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Old 05-06-08, 10:16 PM   #1
forestsoul
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Custom Ebike from treadmill motor?

Hello. Been doing some research about ebikes and decided to try to make my own from scratch. Went to the local dump today and found a treadmill, which I took apart, as well as a bunch of batteries that were holding good charge, to get me started. The only thing wrong with the treadmill was that there were 2 resistors that had come unattached from their solder points. Easy fix.

So far, here's what I have:

MOTOR - Brushed, Permanent Magnetic DC Motor, 2.25 HP, 130 VDC, 18 AMPS


BATTERIES - 4 SLA "YUASA" 12V, 17.2Ah


So I don't know TOO much about electronics but I understand that the AC to DC controller will not work with the setup as it is now. The motor works great when plugged in but I need to get a new controller.

One question is, will a 36V 30A Brushed DC Controller from ebikes.ca ($75) work with this setup? I'm hoping to rig only 3 batteries in series to get 36V (I know, a lot of weight but I'm thinking of possibly transferring to a trike in the future with more power). Anyone know of any other DC controllers that could work and where to get one?

Also, anyone have experience in rigging up chain drives to their bikes and what have people found to be the best way? I'd like to rig to the rear tire to allow for peddling, but also considering a straight electric-only bike with the motor rigged under frame to front pedal chains (pedals removed). Any suggestions?

Something similar to thing perhaps.

http://www.youtube.com/watch?v=sGTB_uZdw0o
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Old 05-07-08, 07:07 AM   #2
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how much does that 2.25hp motor weigh? You should expect nowhere near that horsepower out of it if you run it at 1/3rd of its rated voltage, but it still might be reasonably powerful. You might have to figure out by trial and error what gearing is required to make it work, if any gearing is really enough for it when undervolted.
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Old 05-07-08, 10:11 AM   #3
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Haven't weighed it yet but it's prolly around 5 lbs. I've been wondering that same thing, about horsepower. If 130V is 2.25HP, then is 65V 1.125HP? I'll be putting some battery power to the motor when I get some wiring made up for the batteries and I'll let you know how it does. Yes, gearing might become interesting.

Well, if all else fails I'll be looking for another motor I 'spose. Thanks for the info.
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Old 05-07-08, 04:21 PM   #4
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Volts have more to do with RPM than power. yes, you do get more power for given AMPS as voltage increases but the primary relationship is RPM and enough voltage so that you don't need huge wire due to voltage drop.

Brushed DC controller provides 0-max volts in a controllable fashion - that's it. Motor power output is a function of available amps through the controller and wiring. For a 36V/30A controller the most power you will see is: 1080W Well under what that motor can handle.

That motor turns 48 RPM for every volt applied. 72V it will run about 3450 RPM. 36V about half that - 1725 RPM. Figure out your gearing for the desired wheel speed and go from there...

Have you considered a large 12Vdc to 120Vac power inverter? That way you can still use the speed control from the treadmill system. Sure, it will exhibit some losses but parallel batteries will probably be much better in the long run. For short distances - you would only need a couple batteries. Minimum 1000 watt inverter, 1500-2500 watt better.
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Old 05-07-08, 07:49 PM   #5
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Hmm, excellent advice! Thank you.

Thought about the inverter option but didn't know what wattage to look for; thanks for that info! I'm starting to wonder if a bike frame will hold all this weight, but so far I haven't spent a dime so things are looking good.

I understand that the purpose of a DC controller is to allow for selection of 0% to 100% volts available in my system, but will using a controller over NOT using a controller limit the power of the motor? You stated 1080W of power using a 36V/30A controller, using W=V x A. If I do NOT use the controller what would my peak power be with 36V? Would it be 36V x 18A (motor rating), giving me 648? My understanding of controllers and that wattage of motors is very limited.

I'm considering possibly a 48V system (I now have 10 of those 12V batteries to play with) which would give me a bit more power, but I guess my range would suffer as there would be 4 batts in series. I only need 10km round-trip max, so I'm not looking to go extremely far on this machine.

As for the motor's power, with a 48V system I'd get ~2300rpm and ~1440W with a 48V/30A controller, it seems. That doesn't sound too bad to me considering other ebikes have 500W motors and spin at ~350rpm.

Well, after I figure out a way to attach and gear the motor to the bike I'll be looking more closely into the electronics, but as it stands now I'm willing to try it out like it is and see where it takes me.
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Old 05-07-08, 07:54 PM   #6
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Oh ya, motor weighs 6 lbs, batteries weigh 12 lbs each (yikes..).

If the system works I'll look into lighter batts...
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Old 05-08-08, 08:15 PM   #7
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If 130V is 2.25HP, then is 65V 1.125HP?
not exactly. If you keep the number of amps constant, then that would be true.

But the thing is that if you lower the number of volts a lot, the maximum number of amps may go down. (motors # of amps can be limited either by the resistance of the motor wiring or by a limit built in to the controller). At 36V, the maximum number of horsepower for that motor might be as low as 130 watts [0.17 horsepower].

This is because if electrical resistance in the motor is what limits your # of amps, then when you divide the voltage by 2, you have to divide the power you get by 2 squared (3, 3 squared, etc).

My guess (and this is only a guess) is that the motor will give satisfactory performance at 48 volts and maybe at 36 volts if you can get a gear ratio that works well for that motor.
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