Ah, but can the BMS do anything about the cutouts? Are the cutouts we are experiencing done by the controller on the bike, or by the BMS?

 

Either way, they are in response to the battery voltage falling below a certain threshold under load. My understanding is that the internal resistance of the LiIon battery increases with age, and the capacity decreases with age. Both these effects will make the cut off voltage appear earlier and earlier in the discharge.

 

 

Nick

I don't think it really matters which Nick. What's needed is a battery that doesn't drop voltage so severely, NiMh for example. Just about solving the cut-out problem will only highlight the other aspect.

 

What gets forgotten in this debate is the severe loss of performance long before cut out when the voltage drops. On one very long climb I do, the performance continuously fades, the bike getting weaker and weaker and forcing me to do more and more, until eventually the first cut out occurs.

 

By contrast on NiMh, the performance is fractionally lower initially but only fades slightly, remaining reasonably constant for the whole climb. On the T bike radical battery I start with a higher voltage which offsets even that small fade and gives me a reliable more constant power under load.

.

Edited November 26, 200718 yr by flecc

Ah, but can the BMS do anything about the cutouts? Are the cutouts we are experiencing done by the controller on the bike, or by the BMS?

 

Either way, they are in response to the battery voltage falling below a certain threshold under load. My understanding is that the internal resistance of the LiIon battery increases with age, and the capacity decreases with age. Both these effects will make the cut off voltage appear earlier and earlier in the discharge.

 

 

Nick

 

Yes I think the consensus of opinion is that it will not stop the cut outs as the cells age - thus my reluctance to buy another li-ion. The only way forward would be to increase the capacity of the battery as Wisper have done or perhaps higher quality cells. Needs must on this occasion and we shall wait and see.

Here's another thought: has anyone done any proper measurements on these batteries? What do eZee and 50 cycles do?

 

If you look around, ebikes.ca publish some battery discharge curves but they are done at 1 Amp. Does anyone do any measurements that are representative, eg., 5 A with pulses to over 10A. Then we could get a quantitative comparison between NiMH and LiIon, and maybe more importantly, between different LiIons. At the moment its too easy for people to dismiss the results as subjective, or dependent on how you ride it.

 

Yesterday I was getting cutouts on the flat after 3 miles, which I wouldn't expect even at full continuous throttle.

 

Nick

That's what happens when it's cold and the battery is ageing Nick. Even on the Quando which is fairly easy on the battery I started to get that that at six months old in Winter weather. On all three Li-ions it's been the cold that's triggered too frequent failure for the battery to remain useful.

.

Li ion

 

Hi Guys

 

I have just returned from a very productive few days in China during which time I went to the Lishen factory near Beijing. Lishen produce Li ion batteries for every one from Apple Ipod to Samsung and HP. After having seen Li ion batteries being manufactured from the initial slurry through the many many processes to the final cell, I will never look at a Li ion battery again without being in awe. Did you know it takes 15 days to produce the finished item before another 15 days of charging and testing?

 

The staffing of the Lishen factory was just as impressive, of more than 7000 staff over 70% are doctors, professors and graduates, this includes the production team.

 

I met Doctor Wu a wonderful Chinese lady who has been working on batteries all her life and is now with the team of scientists working on Lithium Ion. Having spoken to her and Lishen's marketing director David regarding the new batteries for Wisper bikes I have a far better understanding of the immense complexity of designing and manufacturing these tiny works of art, and how massively important the managements systems are, Suffice to say I did not understand any of the science but they are in general agreement with Flecc's point of view, they have not to date been able to produce lithium ion cells for larger applications that are anything like 100% reliable. The small battery cells that work in mobile phones, computers etc are pretty well bomb proof now but they are still perfecting the larger cells.

 

The batteries that are being used in the Wisper range now are state of the art and if they are going to be unreliable then we know within a few weeks of use, if they work well for the first 10 to 20 charges and discharges then they will, in the vast majority of cases, continue to give perfect service for the rest of their lives, because of this we are extending the testing periods to cover these first charges. It seems one of the biggest problems is the connection between the cells in the battery, if one of them falls out then the whole battery gradually becomes infective.

 

Lishen are working on a new Li ion battery cell and connection system along with a new management system that will be ready for testing in the local market in March 2008 and ready for export in October 2008, these next generation ebike batteries will be 10 amp 36v thus saving weight but in the opinion of Lishen will be even more reliable than the 13a version that we are currently using and will have a life of between 1500 and 2000 charges.

 

The most important point that the people at Lishen made was that in their opinion the only battery worth such massive investment for almost immediate use is the lithium ion battery and although they have new wonders on the drawing board involving nano technology, they will not be available commercially for years.

