied across different bikes.

There are many variables:
1. Price of the battery pack
2. Voltage and current ratings when new
3. The reduction in storage capacity over the battery life - indicated by the range of the bike over similar tracks
4. The increase in internal resistance over the battery life - indicated by how often the controller turned itself off
5. Controller design
6. Usage - 1 hour per week vs 2 hours per day
7. Bike drive mechanism - front motor, rear motor, drive through the gears, Swizzbee indirect drive
8. Weight of bike plus rider
9. Height climbed
10. Gradient of steepest hill climb
and many more

The generally feeling on this forum is that NiMH is better than Lithium for electric bikes but is that based on the performance of just a few bikes? Are we seeing much variation in performace of Lithium batteries across different bikes?

 

[flecc]

The evidence we have is that the lower power bikes like the Powacycle are best suited to lithium batteries, and it's the highest power ones that get into the most difficulties with them.

The fact is that despite all the promotional claims, they don't like delivering sustained high currents, so with a powerful motor and climbing long hills, the voltage drop soon gets down to cut-off level.

Most reports of this cut-off have been on the Torq, but it's also happens and been reported in here on the Sprint, the Wisper 905e and I've even had it on the Quando, which uses the same motor as the Torq. All these are 500 watts or more gross.

I'm in a very hilly area, and I've worked my Torq and Quando hard, the latter with heavy trailer load pulling, and I can bring a Li-ion battery down to regular cutting out within six months. But the last one received is performing better and after 8 months only cuts when trailer load pulling up a long but gentle hill. The first battery was changed by 50cycles at 6 months old, the second one I scrapped at 10 months old, and the third 8 month old battery I now reserve for solo riding in the Q bike (Quando), and I've no idea of how long it will ultimately last. These short lives are due to abnormal use and are not the norm by any means.

Owners like Russ in mainly flat terrain get far, far better life, range etc, showing once again that when running at low current drains, typically about 100/150 watts (3 to 5 amps) at full speed, Li-ions perform well. However, the overall consensus, including from the manufacturers, is that they are best used conservatively to only part of their charge, and that fully using their capacity between charges regularly drastically shortens their life.

The Li-ion batteries installed in satellites have 7 times the capacity necessary for their daily duty cycle of 1/7th between charges and last for years as a result, illustrating very clearly that we can't expect many years when we consume most of the rated capacity each use.
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[prState]

The first battery was changed by 50cycles at 6 months old, the second one I scrapped at 10 months old, and the third 8 month old battery I now reserve for solo riding in the Q bike (Quando), and I've no idea of how long it will ultimately last.

Wow, that's particularly bad value for what they cost.

I noticed the new, (I think it's fairly new) "Intro" has Nimh batteries.

At first, all the Ezees, (at least the ones at Northwest in the states) offered either li-on or nimh as a choice.

 

[flecc]

It won't be anything like that for owners generally prState.

My usage amounted to accelerated intensive testing. Because of my long term interest in e-bikes and bikes in general, I've done loads of experimentation and pushed everything to the limit and beyond to provoke failure, all in the interests of better understanding.

This gives me a good all round picture of what the technologies can and can't do, but normal usage gives very much better life.

The eZee Intro is known as the Liv over here, and it originally had an NiMh battery. Following a panic over nickel prices, a huge increase in NiMh cell prices caused the change to Li-ion. You've only very recently got the Intro, so it's back on the NiMh now, as ours might be eventually, since a trickle of NiMh are becoming available again.

On the Q bike (Quando derivative) I use NiMh for my trailer pulling and very steep hill routes, the remaining Li-ion for normal solo use until it's spent. On the T bike (Torq derivative), I use my own special, a 39.6 volt NiMh battery for all round high performance.
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[aroncox]

It won't be anything like that for owners generally prState.

My usage amounted to accelerated intensive testing. Because of my long term interest in e-bikes and bikes in general, I've done loads of experimentation and pushed everything to the limit and beyond to provoke failure, all in the interests of better understanding.

This gives me a good all round picture of what the technologies can and can't do, but normal usage gives very much better life.

