03-05-2009, 05:14 PM
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#11 (permalink)
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Master EcoModder
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Two questions I"ve been pondering...
1 - Can you run a 120V motor off of 12V and 10x step-up transformer? Similarly, could you run a 208V 3-phase motor from a 10x step-up transformer and 24v? (or more generally, can you run a motor off of step-up transformer?)
2 - What about a vaccuum cleaner motor? These things are 120v at 10amps = 1200W (approx 0.8hp?). That's plenty for a scooter. Maybe 4 of them could each power a wheel of a small car? I'm pretty sure they run at very high rpm, but doubt they have any reasonably good torque or dyanamics.
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03-06-2009, 02:42 AM
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#12 (permalink)
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Quote:
Originally Posted by MazdaMatt
Two questions I"ve been pondering...
1 - Can you run a 120V motor off of 12V and 10x step-up transformer? Similarly, could you run a 208V 3-phase motor from a 10x step-up transformer and 24v? (or more generally, can you run a motor off of step-up transformer?)
2 - What about a vaccuum cleaner motor? These things are 120v at 10amps = 1200W (approx 0.8hp?). That's plenty for a scooter. Maybe 4 of them could each power a wheel of a small car? I'm pretty sure they run at very high rpm, but doubt they have any reasonably good torque or dyanamics.
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It would make more sense to step up the voltage using a DC/DC converter and then convert to AC. 24v is on the low side even for a bicycle, so it would be more usual to simply start with a high battery voltage.
Most vacuum cleaner motors are universal meaning they will operate from DC. I don't think they'll last long for constant service, but it could get interesting to use one with a centrifugal clutch connecting it to the belt as a heavy duty starter. It would work great for EOC and FAS.
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03-06-2009, 02:51 AM
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#13 (permalink)
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nut
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120V@100A would require (at 100% conversion efficiency) 12V@1,000A. the formula to remember is P=V*A so Power in Watts = Volts * Amps
You can increase the voltage or amps but the other will drop if you are using the same amount of power from the battery.
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03-06-2009, 09:18 AM
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#14 (permalink)
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Oh, i understand that VA is constant (minus transformer losses). I'm just thinking that AC motors are said to be more efficient, and better suited to doing more than just launching (low end torque of a dc motor)... But if i want to run a 120VAC motor on a bicycle, i don't want to carry 10 car batteries with me. So i was curius if i could use, say, 2 batteries to generate a control signal from a lower cost, lower voltage controller, then step it up and run a motor. Say i wanted to use a vacuum cleaner motor - 120V@10A = 1200VA. So 1200VA/24V = 50A. It would be easy for 2 car batteries to run at 50 amps, no?
As for stepping it up with a DC/DC converter FIRST - that sounds more lossy to me because that DC/DC is probably generating an AC sine wave, then stepping it up, then rectifying it, then i feed it to my controller, then generate an AC wave again. In my case, i'd just be taking the battery DC, converting it to sine, then stepping it up.
Anyway... just thinking outside the box. No real merrit to this.
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03-06-2009, 09:58 AM
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#15 (permalink)
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Quote:
Originally Posted by MazdaMatt
As for stepping it up with a DC/DC converter FIRST - that sounds more lossy to me because that DC/DC is probably generating an AC sine wave, then stepping it up, then rectifying it, then i feed it to my controller, then generate an AC wave again. In my case, i'd just be taking the battery DC, converting it to sine, then stepping it up.
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It's more efficient to convert at high frequencies as higher frequencies need less wire in the transformer. And DC/DC converters usually operate on square waves.
Take apart a modern inverter and analyze how it works.
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03-06-2009, 10:33 AM
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#16 (permalink)
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That's a good point, Mike. Does the fact that i'm sending a variable PWM signal make it so the transformer is actually converting a 16khz source, thereby making it efficient? Or would i be running into the same kind of current "filtering" due to back emf from the motor working its way back through the transformer?
Maybe i should jump back on my "1kw audio amplifier to drive a motor from 12v" concept... i now have a low powered 120v AC motor at home to play with... and an audio amp (but only 400Wrms). Those audio amp people have been doing voltage step-up and signal amplification for years... i'm sure they're good at it.
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