Does anybody know how to brake an electric motor - with a VFD?

[zongatron]

Hi everybody,

I have a spin machine, imagine a potting wheel except it spins a flat canvas and then you pour paint onto it.

It has a VFD to control the speed.

My electrician is having a little trouble working out how to brake the spinning wheel once i slow it down or press stop.

As it happens now - I run it at about 1100 rpms and then when you switch it off, the VFD seems to brake it to about half that quite quickly and then it "disengages" and the wheel "freewheels" until it stops completely. (As it has a metal plate on it, there is a little weight which encourages the motor to keep spinning.)

It takes a long time to come to a complete stop and I want to make it stop a lot quicker.

I do a lot of stop/starting with my customers and the wait time is too long...

Anybody out there able to solve this?

Thanks

Ben

[BobL]

Every VFD is different so your answer depends on what VFD you have.
Have you read the manual?
You should be able to specify the acceleration and deceleration time
The manual should tell you at what frequency the VFD should stop the braking.
Bear in mind that not all VFDs can brake a motor to begin with

[zongatron]

Hi Bob

Okay thanks.

I will find out what type it is and take a look at the manual.

Ii had a brief look at it once and it may as well have been in chinese as I couldnt understand much at all.

I would be willing to change out the VFD though to one that brakes.

Do you know of a brand I could use which will brake it to a standstill?

Its a .18kw single phase motor.

Thanks again

ben

[BobL]

The used VFDs (HT1000)that Joe Hovel organised a group buy on (HT1000), out of the package, stop the motor in under one second.

[zongatron]

okay,

Thats a bit too quick.

I would like to stop it in about 3-4 seconds.

Im guessing that the stop time is adjustable on that VFD?

And would it be the same under load? Like with a spinning plate (40cm x 50cm spinning aluminium treadplate)

Thanks

[jhovel]

I suspect you have a Huanyang VFD? If you confirm that, I (and several others here) can help you easily to configure it to stop your little motor as quickly or a slowly as you like.
Do you know how to find and read and set the parameters on your VFD? If not, we can help you with that too.... :)
Once you get your head around that it's all pretty sraightforward.
When you are reading your manual, make a note of all the words you don't understand (in the sections that are relevant) and we'll interpret for you. The words are generally correct, but the grammar (and a few misspellings) make the manual a bit difficult to follow at first.... We have got our heads around it now though. :)

[BobL]

This is not going to help you the OP with his VFD but I recently pulled apart a very rusty 2kW 1P garden mulcher I picked up from kerbside pickup. I thought the motor was stuffed because the shaft would not turn easily but when I opened it up the motor itself were fine and what was stopping the rotor turning was a built in magnetic activated friction brake.

The brake "drum" is a semi-floating steel ring held by clips and a spring around one end of the rotor while a ring of frictional material is fixed around the bearing at the same end as and up against the drum.
In a off/stationary state the spring pushes the drum onto the frictional material making it difficult to turn the shaft.

When the coils are energised the induced magnetic field in the rotor pulls the ring away from frictional material and up against the rotor.

When the power is switched off the spring pushes the ring along the shaft to make contact with the friction material.

The brake stopped the motor without any load in less than a second and in about 3 seconds with the 200 mm diameter mulcher head fitted.

One more thing was the fan on this motor was the biggest I have seen for its size clearly taking into account that it had a frictional brake.

Pretty neat really, I'm surprised its not used more often.

[pjt]

In my VFD there is a starting/stopping menu, in the "ramp to stop" submenu I can specify the time taken to stop and an S time, there is also the start submenu, but as others have said check the manual for something like this.

I can also fit options like dynamic braking which is intended to stop overunning loads, the metal disc in your case, try the ramp to stop first tho

There are other options as well but the motor needs to be a 3ph


Pete

[zongatron]

Hi

Fantastic. Thanks guys.

I dont kow the brand of vfd as its encased in a box inside my machine and I cant read the brand.

The manual is at the electricians and so I will give him a call and see if i can come and get it.
I seem to remember I might have been able to read one online as well.

He did mention if he cant get the VFD to stop it he might be able to replace the motor with a braked motor like Bob described.

I would much rather just get the VFD working, or replace the VFD.

Its a childrens Painting activity and I suspect that the brake might be a bit clunky and noisy? And maybe scare the kids?

I cant get out there for a day or two, but will check back in ASAP to see if you can help with programming.

