Voltage drop on lifepo4 v limn2o4

[Kudoscycles]

LiFePO4 versus LiMn204
We have a number of bikes in our warehouse that are under test – some have LiFePO4 batteries and some have LiMn2O4 batteries (manganese spinel based lithium-ion polymer or lithium-ion batteries). We have noticed that the 10AH LiFePO4 battery has a sustained voltage up to 30-35 miles and then drops suddenly. Whereas the 14AH and 20AH LiMn2O4 batteries, whilst having a potentially longer range, the fall off of voltage is progressive from O miles and becomes critical at about 35 miles for the 14AH battery and 45 miles for the 20AH battery. These figures are not merely theoretical, if you read reports of Kudos users on Pedelec they all report strong performance from the LiFePO4 battery up to the point when the battery is technically exhausted.
However, if you look on my graph the 14AH and 20AH LiMn2O4 batteries start to experience critical voltage drop off at 34 miles and 47 miles respectively – in practice at this point the bike will start to become sluggish to ride in assist mode. Whilst a total mileage of 50 plus miles (14AH) and 80 plus miles (20AH) is potentially possible, the last 16 miles of the 14AH and 30 miles of the 20AH will be unpleasant to ride – someone elsewhere on this forum described it as ‘like riding through treacle’!
The LiFePO4 equipped bike never experiences this sluggish riding except in the last few yards before the battery is exhausted.
Therefore if you use (2) LiFePO4 batteries you can expect 70 miles of almost full power riding.
The effect is exaggerated with storage life – the LiFePO4 on average experiences only 2% drop in capacity in the first year and 3% drop in the second year, whereas the LiMn2O4 battery loses on average 14% capacity in each year. If you move point A and B some 20% back it is now easy to see why this LiMn2O4 type of battery loses working range rapidly after 2 years of usage, coupled with the high cost of replacement I just cannot understand why this battery type is preferred over the LiFePO4 battery.
Dave
Kudos Cycles

 

[cwah]

Sorry for my newbiness, but is the LiMn2O4 equivalent to the NiCoMn?

Is it the same battery as this one?
48V20Ah Li-Ion Shrink Tube EBike Battery Pack - BMSBATTERY

 

[amigafan2003]

You can reduce the capacity loss of lipo/limn/lico based batteries by storing them @ 40% charge when not in use, which is doable if you know when you'll be riding (i.e regular commuting).

 

[Kenny]

Interesting findings Dave, I have noticed this reduction of power as my battery reaches full discharge although most people probably wouldn't reach that stage with the long range 18ah Kalkhoff battery. I wouldn't describe it as riding through treacle though and you still get a reasonable amount of power.

I would certainly consider a LiFePO4 battery if someone produced one to neatly fit the panasonic drive system.

 

[cwah]

The real strength of this battery is its weight. It's 50% lighter than lifepo4 for a cheaper price. The 2 lifepo4 in your graph are probably way more heavy than the limn2o4.
If you want to do an equivalent comparison, the 2 batteries have to have similar weight. In your chart, the lifepo4 at 36V10AH is comparable to the limno4 at 36V14AH. And from this chart, I think the limno4 wins.

HOWEVER...
What worry me the most is the 14% lost every year. So if in average we do 200 cycles a year, we loose something like 7-10%.

So in 2 years, we should expect have between 50-65% battery remaining...

And that mean we'll have to change battery every 2 years??? Non acceptable.

I think I have this battery from Conhismotor:
http://www.conhismotor.com/ProductShow.asp?id=161

So I'm worry about my battery. (it has already lost 1/3 of its capacity this winter). How did you get the calendar life data?

 

[Kudoscycles]

Cwah...From memory you did spend some considerable time researching your ideal bike and I assumed you must have researched the advantages/disadvantages of LifePo4 v Lithium-Ion. Flecc and myself have made many postings on this site....I suggest you google LifePo4,the amount of info is almost overwhelming. But in conclusion LifePo4 is heavier,about 1.2 kilos for a 10Ah battery but it lasts longer...the average lifespan of Lithium-Ion is about 400-600 cycles,whereas the average lifespan of LifePo4 is 1200-1500 cycles.
So you pays your money and takes your choice...if you want a light battery then as you say LiMno4 wins but if you want longevity then LifePo4 wins...LifePo4 is also cheaper,so the net deprciation cost is considerably less with LifePo4,if you look on my website I have used flecc's formula to estimate the depreciation costs of an e-bike equipped with either battery.
Yes,with LiMno4 you would expect to change your battery every 2-3 years to achieve acceptable performance,this is not merely theoretical, you have many postings on this forum of members who's batteries are past their useable life but are putting off the day when they need to change.
Dave
KudosCycles

 

[10mph]

No Treacle felt here either

Interesting findings Dave, I have noticed this reduction of power as my battery reaches full discharge although most people probably wouldn't reach that stage with the long range 18ah Kalkhoff battery. I wouldn't describe it as riding through treacle though and you still get a reasonable amount of power.

