3 phase motor starts automagically on 1 phase power??

[Ulma Doctor]

Hi everyone,

I finally got my Burke #2 back together and was going to setup an RPC to run the gear motor on it.

When I purchased the burke, the seller threw in another 3 phase telling me that I could build a RPC from it. (did a google search on how to wire)

I wanted to test the whole RPC setup and figure out what size run capacitors I would need..

I hooked up the extra motor as follows:
L1 (as indicated on the wire) -- 1 leg of the 220 Circuit out of the wall and to 2 capacitors wired in parallel, 40 mf and 15 mf (I bought a whole assortment as I wasnt sure what i needed).
L2 -- 2nd leg of the 220 circuit out of the wall
L3 -- to a momentary switch which then goes to the other side of the caps.

ground to the frame of the motor.

turned off the circuit breaker, plugged the wire in.. turned on the circuit breaker expecting to have to hit the switch to get it started.. low and behold the motor started spinning w/o me touching the switch (i checked the switch to make sure it was infinite resistance as is and 0 resistance when the button was pressed).

thought maybe the caps were in the circuit somehow so I pulled the wires to take them out of the circuit completely.. the motor still starts??

questions:
1. is it possible this was converted to 1 phase (i doubt it since the wires say l1, l2, and l3)?
2. it the motor going to burn out ( i only ran a few seconds each try since I was not expecting this)? if so what should I be looking at/testing?
3. if not, do i still need start (and run capacitors)?

thank you,
Roger


some info on the label of the motor:
Rockwell 1 hp motor, manufactured by baldor. 1725 rpm, 4.4 amps, 3 phase. rockwell no 66-018
View attachment 36500

Roger what has happened to you when you fired the motor off with your original configuration, you were creating the potential difference to start the motor, if you were using start capacitors they would burn up very quickly the way they were wired in.
a static or rpc starts the motor in single phase, boosting the third leg with a discharge of the start capacitor. once running the intended motor whether it's an idler or a mill/ drill press or any other type of 3 phase motor, the third leg will be induced , provided that there is a single phase of sufficient power being supplied uninterrupted.
once your 3 phase motor starts, there is no need for the starting capacitor. it is taken out of the motor circuit by a momentary switch . if you are starting a idler motor the idler will produce three phase power being started on single phase power, then after generating the third leg, can start multiple motors on three phase power.

you will need at least a start capacitor to start the idler motor
if you wish to balance the voltage between phases you will add run capacitors
your start capacitor should be greater than 80 microfarads for a 1 hp motor, put that in series with any 1 lead 1,2, or 3, with the normally open momentary switch, then connect 1 hot leg (i.e. red) to 2, then the other hot leg(i.e. black) to line 3.
you will make a jumper wire from either 2 or 3 to the start capacitor, this will go to the common side of your star capacitor to power
i made a diagram in an earlier post here it is, this will start you motor without question.

[video=youtube;xD8xwh_P8mI]http://www.youtube.com/watch?v=xD8xwh_P8mI[/video]


let me know if it helps u out!

 

[rogerrabbit]

Thanks, I will need to study this a bit more.

I did get it running, here are some pics of the RPC & wiring.

Here is kinda the wiring situation:

• black wire going into the junction block is house hot , comes out as a blue wire and is L1 of the rpc, L1 to the mill motor (one of the black wires going up the frame) and the 40uf Cap (red wire to cap).
• white wire going into the junction block is house neutral (other hot leg?), comes out as a red wire and is L2 of the rpc, L2 to the mill motor (the other black wire going up the frame) and the 15uf cap (another black wire)
• the 2 white wires coming out of the caps to L3 on the RPC and L3 on the mill motor (white wire going up the frame)
• green wires are all ground (1 from mill motor, 1 from rpc)

The romex goes to the switch.

confused yet? i was.. the first time I fired it up it ran backwards, ended up switching the 2 black wires at the mill and all is well.



here is the on/off switch, first time I tried a regular 220V switch, turned on great, but refused to turn off the mill.. solved that with a 2 pole on/off switch..

todos:
figure out how to cover the junction block and caps.. the holder is a couple pieces of mdf with holes bored out to hold the caps in place

wish I would have gotten more colors for the wires, but I didnt know that at the time..

-- Roger

 

[Ulma Doctor]

Thanks, I will need to study this a bit more.

I did get it running, here are some pics of the RPC & wiring.
View attachment 48906
Here is kinda the wiring situation:

• black wire going into the junction block is house hot , comes out as a blue wire and is L1 of the rpc, L1 to the mill motor (one of the black wires going up the frame) and the 40uf Cap (red wire to cap).
• white wire going into the junction block is house neutral (other hot leg?), comes out as a red wire and is L2 of the rpc, L2 to the mill motor (the other black wire going up the frame) and the 15uf cap (another black wire)
• the 2 white wires coming out of the caps to L3 on the RPC and L3 on the mill motor (white wire going up the frame)
• green wires are all ground (1 from mill motor, 1 from rpc)

The romex goes to the switch.

confused yet? i was.. the first time I fired it up it ran backwards, ended up switching the 2 black wires at the mill and all is well.


View attachment 48905
here is the on/off switch, first time I tried a regular 220V switch, turned on great, but refused to turn off the mill.. solved that with a 2 pole on/off switch..

todos:
figure out how to cover the junction block and caps.. the holder is a couple pieces of mdf with holes bored out to hold the caps in place

wish I would have gotten more colors for the wires, but I didnt know that at the time..

-- Roger

sweet, wire color really doesn't matter as long as you know where they go)
as far as the cover for the caps you may wish to consider fiber glass fabric, it's flexible and non conductive..
just a thought!