Time to make something better
I've just managed to release the magic smoke from some or most of my
battery management modules - the little boards which sit on each cell and
make sure that it doesn't over-charge and notifies you when the cells are
getting low. Unfortunately, EV Power's basic design has a fundamental
flaw: they require two through-hole soldered connections which are very close
to the cell terminal. With the large cell interconnect blocks, this makes it
rather easy to end up with one cell's sensor wires touching the traction
battery. When another cell somewhere else also has its sensor wires touch
the traction battery, the tiny MOSFETs that do this switching end up with
a potential difference of several tens of volts with over a hundred amps
ready to gleefully emit magic smoke.
I consider it a basic flaw in EV Power's design. They could supply the modules with wires already soldered in and epoxied over. They could have supplied explicit instructions about how to wire them up which warned me of this possibility. The most recent design had an even worse flaw in my opinion - the holes which you feed the sensor wires through to provide some strain relief on the solder joint were on the wrong side. Earlier designs had it so the insulation of the wire would be the bit touching the terminals if things went wrong; the new design makes sure that you put the solder joint is right there to contact the traction battery.
In addition, the circuit board didn't go all the way across, instead using a wire and a lug (in some kind of supererogatory effort to save a fraction of a cent in circuit board cost, as far as I can see). This means that the sensor wire solder joints are literally pressed against the terminals unless you turn the board sideways. I did try to avoid this, but apparently not fervently enough, and the result seems to be numerous module boards with scorch marks and (in the next-to-most-recent design) burned-off heat-shrink.
Now I have to find another BMS, because there's no way I'm paying for any
more EV Power products. I would strongly recommend anyone considering
using them on 60AH Thundersky cells look elsewhere. I will now be ordering
a Lithiumate Lite
BMS from Elithion - the communications interconnect is top-soldered only.
EV Power's BMS probably works fine for 90AH cells and anything larger than a
61mm between-centres connection. But for me this is definitely a dud.
posted at: 23:58 | path: /personal/ebike | permanent link to this entry
Catching the EV bug
In the past year or so there's been a fair number of people who have come
along to one Canberra EV group meeting
and never come again. Based on what they were interested in and what the
meetings have consisted of, I suspect they saw that we were (at the time)
more dealing with the theoretical and policy ideas rather than practical
vehicle making - Canberra EV has a vague idea of running a group project but
no actual plan, no shed to build stuff, few tools, and most of the people
are either not building one or have already built their own. Seeing what
they perceive to be a lack of practical action on our part (myself, possibly,
included), they go away again.
(Or maybe they realise that it's a bit more difficult than just having someone invite them over to convert their old vehicle in a weekend for the price of a couple of beers and a few lead-acid batteries. But who knows?)
Recently, a young guy has started coming along who's dead keen and a tinkerer besides. He built his own electric go-kart out of an old frame, a bunch of second-hand free starter motors, a bunch of second-hand free lead-acid batteries, and an on-off switch. It fuses starter motors fairly quickly but he's worked out its something that he can do. And I, in my own way, am keen to see him not leave because we're not doing enough to help new people - and I'm also interested in building an electric go-kart, too.
He lives in Goulburn and commutes to Canberra each day, and he wants an electric vehicle to do that. I've suggested to him that he gets an old ute - something with a bit of carrying capacity for the batteries. To give him some leeway in his journeys - no good having to do a run to the post-office at lunch and finding out you can't make it home - I've suggested to calculate for 300Km and a top speed of 140Km/hr. But how do we actually convert those abstract numbers into an idea of what to actually buy?
Well, let's do a bit of research. From the Green Vehicle Guide we know that the Tesla Roadster uses 231Wh/km (watt-hours per kilometre) and the Mitsubishi i-Miev uses 132Wh/km. So let's settle on 200Wh/km as a rough guess of how much our car conversion is going to use. We need to go 300km, so that's 60Kw that we need to store in the batteries. Picking 192 amps as a reasonable maximum for our motor - the Kostov 11" motors are rated at 192A - we can then derive from W=VA that we need about 312.5Ah in the batteries.
Picking two 160AH Thunder-Sky LFP160AHA cells to supply 320AH, we need 120 cells to provide 192V at the battery pack's standard resting voltage. That would deliver 960A continuous and up to 6400A peak, making the pack able to deliver 184 electrical kilowatts continuously. The whole pack would weigh about 660kg and cost about $24,960 from EV Works - or possibly less if you bought direct from the manufacturer.
Then you've got to buy the motor, controller, wiring, and various electrical accessories to run the traction side as well as the accessory side. And the car, of course. So you're easily looking at the thick end of $30,000 to do the whole conversion. It's not a way to save money, by any stretch of the imagination. But I think I've got the EV bug pretty badly, because calculating this kind of stuff is interesting to me.
Aside: Steve Walsh has taken the time to correct my statement that going at 120km/hr would use 'a lot of' petrol. In analysing this graph from this page on fuel economy in automobiles, we determined that for most of the cars on that graph there was about a 10% drop in fuel economy at 120km/hr compared with going 110km/hr. Someone going 130km/hr would be losing about 22% or so. The average loss between 55mph (~88km/hr) and 75mph (~120km/hr) is around 25% (taken from the study that the graph gets its data from).
