Re: [CAD_CAM_EDM_DRO] stepper amperage question

Hi Bill,

Apply ohm's law: E= I*R. Double the voltage, the current doubles. IF
you wanted the wattage to remain the SAME, and you double the voltage,
then you NEED to halve the current. P= I*E

HTH

Alan KM6VV


Bill Vance wrote:

>
> 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