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Thread: Ex-7 - Electric RX-7 conversion

  1. #11
    Low Bitrate no_hazmats's Avatar
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    Mage: I can sum up the decision for Lead Acid Vs. Lithium in one word: Cost. And availability. Cost and availability. Two words. Cost and availability and simplicity. Three reasons: Cost, availability, simplicity. Lithium batteries are not widely available and comparable in cost, and commercially available things like battery chargers & controllers are not necessarily compatible with them, off the shelf. For this reason, almost ALL EV conversions still use lead acid. This car will have regenerative braking - the motor will become a generator when decelerating and put energy back into the batteries. One advantage of L-A is that they can take in huge amounts of energy in the short term, an advantage for regenerative braking. If I had it to do over again, I would consider Absorptive Glass Mat (AGM) batteries rather than flooded Lead Acid. But the batteries I chose have about the highest energy / Lb and the highest energy / Cu. Ft of any commercially available battery.

    Nobb: The batteries are 130 Amp-Hour which at 240 Volts = 31 Kilowatt-Hours. The motor is about 43 KW (peak) and can maintain about 18 KW continuous. That equates to about 41 HP peak or 24 HP continuous. But it doesn't equate to a car motor. A 3 phase AC motor like I'm using has high torque across nearly it's entire operating range. It makes in the 50-60 ft-lb across the entire range.

    The truth is I really don't know what the range will be. I do know it will depend a lot on driving style - hot-rod starts and stops will have a huge effect on the range. I plan to test it and take measurements of the range.

    One reason I bought the particular car I did was that it had been set up for autocross racing. The suspension is MUCH harder than a standard car - very heavy springs. I'm not happy about the weight in the back and I don't know how it will handle. But I don't expect RX-7 handling. I just want it to work! I do hope the mileage will be greater than 100, but the only way to find out is to drive it some.

    Thanks for the questions - as this project moves on, I'm getting pretty excited to try it out!
    Shep

  2. #12
    Sheepdog rdholtz's Avatar
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    Quote Originally Posted by no_hazmats View Post
    . . . I'd love any comments on RR vs. Centrafuse as a front end to integrate with this....
    For me, Centrafuse has been a fine ready-right-out-of-the-box solution, because I'm not a programmer. RoadRunner/RideRunner was too much pain to configure; it was as if I was being asked to conduct an orchestra without knowing how to read music.

    CF has a new plug-in architecture intended to help developers integrate their work with CF. With the retail price pf the program down at $75, that seems like a good deal for nearly no tweaking. YMMV, but I'm really happy with the new version.

    EDIT: There's a developer's SDK available.
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  3. #13
    Maximum Bitrate Crinos's Avatar
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    Nice conversion...

    Just as a tip for your battery management program...

    A friend of mine have an electric Reva, that have a custom battery management program... There he can see voltage, charge and "status" of every single battery in the battery pack. (he have standard 12v 55mAh car batteries).

    This proved quite useful when one of the batteries where dead, and the car acted quite strangely. Quick change of one cell and everything where back to normal

  4. #14
    Low Bitrate no_hazmats's Avatar
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    I agree. I'm not a programmer either. The tool I'm using to build the hybrid controller is primarily graphical and menu driven. I'm slowing learning it's scripting language. I don't have the skills to do large scale SW development and I have to face that it's not something I am going to pick up easily.

    That being said, I have been testing CF and RR and they both have advantages and disadvantages. The new CF is slick. And I agree about the pain to configure RR, although it seems more versatile and also seems to have a significant community of independent developers.

    The tool I'm using on the Hybrid side is called DaqFactory, and a free trial can be downloaded from www.azeotech.com. It's primarily a SCADA tool (Supervisory Control and Data Aquisition). It can collect and store large amounts of info from a variety of sensors and do all kinds of data manipulations and statistics, etc. It also has a lot of control features - I will be able to use it to start & stop the hybrid engine based on battery status, etc. I'm sure a skilled programmer could build everything I want as an independent program on a microcontroller, but as I said, it's not what I do. I'm a hardware guy. I'm lucky to live pretty close to the world headquarters of mp3car. I'm going to stop in there today to see what new stuff they are testing and talk to them about front ends....
    Shep

  5. #15
    Low Bitrate no_hazmats's Avatar
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    Quote Originally Posted by Crinos View Post
    Nice conversion...