Our car does about 15km/l in a 300km journey from Canberra to Sydney - with
fuel at about $1.40/l, it costs about $28.00 for that journey. An extra 10%
on that is about $2.80 - 25% would be about $7 extra. So not, perhaps, the
'lot more' that I'd speculated, but still needless. Instead of 2h43m to do
300km, it's about 2h30m - so they've saved 13 minutes for about $2.80. If
that gives them a smug feeling of pleasure at being faster than those other
mundane people that just do the speed limit, then I suppose it's cheap
entertainment - unless they pick up a speeding ticket, where it gets a lot
more expensive.
posted at: 22:03 | path: /personal/ebike | permanent link to this entry
Shiny Stuff!
I got my battery frame panels at the end of the weekend, and they look really
cool:
To get these I had to:
And how much is that? Well, according to NCOP 14, the frame has to hold the batteries against 20 Gs of force from the front, 15 Gs from the side, and 10 Gs from rear, top and bottom. With 83 Kgs, this means I have to support about 1245 Kgs from the side. In other words, I have to imagine the bike hanging on its side and 1.2 tonnes hanging directly from the central battery frame panel.
And, you know, I'm pretty confident of that. Most of that weight is going to
be directly transferred to the frame, which is already designed to take that
carrying the combustion engine anyway. The panels feel strong enough to hold
that load and transfer it to the bike frame easily. The edges, from the water
jet, feel a bit rough but the corners are sharp and there's no tearing or
wavering. Now to actually get enough time to start putting bits of it in the
bike! (I need to find a tame person with a decent metal
brake
to do some of these bends, though...)
posted at: 15:54 | path: /personal/ebike | permanent link to this entry
TTXGP Round 1 - Wakefield Park
On Saturday afternoon I rode up to Wakefield
Park for the first round of the TTXGP in Australia - the electric motorbike
racing series. I joined Tony, who is
also building an electric motorbike and who had ridden up the day before.
(Aside: riding the GS-500 long distance isn't really comfortable, and what is it
with all these people that do 120Km/hr? Here's a hint, going that much faster
will get you a fine and waste a lot of petrol but won't get you there any
appreciable amount faster). We were staying at the on-site cabins, a cheap
accomodation for race crews, which was simple, clean and pretty decent. The
Formule One is not as nice, and a bit more expensive. But anyway.
I got to meet the team from Catavolt, who've been putting together a race bike and had set the record (for a while) for land speed on an electric motorbike. They're running a forced-air cooled version of the Enertrac hub motor I'm using, and are looking at the dual coil version. Team Ripperton lead by Daniel (who finally got sick of all the usual hassles of petrol engines and decided to go electric) was also there, as was Anthony, the guy (I think) who's making the electric drag car up in Sydney. Going out to dinner with them was an experience - this is car talk as you'd hear in any Goulburn pub, but fully technical and all about electricity and construction. Then back to the cabin to talk more technical stuff before bed.
Next day after a cobbled-together breakfast I walked down to where the two groups had set up. There was a lot of checking chargers, checking voltages, checking duct-tape (called 'race tape' to make it sound more authentic) and general talk. The two teams knew eachother fairly well and they obviously got on together. The biggest problem was trying to get a good supply of power - the various circuit breakers on power boards and in the shed kept on tripping as the chargers sucked down the power, competing with the tyre warmers and compressors and so forth. Finally (oh, the irony) they set up a petrol-driven generator to get clean, reliable power.
The really interesting thing was that each group had many things in common but many differences. Ripperton's bike is a Mars brushless DC motor with an A123 60AH battery pack; Catavolt uses the Enertrac motor with a Headway 38120S pack. Voltron over in Perth runs two Agni brushed DC motors with a prefabbed pouch cell battery. I suspect as we get more entries - and I'm told there will (hopefully) be six different teams competing in the next race event - we'll just see more combinations of motors, battery technologies and controllers. That's the fun of it!
The actual racing was, let's be honest, not particularly exciting. Two bikes on a 2.2Km circuit was never really going to be dramatic, and with both teams running fairly conservative throttle limits, the acceleration and top speed were sedate compared to the regular petrol bikes - around 110Km/hr top speed and 1:22 lap times for the Ripperton bike. There were a few worrying things - the Enertrac motor heating up enough to smoke the anti-corrosion compound in the motor, the controllers switching off for a variety of reasons - that made all of us that were really keen to see the bikes do well cringe momentarily. Yet for the most part it seems to have gone quite well - both crews had literally finalised their bikes in the last week before the race and were trying new things, and with no major component failures or crashes they'll be improving and perfecting for next time.
And I have to say that if that's the future of racing, then bring it
on! A race where I can speak at a normal volume while competitors fly by
six feet away? Awesome! The Catavolt made the barest whisper of tyre and
slip-stream noise as it went by - the Ripperton bike with its chain drive was
only slightly noisier. We've come to see howling exhausts as a manifestation of
power, but really that's just lots of wasted energy. Light the tyres up in
burn-outs, pull wheelies on the straight, and do faster times than other people
- that's the real show of power. It's going to be awesome!
posted at: 07:40 | path: /personal/ebike | permanent link to this entry
Constantly learning
After I build my tenth Electric Vehicle, I think I'll just start to have
a basic knowledge of how to do so.
