Trouble starting big compressor on RPC

[Charliefoxtrot]

Just got done fixing up a 10hp Kellogg compressor, repaired the unloaders, and installed a new check valve. My big old 25hp RPC started it before I had hooked it up to the tank no problem. After hookup, the second startup sparked a little, but the contactor latched. Third time, it really wouldnt latch and I had to shove it shut with a stick. Takes about 5 secs for the motor to get the pump up to speed.....the starter is an old Westinghouse Lifeline, the heaters in it are sized correctly.

Compressor is set up for constant run, it doesnt use a pressure switch, just a pilot valve.

I cleaned the contacts really well and that did nothing....I would love to know if the coil is bad, it reads 9.7 ohms when measured across the two brass screw terminals, its a 220v coil.


I took of the belts, motor alone does the same thing, it wont latch, and just sparks.

Hell, removing the motor leads from the box completely it wouldnt latch when I pressed start.
Tried switching the incoming power around, thinking the wild leg was screwing up the coil, no changes.

Ive never played with balancing the RPC, its a commercial Snyder unit. I get
L1-L2-236V
L1-L3-224v
L2-L3-240v

L2 is my generated leg.

Please help. This shotgun barrel tastes like ****.

 

[marinusdees]

Compressor motors DO NOT like phase convertors.

 

[Charliefoxtrot]

Well duh. Even though I switched two feed wires already, to make sure coil wasn't seeing the wild leg of RPC, when I swapped the next two pairs as a last ditch effort, bam, she latched beautifully. 25hp RPC runs my Kellogg 10hp 352 pump like a dream, and I'm a happy camper!

 

[ishiboo]

Compressor motors DO NOT like phase convertors.

Curious why? A rotary phase converter is simply a single-phase AC motor coupled to a AC 3-phase generator, right? It should produce pretty clean, accurate 3-phase true sine wave power.

Glad the OP fixed his problem though!

 

[larry_g]

Curious why? A rotary phase converter is simply a single-phase AC motor coupled to a AC 3-phase generator, right?

Not quite right, see here and look at figure 1. to see the schematic. http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

Rotary phase converters tend to droop the generated leg under full power and a compressor is considered a large load wear-as a mill or a lathe does not tend to be used at full power all the time and the operator can back off the cut if necessary.

What your thinking of is a motor/generator.

lg
no neat sig line

 

[A_Pmech]

My first suggestion was going to be the third leg on one side of your control xfmr. Glad you found it.