My own observations agree exactly with yours, Kenny. On my Kalkhoff Agattu with the 18Ah, 26V Li-ion battery one cannot detect even a slight loss of power on hills until battery is significantly past the 90% discharged point, which is reached when the last LED starts flashing.

In fact I have just today ridden the bike to cut off. I was riding hard in maximum assist, over a hilly circuit where I tried to pull near maximum power from the battery by keeping to around 15 mph when I could (a bit faster, of course, on the downhills). I finished with 8 repeats of a 0.6 mile loop containing a small hill. Only on the last 2 laps did I detect any any drop of speed on the hill climb. I then headed home, and judged it almost perfectly since the battery cut out after a further 1.7 miles about 0.1 miles from home!

I had started detecting loss of power about 2.5 miles before cut off. Too describe these last 2.5 miles as treacle would be to over dramatise the reduction of my hill climb speed from 12.5 mph to 10.7 mph.

I conclude that the Kalkhoff battery must be really better than the LiMn2O4 battery tested by Dave in the first post on the this thread.

The curves plotted by Dave for his LiFeO4 show a tiny fall off in voltage before the critical point is reached. This must make it very hard to provide an accurate indication of state of charge using voltage driven LEDs. I saw in a post on this forum, which I can't now find, someone with a LiFeO4 experienced a very short distance being covered between all LEDs on to 1 on then cutoff.

Dave does not give values on the voltage scale on his graph, and there are no actual data points shown, just what I take to be smoothed curves, so it is rather hard judge just how marked the rapid cut off without warning is going to be for the LiFeO4. By contrast with the Kalkhoff Li-ion you soon know exactly where you are on the discharge curve and can judge the remaining range quite well with a little experience.

 

[indalo]

On my Kalkhoff Agattu with the 18Ah, 26V Li-ion battery one cannot detect even a slight loss of power on hills until battery is significantly past the 90% discharged point, which is reached when the last LED starts flashing.

Given your test results, are you able to extrapolate or draw any comparisons with the performance of 36V batteries while remaining within the legal parameters?

I think what I'm asking is, would we experience significant improvements in bike performance through going to 36V XAh batteries instead of 26V 18Ah? If the answer to that is yes, is there a downside, financial or otherwise. It seems that the trend is towards higher voltage batteries but I'm not entirely convinced that there's a need.

Were it the case that 36V meant that we could all ride our bikes for 100 miles without recharging, then obviously the case would be made spectacularly. I'd appreciate your view as I'm sure there's more to it than just numbers.

Indalo

 

[10mph]

Given your test results, are you able to extrapolate or draw any comparisons with the performance of 36V batteries while remaining within the legal parameters?
I think what I'm asking is, would we experience significant improvements in bike performance through going to 36V XAh batteries instead of 26V 18Ah? If the answer to that is yes, is there a downside, financial or otherwise. It seems that the trend is towards higher voltage batteries but I'm not entirely convinced that there's a need.
Were it the case that 36V meant that we could all ride our bikes for 100 miles without recharging, then obviously the case would be made spectacularly. I'd appreciate your view as I'm sure there's more to it than just numbers.
Indalo

One can't draw any conclusions about 36V systems from the measurements of the performance of a 26V Panasonic system with the Kalkhoff 26V 18Ah battery. Kenny and I were just reporting absence of a severe "riding through treacle" effect when using these batteries.

I would not be too surprised if an optimally engineered 36V system were to out perform an optimum 24V system, but I would be surprised if the improvement was very large, especially if cost was also taken into account.

Taking a very simple view: the energy (watt hours, Wh) that is stored in a battery of given weight and volume and cell chemistry and construction, does not vary when the cells are placed in series to give a higher voltage or parallel to give a higher current. So, if the motor is matched to the battery, we get the same range.

Obviously the lower voltage system will run higher currents and will need thicker wiring and windings in the motor, which will have a slight weight penalty. But the higher voltage system needs slightly better insulation and higher voltage ratings for the semiconductors and capacitors in the controller. The best system would only be known as a result of very detailed engineering study.

I have also noted that a lot of new systems are 36V so presumably this is a good engineering choice. However, my 24V 18Ah Kalkhoff system certainly works well and gives much more range than I absolutely need. It is only 9 months old and shows no sign of deterioration so far. The crunch may come after 2 or 3 years depending just how fast the battery deteriorates. I bought a big battery and could manage with 50% loss of capacity before I have to buy another.

 

[indalo]

One can't draw any conclusions about 36V systems from the measurements of the performance of a 26V Panasonic system with the Kalkhoff 26V 18Ah battery.

Thank you for that 10mph. I realised when I posed the question that, in the absence of specific data, any reply would rely on speculation allied to some fundamental electrical understanding.

Elements of your answer bring back memories of my college work in the early 1960s and I'm sure I have a couple of certificates somewhere in the loft which suggest I must have picked up a little knowledge of such matters once upon a time.

I have also noted that a lot of new systems are 36V so presumably this is a good engineering choice.

