MOTOR SPECIFICATION REQUEST WITH GIVEN CONDITIONS

[Ethnan]

Hello Everyone,

Please I need recommendations for the affordable commercial motors to be used, given below specifications and required functionalities.

First Case
1. Torque of inertia weight to be driven(load) and all opposing torque will vary from 1Nm to 4Nm.
2. Constant speed of revolution required for load: 3,000RPM
3. Minimum power of motor: 1,200W
4. Speed sensor is attached to load to send feedback on speed to motor
5. Motor required to automatically adjust power to maintain load speed at 3,000RPM, as the opposing load torque keeps changing
6. It's desirable to be able to start the motor with batteries in 30 seconds, after which switchover to normal supply source is done

Second Case
1. Torque of inertia weight to be driven(load) and all opposing torque will vary from 1Nm to 4Nm.
2. Constant speed of revolution required for load: 1,500RPM
3. Minimum power of motor: 1,000W
4. Speed sensor attached to load to send feedback on speed to motor
5. Motor required to automatically adjust power to maintain load speed at 1,500RPM, as the opposing load torque keeps changing
6. It's desirable to be able to start the motor with batteries in 30 seconds, after which switchover to normal supply source is done

 

[waross]

A 1.5 HP induction motor will run at about 2850 RPM at 4 Nm and about 2950 RPM at 1 Nm.
Direct start across the line (DOL).
No need for batteries.
If you need better speed regulation than that it gets more expensive, quickly.
By the way, an oversized motor such as 3 HP or 5 HP will give better speed regulation with that load if you can start it on your supply.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Ethnan]

Speed regulation is a key requirement in the design as I mentioned earlier, as the Load will keep changing. I need an available product in the market

 

[BrianPetersen]

Does "3000 rpm" mean 3000 +/- 0.001, or does it mean "somewhere near a nominal 3000 rpm", or does it mean "3000 rpm +/- 10%", or what does it mean?

The cost of maintaining 3000 +/- 0.000001 rpm is much much higher than the cost of maintaining "somewhere near a nominal 3000 rpm".

Back up and tell us "the big picture" of why you need to start this motor using batteries and then switch to AC power. The fact that you can switch to AC power means the AC power is available, so why not just start it with AC power and forget about the batteries?

An off the shelf Allen-Bradley Powerflex VFD connected to an off the shelf 2 horsepower AC induction motor will do most of what you want the least expensively. But no encoder feedback and no battery start-up. If all you need is "somewhere near 3000 rpm" you don't need a speed sensor or encoder feedback. The drive and induction motor will be good enough on their own.

If you really, really need the encoder feedback to hold speed/position precisely, an SEW Movidrive or MoviAxis with the right options will do it - But no battery back-up! I don't know how to do that. Contact your local SEW Eurodrive sales representative.

 

[waross]

What percent speed regulation do you need?

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Ethnan]

Thanks guys for your time. Really appreciate this.

The speed regulation would be within +/-5%. That will be fine.

An inverter system would do the job with a battery startup. So no issues for me.

The feedback system to maintain the speed at 3000 RPM +/- 5% is the challenge.

I dont have a deep experience on brushless DC motors, but dont some of them come with speed regulation feedback system?

 

[davidbeach]

Pretty sure that a sensor-less vector drive can maintain +/-5% as is.

You stll haven't answered the question about why batteries for starting?

 

[Ethnan]

Remember the load is changing from 1 to 4Nm opposing torque. Can a sensor-less vector drive can maintain +/-5% speed regulatiom without any feedback on system speed?

Actually, want to be able to run the system also off my battery bank, as AC power is hardly reliable (not upto 10 hours a day in my locality)

 

[davidbeach]

Back EMF from the motor provides the necessary speed feedback.

You’d need drive without a front-end, a battery bank with the right voltage, and a charger that can carry the load and charge the batteries at the same time. Otherwise you’d be going ac-dc-ac-dc-ac and that’s not the most efficient set up.

 

[itsmoked]

"Sensorless" really only means "no additional sensor added". The motor itself provides a sensing ability. In sensorless vector mode the VFD know precisely where the rotor position is at all motor speeds above a couple of RPM. You need additional sensoring only if you care about precision around 0rpm.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[FacEngrPE]

Most inverter drives will fault if no AC SUPPLY IS PRESENT. If you want to run the drive with a battery connected to the DC Bus Link, or in place of the rectifier section talk to your supplier. You might need a custom drive program to do that.