After all, just today I learnt about the Tritium Wavesculptor, a high-end controller for brushless three-phase DC motors (which aren't really DC motors, they're actually AC, it's just that the simpler controllers just output on-off square-like waves to energise each phase in turn, but that's another story). And they make a battery management system too - one that is actually formed (by chance) for the specific type of cell I have.
I learnt this not in a search for controllers - apart from already having one, I had discovered the EVnetics Soliton One (I refuse to link to EVnetics' site since it's Flash-only, but here's Rebirth Auto selling one for a mere $2,995 USD). Since that was far more controller than I needed - even the Soliton Jr doesn't really work under 240VDC, which is twice my standard pack voltage - I hadn't really looked around for more. I actually noticed a reference to a "Tritium Wavesculptor" in a post on the AEVA forums about converting (of all things) a VW Type 3.
Tritium are an Australian company that's been around and creating EV controllers for, oh, nearly a decade! How is it that I haven't heard of them?
Clearly, this is a field that needs a really good directory of motors, controllers and batteries. And, just as clearly, the market is fragmented - dozens of forums (with names from the normal to the incomprehensible and unguessable), dozens of suppliers, minimal coherence of specification (e.g. some cells are measured in grams per watt hour, some in litres per amp hour, etc.) and dozens, even, of supplier lists and directories on forums, enthusiast and club sites, and elsewhere. I feel the need to create a motor comparison and controller comparison site, if I didn't think I was already struggling for time just to do the things I want to do that are relevant to me right now.
Sigh.
posted at: 17:12 | path: /personal/ebike | permanent link to this entry
Great minds think alike
The next major task for the electric motorbike is to build a frame that
can store the battery. They need to be held in place with a lot of
strength - the battery frame and its contents need to be able to withstand
a 20G impact from the front, for example, and it needs to be able to fit
the 38 cells I have as low as possible to make the bike handle well. I'd
made up some cardboard mock-up cells and had worked out a way to get them
into the frame - just.
Then I'd realised that I'd forgotten the space on top of the cells - there needs to be about a three centimetre gap above the top of the cell for the interconnects and cell management module. And then I needed to include the thickness of the actual frame. And I realised that one of the frames would be sticking right where my toes were supposed to be. This needed a rethink.
I've found that I get a lot better results and ideas when I brainstorm with friends, so I invited my two brothers-in-law to come over and play with some cardboard boxes. I showed them what we had to work with and, between drinks, we started rearranging things. We also talked about the actual requirements, and we started discarding the ideas which had been limiting me - like whether we used the side fairings I'd bought for it.
It's often said that progress doesn't happen with the word 'Eureka' as often as it does with the phrase 'that's interesting...'. And sure enough, Trev came up with the break-through idea by just rearranging things and observing, testing and improving. Then I made a few suggestions, then Rob made a few more, then we talked about how to build it, and before an hour was up we had a pretty much complete idea of how to construct the whole thing. And it all fits lower than the original fuel tank!
The key insight, as it later appeared, was that making room for the cell interconnections inside the frame chews up lots of space. Turning the cells on their side used horizontal space, which is less constrained. By putting the interconnects on the outside, I can see every cell's monitoring state and check the connections easily. The only variation is the bottom row, which faces forward because that way I can fit six batteries across the bottom row and still have room for my toes.
This photo illustrates the whole thing. The bottom layer is six cells across (facing forwards), and each other layer is made of eight batteries facing side-out. (The smaller squares are one cell, then I made three- and four-wide groups for ease of construction and reduction in cardboard). You can see on the right the rear upper engine mount which sticks into the second layer of cells - when this is removed that row can move an inch back; this in turn allows the front group to move down, which then in turn allows the top group to move forward. There is plenty of room there even with plates between each row.
Then the whole outside is covered in a solid plate of something - we're currently debating whether steel, aluminium or acrylic is better - that provides water and abrasion resistance. Steel plate with laser cut holes with an acrylic plate behind it is my current favourite - the holes provide viewports through to see the battery management system, and also mean that the bike has pinpoints of green light glowing from it at night. Inside the plate there are rubber offsets which both keep the plate away from the interconnects and press the cells into their niches. The outside plates attach at hinge points at the bottom and bolts go through from the top to a central plate which holds the whole thing together.
If the outer plate isn't seen to be enough to hold the cells in place, I have idea to fix that as well: put a steel strap around each group of cells and, on the ends, attach a flat plate to which a bolt has been attached. This then bolts down to a rod attached to the plate in the middle. The steel strap will sit inside the channel on the side of the batteries, holding them just as well as the frame I made up before.
The method of construction is still a little up in the air. Rob likes the idea of just bending acrylic into place around wooden moulds. Trev likes aluminium for lightness and for the horizontal plates to support the cells I think that's good. The central vertical plate I think I would make from steel and I would definitely prefer the outer plate to be steel for abrasion and impact resistance. All these can be cut from plate using water jet cutting - in fact, this design lends itself much more to water jet cutting than other designs I've considered. That makes it cheaper, as well as much more awesome.