Yes, that fact hasn't escaped my attention although I'm not necessarily persuaded that it has anything to do with engineering. Given your experience of a 24V system, I think the case for 36V is diminished somewhat, bearing in mind I'm only interested in performance compliant with existing regulations. Taking account of both pros and cons, any net gain achieved by a 36V system is likely to be relatively minimal.....if I'm wrong in that, please tell me.

Your experience of the Kalkhoff 18Ah battery somewhat negates the argument that 24V systems per se don't cope as well with hilly terrain. I realise that the Kalkhoff is crank-driven which provides advantages absent from most hub-driven bikes. Moreover, some of the best ebikes in the market still utilise 24V systems, some even remain faithful to Ni-Mh battery technology. Perhaps next year, all those will have gone over to 36V but I'm not sure I see the point.

We know that there are bikes equipped with 48V, indeed as much as 72V systems, some even more powerful which can generate an awful lot of power; so much, in fact, that they can no longer reasonably be referred to as electrically-assisted bicycles. I accept that for some people, the world is not enough; they always need a bit more but your 24V 18Ah system seems to achieve all that any reasonable person in need of a bit of assistance while cycling might wish so why are we being fed all this 36V stuff?

My best guess is that we may be seeing this change in preparation for a more powerful class of ebike, (suggested many times) and those would probably benefit from the extra grunt of a heavy-duty system if they should be permitted higher top assisted speed. It would then make some sense for producers to standardise the basic electrical infrastructure for all their bikes........or am I completely wrong?

Indalo

 

[jhruk]

My best guess is that we may be seeing this change in preparation for a more powerful class of ebike, (suggested many times) and those would probably benefit from the extra grunt of a heavy-duty system if they should be permitted higher top assisted speed. It would then make some sense for producers to standardise the basic electrical infrastructure for all their bikes........or am I completely wrong?

My guess is that this change from 26 to 36 volts has more to do with marketing than engineering. Whilst there may be small engineering advantages most of these are more applicable to those bikes with long power cable runs than with the integrated Panasonic system. The real advantage is on the spec. sheet - 36 volts sound more powerful than 26. Given the choice between two otherwise similarly specified & priced bikes the one with the higher voltage may well appear better value.

 

[indalo]

My guess is that this change from 26 to 36 volts has more to do with marketing than engineering.

While my conjecture may have a little merit, I think you have hit the nail on the head JHR. That's why I was at pains to convey the message about legal parameters. Clearly, if all one is interested in is producing a two-wheeler that goes really, really fast, then upping the power using a variety of electrical methods would be the obvious way to go, short of an I/C engine.

However, if an assisted bike can perform all that any rider might reasonably expect within the law, using only 24/25/26 Volts, I can't see why 36V is required. 10mph seems to have no problem with his Kalkhoff set-up.

Indalo

 

[flecc]

Technically the design balance is in favour of specifying 36 volts, but the cost balance, of batteries especially, favours 24 volts. That has been clearly reflected in the market, especially in lower cost bikes like the Synergies, Cyclamatics and Powacycle Salisbury/Windsor models, all 24 volt and available with degrees of continued support.

Lower cost 36 volt bikes have mostly been marketed at very low cost such as on ebay, usually with no support and often with SLA batteries, though we are now starting to see some exceptions as the market gets more competitive.

 

[Kenny]

My guess is that this change from 26 to 36 volts has more to do with marketing than engineering. Whilst there may be small engineering advantages most of these are more applicable to those bikes with long power cable runs than with the integrated Panasonic system. The real advantage is on the spec. sheet - 36 volts sound more powerful than 26. Given the choice between two otherwise similarly specified & priced bikes the one with the higher voltage may well appear better value.

I also think this is the reason for the shift to 36v. Unlike many forum members, most ebike purchasers probably don't really understand the differences and think of it simply as the higher voltage the better.

I'm sure Bosch's very successful 36v entry into the market was the main reason behind Panasonics change to 36v rather than any engineering advantage.

 

[flecc]

most ebike purchasers probably don't really understand the differences and think of it simply as the higher voltage the better.

They're right, it is better.

Uses less of the expensive materials. Reduces motor weight. Less heat developed. With the same power developed, a higher voltage uses lower current, better for the reliability of many components. Voltage differentials easier to measure for better battery meter accuracy. Lighter gauge wiring makes for more neatness, especially with front hub motors having wires transferring to the frame when greater reliability results as well.

 

[NRG]

But its marginal for the Kalkhoff change to 36v the bigger benefit is the new marketing angle...

 

[flecc]

But its marginal for the Kalkhoff change to 36v the bigger benefit is the new marketing angle...

I'm quite sure that's true, the change for Panasonic in particular is a marketing measure.

I just didn't want the emphasis on that aspect to hide the advantages of designing with a higher voltage, something those technically unaware might not appreciate after those last few posts.

 

[aseb]

You can get an idea of the effect of Voltage changes, as well as current limits, ranges, consumption etc by using the ebikes.ca simulator program. Worthwhile playing with- watch the hours fly by.