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Author Topic: $Cheap$ Motor Speed Controller, 300A  (Read 2879 times)
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I'm going to be attending a university next fall and I've been thinking that to save on transportation costs I'll build an electric motorcycle. Well tuns out out i do NOT have enough money for anything fancy, but bare bones is do-able. (that means junk yards and more junk yards) The biggest problem i think i will run into is a speed controller for everything. I don't actually have any of the materials but i was thinking 48 or 72 volts. that means up to 300 amp speed controller, like these:
http://www.alltraxinc.com/Products.html
All the research i have done points to speed controllers like the ones alltrax sells. I don't need something with configuration software or any of the bells and whistles, just one to make it run good and reliable. From my basic understanding there would be a lot of high current MOSFETS connected in series being driven by the arduino pwm, receiving input from a twist throttle pot. Is this right?
Anyone have experience in this field and can point me in the right direction? Thank you. 
 
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Wow, 300 amps!
I don't think a golf cart motor draws that kind of amps through it's controller.
Since you are talking junk yards, how about a flea market/ yard sale trolling motor, stripped down and geared/belted to the rear wheel. They have a twist controller in the handle and run on 12 volts, much easier to get batteries and parallel them for more AH. Possibly a heat problem, they do run under water and may be engineered to use that for cooling. Of course this would be more in the range of a scooter or moped.  Lots of Alternative Energy Vehicle DIY resources on the web.
TomJ
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HOW MUCH?
boat parts
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Check this out:

http://www.recumbents.com/wisil/shumaker/

Maybe you can go with a larger RC brushless motor/esc system to get what you need...?
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Maybe something like a IGBT.  They're made for things with high voltage/current
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Quote

W0W! Cr0sh that is indeed a very nice example but that guy is a hardcore DIYer it seems with a CNC and all ,
How this Cute  smiley-red little lady would be able to handle all that? but then she can email him to get the ready made gear housing and gear's for her implication.
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Motor speed controllers.

http://www.electricscooterparts.com/speedcontrollers.html
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 i was thinking 48 or 72 volts. that means up to 300 amp speed controller, like these:
 

How much power are you expecting to have? Presumably you're taking some type of battery with you, so you have a limited amount of energy available. 72 Volts at 300 Amps corresponds to 21kW or about 30 bhp in old money. That is a heck of a lot of power to deal with on a light bike, you will be doing burnouts and pulling wheelies. For a couple of minutes, until the batteries go flat.

I think you probably need to produce some realistic estimates of the physical size of battery you can afford to carry, the amount of electrical energy available within that size using affordable battery technology, and then work out how long you need to run for; that will give you your average power output, then you can start figuring out your peak power output and motor type, gearing etc and what you need to control all that.

I would be surprised if the answer was anywhere near 300A.
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Wow, thanks for all the replies! You are probably right about the 300 amps, I just want to be safe. I want some decent range so at least 100 amp hour deep cycle lead acid batteries. What about a diagram?? I'll try and make up one that I think would work. Thanks again!
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If you use a motor/generator then you can recover some energy lost when you have to slow down by using regenerative braking. In stop and go or riding in hills it will stretch your battery time. It will even save wear and tear on your regular must-have brakes, probably better than shaft drive on an IC motorbike (which is nice).

With lead-acid batteries, protect them _well_ or when you dump the bike it could be pretty tragic.
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Wow, thanks for all the replies! You are probably right about the 300 amps, I just want to be safe. I want some decent range so at least 100 amp hour deep cycle lead acid batteries. What about a diagram?? I'll try and make up one that I think would work. Thanks again!

Are you sure that is a realistic size/weight budget? Have you ever tried picking up a 100 AH 12V lead acid battery? They are big old things.
If you're planning to be up around 72V you need six of them. How do you physically fit them in/on the bike? Is the frame strong enough to carry all that weight, and can you actually ride a bike that heavy? Also remember that lead/acid won't like being tipped over, I guess with a bike that weighs more than you do this might be a risk.
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Maybe something like a IGBT.  They're made for things with high voltage/current

IGBT's outperform MOSFETs at 100V or more, but they have 2 to 3 volts of Vsat so aren't viable at lower voltages / higher currents.

300A motor controller from scratch is a major project, if you haven't a history of building motor controllers this is not a recommended project, you'll get really demoralized when the Nth incarnation explodes all its MOSFETs yet again...

Check out the woes people have on the OSMC.org mailing list for example:
http://tech.groups.yahoo.com/group/osmc/
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Are AC motors easier to control?
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@PeterH, sorry forgot to mention sealed lead acid batteries. I have access to welding and metal working equipment so i was intending on modifying the frame so they would fit and be protected.

@GoForSmoke, i have considered using an ac synchronous motor, they have benefits in efficiency and speed, i think. But getting all the electronics equipment to do this is very complicated. DC-AC converter, variable frequency drive, blah too complicated. I was also thinking of regenerative braking, you read my mind.

@MarkT, thats a little saddening but hey i think you learn so much more whn you try things yourself.

So for people who want specifics i think 4 75-100 amp hour sealed lead acid batteries. 48 volts seems a little more reasonable to me. motor could be a briggs and stratton etek pancake brushed 48v 150A continuous. Thoughts?   
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@PeterH, sorry forgot to mention sealed lead acid batteries. I have access to welding and metal working equipment so i was intending on modifying the frame so they would fit and be protected.

Worth checking the current ratings then, since sealed batteries tend to have low charge and discharge currents. But mainly I'm concerned about the physical size and weight of the things. Have you seen and picked up a battery of the type you're proposing?
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