Hopefully I'll have some plans together this week and I can start taking
them around to fabrication places to see what they'd charge to make. The
other good thing about this plan is that it's probably even possible for
me to make it so that I can simply bolt the bits together myself, rather
than having to pay someone to put it together. It feels like I've got
the whole project back on track!
posted at: 21:31 | path: /personal/ebike | permanent link to this entry
I should be more electrified?
Last weekend I got the electric hub motor running. You'd think this would
be the cause for great celebrations, fireworks and national days of
rejoicing, but strangely it leaves me feeling like it's a fairly hollow
victory.
I'd spent the week assembling bits and pieces, soldering and crimping, fixing things and getting things running. I managed, somehow, to avoid frying the DC-DC converter supplying the 12V power for the controller and contactor after connecting its 12V leads to the 130V battery. I checked everything with a multimeter. I ran through every possible combination of wires and, on the very last possible sensible combination got the motor turning over without sounding like it was trying to chew up a cheese grater. I uploaded a video at the time. It was still sounding a bit odd and the controlle was occasionally cutting out when I backed off the throttle, so I got a friend with an oscilloscope to come over and have a look at the signal. I also layed out the controller flat on the table, which meant I could get the power wires straight rather than crossing over eachother. We fired up the motor on Friday and had it running for five minutes or so. The waveform looked OK, but since neither of us really knew what a bad or good waveform looked like it was somewhat moot.
At this point we noticed the cheap plastic caps that came with the lugs that I'd bought for the power leads were melting. Then the solder in the power wires started melting (why they put solder into the wires is beyond me). I went and got my thermometer cable for the multimeter and determined that the power wires were sitting at about 70°C! And that was only running for five minutes! This raises all sorts of questions.
Anyway, I decided to get a better video than the previous one. Armed with the knowledge that my phone had a high-definition video camera, I tried taking videos with that. Kate suggested putting light on the motor so you could see it moving rather than just a dark blob. I tried my other video camera, a ContourHD unit that I bought for attaching to the front of the bike, on helmets, and so forth - but the field of view is too wide and the sound is pitiful. And in a burst of idiocy I deleted the good video and kept the eight second out-take. (As strange as it may seem, these weren't excuses to start the motor up again.)
So now that I've got the video uploading away I thought I'd write this update. I should feel happier - a major milestone has been passed, and theory has turned into practice. But the major work now is to try and get a battery frame welded up on the bike; I want to use a professional metal fabricator for that. That has to go past the engineer to get his approval. Then I have to get all the batteries, controller, contactor and other parts actually in it, and attach all the cables. Then I have to get the 12V system working. Then I might be ready to actually run it down the street.
So it still feels a long way off. And I'd like to get the bike at least running in some fashion for the first practice event of the TTXGP at Wakefield Park near Goulburn at the end of April. And there's that cable heating problem to watch, or better yet fix. And how does one register an electric motorbike anyway? It still feels like a long way to go.
Here's the 'better' video:
posted at: 02:43 | path: /personal/ebike | permanent link to this entry
A crimp in my plans
Well, yesterday I hooked all of the cells up and installed and wired up all
the BMS modules. That's 76 wires about three centimetres long, 76 crimp
connectors and 76 solder joints - two per cell module. I used crimp
connectors because I had a bunch of them from hooking up the controller
cables - Jaycar has 100 packs of connectors for about double what a pack of
12 cost - and so that I could disconnect and rearrange every module if
necessary (i.e. I wouldn't have a mess of cables when I disconnect it).
After a while I got a technique up. I borrowed a friend's crimping tool (I tried pliers and they either didn't get enough force or cut straight through the connector), but because it's fairly cheap it tends to bend out of line when you squeeze it as the normal hand motion applies sideways force (due to the way your fingers curl). Solution: put the bottom half in the vice. This way I could exert all my force straight on and the tool itself wouldn't twist in my hand. This reduced the number of bad crimps down significantly. I also got into a bit of a production line - cut a number of segments of wire, trim all the insulation with a stanley knife, then crimp all of the segments and arrange them. This meant less tool swapping and allowed me to get a good technique on each operation.
I worried a bit as I was soldering everything up, but not because I thought that I would accidentally adger the circuit on the BMS modules. They're copy-protected in a crude but effective way - a blob of translucent epoxy on the centre of each module. You can see the LEDs shining through but nothing of the circuit or components. It wouldn't stop a dedicated counterfeiter for a second, of course, but it's enough to stop me making my own. I don't really care about this - if I need one I'll buy one, and if the company that makes them goes out of business I'll just cut the epoxy off one and figure it out on my own - or just buy a new circuit. I like the ones Elithion make - expensive compared to an analog BMS but you get so much more neat information!
No, I worried because I was hovering over a bunch of exposed metal connectors that could easily kill me if I was stupid enough to make a good circuit between two ends, or even parts, of the battery. It's only 130V, but if it gets a low resistance connection it can do 180A for as long as you please - about a quarter of a second will do it to stop your heart permanently. Fun, eh? The problem is in getting too used to handling them, too blazé about the accidental touch, until I do something stupid.
Anyway. There was a fraught moment getting the charger working. The charger takes a feed from the battery that goes through the relay in the BMS, it recommended hooking it up on the positive side (why?). I then proceeded to attach the other lead of the charger to the positive terminal, and wondered why it wasn't charging. Moving the connection to the negative terminal started it up just fine.
