480 v Motor with 208 v brake?

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hockeyoligist2

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I had a 480v motor, with brakes, go bad on a bar screen climber that got submerged in sewer water.

The manual release was stuck, so we tried to release it electrically.

Due to a broken rib and the position of where it stopped. I couldn't un-wire it or release the brake so that we could pull it up with our truck crane. So a mechanic removed the wires to try to energize the brake and release it.

Since I couldn't see, I told him to just connect two of the leads to the brake wires thinking that it was a 480v coil.

It smoked and didn't release.

He removed the cover and manually released the brake so that we could pull it up.

After we got it up to where I could see and he told me where he disconnected the wires.

It was a nine lead motor.

The brake was tied in to the wires on 6 and 9 and 4 and 7.

I must have missed that class on how that reduces voltage by wiring it that way!

Can anyone explain? Google doesn't help!
 

Jraef

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Did it SAY it had a 208V coil or is that what you are asking?

More likely it is a 277V coil and if the motor is connected for the higher voltage, i.e. 480V, then the connection of the coil between the 6/9 junction and 4/7 junction would be to a virtual wye neutral point inside of the motor and the voltage would be 277V (480 divided by the square root of 3).

And often, the brake coil itself would be DC and there is (was) a simple little bridge rectifier there to energize the DC coil. They do that because DC coils run cooler, and a brake coil must be energized the entire time the motor is running. An AC coil would add significant heat to the motor. So more likely it was a DC coil inside and you instantly smoked that little bridge rectifier by connecting the higher voltage, rendering the brake coil useless.
 
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topgone

Senior Member
Did it SAY it had a 208V coil or is that what you are asking?

More likely it is a 277V coil and if the motor is connected for the higher voltage, i.e. 480V, then the connection of the coil between the 6/9 junction and 4/7 junction would be to a virtual wye neutral point inside of the motor and the voltage would be 277V (480 divided by the square root of 3).

And often, the brake coil itself would be DC and there is (was) a simple little bridge rectifier there to energize the DC coil. They do that because DC coils run cooler, and a brake coil must be energized the entire time the motor is running. An AC coil would add significant heat to the motor. So more likely it was a DC coil inside and you instantly smoked that little bridge rectifier by connecting the higher voltage, rendering the brake coil useless.

If the brake supply was sourced from motor leads 6-9 and 4-7, that brake is rated 240V. See the wye connection of the diagram below:
fig2.jpg
Just see if you toasted the rectifier bridge or the brake coil itself (whar jraef said).
 

don_resqcapt19

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If the brake supply was sourced from motor leads 6-9 and 4-7, that brake is rated 240V. See the wye connection of the diagram below: ...

The coil voltage of each coil in a wye connected motor is 138.5 volts. The coil voltage for a delta motor is 240 volts.
 

kwired

Electron manager
Location
NE Nebraska
The coil voltage of each coil in a wye connected motor is 138.5 volts. The coil voltage for a delta motor is 240 volts.
That be what I was thinkin. But from T7 to T9 and considering the phase angle should give you about 240 volts, just like would be applied to 7 and 9 when connected to the lower voltage of a dual voltage motor.
 

don_resqcapt19

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Illinois
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retired electrician
That be what I was thinkin. But from T7 to T9 and considering the phase angle should give you about 240 volts, just like would be applied to 7 and 9 when connected to the lower voltage of a dual voltage motor.
Yes, you are correct.
 
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