Another EV bike :)

An area for all you bikers who now run your two wheeler on battery power, scooter owners to.
mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Tue Nov 12, 2013 9:56 am

Sounds like having the smaller packs will give you the flexability of putting them together in any combination that you need to, and to then change them around if required.

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Tue Nov 12, 2013 10:10 am

Yes, I'm looking now at battery packs made up of ten 12-cell blocks so i can switch it about as required.

I just had an email from Fedex to say my battery holders had been delivered at my home. I've arrived home and there are no battery holders, yet the online tracking system says they were sent for delivery in China 1 minute before they were delivered. I was hoping they'd arrive today because I have the rest of the week off.

I've requested clarification of the shipping, fingers crossed they turn up somewhere local !

Chris

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Tue Nov 26, 2013 4:50 pm

Yet more power :twisted:

All of my battery holders have arrived and fit like a glove. I have about 300 extras so I've looked at getting a few more lithium cells. I've bought about another 40 used cells off ebay, hopefully I'll find some good ones.
I've also bought some new cells too, in the form of brand new OEM laptop battery packs which are on special offer because presumably the laptops they're made for aren't popular any more. For example I just bought a 9-cell pack for £6 (11.1V 7800mAh - therefore each cell is 2600mAh). So 67p per cell (including shipping) for what I hope turn out to be good quality Sony, LG or Samsung etc cells. In total I've bought about 40 cells just by bidding the minimum amount, and if it wasn't for the shipping charges I could have done so much better !

I've also bought a 'new' supercapcitor, rated at 165F at 48V. The specs say it's short circuit current is above 3000A and it's design max current is 1900A. A bit pricey at £200 (but the RRP is over £1000), but I can replace any lead acid cells I was going to use for the high current demands with that (and it's probably lighter too). I know the lithium ion cells will probably be fine without the need of a parallel current kicking source, but because the majority of cells in my pack are used I don't want to tempt fate so I'm seeing the supercap as an insurance policy as much as anything else (And I also like the fact that it's being sold from a cancelled sports hybrid car project - the seller has 80 more if anyone is interested) It's made up of eighteen 3000F 2.7V caps, which I'm sure would sell individually on ebay if I chose to break it up to recover the cost.


I'm a bit pulled around between other projects and a full time job but I'm going to get on with pack building very soon once the new cells arrive.

I've also had somebody volunteer to race the bike at the TT zero next year for free because they have a current race licence and i don't. There's nothing like a bit of pressure to make you wonder why you do it ! (but I think 2015 is a more realistic target :) )

Chris

User avatar
Kevin Sharpe
Posts: 489
Joined: Thu Jul 29, 2010 5:39 pm
Location: Bradford on Avon
Contact:

Re: Another EV bike :)

Postby Kevin Sharpe » Tue Nov 26, 2013 6:32 pm

Kevin Sharpe - Founder and Patron for UK registered charity Zero Carbon World. Founder and Chairman Mainpine Group. http://about.me/kevinsharpe

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Tue Nov 26, 2013 7:41 pm

Kevin Sharpe wrote:don't know if you've seen the Jehu Carcia 18650 project?

http://www.youtube.com/watch?v=m90ibjcvR68&feature=share&list=UUcMfCkN1juSa49DJFYltOTw&index=2



Wow ! A soul mate :)

Interesting/reassuring to see that he can make similar observations about the usefulness of this form factor....as well as confirming it is about as labour intensive as you can get....but if you're up for it you can reap financial rewards.

I'll definitely be watching his progress. Thanks for the link
Chris

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Wed Nov 27, 2013 7:55 pm

The supercapacitor arrived today....quite a bit bigger than expected but it will squeeze in.

I don't really vocally exclaim, very much, but after charging the cap to 34V and connecting it directly to the motor.... huge spark...motor jumping off the bench and accelrating harder than I've heard it do before....

The capacitor might not have the capacity of lead acid, but it can definitely trump it in the maximum current department.

