Ian Hooper's RX7 Conversion

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Post by woody » Tue, 14 Aug 2012, 20:40

PlanB wrote: I take your point about DC being way cheaper Ian but $9k for a Eurodrive/wavesculptor seems in proportion to $30k-$40k worth of car/batteries.
SEW Eurodrive + wavesculptor = 240Nm.

Impulse 9 = 70 ft/lbs = 95Nm @ 450 amps.

The Zilla 2K does 1900amps, over 4 times that.

Assuming it's a bit less efficient/effective at 4 time the current, lets say just over 3 times the torque:

2 motors x 3.16 x 95Nm = 600Nm :-)

Maybe 2 tritiums + 2 ABB 132007's = 630Nm?
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Post by Tritium_James » Tue, 14 Aug 2012, 21:41

Might not need quite that, Woody - if you look at a plot for the series wound motors, the efficiency starts dropping pretty fast once you push them - at 1900A they're probably down to under 50%... I've never seen a manufacturer's curve go out this far, so this is from extrapolating the ones I can find - I could have it wrong.

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Post by zeva » Wed, 15 Aug 2012, 00:49

I certainly sympathise about the psychological hurdle of possibly ruining an expensive car! That's how I felt when I was about to take an angle grinder to the boot of this RX7.. and I have a lot of EV builds under my belt. I can't imagine having the confidence (or ability) to do this one as my first conversion.

My rough budget was $10K on the drive system, $10K on batteries, and $5K on ancillaries. I did consider the WaveSculptor 200 option, it seems like a great controller and was my #1 choice for AC, but I ran the numbers (like woody above) and one just wouldn't be enough to reach my performance goals (of being no slower than the car was as a petrol burner). Two probably would get the job done, but then it'd creeping towards $20K for the drive system.

So I went the Z2K + 2x 9" DC option, which comes in just under $10K. The Z2K is effectively a ~600KVA controller, and whilst I'll never pull close to 600KW from my batteries, it gives wonderful flexibility with the high current rating for loads of torque down low, and the high voltage rating for plenty of speed up high - definitely no gearbox needed.

From memory, John Wayland's White Zombie sees about 800Nm combined from his two ADC 8" motors. Mike Willmon's Pinto has dual Warp 9s and gets over 1000Nm. The Impulse has about 25% less torque per amp than the Warps, but it still means I'll be in the ballpark of 750Nm from the motors.

(Torque vs current with Series DC is quite non-linear since the current is effecting both stator and rotor field strength, giving a kind of quadratic relationship, then around perhaps a thousand amps magnetic saturation comes into play and it drops back to linear at best - but as TJ says I don't think anyone's ever done a dyno plot all the way to 2000A.)
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Post by weber » Wed, 15 Aug 2012, 01:02

PlanB,

This one's for you:
Concerning all acts of initiative (and creation), there is one elementary truth the ignorance of which kills countless ideas and splendid plans: that the moment one definitely commits oneself, the providence moves too. A whole stream of events issues from the decision, raising in one's favor all manner of unforeseen incidents, meetings and material assistance, which no man could have dreamt would have come his way. I learned a deep respect for one of Goethe's couplets:

          'Whatever you can do or dream you can, begin it.
          Boldness has genius, power and magic in it!'"

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Post by PlanB » Wed, 15 Aug 2012, 15:40

Beautiful quote man. It's a funny old world. Back in the late 90s I had this romantic vision of assembling a kit built helicopter in a shed then flying it off into the sunset. What happened was I ended up buying an R22 with 2 years left on the clock from a mate. It was a better machine at half the price of the kit builts & I saved all that labour. My head always gets in the road of my heart.
Things are different now, the kids have grown up & moved away, I've got time on my hands, and good used EVs are a bit thin on the ground. I just need to kidnap Ian & lock him a shed with some good AC gear & a red pill. Have you met my mentor Neo Hooper?
Last edited by PlanB on Wed, 15 Aug 2012, 05:41, edited 1 time in total.

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Post by drgrieve » Fri, 17 Aug 2012, 03:56

Now no dyno charts unfortunately but if you haven't already you should read John Metrics dual stock warp 9 (but with new Helwig brushes as now sold with) matched with dual Zilla 2K HV controllers.

He's running 199v and 2000 amps to each motor and the thread is packed with charts from the Zilla logs.

EV race porn.

http://www.diyelectriccar.com/forums/sh ... 69476.html

PS he estimates over 80% efficiency at 2000 amp, you kinda have to give him the nod but there is no dyno figures to back that up. Also in another thread (have a look around) Major and Tes figure the saturation is around 400 amps for a warp 9.

Love your build by the way.