 

Please accept my apologies for not being at all technical but I could not even try and explain the science behind these mighty marvels!

 

On another note we have a 14 amp lithium polymer battery from our second manufacturer, with a wonderful new controller specifically designed and matched for this battery, on trial as I write. Being lithium polymer it is as a little lighter than the hard cased cells and being 14 amp it seems to be able to cope with the huge demands of an electric bike. First tests have indicated that we can pass the 100 kilometer barrier under power assist with a 70kg man on a flat surface and 65 kilometers under power only. There also do not seem to be any of the cut out problems discussed in this thread. (We have not experienced any problems in this area since we introduced the 13a unit.) All safety tests including, piercing, crushing, exposure to heat have been fine, I will keep you posted.

 

Best regards David

Update

 

Well my battery arrived today and fully charged I took it out for a test ride. What a difference it makes and what a relief to be able to use full throttle again without fear of cut outs, it was even difficult to get the yellow light to show on hills. My old battery was well and truly exhausted.

 

What I have done is to calculate how many charge cycles the old battery had taken. This was done by counting up my shifts at work and counting one charge cycle as a return trip or 20 miles (although the battery was always charged at work).

 

The result is quite shocking and comes out at well under 130 cycles. Of course I have used the bike locally but there are times I have not cycled in to work so I think 130 is a fair assumption and a long way short of the claimed 500 cycles. Maybe the battery was faulty after all the first one supplied was faulty (maybe I am unlucky). In April the battery was tested and found to be 8.5Ah so the rate of decline seems to be pretty consistant.

 

The sooner I get the NiMH the better.

Edited November 28, 200718 yr by HarryB

Having re-celled an Ezee battery I can say that space inside is very limited, the main body of the case has just enough room for the 6 vertical sticks of 5 cells with room for one more between the detents at the top.

 

The cells I used were originally tagged but the tags had to go as their thickness added up to about 6mm for the 5 high stack which was too high to fit.

 

 

In doing some research into the NiMH cells it seems they might vary in size - from 58mm to 61.5mm (according to some websites). I presume that it is the larger sizes that will have trouble fitting. Interestingly some of the button D cells are quoted at 60mm and they seem cheaper so maybe a solution if 50 cycles don't come up with the goods.

 

 

Flecc - just out of interest - do you think that my battery was faulty or do you think that 130 cycles is about it for the Li-ion. I believe you have had three and (with one faulty) and I wondered if you concur with the result. I know it is very difficult to judge what is a charge cycle.

Hi Harry,

 

I take it your new battery is a Li Ion. You say the sooner you get NiMH the better, but surely what we would really prefer is a Lithium that was actually reliable.

 

What's not clear to me at the moment is whether all Lithium batteries have turned out to be a disappointment on e bikes or just some of them.

 

Anyway, I have just fitted a Cycle Analyst from ebikes.ca so that I can get some quantitative measurements of current voltage and Ampere-hrs rather than the more subjective observations on distance and gradient.

 

Nick

I concur with that Hal, and it could be said my case is worse.

 

Six month equals 182 days, but not cycling every day, having three bikes for the duration and only one of them on Li-ion, that bike was probably used between a half and two thirds of the days. So my experience is 90 to 120 charges, and most of those only part charges no more than a third of the capacity. The total mileage per battery is about 600. Yes really.

 

The true number of full charges doesn't bear thinking about.

 

Mind you, single use D cells would have to be only 41 pence each to match my Li-ion cost, so from that point of view still ok.

 

Well, you have to look on the bright side, don't you!

.

.

 

Please accept my apologies for not being at all technical but I could not even try and explain the science behind these mighty marvels!

 

Best regards David

 

No apologies needed David, many thanks for the detailed explanation and update on progress.

 

I first posted nearly a year ago that larger capacity was the best way to get out of cut out problems with the current technological limitations, so we're very much in tune here. It's interesting though that a return to 10 Ah with better management control is now on the cards, for that's the other solution, amply demonstrated by BionX and Panasonic using top drawer battery management.

 

I've just been riding such a Li-ion system well into battery empty flashing LED mode while climbing a 1 in 7 (14%) hill on full power mode, without a trace of it wanting to cut out.

 

So there's hope yet.

 

I agree that most research investment has to go into Lithium, anything else would be silly, but wish that some production investment could be put into NiMh while a real need for those still exists. It may be yesterday's technology, but tomorrow hasn't arrived yet and we're in trouble today.

.

reading between the lines is it possible that the same problem could arise on the powabyke lithium ?

reading between the lines is it possible that the same problem could arise on the powabyke lithium ?

 

I've been wondering exactly that, given the power of the Powabyke motor. Perhaps Frank of Powabyke can enlighten us.