The equivalent of speed regulation in an across the line AC Motor is "slip".
With a synchronous motor slip = 0.
With an asynchronous motor slip at full load is between 2 and 5 % depending on motor size.

If you want to do this with a DC Motor with across the line start, and can accept the motor's natural regulation, this reference

https://www.electricalexams.co/speed-regulation-dc-motor/

indicates that that a DC differential compound motor can provide 3 to 5 % regulation on a constant voltage power supply.

You need to ask your motor supplier if they have or can make what you want for a reasonable price.

 

[Ethnan]

Thanks so much guys!!

The sensorless vector drive incoporating a VFD is cool for this really. Wasn't familiar with the term vector drive. Now the draw back is the cost of an inverter system required to invert battery voltage to AC, when AC power isn't available. And this complicates the system, introducing more failure points and reducing reliability.
A DC motor wont require an inverter,could this be the way to go? A DC differential compound motor would have the best speed regulation as read on the link provided. If my thinking is correct, I would appreciate any link on these motors in the market.

 

[waross]

2850 RPM is a standard full load speed for a single phase induction motor.
It will run faster with a lighter load (less torque demanded).
It will approach 3000 RPM but never actually achieve 3000 RPM.
Off the shelf and cheap.
Off the grid? A suitably rated single phase inverter.
or
Spend more time and money.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Ethnan]

Many thanks guys!!

So I presume that with a vector drive like the GS4,one can control or set the RPM of a single phase induction motor to 1500RPM or any value below 2850 for that matter?

 

[waross]

If you are going to use a VFD, use a three phase motor.
If the motor is physically capable of taking the forces, (most are), a 1425 RPM motor can be run up to 3000 RPM and faster.
If the voltage is doubled as well as the frequency, the Volts per Hertz ratio is maintained and the HP may be double.
That is with a three phase motor and a VFD.
Note that a VFD is a special inverter.
There is not much overlap in the design and capabilities of a VFD inverter optimized to run a motor at varying speeds and an inverter used in solar farms.
The solar inverter will run at a fixed frequency, it will be able to match its output frequency to the small variations in grid frequency that most people are not aware of, while matched to the grid frequency the grid tie inverter will be able to offset its phase angle a few electrical degrees to allow and to control the amount of energy regenerated into the grid.
Then there are the basic inverters that generate a fixed frequency to run loads but are unable to sync to the grid.
I am suggesting that then third type of fixed frequency inverter, with a suitable surge capability driving a single phase motor may be an economical solution to running a motor within 5% speed regulation.
I may be wrong.
When you price it out, the three phase motor with a VFD may be more economical.
The three phase motor with VFD is a much more versatile solution.
It depends on your budget and possible future needs.


[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Ethnan]

I am going to weigh the options, seems I have plenty of information now to make my decision.
1. The 3 phase induction motor with a VFD system is a versatile solution. Drawback: May not work with my battery bank.
2. A single phase induction motor with an inverter may be more economical and would easily work with my battery bank. Drawback: maybe unable to sync its frequency with grid frequency.
3. Differntial compound DC motor is a possible good option. Wont require any inverter in between, but a rectifier is of course required to have it run off the mains supply.

 

[davidbeach]

That DC motor may also be far more expensive than the AC motors.

 

[itsmoked]

2hp 3phase induction motor
339V of battery
some sort of charger that can keep 339V of batteries charged.

Run the unit exclusively on the 339V battery with the charger capable of supplying more than 2hp of current. The charger will then be able to recharge the batteries even while running the motor. It will be "uninterruptible".

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You could do this much easier using a hobby BLDC motor with a hobby speed controller. Only problem would be the need to reduce the speed of most typical hobby motors. Perhaps a geared one or a belt reduction. Then it could all be done with a typical hobby battery pack and chargers at much much lower voltages, like ~20Vdc.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

2. A single phase induction motor with an inverter may be more economical and would easily work with my battery bank. Drawback: maybe unable to sync its frequency with grid frequency.

But why would you want to do that?
You are not exporting energy to the grid.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Ethnan]

Yeah you are right. Just saying.