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# Higher than Line Voltage Voltage!

Member Posts: 1,380
Start and run windings are in intimate contact with each other inside the shell of the motor. When voltage is applied to the motor and current flows through the start and the run winding, an induced voltage is generated. This is the same concept that facilitates the operation of transformers. At any rate, the current flow through the run winding induces a voltage across the start winding. So, when you take a voltage reading across the start winding, your reading will be higher than the line voltage.

This is the same exact concept on which the potential magnetic relay operates.

• Member Posts: 2,144
Potential Relay Voltages

Hi All!Professor,On 1ph compressors the voltage reading[ on a running unit]on the" C to S "terminals is always higher than "line voltage".What is this higher voltage called?Does this happen on 3ph units ?
• Member Posts: 2,144

> Start and run windings are in intimate contact

> with each other inside the shell of the motor.

> When voltage is applied to the motor and current

> flows through the start and the run winding, an

> induced voltage is generated. This is the same

> concept that facilitates the operation of

> transformers. At any rate, the current flow

> through the run winding induces a voltage across

> the start winding. So, when you take a voltage

> will be higher than the line voltage.

>

> This is

> the same exact concept on which the potential

> magnetic relay operates.

• Member Posts: 2,144
Higher Volts!

Thank You ,does this "higher voltage have a name?Saying "higher than line voltage voltage" tends to get stuck in conversation,especially, with electricians,and apprentices. Thanks ,again.
• Member Posts: 1,549

When I was in school, a hundred years ago, we called it Back EMF (EMF is electro-motive force). This voltage is used to trigger the start relay to take the start capacitor out of the loop.
• Member Posts: 2,144
Back EMF

HI Paul,That is what I've called it for Years but in the past 8-10 months some college electrical engineering students have said "NO WAY-OLDTIMER". So ,what is the proper term ?[YOU YOUNG WHIPPERSNAPPER!].GOOD DAY!
• Member Posts: 1,549

They wanted you to stew awhile before they told you? I have no idea. Back EMF works for me. How about winding induced voltage? Or magnetic voltage transferance (I'm making this up, but it could be).

Or Wattage Heat Amperage Transfer Energy Vector Electric Replacement, also known as WHATEVER.
• Member Posts: 1,380
It's Induced Voltage

I though I mentioned that earlier.

Oh well..

I do like the WHATEVER idea, though.
• Member Posts: 306
Techman

Tell the young whippersnapper to put one finger on C and another on S while it's running and let HIM tell you what it is.
• Member Posts: 1,059
All wrong

you put (C) Common on his tongue and (S) Start in his ear and ask him to shake his head when the compressor starts. Best Wishes J.Lockard
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