Hi All,
Inspired by the topic and discussion on storing Zeros over winter, I decided to do some research and have written the following article as a result. I welcome any comments and hope that people will find it useful.
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Lithium Ion (Li-ion) Batteries used in Zero Motorcyles - all you need to know.
I've never really understood Li-ion battery technology properly before and as it turns out, I had some of the key facts wrong in my mind until very recently. Since the battery pack is by far the most expensive component in an electric vehicle, it is worthwhile having a basic understanding of the technology. I hope the reader finds that a few minutes spent reading these notes is time well spent.
Top Tips1. If you run your bike to empty, do your best to give it at least a partial charge (ideally to 40-50%) as soon as you can.
2. Charge and discharge your bike freely and at your convenience.
3. Don't worry about keeping the bike topped up, like standard car batteries.
4. Don't feel you have to run the bike to empty before re-charging, it's fine to charge if you've only used 10%, for example.
5. If you can afford extra chargers to reduce charging time, Zero's fast chargers won't hurt the batteries.
6. Use the bike as much as you can. If you aren't using it for a regular commute or aren't lucky enough to have the freedom to ride regularly then it will work out a lot cheaper to own a conventional motorbike.
7. Zero's engineer's have done the work to ensure a long service life from their battery packs and have backed it up with a five year warranty with the 2014 model range onwards. That should be enough to drop any anxiety you may have and just concentrate on enjoying the bike.
I trust those tips are enough to put your mind at rest. Please read on as you may find the rest of this article of interest.
Battery Chemistry and ManufacturerThe current manufacturer is Farsis who are supplying cells for the 2014 & 2015 model range.
The chemistry used is Lithium Nickel Manganese Cobalt: LiNiMnCoO2 (NMC) - Also know as NCM, CMN, CNM, MNC and MCN.
NMC is a relatively new battery chemistry which differs from the Li-cobalt chemistry we are familiar with from mobile phone batteries and laptops. While Li-cobalt has a higher energy density than NMC (storage capacity per kilogram), it doesn't cycle as well and ages quicker. That's fine for a mobile phone that is likely to be obsolete after 2-3 years, but not for an electric bike.
The automotive grade NMC cells that Farasis supply should easily satisfy the requirements of the five year warranty that Zero are providing with their current Z-Force battery packs. From what I have read, I would expect them to last 8-10 years if they aren't abused. Even if you start to notice some significant deterioration after five years, the rate at which battery technology is progressing means that you should be able to buy a new battery pack with much better capacity (range) than the original for substantially less money. It's worth getting a battery pack that provides perhaps 50% more range than you require for your commute or average needs, so that you can suffer some loss of capacity and still have a safety reserve. That way you never need to worry about it and you'll easily get your 8-10 years of useful service by which point you've certainly had your money's worth from the bike and can upgrade.
Further reading:
https://evmc2.wordpress.com/2013/12/01/2014-zero-battery-chemistry-z-force-power-tank-secret-sauce/Storage and Capacity Loss with AgeYou just have to come to terms with the fact that from the moment the battery pack is manufactured it will slowly lose overall capacity regardless of whether you use it or not. Li-ion batteries are good at holding their charge so you don't need to worry about letting them stand for a long time, providing they've got a reasonably good state of charge (SoC). At 40-50% SoC the overall capacity loss due to ageing is minimised. At full charge the ageing effects are increased but not by such a great amount that it should cause any great concern. For some owners it might be wiser to follow Zero's recommendations and just leave the bike plugged in for however long you plan to store the bike. This at least makes sure the individual cells stay balanced with each other and there's little risk of them dropping to a very low SoC at which point the ageing effects begin to increase. If you let the SoC drop below their minimum threshold you run the risk of the battery pack becoming unusable. I think that's why Zero recommend leaving the bike plugged in over winter. If there's some sort of power cut mid-winter and the bike isn't checked for a few months, then at least there's a good chance the battery won't have discharged too much.
If you do decide to leave it at 40-50% SoC you also need to be organised enough to check the bike every couple of weeks or so. It wouldn't hurt to charge it up after a few months, leave it plugged in for a few days to make sure the cells get properly balanced, then take it for a ride to bring the SoC down to the 40-50% level again before leaving it for the next few weeks or months.
I have no doubt that the good people at Zero have done their sums, know the specifications of the batteries in detail and are confident that their battery packs will have at least 80% health after five years even if the bike is never ridden and left plugged in all the time. Zero also state in their specifications that their battery packs are good for hundreds of thousands of miles before they reach 80% of their original stated capacity. That in itself should be enough to put your mind at rest, but if it isn't then perhaps these golden rules should help:
1. Don't leave the bike standing empty for more than a few days.
2. If you have to store the bike for a long time, then either leave it plugged in and don't worry about it, or leave it at 40-50% SoC but keep an eye on it.
