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setrite
14-06-2014, 05:16 AM
Working for an OEM that uses these compressor on products I noticed that the trainer mentioned these motors as Permanent Magnet brushless DC motor, where I am sure that there is an IGBT used that converts DC to AC and sends AC current to the motor.

Have an discussion going on with Boss who says these are DC motors, but I say no these are AC. Although it is proven that the motor is supplied with simulated AC current but it nowhere mentions that the motor is an AC motor.

What motor is it ?

RusBuka
14-06-2014, 09:31 AM
http://c2n.me/ije74P
http://c2n.me/ije8dl

Tayters
14-06-2014, 11:04 PM
The term DC is a bit misleading in this case.
Not that I've got any proof anywhere but I'd take it the DC stands for Digitally Commutated or Digitally Controlled.

The motor itself is wired as a three phase star winding. The rotor is a permanent magnet (makes it brushless then...) so the stator is where the Direct Current voltage is fed through the windings first one way then the opposite way to get the change of magnetic field or as the electric world call the process, commutate.

So that's one to you, nil to the boss. Time for a pay rise!

Grizzly
15-06-2014, 12:15 AM
Basically, a DC supply is converted to DC the supply is then chopped and adjusted.
Before being converted back to AC and supplied to the motor.
Effectively the frequency is adjusted.
Hopefully that is put simply enough.
That's where VSD's are scary because of the huge DC voltage's within them.
Also many have large capacitors which need to be allowed to discharge before going near them.
Or DC is not for Direct Current.
And Taters explanation is correct?
Not 100% sure on the turbocore, but others are as I describe.
Maybe others can clarify more?

Grizzly

Tayters
15-06-2014, 12:24 AM
Just to clarify the term I describe is when you see Brushless DC motor or DC Inverter

Otherwise when you see DC being chopped up and made to AC then this is talking about the DC we know and love. Perhaps not love if you touch the capacitor though.

setrite
15-06-2014, 06:05 AM
Thank you for all the replies here.
This link finally helped me win. http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

So now, can all motors that are VSD driven be called a DC motor. As Grizzly said Digitally controlled.

FreezerGeezer
15-06-2014, 07:24 AM
The couple of Turbocor-fitted chillers that I've looked at had 3~ power, so I assume they're either VSD 3~ or Digitally Commutated. But why would you bother with DC if you have a 3~ supply anyway?
I'm afraid I always assumed the reason for domestic DC inverter systems is because there's not normally a 3~ power supply available.

Edit: I'm obviously a bit late to the party. ;)
But am I right about domestic DC?

setrite
15-06-2014, 08:06 AM
The couple of Turbocor-fitted chillers that I've looked at had 3~ power, so I assume they're either VSD 3~ ?

These machines too have 3 phase incoming power which is internally converted to DC and then to simulated 3 phase AC ( chopped DC ) to control motor frequency by the built in turbocor VSD. The confusion rose because the manuals mentioned the motor as being "Permanent Magnet Brushless DC motor".

glenn1340
15-06-2014, 10:05 AM
One thing to be aware of on the big VSDs are the capacitors: ALWAYS allow them to discharge, the manufacturers place warnings stating the time for them to do so. There was a case in America where an engineer had shut the power off to a machine and removed the covers but hadn`t allowed the capacitors to discharge, he slipped, fell onto the capacitor bank and was killed. I always allow twice the time stated by the makers just to be sure.

setrite
15-06-2014, 04:32 PM
One thing to be aware of on the big VSDs are the capacitors: ALWAYS allow them to discharge, the manufacturers place warnings stating the time for them to do so. There was a case in America where an engineer had shut the power off to a machine and removed the covers but hadn`t allowed the capacitors to discharge, he slipped, fell onto the capacitor bank and was killed. I always allow twice the time stated by the makers just to be sure.

Before starting any work on a VSD I look for a LED (most VSD's have it) that indicates presence of DC voltage, Switch OFF and watch the LED till it goes OFF, then measure the DC bus with a voltmeter to be sure that there is no DC voltage present.