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Old 12-30-2008, 05:30 PM   #1
SAcharlie
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Default HP and RPMs

Is this a reasonable rule for motors.

A motor produces its max horsepower at half its max rpms while at half the volts of a given voltage system.

An example of a 48volt system is where the motor runs 4000rpm at 48v pulling 5amps.
Now you load the motor down to were it is only turning 2000 rpm but you are telling the controller to feed 48v.
At 2000rpm the motor only wants 24v, so the controller feeds 24v and converts the excess into amps.
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Old 12-30-2008, 08:08 PM   #2
roady89
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Default Re: HP and RPMs

No. A controller doesn't manipulate voltage that way. A controller is like a big light switch (or a bunch of switches working together)...the slower the switch switches on/off the less "On time" you have, less "on time" = less speed. The faster it switches the more "On time". The more on time the faster the motor will turn. Amperage is dependant on load, the controller will output as much as required up to the controllers amperage limit. If you have a 400 amp controller and your motor can't use but 300 of those amps at max load then thats all you will see out of the controller.
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Old 12-31-2008, 12:21 PM   #3
DOOmsman
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Default Re: HP and RPMs

Roady Is the controller on and offing or cycling the voltage up and down?
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Old 12-31-2008, 06:32 PM   #4
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Default Re: HP and RPMs

Quote:
Originally Posted by DOOmsman View Post
Roady Is the controller on and offing or cycling the voltage up and down?
Controllers do not vary voltage up or down, they only switch on/off....sorta.
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Old 12-31-2008, 06:31 PM   #5
SAcharlie
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Default Re: HP and RPMs

Its as Roady said the faster the switching the closer it gets to delivering the full pack voltage. Ive seen the term "chopper" used to describe these controllers.

Has anyone ever heard tell about a motor delivering its max HP at half its max RPMs?
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Old 12-31-2008, 06:36 PM   #6
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Default Re: HP and RPMs

Quote:
Originally Posted by SAcharlie View Post
Its as Roady said the faster the switching the closer it gets to delivering the full pack voltage. Ive seen the term "chopper" used to describe these controllers.

Has anyone ever heard tell about a motor delivering its max HP at half its max RPMs?
Not to sure what your asking.....it would depend on if the motor is designed that way.
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Old 12-31-2008, 09:59 PM   #7
SAcharlie
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Default Re: HP and RPMs

Well Im wanting to get some realistic RPMs with power output under various loads on either the GE D-394 or D&D 170-004-0001 for the ezgo H-12 transaxle. Believe the GE is known as the Beast and the D&D is known as the Stealth Stalker.

Most dealers list 11hp2700rpm@48v as Peak for the StealthStalker.
I take this to mean MAX hp.

Most list 11hp2300rpm@48v as NON-Peak for the Beast.
This may provide more hp...dunno.

Either way I would like to pin down the Max RPMs for these motors at 48v drawing ~40amps.

The dealers end up writing 2 or 3 paragraphs on what speeds to expect with this tire or that lift, when all that is needed are RPMs at 2 or 3 different amp draws to let ya know how the motor performs speed wise.
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Old 01-01-2009, 01:40 PM   #8
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Default Re: HP and RPMs

http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm
I looked this up click on formulas and there are formulas for watts amps hp it is a little deep for new years morning
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Old 01-09-2009, 04:12 PM   #9
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Default Re: HP and RPMs

The only way to truly test two motors against each other is to put them each on the same dyno and run the same conditions. You can't use the advertising numbers unless they give you all the details.
You need to know what is the voltage at the motor?
What is the current though the motor?
What is the load?
What is the RPM?
What is the ambient temp and motor temp?

Typically as the amps go up the volts go down, just the nature of batteries so I would need to know all the above questions every time they change to another RPM band.

You guys are close on the controllers, they don't switch faster, and the switching frequency remains the same. Controllers do vary the duty cycle, 5% means ON for 5% of the time and OFF for 95% of the time. 50% is half throttle and 100% is full ON.
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