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Hi all,

Long time lurker, first time poster :) Some people may have read my build thread on the Australian Electric Vehicle Association forums, but I thought I might share it with DIYEC members too: http://www.zeva.com.au/Projects/RX7/

In brief I started the project about 18 months ago, with the goal of building one of the quickest EVs in Australia. It was my second personal EV project (after doing an MX5/Miata in 2007/8) though I've been involved with building quite a few EVs for other people over the years! The RX7 uses dual Netgain Impulse 9 motors, direct drive to the tailshaft, controlled by a Zilla 2K-EHV controller and powered by a (currently) 17kWh Headway battery pack.

There's literally a couple' hundred pics at the web link above, but here's a selection of the more interesting ones:


The complete vehicle as it is today.


The motor assembly. Uses the original end section of the RX7 gearbox to ensure alignment with the tailshaft and torque tube, and the little arms up front bolt to the original engine mounts via rubber feet.


Motors installed in the engine bay. Zilla controller to be mounted above it on a panel fastened to the firewall, and front battery pack occupying the rest of the engine bay (above and in front of the motors).


Assembly of front battery pack. Aluminium box construction with polycarbonate lining, with four rows of 12S6P Headway cells. (I designed the boxes to actually hold up to 9P (90Ah) cells, but budget and weight constraints limited me to 6P (60Ah) for now. Total front + rear pack is 88S6P, or about 280V 60Ah.


Wiring up the Zilla controller to the motors via reversing contactor.


Installing the front battery box in the engine bay. A very tight fit!


Zivan NG3 charger installed behind the rear seats.


MES-DEA vacuum pump installed adjacent to brake master cylinder


Pic of the power steering pump and IOTA DC-DC converter, in front of the motors / under the front battery box. I wasn't particularly happy with the DC/DC location because it was a bit exposed to the elements (hence the splash guard on the front), but had nowhere else in the engine bay to put it.

PS: Happy to share my plans/designs/ideas with anyone else doing an RX7 conversion if interested, just send me a MSG!
 

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Great looking conversion ZEVA :)

I flipped through some pics on your site - very well documented build! I like your heater controls. And "clean" OEM-looking instrumentation.


I have a couple of questions:

1. What is your real world power consumption?
2. What Chinese company did you buy your PS pump assembly?
3. What brand of TIG do you have (I'm currently shopping around).
4. Have you done any 0-60 times? 1/4 mile?
 

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1. The way I drive, it seems to use about 250Wh/km (400Wh/mile). I expect with a bit of "hypermile" style driving I could get that down to 200Wh/km, but that's not the point of an RX7 ;)

2. The pump comes from KVD New Energy Technology, purchased direct from them in China. It's the 12V version of the link below. It's OK. Works nicely, seems well made, reliable and runs cool, and not too expensive.. but compared to the OEM electro-hydraulic P/S pumps the automakers use it is relatively noisy, big/heavy, and uses a fair bit of power (15-20A idling, 50A max).
http://kvd.en.alibaba.com/product/547763855-213438583/electro_hydraulic_power_steering_pump.html

3. My TIG came from a local (Perth, Australia) company called Weldsmart, though I'm pretty sure they just import the TIG from China and slap their logo on them - not sure of the actual manufacturer! I've had it going on 5 years now, so far so good. I can't imagine ever going back to MIG/stick/oxy welding!
http://www.weldsmart.com.au/welding-australia/tig-welders/weldsmart-200a-ac-dc-tig-arc-pulse-inverter-aluminium

4. No timed runs yet, no. In truth I've been putting around with the Zilla programmed to 1200A max motor current. It's still got all the power one would ever need on public roads, probably 0-100km/h (60ml/hr) in about 6s.

I'm a bit nervous that things will start to break when I turn it up to 2000A! In particular, the spider coupling between motors, the final keyway (I'm incredulous at the amount of torque/power keyways can transmit), and the possibility of welding contacts in the reversing contactor (I know someone who had this happen with some regularity in their Z2K vehicle). But I'll have to give it a go one day soon..
 

