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Old 08-05-2011, 06:39 PM   #11 (permalink)
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Thanks for your quick replies everybody,

Frank Lee, I actually did look at that discussion quite in depth before posting this. There's a lot of good info there.
I was thinking of mounting the batteries on the bottom of the car. They would weigh a few hundred pounds, but if placed properly could offset the weight of not having a transmission, and the reduction in weight from a "large" engine to a small generator.

Daox, yeah it's going to be a pretty hefty battery pack. I don't think it's going to be quite 16kwh though because the chevy volt has a 16kwh battery pack for 40mi of range, and the CRX is lighter and has a lower drag area. According to the calculator on this website, it should take about 4.3kw to maintain 45mph, so if I were going at 45mph for an hour it would take 4.3kwh of battery. But I have to deal with start and stop, acceleration etc.(regenerative braking should help but not eliminate this problem) So in order to get 40mi of city range(less than 45mph top speed) I'm thinking I need to make my battery pack around 6kwh. If I get around 30-35mi of range it should still be ok, and I can always add more later if need be.

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Old 08-06-2011, 12:43 AM   #12 (permalink)
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So your setup is going to have regenerative braking? Many DIY conversions don't due to the added cost of going with an AC system. Still, I think a 16kWh pack is prudent for 40 mile range. 6kWh is definitely not enough. Even with the streamlined CRX you will still use at the very least 200Wh/mile. This is perfectly flat ground, ideal road conditions, etc. Take a look at evalbum.com and see if anyone has posted Wh/mile ratings for their CRX, I found 240 Wh/mlie. That will give you an idea of how much power it will take you to get your 40 mile range. Keep in mind that you also do not want to cycle your batteries to fully discharged. For lithium you should definitely not take them lower than 80% depth of discharge (DOD), and 70% will give you much better life out of the batteries. So, you need to add an additional buffer there. Now, as the batteries age they will also loose capacity, so you need to account for that as well. All these things add up and in the end a larger battery pack is what is needed.

For the EV I'm planning (if I ever get around to it), I am using 500Wh/mile as a worst case scenario for winter driving (cold bearings/trans oil/heater/etc). This is with a Toyota Paseo which isn't a whole lot bigger or less aerodynamic than a CRX. With these conservative numbers I know I'll be ok after a few years and still be able to make my commute. Don't skimp on the battery pack.
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Old 08-06-2011, 01:16 AM   #13 (permalink)
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The weight of a CRX's engine is less then 200 pounds, light enough that I can pick it up off the ground and carry it by my self to the back of a vehicle, you might have another 100 pounds to remove but things like the radiator are small and light, exhaust is pretty light.

Also remember that with lead acid batteries you don't want to discharge them below 50% unless you like buying new batteries and in the winter the useful energy in the battery drops so you need to over size your pack unless you are not easily frustrated.
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Old 08-06-2011, 05:44 AM   #14 (permalink)
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Daox, thanks so much for the site. There were quite a few conversions for the Honda CRX there, but I could only find one with wh/mi figures or a battery that I could find specs for. From what I read he had a total capacity of 7.9kwh (72V*110ah), which allowed him to get 25-50 mi depending upon his driving style, so he got about 240wh/mi (he doesn't say how far he took the batteries down though) . Thanks for the advice on the battery pack, I'll make sure to make it bigger so it lasts longer. I was thinking of using two 10kw continuous, 20kw peak brushless DC motors found here hub motor, brushless motor, BLDC motor, bike conversion kit, brushless controller,electric bike,wheelchair controller,electric wheelchair,dual drive ebike, electric motorcycle,EV battery,electric unicycle ,brushless joystick controller, regenerative which can do regenerative braking.

Ryland, thanks for the info on the weight. I was thinking the transmission must weight at least 100lbs too, right? That along with the engine, and exhaust, etc should be at least 300lbs right? That would give me some room to work with as far as the generator, batteries, and motors go.
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Old 08-06-2011, 09:35 AM   #15 (permalink)
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Here is a good example of a CRX conversion with AC drive: Advanced electric vehicle conversion project
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Old 08-06-2011, 09:38 AM   #16 (permalink)
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Quote:
Originally Posted by newguyintown View Post
I was thinking the transmission must weight at least 100lbs too, right? That along with the engine, and exhaust, etc should be at least 300lbs right? That would give me some room to work with as far as the generator, batteries, and motors go.
The transmission weighs about 75 pounds and is tiny, the only reason that I had some help me carry the engine and the transmission while they were bolted together for my CRX was that there wasn't any good hand holds, but if you are wearing cloths that can get dirty picking up and carrying the two bolted together is not a problem, so altho I didn't put them on a scale, I know that they are not heavy, nor big.

You said you plan to bolt the batteries to the underside of the car??? figure that you need around a foot of height for batteries and that again, unless you like buying batteries, you want to be able to get to them to check them every few months to check your cable connections and your water level, last time I looked at my Honda fuel tank, it looked to be about 6" thick and was pressed up to the under side of the car the other 6" is needed for ground clearance.

As for hub motors, do you have fabrication skills? a machine shop? I do and I would still stay away from hub motors because they are going to take a lot of work to make the rest of the parts you need to fit it to an existing vehicle.
Before you order from Golden Motors, you might take a look at what vehicles use their motors Motor Brand: Golden Motors and notice that if you manage to put together a car using one of their motors you will be the first and it's not because that company is new, I started looking at their products over ten years ago.
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Old 08-06-2011, 06:40 PM   #17 (permalink)
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Thanks for the site Patrick!

Ryland, Thanks for the info on the weight. The total weight of engine, transmission, exhaust, etc should still probably be between 250-300lbs right?

I was thinking of wiring my own Li-ion pack that would just be a few inches thick.

I was just thinking of using the brushless 10kw dc motor they have, not the hub motor. Has anyone had any success with those? They look like fairly good motors, but I have no experience with them. Do you have any other recommendations for motors? I'd like to get something with a high efficiency so that I don't need to make the battery pack as big, or the generator. The price looked fairly good for them, and they had a controller matched for them, so that's why I was interested. Do you have a recommendation on an efficient motor/controller setup for a good price? I'd like to have at least 40kw peak power, but I could probably do less.

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