3. Just use your bike as much as you can and don't worry about the battery. The engineers have thought all this through and are backing it up with a five year warranty. The whole scene will be different in five years time, so it isn't worth thinking about.
Deterioration with TemperatureTemperature is a bigger factor than state of charge when it comes to ageing. It is worth noting though that Li-ion batteries shouldn't generate a lot of heat when charging at normal rates. Therefore, even if you live in a hot climate and have just been on a ride, the cells should cool down overall even while they are charging. You might want to be a little more careful if fast charging in a hot climate but don't forget that the Zeros have a sophisticated Battery Management System (BMS) that will either reduce the charge rate or stop charging altogether if the cell temperature exceeds the limits that the engineers have set. They will have set these limits on the conservative side to avoid any claims on that five year warranty.
If you are going to store the bike, it makes sense to store it somewhere cool. Fridge temperature is probably best but never store below freezing. If you don't have the option of storing it somewhere cool, then don't worry about it.
Memory EffectsThere are no memory effects with Li-ion chemistry. Some 'Smart' battery management systems might recommend performing a deep discharge followed by a full charge from time to time. This helps re-calibrate the system and give better estimations of capacity remaining. However, there is no need to do this from purely a cell maintenance point of view. All Li-ion batteries have protection circuits to keep the cells within their safe operating voltage range. You can therefore simply charge and discharge at will and not worry about charging a battery that is half full.
Battery LifeThe manufacturer might state that you will get 500 cycles from a battery and they will be referring to full cycles. However, if you only ever use 10% of the capacity from a full charge and then top it up, you will get more cycles from it before the battery health drops to 80%. In this example you are likely to get 1500 cycles from a battery that you only ever discharge to half it's capacity. That's assuming that all other variables remain the same. In day-to-day use, variations in state of charge and temperature are more likely to affect battery life than how you cycle the battery. Taking Zero's claim's of an estimated battery pack life of 496,000 km using city ranges it would take at least 2,250 full cycles to achieve this (2014 Zero S 11.4 kWh). Taking into account the loss of capacity in this period and the figure is bound to be more like 2,500 cycles. Most trips and daily commutes will probably drop the battery to 40-50% SoC thus increasing the number of cycles we would get from the battery. Let's say we average 60 miles between charges of a 100 mile combined range over the life of the bike. Then let's allow ourselves 3,000 cycles before the battery drops to 80% health. That's still 180,000 miles. Even if we then halve that to allow for temperature and ageing (very unlikely even in harsh conditions) we get a very, very conservative estimate of 90,000 miles. That should give even a heavy commuter a good five or six years of use before noticing significant reduction in range. Even then, a daily average of 60 miles would still give you a 20 mile reserve.
Rate of Charging and DischargingThe Farasis cells have a nominal capacity of 25 Ah. Each cell has a maximum continuous discharge rate of 100 A. You would have to discharge the battery in 15 minutes to achieve that, which I don't believe is possible. Conveniently, the Zero S 11.4 should achieve a range of approximately 70 miles at a constant speed of 70 mph. That would result in a full discharge in an hour. Even maintaining 80 mph, the maximum sustained speed of the bike, I doubt you could empty the battery pack in less than half an hour. So the cells are operating well within their specifications.
The maximum charge rate is 25 A for each cell, which would mean a full charge in an hour. Even with 2 x 2.5 kW Elcons, you're only going to get a full charge in 2 hours, probably more like 2.5 hrs as the charge rate will drop as the battery reaches capacity. Yet again, the cells are under relatively little stress even with a fast charge.
Buying a Second Hand BikeIf Zero are putting a five year warranty on their battery packs, it's quite possible that they believe they will last ten years. Tesla are saying that their battery packs are good for 15 years apparently. I guess it's a lot like buying a normal bike or a car. Feel confident that it will give you at least five years or 50,000 miles of good service. If you don't mind buying a five year old vehicle and taking a bit more risk, then you should achieve double. Time will tell and sellers will be able to quote actual range figures to prospective buyers.
SummaryBattery technology is improving every year, but not at the same rate as computer technology. A 10% per year increase in capacity might be a reasonable expectation. We can always hope that there will be a significant breakthrough that makes is way to production and changes the state of the art much quicker. For the time being though, we have robust technology that should give you five to ten years of service and a range of about 100 miles of mixed riding as long as you don't spend much time on fast roads. Perfect for many city commuters and people who like relaxed rides taking the country roads. You will need an ICE bike for longer journeys and touring, unless you are willing to plan in long charging stops. If you can use your bike for your commute or have regular trips that cover less than 100 miles a day, then range anxiety won't be an issue. If I have managed to quell any anxiety you may have had about battery life and charging, then this article has served it's purpose.
References and further readinghttp://batteryuniversity.com/Batteries in a Portable World by Isidor Buchmann
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Topic: Lithium Ion (Li-ion) Batteries used in Zero Motorcyles - all you need to know (Read 41566 times)