Re: Confused over My own Calculations!

Jon Elson wrote:

> No. Wattage is a better way to calculate it for a chopper-type

drive.

> Each winding is, say, 2 V at 4 A, so that is 8 W. So, the real

power

> delivered to each winding at idle is 8 W, or 16 for both. Now, you

have

> to add some factor for losses in the motor and the driver. This

might

> be 5 W or so at idle. So, 21 W as a rough guess. With a 65 V power
> supply, the draw should be I=P/V = 21/65 = .32 Amps.
>

Thanks Jon:

I feel much better now.

So where does that "2/3" factor I keep seeing come from?
Or is that one of those good ol empirical rule of thumbs?

And that pesky Name Plate Amper Spec.
Is that a max. per winding or some total?
And the Gecko drive amper setting should be set to this value for
series (8 wire motor) and twice this value for parallel?

Tom M.















mayfieldtm wrote:

>
> > Thanks Dave:
> >
> > I understand what your saying, but it just does not make sense

that a

> > the name plate rating would be specifying any particular mode

such as

> > bipolar or series or whatever unless it specifically says so.
> >
> > I take the amp rating to be the maximum amperage on any one

winding.

> > All the other specs such as ohms refer to only one winding.
> >
> > If a motor has 8 leads or 4 windings, then each winding can

handle up

> > to 3.5 amps, and if you tie two of the winding together in

parallel,

> > then that pair can handle 7 amps. Then you tie the other 2

together,

> > then that winding pair can handle 7 ampers also. So the total

motor

> > current is 14 amps.
> > Take this same motor and connect in series, and each winding pair

can

> > handle 3.5 Amps for a total motor current of 7 amps.
> >
> > Is what your saying is that the stated maximum current is the

TOTAL

> > maximum motor current in any configuration? Now that just might
> > penetrate my thick skull. But, in that case, you would think a

better

> > spec would be maximum wattage.
>

> Now, this is ONLY at idle, and will vary due to the design of the

motors

> and drivers. When the motor is producing substantial torque at some
> speed, the power drawn will increase dramatically, and therefore the
> current mist also rise. But, the peak power may occur only during

acceleration,

> and therefore be transient. So, you should not need a power supply
> rated for continuous output of 8 A per motor in the above example.
> Probably 4 A/motor would work in most cases, except where you know
> all motors would be accelerating simultaneously.
>
> Jon