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Old 02-11-2012, 11:22 AM   #1
CART-ZILLA
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Question motor rpm's

i understand how amps = torque ...but what determines the rpm's a motor turns ? is it the motor and how it's wound? i was wondering because in a week or two i'm getting a pq bandit and my stock motor says 2800 rpm and i would like to get more rpm's than that ...without going down a hill...lol oh and i have a 400 amp controller NEW batteries and i'm getting some better 4 ga cables too!
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Old 02-11-2012, 02:13 PM   #2
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Default Re: motor rpm's

Warning: Technical Content!

When current flows through a wire, a magnetic field is created.
When a wire passes through a magnetic field, an electrical current is created.
When an electrical motor is spinning you have both current flowing through wires and wires passing through magnetic fields.
In a motor, the current being generated by the wires passing through the magnetic fields opposes the electrical current creating the magnetic fields.
Therefore: A series wound motor will accelerate until the voltage of the current being generated equals the voltage of the current being applied to create the magnetic fields (Or the armature explodes from the centrifugal force, or other physical malady)
Hence: With an unlimited current source, applied Voltage determines RPM of a series wound motor.
The same is true with shunt wound motors, except the field windings can be excited separately from the armature windings and that alters the equation.

I used the phrase "Unlimited current source" in the explanation because the current source in a cart is limited by undesired resistance in the cables, connections and components often found in carts, as well as the way batteries themselves work. (IE: Terminal voltage is lower while under load)

In instances where the high current circuit has excessive resistance, or the batteries are weak, some speed can be gained by installing new cables, batteries and other components, but the gain is due to reducing the voltage losses in the motor circuit, therefore increasing the voltage actually being applied to the motor.

Yes, a motor's max RPM it is determined by how it is wound, among other things.
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Old 02-11-2012, 06:56 PM   #3
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Default Re: motor rpm's

ok sooooooo ...... when pq rebuilds my motor will it be wound differently than before = more rpms?? .....redneck terms please....
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Old 02-11-2012, 07:04 PM   #4
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Default Re: motor rpm's

basicly are the guys at pq gonna do this ....a guy posted this here :Re: Stock '91 - Just a little faster?

--------------------------------------------------------------------------------

Well folks here it is: DONE. My 1991 36V Ez-Go "tank". Standard Wheels, Standard (275 amp) Curtis controller, New batteries, home-build 2ga wiring, standard (now cleaned and restored) solenoid & FR switch. Freshly restored Total Charge (manual timer) charger.

I decided to modify the motor myself. I replaced the motor bearing, replaced the brushes, resurfaced the commutator, and re-wound the series coil on the stock GE 2800 rpm motor.

During the re-wind, i re-varnished the coil wire and wound it closer/tighter against the ferrites. I removed precisely one turn from each of the four ferrites, then re-wrapped each with fresh high-temp teflon tape.

The results: from a stately 11-12mph NOW a brisk 17mph (18-19 if we're down hill ) - Measured with a Bushnell sports radar gun......he said it is now spinning 4400-4600 rpm's
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Old 02-11-2012, 07:36 PM   #5
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Default Re: motor rpm's

Please be careful, as these motors can self destruct!
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Old 02-12-2012, 08:42 AM   #6
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Default Re: motor rpm's

I watched a video on youtube where pq were dynoing a bandit motor and spun up to 10,200 rpm's That leads me to believe 4400 to 4600 rpm's is pretty safe...
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Old 02-12-2012, 09:07 AM   #7
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Default Re: motor rpm's

Quote:
Originally Posted by CART-ZILLA View Post
ok sooooooo ...... when pq rebuilds my motor will it be wound differently than before = more rpms?? .....redneck terms please....
Being a redneck myself, I thought those were redneck terms.

Kidding aside, I don't know what PQ does when they apply their magic and I've never studied motor design, or given much thought to it, so I'm not sure why removing one loop in the stator windings would reduce the generation of Back-EMF enough to significantly increase the max RPM for the applied voltage. I can see how doing so can increase max RPM, but almost doubling it amazes me.

I'll probably put on my tin hat, go into my screen room, play some Rock 'N Roll from vinyl disks through tube type amplifiers, smoke a Macanudo or two and figure it out, but only to satisfy my curiosity.
Personally, I'm leaving building and modifying motors to the people that have conducted some R&D and their livelihood is dependent on the products they produce.

If I wanted more speed, which I don't, or at least not much, I'd go to taller tires and throw more amps at the motor to make up for the lost torque. If that wasn't enough speed, I'd go to a commercially available higher RPM motor and/or more voltage.
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Old 02-12-2012, 09:12 AM   #8
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Default Re: motor rpm's

I see in your sig you are on 36 volts. AN increase in voltage will increase the rpms and torque.
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Old 02-12-2012, 09:33 AM   #9
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Default Re: motor rpm's

Quote:
Originally Posted by CART-ZILLA View Post
I watched a video on youtube where pq were dynoing a bandit motor and spun up to 10,200 rpm's That leads me to believe 4400 to 4600 rpm's is pretty safe...
I think bearings and balance would be the more critical issues up to about 6K and structural integrity would also become a major concern at RPMs above that.

If I was going to spin an armature over about 6K, I'd want every aspect of it to be X-rayed and/or Magnafluxed before I sat two feet away with my back facing it.

FWIW - The stock motor in my PDS cart spins at 4400 RPM (18.2 MPH on 17.4" tires) and will spin at about 5500 with an aftermarket controller. (24 MPH on 18" tires)
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Old 02-12-2012, 01:41 PM   #10
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Default Re: motor rpm's

Quote:
Originally Posted by scottyb View Post
I see in your sig you are on 36 volts. AN increase in voltage will increase the rpms and torque.
I thought about that but I don't want to upgrade my controller I just bought the 1 I have.could i have an extra battery with that controller its a curtis 1204.
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