Thanks again

Ben

[pjt]

If you are thinking about changing the motor I would suggest change it to a basic 3phase (which will need to be wired in delta for 240v, this is a simple change your sparkie can do) plus some additional circuitry, this then opens up the possibility of braking the motor electrically independantly of the VFD.

Changing the motor to 3ph will also help with the "ramp to stop" and eliminate the free wheeling at the end of the slow down period as it is now, with the "ramp to stop" feature you will be able to fine tune the stop time to exactly what you want.


Pete

[RustyArc]

If you are thinking about changing the motor I would suggest change it to a basic 3phase (which will need to be wired in delta for 240v, this is a simple change your sparkie can do) plus some additional circuitry, this then opens up the possibility of braking the motor electrically independantly of the VFD.

Changing the motor to 3ph will also help with the "ramp to stop" and eliminate the free wheeling at the end of the slow down period as it is now, with the "ramp to stop" feature you will be able to fine tune the stop time to exactly what you want.

If the machine already has a VFD, it strikes me as fairly likely it has a 3 phase motor in it. You can run a single phase motor off a VFD, but not if you want to run it slowly, which I think would be the case here.

Since the motor already exhibits some kind of braking behaviour, it sounds like it may just be a matter of changing a parameter.

[koshari]

Firstly it's the nature of ac motors that electrical braking will be most effective at full speed as this is where the back emf if strongest but having said that I would imagine it should still pull up a little more linear than you describe. In fact we can get drives at work with danfoss controllers to literally stop on a dime
Without knowing the details of the VSD it's hard to comment on the configuration of your particular situation.

If the drive is set up correctly there are further measures that can be implemented such as a thruster brake assembly on the output shaft to improve braking.

[BobL]

Ben, did you ever post any pics of or links to the art the machine makes.

[zongatron]

Hi guys,

Yes i think you are right about the three phase motor. I think it is a 3 phase and they have configured it etc.

I have 4 smaller machines with a smaller plate. Its about 10 x 12 inches which has exactly the same motor and VFD as the larger one and all four of them stop just fine in about four or five seconds.

The only difference is the larger machine simply has a larger plate on it at about 16 x 20 inches. And it free-wheels and takes about 20 - 30 seconds to stop.

Another issue we are trying to solve is that it will not run slowly. It jumps from 0 to about 7-10 Hz and is running too fast for a bottom speed.

So the two issues I am trying to solve on the larger machine is to get it to run slow.... and also to stop quicker.

With the small machines you simply dial in the speed with the dial on the VFD which changes on the digital display. It will run at very slow speed so its hardly moving right up to full speed.

With the larger one, I have had an external pentiometer put on so the customer can control their own speed.
But it wont run slow and it goes from zero then just jumps to nearly 7- 10 Hz as its slowest

I should also probably mention that without the plate on it the shaft runs a lot slower, but is jumpy and wont hold a steady speed. Perhaps the pentiometer is not sensitive enough and so it cant hold a slow speed.

Also worth mentioning is that without the plate on it the shaft will also stop in a second or two with no freewheeling.

Its quite frustrating as I kind of need it to do those two things for the machine to become practical to use.


Just lastly, i never posted a link of pictures but if you would like to email me I can send you some pics - or if you look at the site below of the caloundra markets, there is a picture of one of my machines with a child putting glitter on their finished painting.
The main picture is a slideshow and I think its about the second picture along

http://www.caloundrastreetfair.com.au/twilight-markets-sunshine-coast

[zongatron]

Here are a couple more pics.

https://www.google.com.au/search?q=spin+art&client=firefox-a&hs=5NJ&rls=org.mozilla:en-US:official&channel=np&tbm=isch&tbo=u&source=univ&sa=X&ei=Yu1ZVJLAB8W48gWhnYC4CA&ved=0CCsQsAQ&biw=1280&bih=699#rls=org.mozilla:en-US:official&channel=np&tbm=isch&q=spin+art+eumundi&imgdii=_

first picture on the top left.

if the link doesnt work, just google - spin art eumundi

You can click on the picture and it comes up better

These are the smaller machines with a 10 x 12 inch plate

[koshari]

Iam beginning to think the potentiometer has a noisy wiper.

[zongatron]

The braking is looking good.

They are looking at some circuitry that will feed the current back into the VFD or somethiing...


Thanks all. Will let you know how it goes.

And I will get that manual so I can learn a bit more about them.