DC motor and drive or AC motor and Vector drive? 1

[parker]

Hi all,

I'm an ME, so please be gentle with the replies....
I would like to replace a 1HP AC motor on a product with a new motor and drive combination, but I would like to add servoing capabilities at the same time. I have limited experience using a DC motor with a PWM drive and know it could get the job done. However, I'm wondering if an AC motor with a vector drive is a better choice?
Can a vector drive servo and hold position if an encoder is used for feedback?
Can a vector drive be used with single phase power?
Cost for the motordrive combination is a major concern. Which choice is "best bang for buck"?

Another reason for this change is that I currently have to supply 8 different AC motors to account for a variety of phase/frequency(International)/voltage combinations as well as a couple different power boards. Ideally, I would like one motor and power boards that could accomadate any combination of phase/frequency/voltage, but reducing the number of motors is my primary goal.

I would like to get up to speed on advantages and disadvantages of both choices, so any links would also be greatly appreciated.

Thanks for you time.

 

[cbarn24050]

Hi, dc is better at this power level.

 

[Lewish]

An AC drive and controller is generally less expensive. And, a vector drive can be made to servo, but most are not designed with capability. It would be a special order. So, I think you might want to go with a DC motor and servo controller.
To your other question, yes vector drives are commonly single phase at this horsepower rating. They convert the power out to the motor to 3 phase.

 

[jOmega]

Lewish,

Could you give us specific references (manufacturer, model, etc.) of 1-Phase input / 3-Phase output AC FLUX VECTOR Drives ?

Thanks.

 

[ischgl99]

Toshiba has what you are looking for, don't know if they will control accurate enough for your application though. The S9 series drives are single phase input w/ 3 phase out. I have used Toshiba for years and am happy with them, in fact I am purchasing one of the surplus S7 drives for my home shop.

http://www.tic.toshiba.com/productgroups.php?family=Drives

Mike Bensema

http://www.dutchmenservices.com

 

[parker]

I'll take a look at Toshiba, but I'm leaning towards using the DC drive and motor at this point.

Is there a rule of thumb for Horsepower when going from AC to PWM DC? I'm currently using a 1HP AC motor, but it looks like a 1/4 HP DC motor with PWM drive may be all I need. (I have a motor and drive on order for testing) Does 1/4 HP seem reasonable? Application: I'm basically spinning up a mass from rest to about 300RPM and then bringing it to a stop.

Thanks again for the help.

Parker

 

[jOmega]

Thanks for the reference, Mike B.
An impressive unit if it performs to the spec sheet claims.

The Toshiba S9 data sheet states that the unit is
rated 1/2 - 3 HP at 200-230vac single phase input - three phase output. Also available in three phase input in 200-230v and 460v chassis.

Information can be obtained at

http://www.tic.toshiba.com/productpages.php?prod=S9

• Up to 250% Torque at 1.0 Hz
• Speed Regulation of 0.5% Over a 60:1 Speed Range
• One Step Automatic Motor Tuning
• All of This Without an Encoder!
• Acccel/Decel range 0.1-3600 seconds

 

[jOmega]

Parker,

Is the mass to be direct driven by the motor shaft ?

What are the acceleration and deceleration requirements; i.e., 0 to 300 rpm i _______ seconds and 300 to 0 rpm in ____ seconds ?

What is the inertia of the mass ?

and what is the Duty cycle ..?
- define 1-complete cycle of operation from zero speed to max speed and back to zero and how long at rest before cycle repeats .... define in terms of time for each part of cycle and don't forget dwell time at speed and at zero speed....

This will help to make some calculations.

AC or DC ... HP is HP and Torque is Torque. 1 HP AC is same as 1 HP DC and 10 inch-lbs AC is 10 inch-lbs DC.

What's important is to get the performance from the drive-motor combination that satisfies the application needs.

 

[jbartos]

Suggestion: It is better to obtain correct information from the DC drive and DC motor manufacturer tech support since the product may have special requirements for its applications.

 

[electricuwe]

For you application both types of drives PWM-DC or Vector drive will be applicable.

Do not base the power rating of the new drive on the power rating of the old design but do a calculation based on the planned load cycle.

Using a motor which is to large would result in the following:

higher cost, higher volume
poor performance, because a larger motor will have higher inertia

The DC drive will available for lower cost but be careful to select the right material for the brushes (carbon or precious metal). Consult the manufactureres literature on that topic (e.g from maxxon).

The AC-Vector drive will be more expensive and should only be choosen if you cannot design an DC-drive to get approbiate lifetime

 

[jbartos]

Suggestion: The DC Drive and Motor may have the higher maintenance and operation costs, which in some cases is important in others not.

 

[jraef]

parker,
A good rule-of-thumb on this is that a DC drive and motor will still cost less up front than an AC Vector drive and motor up to and including 2HP. Make sure that you order a 4 quadrant DC drive by the way, it is necessary for a servo-like application. Above 2HP, the DC motor and drive combos tend to get more expensive if you want 4 quandrant. In the long run, the DC package will require more maintenance but how much is difficult to predict based on useage.

If you choose to go AC, make sure your vector drive is a Closed Loop Vector using an encoder feedback. As good as they have become, you cannot do servo performance with any open loop vector drive. Servo implies positioning control and/or 100% torque at zero speed (for holding) and an open loop vector drive is never going to be accurate enough for that. The Toshiba S9 mentioned above is a nice drive, but it is an open-loop vector drive, not suitable for servo applications.

Another thing to consider by the way is actually using a servo drive and motor. Prices have beenm dropping like a rock in this HP range. Check out Baldor and Yaskawa. I have lost several VFD orders to their servo drives recently.

Good luck.


Quando Omni Flunkus Moritati

 

[parker]

jOmega,

Is the mass to be direct driven by the motor shaft ?
It's a belt drive with about a 5.75/1 speed reduction.

What are the acceleration and deceleration requirements; i.e., 0 to 300 rpm in ______ seconds and 300 to 0 rpm in ____ seconds ?

About 5 and 2 seconds.

What is the inertia of the mass ?
It varies...This is for a wheel balancer with a maximum assembly weight of 175 pounds. ( Note tread design and corresponding wind resistance plays a major role and complicates things)

and what is the Duty cycle ..?
- define 1-complete cycle of operation from zero speed to max speed and back to zero and how long at rest before cycle repeats .... define in terms of time for each part of cycle and don't forget dwell time at speed and at zero speed....

Again this is tricky to define due to mounting/ demounting/ re-remounting issues. Basically, one spin every minute with an expected life of 75,000 cycles. The minute would be from start to start with the worst case wheel taking a maximum of 30 seconds to spin up to 300 rpm/ spin for 16 revs/ spin down/ pause/ and repeat.

I currently use a PWM drive with a DC motor to do something similar, but it's a 1/2 HP motor and "home-grown" drive that I think would be overkill in this situation. Cost is a big factor, so I want the cheapest motor and drive system that will work.

Thanks again for all the great information/advice on this thread.

Parker