Re: [CAD_CAM_EDM_DRO] Re: Increased power to Gecko 201's

caudlet wrote:

>>Torque at rest will not change at all. The high speed torque will
>>
>>
>improve
>
>
>>about twice at any speed above a crawl. And, so, whatever your top
>>
>>
>speed
>
>
>>is now (I'm assuming you are limited by the motors losing steps)
>>
>>
>should
>
>
>>roughly double. Also, your motors will run quite a bit hotter. I'm
>>guessing those big motors run pretty cool now, so that may not be a
>>
>>
>problem.
>
>
>>This is a 50 VAC transformer (or 100 VCT with a 2-diode rectifier)?
>>
>>(If your speed limit is due to the computer's speed at producing
>>
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>step
>
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>>pulses,
>>then you'll get no benefit, of course.)
>>
>>Jon
>>
>>
>
>Jon, I am not disputing what you say but I don't understand the
>physics here. If you limit the current to 6A by controlling the
>pulse width how can you get more power out (torque) when the input
>power remains the same? Does charging and discharging the inductance
>faster show up in efficency gains?
>

Not efficiency, but the inductance is the key. The definition of inductance
is voltage divided by inductance = rate of current rise. So, if you
increase
the voltage, you get a faster voltage rise. This is what limits the top
speed.
When the step rate increases, more and more of the time between steps
is taken up with the current ramping up to the limit. And, finally, above
some speed, the current never even reaches the setpoint before the next
step comes.

> I can see how the stepper would
>move postion faster but is it a 1:1 ratio gain? I assumed the larger
>heat rise is due to IR losses to an extent.
>

No, in fact, IR loss is constant (although it actually goes DOWN when the
driver can no longer even reach the current limit.) What causes the
increased
heating is eddy losses in both the copper and iron, and also hysteresis loss
in the iron. Mariss points out the Iron eddy and hysteresis losses are so
large, you can hook a stepper motor to a machine spindle and overheat it
at several thousand RPM. This is with NO current in the windings!

> Am I making false
>assumptions that the pulse width per pulse is not limited to whatever
>products the current? Help me out on the concept and where the power
>gain comes from.
>
>

It is not a gain in power. Just the ability to ramp winding current
quickly up
to the limit. Double voltage, you get the current to rise twice as
fast. So, the
speed at some torque should be about twice as high. The high losses in the
motor defeat this somewhat, but it will still make quite a difference. And,
the higher the inductance, the more critical it is. I think the
original question
was in relation to size 42 motors with modest current and higher IR drop,
which implies very high inductance.

I am talking almost exclusively about Gecko 201 (and 210) drives here, as
that is what the original question was pertaining to. It probably
applies to
most bipolar chopper drives, as well. It may, or may not pertain to other
types of drives, such as unipolar.

Jon