The only minor annoyance at the moment seems to be that the BMS turns off the charger as soon as the battery reaches 3.65v per cell. This means that about seven or eight of the modules show their red "I'm diverting current around this cell to stop it overcharging" before the BMS turns charging current off. I figure I'm going to have to this cycle about half a dozen times to get all the cells up to roughly equal charge - I can see cell voltages of between 3.34v to 3.44v at the moment. It only takes about two to three minutes for it to go from starting the charge to stopping it, though, so I'll do that a couple of times this afternoon and monitor the cell voltages and see what happens. The readout on the charger isn't getting beyond around 137V anyway, so I don't think there's any damage being done.
Now to start getting the controller inputs wired up and see if I can starts the motor up!
P.S. Here
are the pictures.
posted at: 21:18 | path: /personal/ebike | permanent link to this entry
Nothing to show off
Due to an interesting but otiose set of circumstances, the
Canberra EV group got permission
to have a stall at SummerNats -
the yearly "more than a car show" festival at the start of January in
Canberra. At first glance this appears a bit like inviting the Skeptic
Society to a Church Fete; but there are many reasons that people have for
converting vehicles to electric power, and fuel economy and helping the
environment are but a few.
Take, for instance, the White Zombie, a 1972 Datsun 1200 that has been converted into an electric drag race car. This thing does 11 second quarter miles - well into supercar territory (quite a bit faster than a Holden HSV GTS). And because all of its torque is there from zero RPM, it takes off like a bullet - you can see in videos, it just doesn't accelerate much after the first six seconds, and that's because the controller is programmed to not ramp up the amps too fast. And that's not the fastest - here's a drag car doing a 7.56 quarter mile. Let's see any of the burn-out champions get anywhere near that.
Likewise, the TTXGP is bringing electric racing to motorbikes. In the year that I've been following this there have been at least half a dozen companies that are now putting out electric bikes both for road, sport and dirt. The dirt bikes are particularly attractive to run on electric motors as they get a lot of torque at low revs, something that dirt bikes are specially customised to do with petrol engines. The process of running these races and having electric drag cars is changing the minds of the racing and horsepower community.
So instead of talking about noise and exhaust emissions, we talked about torque curves and quarter miles. I also talked about customisation - one of the big things at SummerNats is that the people bringing along their cars are customising them and making something that is distinctly their own. I saw a customised Suzuki Mighty Boy (which was rad) - so even if it's not a fully blown 351 Chevy with triple weber carbies and a supercharger, someone can still get into customising it and showing it off. I think the scope for that kind of customisation is one reason for doing electric conversions - you can choose your motor, drive train, batteries, controllers, everything - and lay it out with the same care and attention that the high-end car audio system competitors do.
And a friend pointed out that there's another attraction. Every car made after about 1986 has to obey increasingly stringent emissions rules. This severely limits the amount of customisation you can do to a 2008 Nissan GTX or Holden HSV. That's why a lot of the cars at SummerNats are older: the scope is wider for modifications. But you could take a current muscle car with a dead engine and convert it to electric running, and you wouldn't have any emissions specs to look at. Maybe that's not a huge selling point, but it's an interesting thing to note.
I'm trying to avoid being judgmental about the people and cars at SummerNats. It's loud, and it's just not really the kind of place that I would normally hang out. When the burn-out competition started I could smell it before I heard it. But all in all the crowd was friendly; no-one came and trolled us, the people we talked to were all pretty interested in the possibilities one way or another, and they could see that we were passionate about our bikes and cars in our own way. The fact that we had a stall there at all is the big revolution. And who knows - maybe next year we'll have the electric go-kart ready to spin the wheels, or get the electric drag car that's being designed in Sydney down to show how it's done.
I haven't uploaded my photos yet but Tony
has
a set online. You can see me standing around in front of my bike
in a few of them. The most interesting one to me is the
second
to last one comparing the different battery technologies. On the left
you have a gel-cell lead-acid battery delivering 80 amp-hours weighing 32
kilograms - annoyingly heavy to lift. Next to it you have four of my cells,
making a 12 volt, 60 amp-hour battery that weighs just over a quarter of
that, at 8.8 kilos. The next yellow battery is another lead acid battery,
capable of delivering as much power as my cells are, and only weighing a
fraction more at 13.2 kilos - but it only has a quarter of the amp-hour
capacity, at 15Ah. That's why we're going with Lithium cells.
posted at: 22:37 | path: /personal/ebike | permanent link to this entry
E-mobiliser
I just thought of an idea for the E-bike. Have an RFID tag sensor in the
bike and one or more RFID tags with things like the keys, my wallet, etc.
The bike will still turn on with the key, but if the correct RFID tag isn't
sensed nearby it will limit its top speed, acceleration, etc. So if
something goes wrong with the sensor it's still driveable, but only to
get to repairs. But if it's stolen it's near useless even if hotwired.