:lol:

Grumpy-b
Posts: 991
Joined: Sat Dec 01, 2007 12:06 pm

Re: Another EV bike :)

Postby Grumpy-b » Thu Nov 28, 2013 8:51 pm

Valence batteries whilst looking like a nice rectangular box are in fact made up from layers of cells fixed to steel plates and folded over, so each 12+v cell has four layers of cells something over 20+ in parallel. I have one in pieces, I also have one that self destructed in a thousand pieces.
I stupidly measured the battery and thought nothing of the fact that it was a multiple of three cells not 4, but when it was put on a simple low level of charge the voltage rose, yipeee I thought, it lives . But I stupidly left it charging and it self destructed. The layer that didnt read (so giving me a low 3 cell voltage) appears to have had a shorted cell. When it was charging most of the current went through that cell causing it to go into a thermal decline and then out of control, taking many other cells around it out as well. It initially melted its casing then blew up spreading carbon / lithium/ alluminium foil all over my workshop.

The point here is that its impossible to monitor each cell in such a large celled pack. The latest versions and the ones that TESLA use have some internal (at least to the overall packaging) protection to stop this happening.
If I can find the photos I took of the damaged battery I will post them. I think I probably did before when I did this over a year ago.

With less than matched cells you do run the risk of putting the lowest under strain, and into a self destructive mode, especially when the cells are of such unknown condition or number of charges / discharges they have already had. Or worse the problem doesnt come to light until it is charging in the shed (About to be ex shed).

What would concern me is that most cells are not like the Valence chemistry and will burn, rather than just get very hot and go pop.

Perhaps you should conside some multiple heat sensors, and thermo meter circuits to try and catch any thermal events.
Grumpy-b

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Thu Nov 28, 2013 10:05 pm

You make some good points. So far I've been very brief with my sketchy plan, but what I've written is not representative of the thinking I've done....I just have a habit of writing reams of detail and indecisive waffle sometimes, which I'm trying to leave behind.

In your case it is interesting that you had a whole layer of 20 parallel cells fail. I'm unusre what chemistry was involved, usually for a pack voltage of 12V three 3.7V li-ion cells are employed. Four 3.7V cells have a nominal voltage of 14.4V, so perhaps your 12V batteries were LiFePo-type cells, with cell voltages of 3.2V. The chemistry should be the clue. Anyway, it sounds very much like one cell shorted and took the others with it. Kindof unusual for that to happen from what I've read, but not unheard of. A more common incidence is for the failed cell to go open circuit eventually. (again, only going by what I've read, not conclusive lab tests)

So I have blocks of parallel cells, similar in idea to yours. Each layer is going to be made of an equal mix of cells of various capacities, to hopefully produce layers of roughly equal capacity and cells of similar age characteristics.

Instead of a nice flat repeating capacity measurement curve during the first few dozen cycles, I expect to immediately see a curve representing a fall in performance. I already have a battery monitoring device to hand which I'm probably going to install at each 3.7V block level, and adding thermal monitoring is definitely on the cards anyway. One of the inherent benefits to using this particular battery holder design is that it leaves a small air gap around each cell through which I could feasibly blow cooling air, right to the heart of the pack, if required.

The thing which is going to exacerbate ageing and increase the risk of early cell failure is going to be high currents, both during charge and discharge. One of the main reasons for spending weeks testing each individual cell, in order to roughly characterise it, was to weed out the obviously weak cells. I've tried to do that by using a combination of decision emptors, rejecting any cell which reached a temperature of even a few degrees above ambient during charge, and again rejecting any cell which got too hot during discharge. Any cell which refused to complete a charge cycle due to low maximum voltage (even if it didn't get warm) was also rejected. I haven't posted a picture of the 'failed' cells, but most of them have the words 'too hot' written on them.

