Cool drive

[Mariss Freimanis]

OK, "cool" as in "your motor will stay cool". I ran data for the attached graph this morning and the results are very interesting.:-)

The "cool" drive is an experimental G203V that addresses motor heating big time. The drive can adjust the power supply voltage to the motor as speed and load changes. The motor always "sees" the optimum voltage for a given load and speed.

"Optimum" means a low supply voltage at low loads, rising to maximum as load increases. This means the motor stays as cool as it possibly can at any load. At no-load, the motor can be as much as 6 times cooler than up until now.

The black "detent torque * RPM" line is the theoretical minimum power that must go into the motor. It is the "price" of turning the motor, equal to detent torque and friction times RPM. The "case temperature limit" line sets the limit for how much the motor can dissipate without overheating.

So, what does all this mean to me? Why should I care?

High voltages gets you high power output (the motor can give 75W mechanical at 60VDC ) but it comes at the expense of an overheated motor. The experimental drive decouples this cause and effect and that is makes it exciting; it is a "you can have your cake and eat it too" moment. You can:

a) Run your motors "as is" and have much cooler motors.
b) Run your motors "hot" (a really high supply VDC) and get much more peak power from them.

Good deal either way.

If it all works out, this new feature will be included in the upcoming G201X, G203X and G250X drives.

Mariss

[Mariss Freimanis]

OK, "cool" as in "your motor will stay cool". I ran data for the attached graph this morning and the results are very interesting.:-)

The "cool" drive is an experimental G203V that addresses motor heating big time. The drive can adjust the power supply voltage to the motor as speed and load changes. The motor always "sees" the optimum voltage for a given load and speed.

"Optimum" means a low supply voltage at low loads, rising to maximum as load increases. This means the motor stays as cool as it possibly can at any load. At no-load, the motor can be as much as 6 times cooler than up until now.

The black "detent torque * RPM" line is the theoretical minimum power that must go into the motor. It is the "price" of turning the motor, equal to detent torque and friction times RPM. The "case temperature limit" line sets the limit for how much the motor can dissipate without overheating.

So, what does all this mean to me? Why should I care?

High voltages gets you high power output (the motor can give 75W mechanical at 60VDC ) but it comes at the expense of an overheated motor. The experimental drive decouples this cause and effect and that is makes it exciting; it is a "you can have your cake and eat it too" moment. You can:

a) Run your motors "as is" and have much cooler motors.
b) Run your motors "hot" (a really high supply VDC) and get much more peak power from them.

Good deal either way.

If it all works out, this new feature will be included in the upcoming G201X, G203X and G250X drives.

Mariss

[BobF]

Looks sweet!
Mariss you continue to amaze.

[Mariss Freimanis]

It's kind of fun to see what pops into your head sometimes. This one came unbidden out of the blue.

Mariss

[D.L]

Hi Mariss,
In 6 to 12 months time I want use a large d.c servomotor for a spindle drive.
Can I hope for a shiny high voltage geckodrive under the christmas tree?
Are you keeping an eye on the ac servo scene?
Somehow they tie ac and dc into the one shebang, a do anything drive.

[Xerxes]

Mariss,

Cool indeed!

Have you verified that winding currents stay constant with cool drive? From graph it seems that most of the time power dissipation is lower than in DC situation (0 speed).

[Mariss Freimanis]

The motor is a resistive load from zero to 100 RPM. Above 300 RPM the motor is an inductive load.

Mariss

[Xerxes]

Coils surely won't lose their resistance above 300 rpm. So I²R loss still should be present if there is current.

[Mariss Freimanis]

The blue curve minima inflection point is 4.5W at 300 RPM, not 0W. 3.5W of that is accounted for as remaining iron losses, leaving 1W as copper losses at this speed. Solving for I, calculated motor current is 1.05A which matched the current probe measurement.

Mariss

[Xerxes]

Ok. What is the current in upper graph @ 300 rpm? Current should be equal at all speeds to make graphs comparable.

The graph text says 2A/phase which would make a big difference against 1.05A.

[Mariss Freimanis]

"Current should be equal at all speeds to make graphs comparable." No, they shouldn't be and that is exactly the point of this circuit.:-)


Note the Y-axis units are Watts dissipated in an UNLOADED motor over a 0 to 3,000 RPM range.

When a motor is set to 2A per phase (as in both instances here), current decreases when the motor speed is past its corner frequency, a speed that separates the constant torque region from the inverse torque region. Clearly a 1.05A phase current indicates the motor is operating in the inverse torque region, forced there by modulating the supply voltage to a lower value.

Meanwhile the red curve shows the motor is happily chugging along at 2A to nearly 1,000 RPM and dissipating an enormous amount of heat. Both motors are running no-load so no mechanical power is being delivered. Both motors are turning; one is stinking hot, the other isn't.

Mariss

[Xerxes]

So does the cool drive increase current from 1.05A to 2A when motor is loaded? It would be the only way to make sense to me.

Otherwise it seems that cool drive doesn't regulate current so well (corner freq @ 300 rpm instead of 1000 rpm).