.

i hope so,i don't fancy forking out £300+ for something that in reality isn't going to be any better than a lead acid

I can tell you where to get 12mah of radio controlled batteries for 180 pounds delivered in 9x12V packs in the UK...I also have a nice lady from China offering me 30 pack crates of batteries for 105 pounds a pack.

i might take you up on that when my battery dies

reading between the lines is it possible that the same problem could arise on the powabyke lithium ?

 

So far tests have not shown any signs of cutting out. Powabyke have been doing Lithium batteries now for over 12 months and feedback has been fantastic. I use a 24 speed commuter with lithium and confess to being very lazy when it comes to charging the battery itself. Living in Bath (for those who haven't had the pleasure of visiting this beautiful city!) it is situated in the middle of a valley so wherever you go you will encounter hills of various lengths and inclines. I weigh 15 stone and have had no problems with the battery cutting out at all on any of the hills. I use the power at all times but admit I enjoy pedalling so I do take some of the strain off the battery. I have cycled up North road to the university and also Bathwick Hill to the same destination. Now these hills are steep and circa 1 mile long.

 

I would be interested to know if anyone has had cutout on a Powabyke Lithium battery.

 

I hope this puts your mind at ease Carpetbagger!

 

Regards

 

Frank

Powabyke Ltd

Thanks for the quick response Frank. If you can climb those wicked hills up to the university, I'm reassured that there's nothing wrong with those batteries and their management.

.

That is good to know Frank. I would like a lithium battery but the price is still too hard to swallow!

 

Off topic(Sorry) Frank, have you ever had the need to use your bottom 16 gears on your 24 speed commuter? I only ever use the top 5 gears - and I encounter many long and steap hills. The 24 gears seem a complete overkill. Although, if the battery ran out, I could see the advantage of them then.

That is good to know Frank. I would like a lithium battery but the price is still too hard to swallow!

 

How far do you travel on a single charge? We now have a Lithium Lite battery which does about 10 miles unassisted or 15 assisted which cost £200. Weight is just 2.5kg.

 

Off topic(Sorry) Frank, have you ever had the need to use your bottom 16 gears on your 24 speed commuter? I only ever use the top 5 gears - and I encounter many long and steap hills. The 24 gears seem a complete overkill. Although, if the battery ran out, I could see the advantage of them then.

 

 

Ha! I have to admit, even with the hills of Bath I have used probably just 3 of the 24 gears!

Sorry, Im still getting used to posting messages on here! I meant to ask ...

 

How far do you travel on a single charge? We now have a Lithium Lite battery which does about 10 miles unassisted or 15 assisted which cost £200. Weight is just 2.5kg

That lithium battery performance is impressive, Frank. It shows that the technology can be made to work in an electric bike application. I guess Powabyke, being based in one of the hillier parts of the country, might be expected to put a bit more emphasis on this than others.

 

On my Powabyke I also just use the top three or four gears - apart from a couple of occasions when the battery has been close to empty. On those occasions I have appreciated the full gear range. Despite its weight (and I have the full fat, steel and lead acid 39kg version, with 21 gears), that megarange + small chainwheel means I've been able to pedal it up some very steep hills, albeit at sub-walking pace.

 

I've tended to look on the Powabyke as having 3 or 4 gears for normal use and 17 or 18 'get me home' gears!

 

Powabykes have not necessarily been the most fashionable of electric bikes but I've always felt they are not only practical, but well-designed to meet the needs of a particular customer segment at a keen price-point, as well as well marketed and supported.

 

Frank

That lithium battery performance is impressive, Frank. It shows that the technology can be made to work in an electric bike application. I guess Powabyke, being based in one of the hillier parts of the country, might be expected to put a bit more emphasis on this than others.

 

 

Powabykes have not necessarily been the most fashionable of electric bikes but I've always felt they are not only practical, but well-designed to meet the needs of a particular customer segment at a keen price-point, as well as well marketed and supported.

 

Frank

 

Ha! I must admit they won't win any awards for style! but as you state they are well built with strong motors and indeed do the job with minimal fuss. Now that we have a good, reliable lithium battery we are in the process of designing 2 new bikes built specifically for a lithium battery which will hopefully be available early next year.

Sorry, Im still getting used to posting messages on here! I meant to ask ...

 

How far do you travel on a single charge? We now have a Lithium Lite battery which does about 10 miles unassisted or 15 assisted which cost £200. Weight is just 2.5kg

 

I travel approx 13 miles each day so the light version might struggle to last the distance, especially if the capacity drops off over the months.

 

I've just thought though, with it only been 2.5KG's I could easily carry it to my office for a charge before riding home.

That is always an option for you especially as the charger is probably 1/3rd of the size of the current lead acid chargers and fits in the panniers with plenty of room for your sandwiches!