[TechAssist] Re: Just One Question
- From: "Ty" <ty1k@xxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 12 Aug 2004 07:58:53 -0700
The question is why a motor runs forward or backward when using 3 phase.
All brush less electric motors need more than 1 phase of power to start
rotation.
When applying power to a motors run winding, nothing happens. It cannot
start. It must have an off phase power applied in order to induce rotation.
This is accomplished by the start winding.
In 3 phase motors there is no specific start winding, for the 3 main
windings are powered out of phase.
As we know, standard 220V service 2 X 110, 180 degrees out of phase.
In 3 phase application, you have 3 sources of power 120 degrees out of
phase.
In actual application, phase 1 peaks in amplitude, than phase 2 peaks while
phase 1 decreases, fallowed by phase 3.
Let us say this will give us a clockwise rotation.
Reversing two of the wires, will give us phase 1 peaks in amplitude, than
phase 3 peaks while phase 1 decreases, fallowed by phase 2.
Giving a counter clockwise rotation.
Most capstan and lower drum assembly motors are 3 phase, and yes, you can
reverse them by switching two wires. Yes, your picture will be somewhat
distorted, and I think it would play hell with the tape.
There is another thing you have to look out for. It is called the Wild
phase.
In some applications this can be devastating to 220 volt single phase
applications.
I will not go into detail, but you should measure your 220V taps.
You might find that it is running at about 270V or more.
To overcome this, simply select another leg of the 3 phase line.
Having switched your main lines to overcome the 220V single phase problem,
you might have to switch wires on your motors to get them running in the
right direction again.
Ty
Tiberius Kraemer
BLUE STAR ELECTRONICS
3312 Silverton Rd. NE
Salem, Oregon
Phone: 503 391 1491
Mailto:ty1k@xxxxxxxxxxx
-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of GOMDWIL@xxxxxxx
Sent: Wednesday, August 11, 2004 10:40 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Just One Question
If you replace the main breaker box on a public building and when you turn
the power back on what would cause a three phase air condition to start
running backwards after the installation?
-There was no problem before. Just curious ,
GRADY
WILSON'S TV SERVICE
GOMDWIL@xxxxxxx
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