I've also worked out how to set up the switches on the bike. For cars, the key switch has four positions - lock, accessories, on and (momentary) start. A bike has three - lock, off and on; but a bike also has a separate motor kill switch (usually near the right thumb) and a (momentary) starter switch as separate things. A bike also has a footpeg switch - if you put the footpeg down and the bike is not in neutral, the motor will switch off (because taking off with the footpeg down is a sure way to have an accident). For combustion-engine vehicles, there is one electrical system - the 12v system; for EVs there is a separate (high-)voltage system to run the motor. (You're crazy if you try to run an EV on twelve volts, because the amperage the wires will have to carry to get the same amount of power will mean huge cables or things bursting into flame.)
So I have the key switch turn the twelve volt system on and off. This allows the headlight, signals etc. to work, and also provides 'system' power to the motor controller. The 'motor kill' switch then engages the contactor, a whocking great relay capable, in my case, of carrying 400 amps. This connects the battery to the controller and everything is ready for take-off. The 'ignition' switch is useless, but I'm tempted to repurpose it to cause a roll of thunder to be emitted from the onboard speaker, or flash the LED strip lighting menacingly, or activate the tesla coil, or shoot lasers or something. Or something useful, like put the motor into 'reverse' mode so that I can have power-assisted reversing.
There are a couple of criteria here. I want to make sure that the systems remain as 'standard' to a regular bike as possible, so I can lend it to a friend without a half-hour tutorial and so that I can hop from it to a regular bike without nuking the engine or something. This means the clutch lever might be dropped but I won't repurpose it (whereas on a scooter it's the rear brake and, when one goes to change gears, can result in amusing and health-endangering stopping). I also need to make sure that the lights and emergency indicators can remain functional even if the main 'motive power' battery is dead (or at least completely unusable - e.g. fuse blown) - this is for the Australian National Code of Practice for building electric vehicles.
Unfortunately for me, I bought a DC-DC converter that outputs 12V in the mistaken belief that I could simply wire that up to the power battery and have power to drive the lights even if it was too low to drive the bike. It turns out that I have to have lighting as a separate circuit so that even if something goes horribly wrong - one cell dies, a cell interconnect fuses, a bit snaps off somewhere, or even just the main fuse goes - I can still be illuminated at night. So I do need a (small) separate 12V battery; and because 12V lead-acid (and similar) batteries charge at 13.4V, the 12V that the DC-DC converter outputs is not enough.
Anyone want to buy a barely used 150W DC-DC converter with an input from 84
to 120 volts?
posted at: 18:03 | path: /personal/ebike | permanent link to this entry
Powered by cardboard
I spent a productive weekend of planning and preparation on the electric
motorbike yesterday. This was different to the week before, where a
combination of bad weather and apathy caused me to stay indoors and flop
around for the time I had planned to be working on the bike. This time
I was better prepared, and as an added incentive I made sure I got the
friend of mine who's been helping me with it enthused so I knew he was
coming around and couldn't prevaricate.
We got the fairings worked out. We discovered that the reason the front and left-hand side fairings weren't fitting correctly was that the headlight mount had been bent in the crash and the headlights were only fitting by virtue of the fact that one of the mounts had broken. We discovered that the measurements on the EV Works website say that the LFP60AHA cells are 203mm tall but that their specification sheet that's linked to on the same page says they're 212mm to the shoulder and 215mm to the top of the terminal post. Rob made plans for the cell mounting cages while I worked on trying unsuccessfully to straighten the headlight mount. We discovered that the controller will fit near perfectly under the seat - with a weatherproof housing for the electrics it will be perfect. We learned that buying a bike that's been in an accident might be cheap but it comes with downsides.
That afternoon I constructed the rest of the cardboard mock-ups of the batteries, and determined that they would indeed fit in the frame - just. Rob's preferred method of construction is to buy the metal, cut it to size, get a welder and start attaching bits of metal to the frame where they need to go. I need a bit more of an idea whether that's going to work, so that I don't find myself grinding it all off because I should have fitted the batteries some different way. We're going for four groups of seven cells in frames, set up so that the cells are fixed together with straps, joined in series, and then the whole group is slid into the frame together, with extra cables between the groups. Then we have two groups of five, or some other combination that's going to fit in the space available, joined together the same way.
The complicated thing is dealing with the tops of the batteries. They each have a BMS monitor module across the terminals, and a cell interconnect (basically a thick piece of braided copper mesh) between the batteries. By my calculations the sides of this interconnect sit just over 10mm away from the edge of the battery, so having a 10mm-wide right-angled piece of metal to clamp onto the top of the cells to hold them down gives too many opportunities to short something out. Yet how do we hold the batteries down, to make sure they don't vibrate in place and wear the interconnects and/or start moving more enthusiastically around the battery frame? Rob's idea was to have foam rubber on the sides of the battery cage and to design it so that tightening the bolts on the end caps clamps the cells in place, but I'm not sure that's going to really stop the cells lifting up if I hit a speed-bump too quickly. I need something non-conductive to clamp the cells down.
So I'm going to do up the plans in something (SketchUp possibly) to take
to the engineer. I've taken the headlight mount off, removed the wiring
loom, and readied it for a bit of blowtorching. I've taken some photos,
but my Gallery setup at home has eaten some really rather toxic mushrooms
and I'm currently trying to triage it. If Gallery2 would actually work,
rather than sitting sullenly and ignore my uploads, that'd be great too.
posted at: 08:06 | path: /personal/ebike | permanent link to this entry
If only I'd set this up earlier
One of the problems with building an electric vehicle is making the battery
pack. There are a number of interdependent variables - weight, amp-hour
capacity, volume, maximum voltage, and cost - and many trade-offs to be made.