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Post by nazar » Mon, 22 Oct 2012, 22:54

really impressed with your conversion,
i like how your a perth ite - me being from down margaret river way.

thanks for documenting your build - at the moment i am just in the research stage. your documentation helps a lot, cheers

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Post by zeva » Mon, 29 Oct 2012, 18:14

Hi all,

I've just finished another update on the blog, in case anyone's interested to read about the latest progress. The big milestone: The drivetrain works! I fired it up for the first time a few days ago. A great relief to see it runs smoothly and vibration free. Here's a short video of that (not very exciting other than what it represents). I think the ticking you can hear was just the rear brake discs/rotors which hadn't been turned over in months.

Here are some direct links to the new/updated content:

Front battery box
Zilla controller installation
12V battery
Power steering
DC/DC Converter

And a few pics for anyone too lazy to follow the links Image

Image
Front battery box being assembled out of the vehicle

Image
Closeup of my BMS boards and wiring.

Image
Mounting the Zilla 2K controller

Image
Temporary Hairball test wiring to give the drivetrain a test run

Image
Power steering pump and DC/DC converter
Last edited by zeva on Mon, 29 Oct 2012, 07:15, edited 1 time in total.
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Post by Johny » Mon, 29 Oct 2012, 19:25

Very nice Ian.

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Post by Richo » Mon, 29 Oct 2012, 20:44

Lol the power steering motor looks like my drive motor Image

No support caps for the cells?!?
They kept snapping anyway...
So the short answer is NO but the long answer is YES.
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Post by PlanB » Tue, 30 Oct 2012, 15:49

Nice battery packs Ian, I really like those wavy cut connector end plates I saw somewhere for your headways. What's the PD across that strip of insulator you've got between rows? Please tell me the insulator is a little bit proud of the connector strips to stop dropped metal things making contact?

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Post by zeva » Tue, 30 Oct 2012, 16:52

PlanB wrote: What's the PD across that strip of insulator you've got between rows? Please tell me the insulator is a little bit proud of the connector strips to stop dropped metal things making contact?

PD = Potential Difference? I suppose about 80V, worst case. The plastic is 1.5mm polycarbonate - super tough and flame retardant, with high dielectric strength (~15kV/mm). The polycarb is the same height as the tops of the cells, which is 10mm higher than the tops of the aluminium interconnectors, so a dropped tool shouldn't short between rows (unless it was a shifting spanner dropped at precisely the wrong angle..)

Well, a good rule of thumb is to not drop metal things onto battery packs anyway Image
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Post by coulomb » Tue, 30 Oct 2012, 16:57

PlanB wrote: Nice battery packs Ian
Yes, indeed.
Please tell me the insulator is a little bit proud of the connector strips to stop dropped metal things making contact?

And please tell me that the presumably unfused wires to the BMS boards will be getting a liberal coating with silicone or some other strain relief. I know fuses are a nuisance when the current through them isn't enough to keep mechanical contacts (like fuse to fuse-holder) clean, but those long unprotected BMS wires are a worry to me. So the last thing you need is vibration causing a break in the wire where the solder stops wicking into the copper. (Disclaimer: Weber and I promote our own cell-top BMUs, which have a surface mount fuse and avoid the unfused wires altogether, so you could say that we are biased on this.)
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Post by Johny » Tue, 30 Oct 2012, 16:59

While we are Ian bashing(something I'm not normally predisposed to do because I admire your work), I am concerned that the aluminium angle that holds all the cells in place could abrade the flimsy insulation (blue stuff) on the cells after a bit of road juggling (not clown juggling - bumping around). I'm assuming that the cells can move which doesn't make much sense but I'll post this anyway.

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Post by zeva » Tue, 30 Oct 2012, 17:26

coulomb wrote: And please tell me that the presumably unfused wires to the BMS boards will be getting a liberal coating with silicone or some other strain relief. I know fuses are a nuisance when the current through them isn't enough to keep mechanical contacts (like fuse to fuse-holder) clean, but those long unprotected BMS wires are a worry to me. So the last thing you need is vibration causing a break in the wire where the solder stops wicking into the copper. (Disclaimer: Weber and I promote our own cell-top BMUs, which have a surface mount fuse and avoid the unfused wires altogether, so you could say that we are biased on this.)

I agree that it is currently a bit dodgy, not having fuses on all the BMS trace wires. It is kind of depending on the wires being so tiny (AWG26 = 0.5A rated) that they'd burn out quickly if anything goes wrong, without taking much energy / creating much heat. (I'm experimenting with voltage monitoring only, no balancing, so the trace wires carry negligible current.)

Some kind of silicon holding the wires in place sounds like a decent idea, I will give that further consideration.
Johny wrote: While we are Ian bashing(something I'm not normally predisposed to do because I admire your work), I am concerned that the aluminium angle that holds all the cells in place could abrade the flimsy insulation (blue stuff) on the cells after a bit of road juggling (not clown juggling - bumping around). I'm assuming that the cells can move which doesn't make much sense but I'll post this anyway.

