Re: [CAD_CAM_EDM_DRO] stepper amperage question

Excuse me, but all other things being equal, doesn't doubling the voltage
usually _divide_ the amperage in two?

Bill

On Thu Mar 7 17:56:49 2002, Alan Marconett KM6VV, <KM6VV@...> wrote:

>Hi Kevin,
>
>All stepper motors want a limited amount of current. 3A in your case.
>Too much, and you fry the stepper (yes, doubling the voltage usually
>doubles the amperage)!
>
>The faster you get the motor current to 3A, the faster the motor will be
>able to accelerate (L/R time constant). SO, we can use MORE Voltage to
>get us to 3A faster. As long as we don't exceed 3A. The simplest way
>is to limit the current, with a BIG ol' resistor. This is often done in
>inexpensive unipolar drivers. If we want to use 12V to "get us there"
>faster, then we need to drop 7V across the resistor (12-5=7). E=I*R, so
>2.3 ohms ought to do it. This is called an L/R driver. 21 watts will
>need to be dissipated in the resistor (3*7), the motor gets 15W (notice
>a problem here?). A better way is to "chop" the current, such that it
>never exceeds 3A. Most all bipolar and some unipolar drivers do this.
>No big resistors! The current is rapidly turned on and off, and only
>allowed to reach 3A.
>
>So, if if you have an L/R drive (formula above), either add, or increase
>the resistance AND wattage of the L/R resistors (the big HOT ones). A
>chopper driver would probably already be running at or near it's rated
>voltage; which is typically limited by the ratings power devices. An
>L/R driver would also be limited by ratings.
>
>HTH
>
>Alan KM6VV
>
>
>kevinagilent wrote:
>>
>> I would like to know if someone out there can shed some light
>> when you have a unipolar stepper motor and a unipolar stepper
>> controller the motor is rated at say 5v. and 3. amps if you want to
>> increase the motor voltage to say 12v. does the amperage also double?
>> lets say i want to increase the voltage to 24v. what would the
>> amperage need to be ? is the a formula that someone could tell me?
>> thanks for the help
>> kevin

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