The eZee Intro is known as the Liv over here, and it originally had an NiMh battery. Following a panic over nickel prices, a huge increase in NiMh cell prices caused the change to Li-ion. You've only very recently got the Intro, so it's back on the NiMh now, as ours might be eventually, since a trickle of NiMh are becoming available again.

On the Q bike (Quando derivative) I use NiMh for my trailer pulling and very steep hill routes, the remaining Li-ion for normal solo use until it's spent. On the T bike (Torq derivative), I use my own special, a 39.6 volt NiMh battery for all round high performance.
.

This sounds like the batteries are interchangeable, can someone have a Troq for example and buy either a NiMh or a Li-ion without changing the bike in any way?

 

[flecc]

Yes, they are completely interchangeable on any eZee model, and I freely use whatever suits the job.

All eZee models except the Forte and Forza were originally designed and sold with NiMh, the Li-ions an introduction for owner retrofit as well as with new bikes.

NiMh performance is minutely slower as they are nearer the 36 volt nominal, the Li-ion nearer to 37 volt nominal. It's only just possible to detect the difference.
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[prState]

The fact is that despite all the promotional claims, they don't like delivering sustained high currents, so with a powerful motor and climbing long hills, the voltage drop soon gets down to cut-off level.
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Does it have anything to do with battery heat build-up?

I'm supposing it doesn't or someone might have made a ventilated and spaced battery pack already.

 

[flecc]

No, its just chemical exhaustion prState. The metal/chemical interface builds resistance as current issued rises, to a point where it can no longer meet the demand, so the voltage drops. A larger capacity battery is a cure for this, but it has to be correspondingly physically bigger as well. That is because capacity and power delivery are tradeoffs for any given physical size, more of one means less of the other.

Although I have no evidence, I suspect this may be the cause of the delays in the arrival of the new Wisper 905se. This bike is intended to be more powerful with Torq like performance, but with a 13/14 Ah battery the same physical size as the 10 Ah. In design terms that higher power delivery and increase in capacity doesn't add up, something may need to give.

The perfect battery for power delivery was the Ni-Cad, all it's power instantly available, and charging at any speed possible, just so long as the battery could be kept cool enough during such use. The problems with memory effect and the toxic contents led to it's demise, but my reason for mentioning it was the capacity, which was typically half that of NiMh at best.

NiMh doubled capacities, but lost the ability to deliver so rapidly. The ensuing Lithium Ion batteries promised even more capacity was possible, but once again the ability to deliver high currents and accept fast charge reduced still further, leading to the present problems. Lithium Polymer was invented to solve those problems at the cost of a lower capacity, but the designs have been subverted for marketing reasons to retain the capacity and have lost the advantage gains in consequence. Basically it's a question of density, higher content density gives more capacity but impedes current movement.

All in all, a sad story of a chemical brick wall that we've been hitting from many different directions ever since the 19th century.
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[kraeuterbutter]

Nimh-technologie is not that bad as fleccs last posting sounds (discharge-currents, charging-currents)

i come from another side (rc-modells)..
i remember - about 5years ago ? - when the first NiMh appeared on the szene..
there was said for Sub-C-cells:
up to 20A NiMh is good, but for more you need NiCd (for example use in fast gliders with 10-15sec. climbs with 70-100A current)

meanwhile there was no new Nicd-cells..
and the best existing Sub-C Nicd can not compare to the best current NiMh which have much lower inner restistance

the same for LiPolymere...
current Lithium Polymere have much more power and much lower inner restistance (considering weight) than any Nicd or NiMh

i think the biggest demand on Lithium-cells which had most effect on development is the mobile phone and laptop-world...
and what do you want from such cells ?
most capacity at lowest weight...
power is not realy nessessary, because you want at least 2 hours of worktime with your laptop/mobile phone..
so 1C cells are the cells which are mostly needed..

nevertheless there are also higher-power cells which can give 10C or 20C continously (some even claim to be able to put out 30C continously, but with a very reduced cyclelife)
but there are not so many usecases for this cells (so far), price is pretty high..

