Motor Starting Issue

t120r · Apr 17, 2016

Hello everyone, I figured I had read enough that an RPC was fairly easy. Obviously not as I can't get it working. Before I hook up the start capacitors I want it starting manually with a rope. I spin the shaft, hit the contactor switch and the motor slows itself down to a stop. I tried spinning it in the opposite direction, same thing. I am using 6awg wiring for the power feeds and a size 4 Square D contactor. I measure 245v going to the motor.

I have the motor wired as follows:
L1 - 1,7,6,12
L2 - 2,8,4,10
L3 - 3,9,5,11

L1 and L2 have the power lines and L3 is the generated leg. Here are the pictures for the wiring and motor specs. Any help would be greatly appreciated.

CalG · Apr 17, 2016

Some motors start hard. I've got an old 5hp that was on the wood planer (2ft jointer) , that was once used as a spinner in the shop prior to My Conversion to VFDs. I tried to use it as a quick and dirty spinner to test some other tool, and it just would not gain speed with a rope pull. Starting caps and a momentary button had the thing spinning at speed as quick as a blink.

Pulling through a sluggish 15HP rotor must stretch your pull rope.

SAF · Apr 17, 2016

That motor is 3600RPM 2 pole motor and pretty large. That's going to be very hard to get rope started. It needs to get to a pretty decent speed before it can take off on 1Φ.

Your connections look correct, you just aren't getting enough speed to get it started. Another motor with a slipping belt driving it (pony start) or a capacitor's start, are likely going to be required.

SAF Ω

Grigg · Apr 17, 2016

I agree with the above.

I too had your same idea and urged on by so many comments about pull starting a motor or just kicking the pulley over with their foot...

Decided those tales must be small motors and likely lower speed motors. Anything I've tried it on was big enough or sluggish enough that I couldn't rope start them. However I've successfully pull started some big stubborn old engines, it's not a new technique for me.

Unlikely anyone can pull start a 15hp motor.
My converter is a 900rpm 15 hp on tapered roller bearings, uses a little motor and flat belt to get it going.

Shawn Ghormley · May 2, 2016

Looks like its time to build a simple "pony start" for that 15hp idler.

JST · May 2, 2016

To pull start you need to get it up to several percent of full RPM. For 3600, 1% is 36 RPM, and you will want around 4 or 5%. So you need at least 1 to 2 rev per second. Sometimes it takes a LARGER pulley and longer rope to do that (more torque, longer time), but with a smaller motor, you can often do it right off the shaft.

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Motor Starting Issue

t120r

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CalG

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Grigg

Hot Rolled

Shawn Ghormley

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JST

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