The Controller: Curtis 1238 Series

In my own independent research, I also chose a similar motor/controller combo as ChargeCar's setup.  Some of you know, I have been planning on building an EV for years and the reason that I started in 2009 with an electric bike because I didn't have the funds at the time to do a car. Plus I figured if I screwed up royally, it would be on a much smaller, and less costly scale. Fortunately the ebike project worked very well and got me 5500 miles or so before I needed to do any maintenance. And that maintenance was directly related to the fact that the original SLA battery was shot. I'm currently wrapping up the upgrade to LiFePO4 [which will last many years] and I'll be on the ebike again in the Spring for my daily 19 mile round trip commute.

I only found out about ChargeCar last summer. This was back when I was still going to convert my black Z24. At the time I was looking at the AC-30 / Curtis 1238 combo, but now that I decided on a CR-V, I figure the motor should be sized up a bit due to the heavier weighted vehicle, but the controller's still fine. When I found out ChargeCar was going to use the same controller and motor that I planned to use, I thought it was cool. It kind of gave me a lot of confidence that I had done my homework, and done it correctly :)

Now, let's talk about this controller [finally, right?]. This controller has a lot of awesome features. The coolest is that it's fully programmable using Curtis's Vehicle Control Language (VCL). Not only does it let you set parameters for how to control current, it also can handle two way communication, so if you want, you can program the controller to make decisions based on internal or external sensor data, GPS information, dash mounted tablet pc... and more [with some programming and electronics work of course.] In some future posts, I'll talk about some ideas I have for this, but suffice it to say that this car could provide a decade of entertainment for me as I refine and invent new things to do with this functionality.

Of course, the controller offers regenerative braking, which converts the kinetic energy [the motion of the car] back to electricity and charges the battery, extending your range. Normally, this kinetic energy is transferred by your brake pads to your rotors for dissipation as waste heat. The controller is also quite efficient at powering the motor which will make the car go even further on a charge. We are expecting to get between 60 (on the low end, with A/C or heat running) and 85 miles per charge with this system. This is similar to the real life expected range of the Nissan Leaf.

You can read the data sheet on the 1238R controller if you like. It gives a lot more basic information that I don't really feel like regurgitating here. Read it though, because it is worth checking out.

In my next post I'll talk about the battery we plan to use in the CR-V.

The Motor: HPGC AC-50

A quick look at EVAlbum will show that lot of people use less expensive series wound DC motors made by companies like ADC or NetGain. A long time ago I decided on using AC drive, but it was just too expensive.

A DC system is cheaper because it's simpler, but it also has certain limitations that are hard to ignore. There are a lot of technical challenges to getting a DC system to do regenerative braking effectively without destroying the brushes. Plus, eventually, the brushes in the DC system will wear out anyway and need replaced.

In contrast, a 3 phase AC motor has no problem doing regen. I prefer a simple and reliable system for regen. Let the motor do the braking. I'm not changing brake pads all the time. Plus, an AC motor uses induction to transfer power to/from the rotor, so it doesn't even have brushes that can wear out. Part of the idea with an electric car is less maintenance. Let's really try and minimize it.

There also exists a type of DC motor that doesn't use brushes. Some electric bikes, like mine, use these. I am talking about brushless permanent magnet motors that even can do regen well with the help of a good controller. You just don't see any PM DC motors that are big enough to push a car to highway speeds.

This is sidebar but, on their Scion EV, ChargeCar was creative by mechanically tying 4 PM DC motors together, but that vehicle can only go about 40 mph. In their defense, this car is used for data collection and research into intelligent vehicle control algorithms, and their goals with that car are very different than the goals of building a daily use commuter EV.

Back on topic, an AC system is still more expensive, although it's getting cheaper. AC systems used to cost 2-3 times or more of the cost of a comparable DC system. Now, you may only pay 50% more for the AC system. So, unless you're really budget constrained, you should consider AC, as it will a be a more efficient conversion.

I've seen the AC-35 motor used in a Honda Civic conversion done by ChargeCar at CMU. The car can accelerate from 0-20 mph in about 2 seconds and has been driven at over 70mph on the highway. Taking that the Civic's stock curb weight is 2600 lbs and the CR-V weighs around 3200 stock, plus the fact that I'm installing a bigger battery than the Civic has, I think it's better to go with the slightly bigger motor that has more torque, so I'm thinking the AC-50 motor will work best. I ran it by ChargeCar's mailing list and Ben, who worked on the Civic, agreed.

[ power curves for the AC-50 at 550 amps. I plan to use a 650 amp controller -more on that later-, so I'll get more power than this is showing.]

In my next post, I'll talk about the controller.

Found the Car!

We are in the process of buying this high mile, but clean 2003 Honda CR-V from a dealer in Illinois. I fly out there next Wednesday to pick up the car and drive it back home. We'll probably drive it for a bit, but once the winter breaks, the conversion to full electric drive will begin.

Here are a few pics from the dealer, Xtreme Motor Sales in Sycamore, IL. Steve Pacchiano, who runs the dealership, has been very helpful so far, and is even going to pick me up at the airport, saving me a $120+ taxi fare for the 60 mile drive to Sycamore. Thanks so much to Steve, and Xtreme Motors.