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Old 02-06-2008, 12:19 AM   #11 (permalink)
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In that picture there is a circuit breaker between the batteries and the motor, if you knew what it was rated for then you would know what amp range we are actually talking about here.

You probably could take an r/c controller and swap out to higher voltage mosfets and just add enough of them to handle double the current you expect to see and I bet it would work pretty well. Then just add a motor to steer the car and you have a really big r/c car

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Old 02-06-2008, 01:05 AM   #12 (permalink)
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What all is in a motor speed controler? the better ones basicly make a square wave that varries the on part of the freqency, right?
I know enough about electronics to know that I wouldn't trust a controler that I built, my citicar is pretty small, and the motor is on the small side for a road going vehicle and still, the cables that go to the controler relays, battery, and motor are all rather big, the relays alone could cost $500 each to replace if I want decent quality, and that is just an electromagnent that pulls a simple switch closed.
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Old 02-06-2008, 01:54 AM   #13 (permalink)
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actually...this wouldn't be the most efficient way to do this, but if you have a manual transmission...couldn't you really just have an on off switch and flick it when you need power and use the clutch like a gas pedal? I don't know if that would actually work, but I was just brain storming after reading Ryland's post about electromagnets pulling simple switches closed...
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Old 02-06-2008, 02:08 AM   #14 (permalink)
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The reason that I'm thinking about spending the money on a better controler is that a good controler will make the car operate smoother then the 3 speeds that the relays give, and a modern controler will use the power stored in the battery pack more efficently, giving my citicar a longer range.
ridding the clutch is going to turn alot of your energy that is stored in heavy lead acid batteries in to heat, it's simple, and would kind of work for very short trips, but then you have a clutch that wears out as well, and automatic tranny is going to have a simaler affect of turning energy in to heat and killing your range.
I rather like the idea of the AC 3 phase controler and brushless motor, it's even more efficent then the controlers that are being talked about here, and even more complex, but it should give both better power, and range, and in an electric car those are things people look for.
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Old 02-06-2008, 09:40 AM   #15 (permalink)
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A 3 step, or more, relay system wouldn't be too hard. I made a home-brew 3 step relay controller for one of my RC cars once when I blew out my PWM controller on a 15 turn motor accidentally. I used it for a few weeks while I waited for my replacement PWM controller to come in and it worked pretty well, but you're right, since all the unused power gets converted into heat, it's pretty inefficient compared to a PWM controller.
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Old 02-06-2008, 09:57 AM   #16 (permalink)
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A series/parallel contactor controller is 100% efficient at getting the energy from the battery to the motor. (Of course, if it's a resistor-based controller, it's not.)

But A PWM controller also burns up energy as heat - it's why they've all got big heat sinks & finned aluminum covers.
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Old 02-06-2008, 11:03 AM   #17 (permalink)
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Ok, now I feel like I have to throw my hat into the ring now, lol.

From my experience owning and working on many different electric golf cars (carts for us older folks), I've learned some facts about some basics:
  • Relay carts are jumpy and will never obtain the same distances as a controller cart
  • Relay carts are not super user friendly
  • Controllers make things nice and simple to work on and operate.
  • If you know where to look, parts are cheap, most cart owners are willing to barter for things like snowmobiles, trailers, and other things to trade a cart for.

Check out a place called Buggies Unlimited and their Forum. you should be able to find what you need there or at least some leads to where you can get it.

I didn't really pay close attention to what kind of voltage you are looking to use on your motor, but there are a few guys on there that are running drag carts with 120V DC+.

There are many good articles on there for helping you to pick out the proper motor for what you need as well.

Hope this stuff can help you out a bit.
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Old 02-06-2008, 02:51 PM   #18 (permalink)
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Alright, we're going a lot of different directions in this thread.

Some people say they would like to try it.
Some people say a budget controller wouldn't work or would be too inefficient.
Some people say they might be able to build something.

So here's what i'll do:

This Friday I'll pickup a motor.
Next I'll get the donor car.
Next I'll see how many batteries i can cram into it.

Then I'll post up the requirements for this car and let everyone use my car as the guinea pig. I'll take the first schematic that the consensus says will likely work and run with it. Then I'll post up the results.

Hopefully - if it doesn't blow the motor - we'll get a basic open source controller for the community start building on.

Hey, SVOboy, can we somehow make that a EcoSticker contest for them? It's likely that in a few weeks I'll be ready to go and can test the controller.

I'll post up the requirements for the vehicle and the info on the motor (etc..) once i get it all together. In the mean time feel free to keep discussing possibilities for controllers.
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Old 02-06-2008, 04:31 PM   #19 (permalink)
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Quote:
Originally Posted by WaxyChicken View Post
I'll post up the requirements for the vehicle and the info on the motor (etc..) once i get it all together. In the mean time feel free to keep discussing possibilities for controllers.
You just want a PWM controller, or not? I've built them before using an MC9S12 mcu, but that was for circuit components not a giant motor. I can cheat, however, and talk to the ECE department at my university since I've taken classes with many of them despite being a mechy
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Old 02-06-2008, 06:02 PM   #20 (permalink)
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Oh, I won't lie. I'd love to get/build a cheap controller to meet my needs.
But so would everyone else on this site who works on EVs.
So why settle for something that can benefit just me when the possibility exists of meeting other members' needs, too?

I'm willing to risk the motor for the benefit of the community.

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