Bash away. Better that than have me overlook some important design flaw!

But in this case, never fear. Between the aluminium bars and the cells beneath them is a layer of 6mm neoprene foam rubber. It is compressed down to a mm or two at the highest point of the cells, but should insulate well and prevent abrasion.
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Post by jonescg » Tue, 30 Oct 2012, 17:47

Yeah, until someone comes up with a BMS that monitors cells wirelessly without any EM interference AND it is no bigger than a postage stamp AND has a profile no greater than 4 mm, unfused wires back to a central point are all we have.
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Post by Nevilleh » Tue, 30 Oct 2012, 18:17

Well, they're not actually!
NZ regs now require all bms sense wires to be fused and that is one of the main reasons I went to a cell-top module for my BMS. OK for prismatic cells, but a bit difficult for Ian's ones, I admit.

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Post by Johny » Tue, 30 Oct 2012, 18:39

It wouldn't be difficult to use a ceramic pigtail fuse close to the cell, inline with the BMS wire, and heatshrink it.

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Post by Tritium_James » Tue, 30 Oct 2012, 19:07

It's difficult when it's a 600V DC rated fuse!

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Post by weber » Tue, 30 Oct 2012, 20:17

zeva wrote:Well, a good rule of thumb is to not drop metal things onto battery packs anyway Image

Yes. No one ever means to. But I've heard plenty of stories. Apparently the world goes into slow motion as the tool is falling, while you think "Surely it won't bridge across those term-i-n-a-l-s". And then bang! And hopefully there was a fuse or circuit breaker in there, and that's where it stops. Otherwise, if we're in 1-volt-per-millimetre territory (more than 24 volts and 100 amps), it just keeps arcing and melting stuff, and boiling and burning electrolyte, until the batteries go flat or someone puts a fireaxe through a busbar.
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Post by weber » Tue, 30 Oct 2012, 20:38

zeva wrote:(I'm experimenting with voltage monitoring only, no balancing, so the trace wires carry negligible current.)
Why no balancing? How will you do (have you done) the initial balance?

I'm currently in the process of doing the first balance on 228 x 40 Ah LiFePO4 cells, all in series, with SoCs all over the place. The idea of doing that manually fills me with dread. The automatic bypass is only 0.4 A so that's a 100 hour (4 day) worst case. But at least I can do other things while I'm waiting.
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Post by zeva » Tue, 30 Oct 2012, 21:09

weber wrote: Why no balancing? How will you do (have you done) the initial balance?

I'm working on a hypothesis that (a) the only reason cells get out of balance is differences in self-discharge and (b) self discharge is very low, so differences in self discharge should be very very low. All in the name of science.. The cells will start top-balanced and I'll see how much imbalance appears over time.

My initial balance was done with a high current lab power supply, individually CCCV charging each parallel group of cells to 3.65V. I only have 88 in series, somewhat less onerous than your 228 cells.. But it still took a bit of effort, to be sure.
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Post by weber » Tue, 30 Oct 2012, 21:11

jonescg wrote: Yeah, until someone comes up with a BMS that monitors cells wirelessly without any EM interference AND it is no bigger than a postage stamp AND has a profile no greater than 4 mm, unfused wires back to a central point are all we have.

I'm conscious that this is Ian's RX7 build thread and not really the place to talk about our BMS, but I'm not polite enough to let that pass without public comment. Ours certainly monitors cells wirelessly (using opto-coupled PCB tracks between adjacent cells and optic fibre elsewhere) and doesn't have a problem with EM interference in tests so far. It would be an interesting challenge to repackage it to fit in the tricuspid space between cylindrical cells or the space between tabs of stacked pouch cells. This should be possible if we do like Neville and pull parts off until it stops working then put the last one back (only not mistaking it for a PIC). Image But not just now. We have a car to finish.
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Post by jonescg » Tue, 30 Oct 2012, 23:53

Post moved to a new thread...
Last edited by jonescg on Tue, 30 Oct 2012, 13:11, edited 1 time in total.
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Post by zeva » Mon, 05 Nov 2012, 23:35

Hi all,

Another update to the blog, and some big news: Today I test drove the car for the first time! Here's the inaugural video of it pulling out of the garage and going for a gentle little drive: RX7 First Drive

This was only running off the rear battery pack, and there are still quite a few jobs left before the car is "finished", but it is getting close. Here are direct links to the main new stuff on the blog:

HEPA installation
12V Control Wiring
Reverse switch
Charging system

And a selection of pictures:

Image
Original OEM pedal next to new HEPA pedal with adapter plate

Image
EVMS, vehicle control wiring

Image
New control panel in centre console (part of a new project I'm working on)

Image
Power steering reservoir

Image
Charge plug installed in fuel door

Image
Mounting the charger to the back of the rear seat
Last edited by zeva on Mon, 05 Nov 2012, 12:35, edited 1 time in total.
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