Another EV bike :)

An area for all you bikers who now run your two wheeler on battery power, scooter owners to.
ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Sat Jan 04, 2014 7:07 pm

Damn that James May for building an electric motorcycle out of meccano, and riding it around the Isle of Man TT course. Watching that program lastnight spurred me on to clear some space in the garage and get my bike's chassis stripped down. and on the bench
Side_w_tank cover.JPG
Side_w_tank cover.JPG (229.75 KiB) Viewed 5121 times


The plastic tank cover is just a fibreglass cover, completely empty underneath

Side_wo_tank.JPG
Side_wo_tank.JPG (224.46 KiB) Viewed 5121 times


The motor controller should sit above the motor in the middle of the frame. (The new motor sprocket, fitted to the motor was the custom sprocket, costing just £45)

motor&controller.JPG
motor&controller.JPG (157.24 KiB) Viewed 5121 times



There are a few more images here http://www.flickr.com/photos/28496053@N ... 401629565/ , there is a vast amount of space for batteries which I'm very pleased about. The upper tank space inside the removable cover will probably be filled with the supercapacitor.

At the rear of the bike there are 2 very strong bars welded to the frame which look like they could be used as additional battery pack supports.

It shouldn't be too difficult to find room for the batteries I have. Front sprocket has 13 teeth, rear sprocket has 46 teeth so a ration of about 3.5:1 . I would prefer 4 or 4.5:1 but I'm not going to worry until I've actually ridden it.

Happy New Year by the way !

Chris

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

Re: Another EV bike :)

Postby ChrisBarron » Sat Jan 11, 2014 10:26 pm

The holidays are gone now, so down to some serious work. I've played about with the form factor of the individual packs I'm trying to build, and to keep the weight low down and as far back in the frame as possible I've settled on having four packs, each containing 210 cells. Each pack is to be split into ten submodules of 21 cells each. Each cell used has a minimum capacity of 1500mAh (measured) and therefore each pack will have a minimum capacity of 30Ah (at 1C) and 37V.

Four packs in parallel produce 120Ah capacity (minimum) at 37V, easily reconfigurable to 74V 60Ah, or 148V at 30Ah

Concerned about the ability of the cells to deliver more than 1C discharge rate and still last well, I hunted about and came across some Headway 38120SE 10Ah cells at £7.50 each. They're lightly used and the couple of samples I've requested hold up well under testing, so I'm going to buy at least twelve, to build a buddy pack capable of dropping 100A (according to the Headway datasheet). I think at this price I might buy 48 cells and do away with the supercapacitor for now in favour of their ability to deliver much more useful capacity than the supercap for about the same weight and volume.

Here's a few pics (the cells in the pics are duds and were just used for test assembling). Each pack weighs 9.5kg, a total of just under 40kg, which is still at least 30kg less than an engine + exhaust + full tank of fuel.

Next job is to clean up the ends of the cells and begin welding. I think my welder needs some more mods but hopefully I'll have something capable of being load tested quite soon.
Attachments
1-pack.JPG
1-pack.JPG (182.49 KiB) Viewed 5113 times
openpack.JPG
openpack.JPG (207.79 KiB) Viewed 5113 times
Batwiring.JPG
Batwiring.JPG (250.28 KiB) Viewed 5113 times

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

Re: Another EV bike :)

Postby ChrisBarron » Sun Jan 12, 2014 10:42 am

Cell monitoring time !

I've only glossed over this issue so far, but before I build up the packs and weld the tabbing strips across the ends I realise that I should consider building the cell monitoring system into the pack itself.

I'm proposing to embed a cell monitoring chip within each block of 21 cells. The chip monitors voltage and temperature. The data is transmitted serially, each block is isolated from it's neighbour via an optoisolator. The chip is left permanently connected to each pack.

I've done some work in this area already. A few years ago I was on an EV web forum where Jack Rickard was calling out battery monitoring + balancing systems for being killers of battery packs. While I didn't doubt there were some times when a BMS was responisble for some battery failures, it also seemed to me that it was usually either poor design, poor operation or poor installation which was present too.

I set out to make a battery monitoring system with no balancing function which could be left attached permanently to a battery pack, similar in the way that it is done on many laptop computer packs.

The system I started, but never finished, was tested by attaching the cell monitoring chip to a single 18650 cell. At the start of the test the cell voltage (measured by voltmeter and also by the internal measurement) was 3.372V. 100 hours later the cell still measured 3.372V. During the test period I requested many parameter reads from the cell monitoring chip and it responded with the voltage and temperature of the silicon die each time.

So it is this system which I intend to install in my 37V packs, and leave connected permanently. The head control unit will be able to show me each submodule's voltage and core temperature. Alarms can be implemented easily, low voltage, high voltage and high temperature.