Even if you limit yourself to a particular voltage (because you have a
particular motor) and total pack weight (because you have a maximum 'kerb
weight' for your vehicle) there's still a lot of options. And you want to
know a fair bit about each choice - cost, number of cells (which determines
the number of joints you'll have to make), maximum amperage deliverable,
and so on.
At about the time that I heard about 'pouch' cells - lithium cells that have a tough but flexible plastic wrapper instead of a hard outer casing, often used in mobile phones and portable electronic devices - I started making a spreadsheet of these options. I threw together a few formulas to determine some of the information about my specific pack but then I shared the (Google) spreadsheet with a friend and he put in his own calculations. Then I realised some of the cells I'd been looking at were Lithium Polymer (normal operation voltage 3.7V) rather than Lithium Iron Phosphate (3.2V) and so some of my packs could have fewer cells. And of course, it hit me - I needed a database.
So I hacked one together in Django, and transferred all my information into the database (by hand). Then I wrote the code to put together a pack of batteries based on your requirements. I released it to the denizens of the Canberra EV group with little fanfare. I added a few extra bits and pieces, like simple displays of the cells by manufacturer and online store. And now I present to you this finely crafted link to release it, still on my testing server at home, to the rest of the world.
Feedback, as always, is welcomed.
As an aside, it is a difficult thing to get some of this information. Many manufacturers are Chinese, with badly-translated, hastily thrown together and hard-to-use websites. Many I'm not sure there's any point in listing since they seem only to cater for manufacturers buying 1000 or more cells or wanting custom engineering. Some, like Saft, seem to have very little information and what little is there looks awesome, but they sell to the defence industries and I've never got a reply from my email to them. Some, like one Australian manufacturer I won't name here, are very hard to deal with by email and seem to think that websites are brochures, not sales desks. Many of the Chinese manufacturers, especially of cylindrical cells, work through Alibaba and various other direct-ship quote-based pseudo-services. A lot of the sellers of cylindrical cells seem to be selling the same thing ('Headway' cells), which triggers my scam detectors. For me, it's just not worth trying to trawl through all those sites trying to find useful information.
I am willing to hear from anyone that can supply more information for me,
especially online stores, but I prefer to get full information (especially
for cells) with verifiable information. There's a lot of "we're totally
coming out with a radical new cell that is ultra-cool and is far more
powerful than anyone else's, but it's all hush-hush because we don't want
our competitors to steal our technology" claims out there, and I don't want
to list speculative numbers. Give me a URL to a full data sheet.
posted at: 22:52 | path: /personal/ebike | permanent link to this entry
Putting coulombs on the charge card
(I have to nod my head to my good friend Dunx for the title, though
an explanation would be otiose.)
Finally I've put the order in for the batteries for the electric motorbike.
This is not a small decision when the cost of the batteries is over $3500. It's more so when there's that feeling that you're going to regret buying something that you're still not quite convinced will fit in the space available. Add to this the feeling that you wanted something larger and more capable but that would be simply impossible to fit, or almost an order of magnitude more expensive. And there's the looming question of how, exactly, is the whole thing going to perform. That's a lot of buyer choice anxiety right there.
We can reduce the choices down somewhat by starting from the fixed things. The engine, muffler, exhaust, air intakes and various peripherals that I removed from the bike and am not going to put back weigh around 84 kilos; that's how much weight, roughly, I can put back in the bike in battery pack. I'm adding the extra weight of the motor over the rear wheel (16kg), the motor controller, DC-DC converter and some other stuff, so it's probably going to be slightly heavier at 'dry weight'. This is something that the engineer can sign off on; we haven't made the whole thing unregisterable yet.
Likewise, to run the motor at 100km/hr requires 96 volts; at 3.2 volts per cell that's 30 cells, but I want to be able to comfortably exceed that for emergencies. A rather unfriendly email from a battery supply company taught me that the next size up of charger is 38 cells - and the cells really don't like being charged much more than their peak voltage. So 38 cells it is then. (If it turns out that I can't fit 38 in the bike, either due to space or weight, I can more definitely fit 30 anyway, and I'll just have to accept that its top speed isn't quite what I'd hoped.)
38 cells fitting into 84 kg makes for a weight per cell of around 2.21kg. By a happy chance, that is almost exactly the weight of the ThunderSky 60Ah cells. Unhappily for me I was hoping to use 90Ah cells as they have a better energy density. It was, I think, this unhappiness that then caused some of the delays.
It started when showing off my bike at the Canberra Electric Vehicle Festival 2010. A friend and I were talking about batteries and he mentioned 'pouch' cells as being his preferred battery component. These are like flattish bags with two metal tabs sticking out of them; Their chief advantage is much better amp-hour per kilogram and amp-hour per cubic centimeter. You can't squash them and you have to build a rigid pack around them, but that's OK since you have to do that for the vehicle anyway.
And some of them can deliver phenomenal quantities of current - the 70Ah cells I started looking at could deliver 350A continuous and 560A peak - enough to give 50mm² cabling a serious headache. Serious electric sports cars use these packs for their mind-cudgelling power delivery. Then we got a quote for them and stopped salivating: at over $13,000 for an equivalent pack to the ThunderSkys mentioned above this was seriously out of my league - at least for this bike.