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I'm a bit nervous that things will start to break when I turn it up to 2000A! In particular, the spider coupling between motors, the final keyway (I'm incredulous at the amount of torque/power keyways can transmit), and the possibility of welding contacts in the reversing contactor (I know someone who had this happen with some regularity in their Z2K vehicle). But I'll have to give it a go one day soon..
I know what you mean about breaking stuff. I broke one of my 28 year old motor mounts. The rubber was just old and brittle. I have the original clutch and I am hoping it will slip before anything breaks. I also have original size 185 tires so not a lot of rubber and hopefully that will slip before anything breaks.

If you are really worried about the reversing contactors, disconnect them and put in a couple of bypass shunts for your race day. You shouldn't need reverse in that situation.

It looks like you are running the motors in series so each one is seeing 140 volts nominal. If the Impulse 9's are wound like the warp 9's you could benefit from running higher voltage. How do the headways handle 1200 amps? How much sag are you seeing as this is a 20C load. Turning up to 2000 amps would increase this to 33C. I think your limit is probably your batteries at this point. In theory you have 280v at 1200 a which is 336kw (450HP). At 1200 amps the motors are probably less than 70% efficient so power into the drivetrain is closer to 315HP. I would expect your 0-60 times to be in the 4's. If I understand correctly you are only using the final drive in the differential, the transmission housing is just to get everything aligned? What is your final drive ratio and what tires are you running? It looks like the FD's used a 4.1 final drive but I don't think you are running stock tires.

It is a beautiful car and a clean looking build! I hope to hear more about it.
 

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Discussion Starter #5
Hi Doug, always nice to meet another electric RX7 owner :)

A reversing contactor bypass for race day isn't a bad idea. That said the usual MO is that the contacts weld together in the forward position from too much current, and you can't get reverse anymore.. but at least you can still drive home.

To clarify the amps situation, I actually have the battery amp limit set to 500A, which is about 8C - no sweat for Headways. The controller does it's buck converter magic to step up the current when stepping down the voltage, to deliver 1200A to the motor without exceeding 500A from the batteries - at least at lower speeds while motor back-EMF is low, up to about 80km/h I guess.

The Impulse motors have a shorter armature than the Warps which results in roughly 30% less torque per amp, but also 30% lower back-EMF i.e they are "revvier" but less torquey. The equivalent would be Warps at about 180V each, but only 900A. I haven't had a chance to try the car above 110km/h (the limit in our state) but it pulls hard all the way there at least! I should do a timed 0-60ml/h run with the current 1200A setting just for interest.. I do have a G-Tech lying around somewhere.

That transmission bit is just the end section, yes. Retained for the sake of tailshaft coupling/alignment, and the speedo sensor, and the mounts to the "torque tube" (aluminium C-channel between transmission and diff). So only the diff ratio reduction to the wheels. I think the diff ratio in this one is 4.3:1. The Type RS got a different diff to the normal ones (Torsen LSD). The rims are an inch bigger than standard but tire diameter is the same as factory.
 

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Hey zeva, I think your driving style is similar to mine. I'm not removing a 200hp turbo-charged ICE to make a NEV grocery-getter. 400Wh/mi would involve some fun accelerating.

Thanks for the links to answer my questions.

Under hard acceleration, say your cells sag to 3.0V. Thats 258V @ 500A ~ 129kW - almost directly to the wheels. At 3,000lb I think you should be close to your estimated 6 sec 0-60.

You might have more success with the taper-lok style couplers between your motors. I think you have a legitimate concern with the spider/keyway strength.

Never-the-less, your build is something I'd like to strive for. Safe, neat, and very OEM-looking integration. Well done!
 

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Nice build. I love Rx7's. Had a few in the past. Makes me dream of them again.
 

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@Zeva. Can this sort of seeing be implemented on any kind of a car, if for instance I'd want to build my own electric car?

What sort of battery chemistry/modules did you use?

I have NIMH packs for a Camry and Prius in my shop.

I thought your calculations in how the modules were arranged, should be in series all through? Then why did you arrange them in parallel series setup?


Dxta
 
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