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Old Sep 12, 2008, 03:37 AM
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Quote:
Originally Posted by satanicoo
Please don't let this one die
I already got an alternator for tests!

I only have two questions:
-What is the expected efficiency of an alternator, with no mods? Simply remove the rectifier and connect the ESC?
-What is the expected efficiency, if you change the rotor of the alternator for a Permanent Magnet one?

Depending on the rise of efficiency, and cost of a PM rotor, it might be a viable solution for a good motor for a small vehicle
When I were an apprentice, the other lads made a gokart with a car starter motor in it.

Huge amount of power, but it flattened the car battery in about 5 minutes, and ruined it after about 10 runs..
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Old Sep 14, 2008, 01:28 PM
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Those are brushed motors right?
Quite high power i'm sure, they have a current draw on the 3xxA during those few seconds to start the engine..
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Old Sep 15, 2008, 02:28 PM
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Any idea how many HP this motor would make on 48V?
https://www.kellycontroller.com/shop...product_id=116
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Old Sep 15, 2008, 07:42 PM
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100 Amps on 48 volts thats...

100*48 = 4800 watts

4800 / 746 = 6.43 HP am i right?
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Old Sep 15, 2008, 09:16 PM
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Quote:
Originally Posted by vintage1
When I were an apprentice, the other lads made a gokart with a car starter motor in it.
Starters are series wound motors, very high torque at low RPM and very high RPM at no load. The HP curve is flat from 0 RPM to infinity for an ideal motor. I have used these motors for combat robots and they are very good for that use, great hole shot and very high top end. Since they do not use permanent magnets they can take heat and have very good power to weight ratio.

But, they suck on efficiency. After two or three minutes they are hot, the batteries are hot and the wiring is hot. As far as trying to use any type of FET for control, Ha, Ha. Relays only. Speed control? Forget that idea.

Another use is drag race cars, see NEDRA (national electric drag race ass.)
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Old Sep 15, 2008, 10:21 PM
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Quote:
Originally Posted by IloveFLIGHT!
Any idea how many HP this motor would make on 48V?
Heres the test data from their website.
https://www.kellycontroller.com/mot/downloads/48VCW.pdf
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Old Sep 16, 2008, 02:03 PM
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I saw that graph. I don't understand it? I don't see torque or hp on it?
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Old Sep 16, 2008, 07:18 PM
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I have found that graph only makes sense if the bottom axis is considered to be "in-lb of torque".
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Old Sep 16, 2008, 09:31 PM
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It is sorta confusing the way they have the graph laid out, and it doesnt look like the motor quite matches their 90% efficiency claims. But if im reading it right, the very light green line across the top represents the 48V constant line voltage. The wavy light black line running downhill(left to right) is RPM. No load rpm at 48V is around 3850, no load current (red line , bottom) looks to be about 2a. Looks like it is most efficient at around 60a where the rpm is around 3300 and power out is around 2200 watts. At 100a load the efficiency starts to drop and rpm is down to around 2950, power out is now about 3500 watts.....ect. If you want to figure the horsepower, divide the power out at the various current levels by 746 as satanicoo did above. If you take his figures and multiply X the efficiency at 100 amps its fairly close to what the chart gives for power out at that current draw.
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Old Sep 18, 2008, 02:29 PM
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Thanks for the help!
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Old Sep 21, 2008, 01:30 PM
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Alternator motor to drive another alternator

What I am trying to do is build a self contained charging system using a 12 volt deep cycle battery, a 12 volt 150 amp alternator and an electric motor of some sort to turn the alternator. My question is, could I use the alternator as a motor and would it put out enough power to turn the 150 amp alternator? If so would the power consumption of the alternator motor exceed that of the alternator therefore defeating what I am trying to do which is to keep a 12 volt battery charged while in use. Hope this makes sense and I appreciate any suggestions.
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Old Sep 21, 2008, 04:07 PM
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Sounds like one of the oldest engineering challenges known. The old Perpetual Motion machine. I would think it would be tough to accomplish. Electricity has to much loss. But you never know. There are some real bright people around here.

Rob...
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Old Sep 21, 2008, 04:36 PM
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Yeah I know.... People are doing it with windmills but man it would be great to find a motor that was so efficient it would allow the alternator to have enough power left over to keep a battery charged. The law of physics says it's impossible but who would have ever thought you could talk on a cell phone to anyone in the world with no cords attached to it. I already read where one guy was successful at building a motor that spun an alterator and the end result was a 43% surplus in power but he is still experimenting with it. That tells me there is hope and from what I've seen on this message board there is probably someone here that knows how to do it. Again, thanks for any suggestions.....
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Old Sep 21, 2008, 07:59 PM
If it flies, I will crash it
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Good points. I do know one thing, if you figure out a way to do it you would be the richest man in the world.

Rob...
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Old Sep 22, 2008, 07:52 PM
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Please do not get into a perpetual motion discussion, it will kill this topic.
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