As is often the way with me I then spent a quantity of time researching different batteries, finding various options and constructing elaborate spreadsheets to compare them. It compares rectangular (including pouch type) and cylindrical, calculating $/Ah, g/Ah and cc/Ah for comparison. The ThunderSkys come in at a very competitive $1.6/Ah but a modest ~37g/Ah and ~23cc/Ah; the best cells get down to ~22g/Ah and 10cc/Ah but an excitingly expensive ~$4.6/Ah. Then again you have to wade through who sells which cells - and half of the manufacturers won't deal with you unless you're ordering at least 1000 cells in one go.
In the end I was back where I started - 60Ah ThunderSkys, which I ordered today from EVWorks. $90 odd for delivery is cheap compared to the cost of the things being delivered, and especially to the $1000 or so charged by a USAdian company to send the same cells here. And with EVWorks I could buy pretty much all the remaining components - contactor (to turn the thing on from the key switch), cables, battery management system, charger, cell interconnects, cable lugs (yes, I get to use lugnuts), and conduit. I'm sure there's something I've forgotten but I can't think of what.
Anyway, the main task now is to read up the National Code Of Practice NCOP14 Guidelines for Electric Drive - its basics are covered on EVWorks's website - and work out what I have to do to make sure it will pass inspection. And also not fry myself or the batteries.
Oh, and the fairings I ordered (from the UK) have arrived too - I may
try and get it looking nicer and take some photos. I have to have something
better looking than
this...
posted at: 23:00 | path: /personal/ebike | permanent link to this entry
Hard electrons
On Sunday I nearly got the electric motorbike working.
The problem is that it's sort of hard to tell how close I got. Everything was plugged in and in place, but nothing actually turned on, went beep or spun round. It's that sort of 'back to the drawing board' feel that I imagine makes scientific research so depressing - what bit of the large supply of things isn't working, and how do I deduce which one it is?
I'd spent the week preparing for it. I got the motor fitted with a tyre (from the excellent TJ's Tyres in Braddon), where it was opined that the fact that the spokes were bent where they attached to the wheel was a cause for concern. I got the awesome Laurie who runs Suspension Smith in Fyshwick to make me up some spacers and find an axle that would make sure that the motor fit in the middle of the rear suspension arms. I borrowed eight large UPS batteries in order to supply the 96 volts that is my aim for the battery pack's minimum potential. I spent the rest of Saturday going through my wiring and control box trying to get all the things that were supposed to connect together to do so correctly.
That bit is the real challenge. You see, there are five large and twenty-eight small connections from the motor controller; the large ones are the battery terminals in and the three motor coils out, the smaller ones do everything from turn a light on when the controller's 'on' to detect the position of the throttle to connections like 'boost' that aren't connected to a wire on the break-out cables and aren't documented in the manual. The motor itself has ten connectors (power for the three coils, hall effect sensors for each coil, ground and five volts, and the temperature sensor to and from). Some of the controller's outputs attach to external things - LEDs, variable resistors for throttle and brake, power supply, etc. which have to be put somewhere. So it's a bit bewildering working out how to connect it all together.
So on the day Rob and I fitted the brake and torque arm, fitted the spacers and axle (which were perfect!) and ran the cable. Then I lugged one of the batteries, the controller and the huge splay of leads out and started connecting things. I'd built a little kit box, used two D-15 ('VGA') connectors for the controller's inputs, and soldered all the wires to a circuit board. It's all reasonably neat but nothing like waterproof or robust enough to run - it's only really there to give me a chance to work out how the electrics all go together before I start actually finalising where everything goes. And the familiarity with its less-than-professional construction made me tentative as to how it was going to go. Would connecting it spin the motor up to maximum RPM? Had I something round the wrong way that would have its magic smoke escape?
With Rob holding on the front brake, I gingerly connected the battery to the controller. Nothing. I connected the mock-up box to the controller. Nothing. I switched the switch on. Nothing. Hmmmm.
I remembered that the controller required separate power and that was the only jack I hadn't soldered up. I did a quick soldering job and checked the polarity, and attached a spare motorcycle battery to the mock-up box's power input.
Nothing. Double hmmmm.
And that was more or less it for the day. We had to go out to lunch, Rob had to go and play hockey, and the next big task was to try and work out why all my clever soldering and wiring had produced a dud. The important lesson was that instead of one big box that everything plugged into, which was a pain to solder and required special connectors, I should have had each little subsystem in a separate box (or a different part of the same box) with its own connector. That way, when something breaks you can narrow it down fairly easily, and you don't have so much that's interconnected and jammed together. The Kelly jumper leads bundle the leads for the same functions - throttle, brake, LEDs, etc. - together, so you can have a separate box for each.
Also, buying an extra set of connectors isn't necessary, since Kelly supply you
with a set and they're push-on pull-off 'quick' connectors so they can be taken
apart again, but it is very helpful as it means you've got a test set if you
botch something completely.
posted at: 23:06 | path: /personal/ebike | permanent link to this entry
All posts licensed under the CC-BY-NC license. Author Paul Wayper.
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