Wednesday, June 22, 2011

Serious Recycling

We were going to wait until the project was complete to post all this. But it should be interesting along the way, so here we go.

Susan and I picked up a donor car last weekend for conversion to electric. It has lots of miles and too few oil changes. It's 14 years old, a 1997 BMW Z3 Roadster.

The engine will be removed soon, along with the exhaust system and gas tank. We're hoping to sell the engine.

The plan is to add a WarP 9 electric motor, a Soliton 1 speed controller, a bunch of lithium batteries and a variety of smaller hardware.

The range should be 100 miles, enough for my daily commute to Tyson's Corner and back. That's twice the range of a Nissan Leaf. The office landlord is installing charging stations, too. All the better.

The performance may be on par with the original engine, maybe even better. Here's the first photo:


  1. Excellent project! Have become a follower, as I find this effort intriguing.

    Since the Z3 is a two seater, 3000 lbs base weight is a bit on the high side, requiring many more batteries and energy than another two seater, the Miata (2100 lbs). Rolling resistance and energy required to overcome hills can be a significant energy requirement.
    I realize that taking the engine, trans, etc out will reduce the overall weight of each, though we could assume this would be roughly proportional.

    The aerodynamics of the two are roughly similar, so not much difference there, if any. If you are not past the point of no return (i.e., engine sold), I would recommend a rethink of the choice of donor vehicle.

    Did you consider regen and choose to forego it?

  2. Since the motor you are considering is 32 hp, a 3000+ lb car may impose performance limitations that are not easy to foresee ahead of time.

    Other resources:

    Will Stewart

  3. My Miata's license plate was "Z3WANAB". I love Miata's, too. That evmiata is a great site. I'll be glad to help you convert yours next! The 32HP rating is at 72V. The max voltage is 170V. The batteries are 15KW and 8C, which means they can deliver 120 KW peak. That's roughly 160 HP. The Solition 1 controller is 1000 amps @150V IIRC. That's ~200 HP. We'll see how it all turns out.

  4. Ok, so you have a vision based upon a specific desire, I can understand that.

    What kind of batteries are you planning? How many? Source? Method of estimating capacity in order to arrive at the 100 mile range?

    Do you have a 3D configuration/array plan for them? Regen?

  5. They're lithium batteries, 80 cells at 3.3V each. The 100 mile range is what Steve at Green Shed Conversions said. He's done 40+ conversions and is coming up in August or September to make it happen. As a commuter car, I'm willing to use all of the trunk in addition to the space where the gas tank was and there may be space under the hood. Each cell is 5 x 7 x 2.5" and all wired in series.

  6. Oh, and I'd like regen, but have seen very little discussion in the DIY EV world. It seems to recoup a useful amount in the Civic hybrid, so I'd prefer to have regen. The WarP 9 is typically set with the commutator brushes mounted "advanced", something like ye olde distributor cap. My impression is that regen would require that offset to be reversed to reduce sparking and wear.

  7. Hi Bruce,

    Regen with a DC system, at least with a Netgain motor, isn't really possible. The brushes are advanced 12° which would cause arcing on the commutator if you tried regen.

    You may want to talk to George Hamstra from Netgain about your choice in motor. When I sent him all the specs on my Z3, his first impression was that a 9" motor would do, but then he said the numbers indicated an 11" would be better. Talk it over with George, he's very helpful. One thing is certain, and that's if you use a 9" motor, be sure you get a fan to force air into it for cooling.

    I think you're a bit optimistic on the range. If my calculations are right, your pack voltage will be 264V (3.3 x 80), then if they are 60 AH cells 264 x 60 = 15840 watt/hours. My car averages 320 watt/hours per mile. So, 15840/320 = 49.5 miles. If it's possible Bruce, you may want to consider bigger batteries, like the CALB 130AH or even 180AH. Fewer batteries means fewer connections and also more power for the same C rating. I think a 100 mile Z3 conversion is feasible, but you'll need closer to a 32 kWh pack.

    Can't wait to see how your project comes along.

  8. Some straightforward calculations for speed and range can be found at;

    However, due to the number and types of hills you will be experiencing, significantly more energy will be required. Plus, what speed are you planning for on places like the Greenway, etc?

    Tim, is the 320 whr/m figure your experiencing in a relatively flat area? Any idea how your terrain compares to Bruce's route?

  9. Tim,

    Any idea of the amp-hours you are drawing at various speeds? If so, what voltage are you running at?

  10. Here's an illustration of the relationship of speed to aerodynamic drag:
    (this blog doesn't allow HTML, so enter link below to see)

  11. The terrain in Phoenix Arizona is the very definition of flat. The steepest and only grade I encounter is an on ramp to the freeway.

    My pack is 160 Volts. I really don't keep track of the amp/hours I use in a mile as it's not a useful comparison that EV owners can exchange since everyone's pack voltage is different. To compare how your car is doing, relative to others, you need to convert it to a standard that works regardless of pack voltage, and that's Watt/hours.

    That said, I have collected some figures on how many Watt/hours the car draws at different speeds and the difference is surprising to some and illustrates just how much aerodynamic drag has on the car.

    40 mph = 250 W/h per mile
    55 mph = 354 W/h per mile
    65 mph = 420 W/h per mile

    The average speed around here is 45 which draws about 280 W/h per mile, but when you add in starts and stops needed in regular traffic, it averages out to 320 W/h per mile.

    Believe it or not, there is a pretty accurate way to predict how much energy your EV will use before it hits the road if you have an idea of how much it's going to weigh. I know there are calculators on line for such things, but they are complicated and I've found not as accurate as this simple method. Take the weight of the car (in my case 3300 lbs) and divide by 10. For me, that ends up being 330. True, it's a tad off from the 320 I report, 3%, but it's close enough for government work and a good starting point.

    Bruce, if you stick with the 9" motor, you'll save 90 lbs off the weight I quoted above. But ideally, you'll want to replace that weight with more batteries ;)

  12. The Greenway is a local highway with a 65/72 MPH speed limit and hills. I could drive that, but wouldn't make it to the office (45 miles) and back home. Dry Mill Road, Sycolin Road and Route 28 all offer more manageable speeds. Once the charging station is installed at the office, there will be even more options.

  13. Schulz Engineering has been tackling the aero aspects of electric vehicles, with this interesting examination of motorcycles;

    They are now working on a streamlined electric motorcycle with the goal of productizing it and becoming a manufacturer. They have very good results so far, which can be found at;

    Their motorcycle consumes about 1600 watts at 40 mph, which translates to about 40 watthours/mile.