    Just as a tip for your battery management program...

    A friend of mine have an electric Reva, that have a custom battery management program... There he can see voltage, charge and "status" of every single battery in the battery pack. (he have standard 12v 55mAh car batteries).

    This proved quite useful when one of the batteries where dead, and the car acted quite strangely. Quick change of one cell and everything where back to normal
    I know that Manzanita Micro makes such a system and it's a really good idea. I won't be able to afford to doit in the first iteration, but I hope I can add a BMS in the future, or if I do any future cars. Can you provide any info about the system they used. It's custom?

    Thanks
    Shep

  6. #16
    Low Bitrate no_hazmats's Avatar
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    Let me add that I would welcome any SW development help if anyone is looking for a cool project!

    Someday the best hybrid vehicles will be more like this than the Prius. While Prius' are great cars, they are engineered to give a familiar driving experience to people that are used to conventional Internal Combustion autos. They are heavy on the IC side of the equations and light on the EV side (The engine on the new Prius was increased to 1.8 L. It's getting bigger not smaller.)

    ALL internal combustion engines are at their maximum fuel efficiency when they are running at their maximum horsepower. That is to say that a 30 HP engine that's running to deliver 30 HP consumes far less fuel than a 150 HP engine that's running to make 30 HP. Since the typical car only needs 20-30 HP to cruise at highway speeds, they are not very efficient machines when they have a 250 HP engine in them. So a hybrid where the engine is small and and either runs at full power or is off is far more efficient than the Prius type.

    (I'm not knocking the Prius - it is a really great car and a necessary evolutionary step to get the mass of people used to driving a different kind of car. But the current Prius design is no where near what we'll have at the end of the evolutionary process towards more efficient cars.)

    Anyway, I have the generator, and the EV, and a cool carputer that plays music and has cell phone and GPS capability. The trick is to make it manage the electrical systems, control the hybrid engine, monitor performance and hopefully provide useful information on how the sysem performs for ourselves and others who want to build similar systems. I think it's an extemely ripe opportunity to develop such a system in the new open-source world, in which car-computing and EV conversions are already a big part. Any takers?
    Shep

  7. #17
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    1988 Rx-7 goes 100% Electric


    Forum member no_hazmats had previously been working to do an electric van conversion controlled by his car computer. Due to the lack of some available parts he has switched to an RX-7. He has started a new work log to show off some of his progress on the new 100% electric rx-7. Things are moving very fast. They hope to do test rides before new years. no_hazmats is an electrical geek with basic programing skills. For those of you who are advanced car computer users and programmers, he could use some of your help. Join the conversion conversation.

  8. #18
    High Voltage blk02si's Avatar
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    What an awesome project. I would also consider li-ion batteries, the power output is much better suited for a car, they run at almost full power until the end, when the just die (sort of like running out of gas) while the lead acid die slowly and linearly. I'm not sure how many it would take but I was thinking about an array made with 100 12v li-ion drill batteries. Like Dewalt of Milwaukee batteries, they both make industrial li-ion packs. I know it will cost more, but it will be much, much lighter because in these types of projects the weight of the vehicle is one of the most important factors to consider in development, because every ounce added takes a bit more power and reduces range.

    Looking forward to seeing your progress no matter how you do it!

    So will this have a 5 speed or automatic?
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  9. #19
    Maximum Bitrate stonestatue's Avatar
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    Wow, carputers AND electric cars? This combines two of my obsessions into one topic! It has long been my goal to convert an electric car myself. I know the majority of "amateur" conversions out there have historically gotten around 50 miles out of a full charge, so doesn't 100 miles seem a little optimistic? Well if you can make that work, then excellent. And are you referring to the lead acid batteries you see in ICE cars? Those aren't meant to be repeatedly drained and charged. That shortens their life span. Unless there is something I don't know. In any case, good luck and keep us posted.
    Check out my GMC Savana worklog.

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  10. #20
    Constant Bitrate
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    I'm looking forward to seeing how this turns out and hope you can prove me wrong, but even with regeneration 100 miles is way optimistic. You are likely to get 30-40 tops. As others have said you can't drain the lead acid batteries too far or you ruin them. But lithiom ion are just too expensive to be practical for a DIY project right now.

    I am very excited to see this here because we do need open source solutions to battery management (hardware and software).

    I assume you are on the EVDL mailing list? I great source of info there.

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