The theory behind going 'massively parallel' is to spread the current demand over as many cells as possible. I have as a reserve a small pack of lead acid gell cells which I can add in parallel to provide the deeply damaging high current pulses, of the sort which I know the SCR chopper based speed controller is going to produce. But my first tests of the lithium blocks have looked quite promising....but the acquisition of the supercapacitor has got me feeling very comfortable (yet still touching wood, just in case)

The supercap has 18 3000F caps in series. Each cap is individually monitored for over voltage and there is an inbuilt balancing mechanism and alarm circuit (plus pack centre temperature monitoring) , making it pretty much 'fit and forget'. It's going to really ease the load on the lithium cells, so that as they become more prone to failure through normal use they aren't exposed to the high peak currents of the sort which could be just enough to take one into thermal runaway.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... t_82wt_987

Anyway, that was why it was so important to me to build a charger/discharger which had identical characteristics for each cell station, because I knew that I wasn't going to read the cell capacity in units of mAh, but in terms of time spent on the discharger before reaching the lower limit. This form of comparative testing is frowned upon by some people because the general belief is that you must use 'correct' units, but ultimately the units don't matter where the aim is to produce a comapratively meaningful result. In this context AFAIC being able to say that one cell ran for 30% longer than another cell is perfectly acceptable...short of resurecting the Duracell bunny test I don't know what else to do !


My whole approach to this project is pragamatic. I am testing this source of lithium cells to see if there would be any point pursuing another similar project, I am building a long dreamt of electric motorbike and have built in the versatillity of design layout to allow me to play some more should either the motor, controller or indeed the cells themselves be inadequate. This isn't an attempt to get it right first time, but to leave the door open for some iteration of the design later on. (All on a very tight (but not safety corner cutting) budget.

Today I priced up a 48V AC drive system, with a controller and 11kw motor, for $900, which is around £600- £700. To my mind, if I find the cells aren't ageing too quickly and work well for the overstretched DC drive system then the next step will be low voltage AC drive. (or even higher voltage AC drive for about the same money). If the cells are letting the design down then I could spend the same £700 on some Kokam or Headway cells and improve the design that way. I can't afford both at once so I have to suck it and see.

I don't feel it is beyond me to try to design a really superb electric motorcycle in one go....it wouldn't be perfect but I have the skills to fix any problems, or know people with the specialist skills to finish it off.....but what I lack are funds, as always, and so what I'm unable to afford I'm having to build for myself.....it's like the beginners EV kit bike. :D

By the end i'll have done enough to put an electric bike on the road and get it through an MOT, and then afterwards it's all down to funds, but I'll have something for puttering about on at the weekends in the meantime.

Chris

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Fri Nov 29, 2013 11:01 am

If it looks too good to be true....

I mentioned I had bought some new laptop battery packs. Apparently they were 'OEM quality'. Listed as 11.1V and 5200mAh 6-cell packs it is implied by the specifications that they should contain six 2600mAh cells.

I've pulled a couple of the packs apart and run some tests on my true capacity tester (only 1 cell at a time can be measured) and it seems like the cells are more like 1600mAh to 1700mAh capacity. It's a good job I didn't buy too many of this sort. So I've emailed the seller and asked for an explanation.

I only paid £4 for 6 cells, so they're still good value, but I look forward to their reply anyway !

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Mon Dec 16, 2013 11:52 am

So I've added another 80 cells or so, with an average capacity which is higher than some of the existing lower performaing cells so i think I can sacrifice the weakest cells and have improved performance too.

Also I've had trouble with my motor which is a GE type of just a few horsepower. The problem has been that the output shaft is designed for taper bore sprockets. How many taper bore sprockets can you find off the shelf ? Almost none. After viewing a Youtube video made by an EV bike builder in the US, he recommended a UK company Lakehurst Limited, www.lakehurstpt.co.uk , he had them make several custom sprockets for him.

After a brief chat with Lakehurst they made me a sprocket to the dimensions which I've supplied and created a nice 13 tooth sprocket for a 520 sized chain which fits perfectly, even down to the keyway.

I'm going to get a few things cleared off the bench first but then I'll be able to bring the bike chassis into the garage, strip it completely and start looking at component placement, which in turn will dictate exactly how and what shape i construct the battery packs.

I doubt I'll have any more updates for a while so here's a to happy festive season !

Chris


Return to “Electric Motor Bikes”

Who is online

Users browsing this forum: No registered users and 26 guests