The schematic is here
Attachments
slave_schem_NO_reset.JPG
slave_schem_NO_reset.JPG (68.95 KiB) Viewed 5111 times

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

Re: Another EV bike :)

Postby Grumpy-b » Sun Jan 12, 2014 11:43 am

Battery monitoring systems dont kill batteries, but battery management systems that do active top bleeding do. I see the results of faulty BMS bleed systems on a virtually weekly basis, I have one car at the moment that has a monitoring and active bleed system, its been in a frontal accident, not too bad, but the pack has been virtually completely flattened. Why well one cell was still 3.3v and its sensor lead had broken in the accident. Result it read 0v so the BMS has tried desperately to take the whole pack down to 0v Im sure a few cells will struggle to be good after this, a number having swolen probably as a result of being over discharged.
By preference, I will bottom balance the pack, and then charge up the whole pack monitoring the cells on the way up. If the whole pack is good to a certain voltage beyond which they start to diverge, then that should be the voltage that the pack gets charged to. If you then go onto top balance then the poor cell which goes high early will get bled down, and will therefore hold less stored power, result it goes low v early and the nice BMS steps in and shuts the system down. Often cells only go high in the last few ah of charge, so shutting off early will not really give you a significant loss of stored power. But bleeding that cell down will seriously unbalance the pack.
Your system will need to balance out at the capacity of the poorest cell, and limit the rest to what it can deliver, if you dont then it will be caused to fail and stress the rest of the pack, or worse if it shorts out it will take the whole charge and discharge of the parallell section of the pack you have it in. I effectively destroyed a Valence battery which is built in four parallell layers as one cell has died and when charged took the whole current for that layer and went into thermal overload, melting the pack and causing other cells to cascade into thermal runaway, the carbon laced aluminium foil mess spread over about a 2m+ circle. Firtunately Valence melt rather than burn. I was lucky.
EVTV advocate no BMS for the Top Balance reason, rather than lack of wanting to know whats going on.

Good progress, keep at it.

Grumpy-b

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

Re: Another EV bike :)

Postby ChrisBarron » Sun Jan 12, 2014 12:48 pm

I think a lot of Jack's concerns were real, I wasn't attempting to say there was anything wrong in his attitude, but as you've pointed out, top management systems ruin cells because they're either poorly conceived, poorly installed or operated incorrectly.

If the car you are talking about had detected a 0V condition, only one line of code is required to be added as a plausibility test, to control the action of the system. In an early version of my own top management system at least 10% of code was dedicated to plausibility and safety testing. There's a video of it here....
http://www.youtube.com/watch?v=tlnbSwkpMcc

I was testing it with lead acid cells. It top balanced by resistors, or by adding charge to the lowest cells but importantly it bottom balanced using an isolated power supply to top up the lowest cells, until all cells were at the same low voltage. You can never discharge to the absolutely lowest possible voltage with this system but you get a perfect bottom balance.

All of that was 6 years ago and times have changed, not least because I'm going to lithium now. My own experience with parallel packs, of any chemistry, is that you get a more reliable system. You are much less likely to damage a weak cell, especially if you never stress it, in other words as long as you don't try to pull maximum amps, in favour of increased range at lower rates of discharge.

As for bottom balancing, it has definite benefits, but, I wonder if it absolute bottom balancing offers massive benefits over balancing at 20% SOC. It is easier and more reliable, not to mention simpler to automate balancing at figures of 10% or 20% SOC, using off the shelf voltage convertors.

I don't expect to overload my parallel cells, hence the use of a supercapacitor (possibly redundant now because of the Headways) and the Headways to meet the serious current demands, and the 18650 cells (considering their used state) to meet the range demands.

I'm going to suck it and see with regards to balancing requirements because my initial feeling I get from performing lots of tests is that a parallel pack is inherently good. In fact in a recent EVTV video Jack comments on the battery company 'ECC' and in the video the professor in charge of development of the ECC cells points out that there is probably no requirement for any balancing in parallel blocks of their LiFePO4 cells, because the load is shared. (The weakest cell is protected by the strongest)

Another type of balancing I've toyed with is a form of bottom discharge/balancing, where the highest cell is brought down to the voltage of the lowest cell using as drain an isolated power supply which charges the auxiliary 12V battery. In fact it ought to be possible to use the discharge energy to slightly charge the whole pack as the strongest cell is being discharged, which I would prefer because of the improved efficiency.....bottom discharging is terribly inefficient if you only warm up load resistors !

Chris

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

Re: Another EV bike :)

Postby ChrisBarron » Fri Jan 17, 2014 8:52 am

Welder woes (again)

When will I ever learn....this cheap Chinese welder is running out of steam, now that I've extended the probes to make a handheld welding attachment. I've used 2 guage top quality multistranded wire to connect to the 4mm brass probes.
The problem seems that in order to get enough energy at the weld point i have to turn the welder up over 55% output and then it starts blowing fuses. I tested it with a 30A fuse and it blew the garage fuses. I took it into the kitchen and used the electric cooker 30A supply, but it blew it's own fuses almost every time, and the 10A mains cable got too hot.