now for electric bikes: the main-factors are:
1.) low price
2.) high capacity

this point 1 results in the fact, that in all electric bikes low power Lithium cells are used instead of highpower-cells which would be much more suitable

a 10Ah or even 14Ah cells flecc mentioned: when using high power cells
(for example a stack of Kokam4000) you would never have any kind of power-problem in an electric bike with such cells..

a 37Volt 12Ah Stack would give you 6000Watt continously and over 10000Watt for acceleration (for short burst count with over 15kW) with a cellweight of only 3.6kg.. and this withoug overstressing the battery or reaching any temperature-limits or exxeding specs..

so the lithium technologie for itself is not the problem..
the problem is the price...
for the above mentioned battery pack you can count about 1200Euro

so: all cells which are used in electric bikes are no power-cells...
they are cells with the technologie and make of mobile phones and laptops..
and such devices don´t need more than 1C.. there powerdemand is usually less than 0.5C

so my opinion: in any application the possible power-output of a battery should be (a lot) higher than realy needed in the application to get high cycle-life of the battery
for electric bikes i would say: at least 5C batteries..
the reason why this is not done: price..
so in electric bikes are batteries used which are (often) overstressed by the electric bikes because the batteries are too weak because price-reasons...

the technologie is already here (for years now)
and it works (not just labor-tests, but real-life tests)

i hope that the power-tool market (A123 systems starting it) and all the
hyprid/electric-car hype will bring prices for highpower-cells down next years..

 

[flecc]

Nimh-technologie is not that bad as fleccs last posting sounds (discharge-currents, charging-currents)

But I was of course speaking of "at that time" kraeuterbutter. Later the NiMh cells did improve a lot due to the different constitution, but if development of Nicad had continued I've no doubt that would have stayed ahead of NiMh in respect of charge/discharge and gained more capacity as well. But environmentally that could not happen of course.

I think it's important to bear in mind the cell sizes as well, the sub C you mention being rather easier for charge/discharge than the D size we use in e-bikes. It's always easier to demonstrate high cell performances in smaller sizes.

Like you I look forward to prices of high capability lithium cells dropping, but if there's much more delay we may get another technology instead!
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[kraeuterbutter]

yes, you are right..
if NiMh are that better for environment ?
isn´t it the way, that Nimh can not be recycled but Nicd can ?
i heard somewhere that the mainreason for forbidding Nicd was, that the
returns of used Nicd for recycling were so low

nicd throughn away --> bad thing
nicd recycled --> better, but the european people are not realy able to bring batteries back for recycling

for other technologies... i love in the moment my Fepo4 cells from A123 very much..
charinging within 10min without doing any harm to the cells -> great !!
meanwhile ~100cycles on the cells and the cells are like new (maybe even better)

i have not stressed any cell sofar that much (high charge-currents, high discharge-currents, charging also the battery is hot after use without pauses)

there are meanwhile also some other companies selling Fepo4-cells..
but the other brands (chinese make) are low-power-cells...
so far the only one for high currents are the ones from A123 systems i know

well going too far now...
time is interesting.. price is (as always) too high..

oh for nimh (and sub-c)
there is in the moment a interesting phenomen ongoing:
the cells become more and more mimosas again..
the first Nimh were mimosas (damaged very easily when handled wrong)
the capacities rised from 3000mah now to up to 4500mAh
batteries became stronger and more robust.. the best were the onces with 3300mAh..
the 3700mAh was also not that easy to damage..
but since batteries-capacity went over 4000mAh batteries get more and more easily damaged again..
discharge one time too low and you have a capacity-loose of 500mah or more..
overcharge the battery one time, and the cells loose capacity and punsh..

 

[flecc]

Yes I agree, Nicad was abandoned too quickly in my view. I think we in the UK are the worst for recycling most things, and Germany always claims the top spot. I would have thought your Austrian population was good at this as well?

Getting people to recycle very small occasionally used things like AA cells will always be difficult though, but I think there should be no problem with e-bike batteries. All that's necessary is a cashback exchange or credit which any supplier can operate with, not just tied to one company for each type.
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