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Couple Of Rpc Questions

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MrFixIt

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#1
Hey all, I just finished making a RPC out of a 1.5hp Baldor motor to power my Bridgeport.
Nothing fancy, 220 1 phase to a disconnect, then from the disconnect to the motor. Then three legs from the motor to the outlet.
No start or run capacitors at the moment.
Runs great, but here's the weird: it starts up on its own! Everything I've read and watched says I'd need either another single phase motor to spin the three phase up or a start capacitor and switch to momentarily power the third leg to start the three phase up.
But I engage the disconnect, (old school blade style), and the thing spins right up, works great, and is quiet. (With or without the Bridgeport plugged in.)
Any idea on that one?

Secondly, I have run a ground wire to the chassis of the Baldor since I'm used to grounding everything. But the motor doesn't appear to have a provision for it; I used a random mount screw. The only connectors the Baldor has is the hot wiring. Is having the chassis grounded going to be an issue? I'm assuming not since whatever the motor would have been installed in would likely be grounded, but I wanted to be certain. First time for me working with three phase and it seems straight forward, but wanted to check with people that know.
TIA!
-Niles
 

Ulma Doctor

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#2
very interesting, does the 1.5 hp motor make a lot of noise upon start up?
i guarantee that it pulls a lot of current without the punch of a cap
an added capacitor would balance phases and reduce power consumption.

a chassis ground is provided inside the electrical enclosure of the motor, the screw is green in color- you'll attach ground there
you can also ground to any part of the motor case or mounting feet as well
 
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MrFixIt

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#3
No, it's very quiet. It's not as quick to speed as a single phase, but I'd say 3-4 seconds.
Good to know I'm okay on the ground. I couldn't find a factory provision anywhere, that's what got me wondering.
Thank you for the help!
 

Ulma Doctor

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#4
a momentary switch with a 100 uf capacitor on the 3rd leg would speed up the starting and put less stress on the windings.
when you make a RPC, you are essentially starting a 3 phase motor on single phase supply-
the third leg is created through induction as long as the other 2 legs are supplied.
 

KBeitz

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#5
If your unit has a run capacitor on it then I have heard that some RPS's will start up off the run capacitor.
 
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