I really think this welder has a 110V pulse transformer inside, hence the blown fuses.

So I'm abandoning it for now, if I can be bothered to put my scope on it and check that it's being controlled properly then I might do that (and write some PIC code to fix any problem)....but in the meantime i want to start welding packs together so I'm looking at making a small capacitor discharge unit and am on the lookout for capacitors, either 1F-5F car audio types or maybe 100V high capacity versions (47,000uF)....I have a voltage supply, plenty of high current thyristors to do the switching, I just need capacitors now, so I'm stripping a lot of old PCB's and raiding parts bins, as well as checking ebay.

It's a pity because i could have started testing the first battery pack this weekend.

Such is life !

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

Re: Another EV bike :)

Postby ChrisBarron » Sat Jan 18, 2014 5:41 pm

After weighing up my options I've decided to try using the supercapacitor as my energy store for doing the battery tab welding !

I only needed some high power silicon switches and managed to get 3 new IGBT modules (1200V, 463A) for about £36. These three in parallel should be able to hold back the potential 2000Amps coming from the supercap ! (Power will pass through a coil and some resistive cable first to help keep the power down)

I'll need to write some IGBT trigger code and make an IGBT driver, but that's all part of the fun !

I've also received my first 24 Headway 38120 cells, thay all sit at 3.334V, accept a charge and don't mind dumping a lot of current if requested. Hopefully they do their job of buffering the current demand.

In an attempt to get better organised (on my bench is the motorbike, lots of batteries and loose metal tools) I've set up a seperate electrical work bench which allows me to seperate the machanics from the electrics.

Looking forward to building this welder

:)

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

Re: Another EV bike :)

Postby ChrisBarron » Sun Jan 19, 2014 5:05 pm

While cleaning up yesterday i came across a box of ex-laptop packs which I had stripped, 'pending testing' at least a year ago.

The packs had 9 cells each, made up of three 3-parallel cell packs in series (3p3s)

I split each group of 3P cells and found, as I had done with many others, that some of the cells were completely dead, yet one or two of it's parallel connected neighbours still had a full charge.

I think I have come across only 3 cells in thousands which appear to have gone short circuit and overheated (if the wrinkled plastic coating is anything to go by), which leads me to think about the necessity for a battery management system which is nothing more than cell voltage and temperature monitoring...do I even need to do more than monitor these parameters and sound relevant alarms and display relevant indicators ?

As cells die in my large parallel pack, experience says that they're only going to go open circuit or high resistance(more often than not)

For simlicity's sake then, i'm going to embed 4 temperature sensors, spaced equidistantly within each of the 4 packs, and bring a 'balancing lead' connector out to the side of each pack so a battery monitor can be built and plugged in, rather than embed a balancing system within the pack itself.

I'm hoping to get some free time this week to write the code for the welder, which I believe i can complete without having to build the welder first. There will then follow some tentative and interesting testing !

mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Tue Jan 21, 2014 5:56 pm

Hi Steve,

You certainly have been busy with all of those cells. Glad to see that you are still marching forward with it all. I wish I had the time and drive that you seem to do.

Matt

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

Re: Another EV bike :)

Postby ChrisBarron » Tue Jan 21, 2014 7:03 pm

I'll be honest and say that I did have a bit of a wobble at the weekend when I realised I needed to up the stakes with the welder, I almost contemplated selling everything and buying a Triumph Tiger, but then it seems like a waste of the time spent (and the support of others) if I don't keep going.

There will be light at the end of the tunnel....how brightly it glows will be the interesting thing to find out !

I tested the supercapacitor lastnight with the brass welding tips attached to heavy welding cable. I was going to try welding across to thin sheets and I quickly tapped one electrode against the other (in 'just testing it's working' fashion) and the flash, bang and atomised brass electrode told me it's going to be a good welder, ....and I then quickly disconnected everything !

I'm starting the welder code tonight and I've found everything I need cheap as 'new old stock' items on ebay. I bought three IGBT modules which I wouldn't mind reusing after welding in the form of a homemade motor controller....three IGBT's will provide 7.5kW continuous, 40kW peak, motor controller.

And I started playing with the Headway cells, charging a series string of 12 and found one crept up to 3.9V in the process, which I've put down to them all being a slightly different state of charge when I started. I've brought out the automatic discharger I built for the 18650 cells and am slowly discharging all Headways down to the same 2.9V, and then from there I'm going to bring them back up to 3.6V together (all being well !)


Return to “Electric Motor Bikes”

Who is online

Users browsing this forum: No registered users and 9 guests