RPC idler motor won't run

[ls2005019227]

I'm in the process of building a 5hp RPC, based on the examples given by Christopherson, Isserstedt, and Hanrahan. Two 120v legs (L1 & L2) coming into a disconnect switch, fused (20a on each leg), and continuing on to the 5.5HP, 3 phase Bauknecht motor. A jumper off of L2 goes to another switch (momentary), which goes to a 250VAC 480 MFD start cap, and on to L3 of the motor. Motor is wired for 220v (L1+T1&T7, L2+T2&T8, L3+T3&T9, T4-T5-T6 COM). After checking with a voltmeter, no continuity exists between the motor housing and any of the wires. I've also verified my connections & fuses from the disconnect switch.

With the momentary switch closed, the disconnect switch is switched on (closed) and nothing happens. I quickly shut it back off. I also tried spinning the motor shaft with a rope and then applying power with no luck. I'm suspecting the motor, although I'm not sure since I couldn't find a short. Any ideas?

Thanks,

Robert

[Al_The_Man]

What do you mean by 'nothing happens' normally if the 240 is ending up at the motor and nothing is turning, you would hear a loud hum, a few seconds later the fuses would blow.
At the point of connecting the start cap, the 240vac should be connected to the motor via a three phase contactor.
Al.

[ls2005019227]

"What do you mean by 'nothing happens'"

When I close the DPST (disconnect) switch to energize L1 & L2 (and also have the switch closed to jump from L2 through the start cap to L3) absolutely nothing happens; no pops, sparks, smoke, or correct functioning. I also spun the motor with the rope and then closed the disconnect switch (to energize L1 & L2 only) and still nothing happens.

After what I have read and me probably being chicken, I've only left the disconnect switch closed for 2 seconds max. I didn't want to see what a start cap exploding is like first-hand.

Does three phase contactor=three pole contactor? What would be different about the momentary switch being closed when the disconnect is switched, so that all three are energized at the same time?

Thanks for the help.

Robert

[Al_The_Man]

Take a look at the files by Fitch Williams, this is what I based mine on.
http://metalworking.com/dropbox/_1998_retired_files/
Look for the ones starting with FRW.
All three are connected through the 3 pole contactor.
If the 240v 1 phase is getting through to the motor and not the start cap/circuit, the motor will not turn and the result the motor will hum loudly and excessive current will flow if the motor does not turn at all.
Al.

[ls2005019227]

Now I remember where I got that schematic from = Fitch's plans. While driving home, I wondered if swapping two of the wires (from incoming L2/start cap) would make any difference; voila! I've found the HUM! The motor will now run (relatively loud, and seems slow) when the shaft is spun with rope. Once out of several tries it started turning by using the starting cap, but mostly the shaft just shudders. Also some weird voltages:

L1-L2=243v
L2-L3=121v
L1-L3=111v

Do I need to swap the incoming wires, or do I have other problems? Shouldn't a 480mfd start cap be enough for this 5.5HP motor?

Thanks,

Robert

[Al_The_Man]

I found the start cap only needs to be connected momentarily, and it should start to spin right away.
Unless it gets up to speed, your 3rd phase is going to be very low.
Al.

[TOTALLYRC]

I found the start cap only needs to be connected momentarily, and it should start to spin right away.
Unless it gets up to speed, your 3rd phase is going to be very low.
Al.

To back up what Al is saying, on mine the start cap needs to be in the circuit for less than one second and if it is in any longer the motor makes a lot of strange noise and it doesn't turn very well.

[bocko912]

Your voltages will be off until motor reaches its full RPM. It sounds like you are not coming up to full RPM you need to add your run caps between L1 and L3 until your voltage is around 255 to 260volts. With a 5.5 hp you should have about 40 to 60 MFD run caps and 480MFD for starting is fine. Your motor should come up to full RPM in about 1-2 seconds then start caps should come off line. When you apply a load to the idler your L1-L3 voltage should drop to about 230 volts. The only problem is that your phases will not be balanced so you will only be able to run other 3ph motors like manual lathes and mills no CNC. Balancing is pretty easy to do if you need it. You just need to add run caps between L2-L3 to balance phases. If you need I can help. Also I would not run the motor too long if its making a loud noise and turning slow you are out of phase and your motor will get hot quick.

John

[ls2005019227]

First of all, I really appreciate you guys taking the time to help.

I haven't ran the motor much under these conditions; after watching a friend's converter work (to full speed in under a sec), I can tell that it's not right and don't want to damage anything. I have the run caps (2 @ 60mfd), I just haven't wired them in yet. I didn't realize that they could affect start up. I was planning on adding them after I had confirmed that things were going to work. I just bought a manual Tree 2UVR which is 3 phase so at this time, a simple rpc should work. CNC would be awesome in the future.

Does the lack of run caps sound like my only problem; or is there something else that I should be looking at? I'm not pessimistic, but I am a bit concerned about the motor (although from my testing thus far [no shorts], it appears to be ok).

Thanks again,

Robert

[TOTALLYRC]

First of all, I really appreciate you guys taking the time to help.

I haven't ran the motor much under these conditions; after watching a friend's converter work (to full speed in under a sec), I can tell that it's not right and don't want to damage anything. I have the run caps (2 @ 60mfd), I just haven't wired them in yet. I didn't realize that they could affect start up. I was planning on adding them after I had confirmed that things were going to work. I just bought a manual Tree 2UVR which is 3 phase so at this time, a simple rpc should work. CNC would be awesome in the future.

Does the lack of run caps sound like my only problem; or is there something else that I should be looking at? I'm not pessimistic, but I am a bit concerned about the motor (although from my testing thus far [no shorts], it appears to be ok).

Thanks again,

Robert

I don't think the run caps are your problem as I don't run any at all.

I would verify your wiring and make sure you are getting 240v across L1/L2 as you incoming power.
I would also take an ohm reading across L1/L1, L2/L3, L1/L3 WITH THE POWER OFF and all the caps out of the circuit. All three readings should be close. A large difference will indicate problems with the motor windings.

[ls2005019227]

I will ohm it out when I get home from work. Is it correct then that I will be checking the resistance between T1&T7 (L1) and T2&T8 (L2)......?

Also, here is some info on the motor:
Bauknecht (sp?)
5.5 HP
1740 RPM
In addition to having T1-T9, I believe that there is a T10-T12. I'm trying to research 12 lead motor wiring diagrams. I will have to see how leads T10-T12 are connected. When I bought the motor a week ago, it was wired in the standard L1-T1&T7, L2-T2&T8...... and I didn't think anything about it. Should T10-T12 be included in some way?

I would appreciate any information that anyone may have about this configuration for a 220v system.

Thanks

[ls2005019227]

I guess that this makes it pretty obvious that this is my first three phase experience.... When looking at the motor to buy, I noticed T10, T11, & T12, but they weren't connected to any of the other wires, and I remembered the nine lead wiring diagram (L1-T1&T7, L2-T2&T8, L3-T3&T9, T4-T5-T6) which is the way it was wired so I didn't expect any different. It may not have worked well for someone else either. Does this explain the groaning? Has irrepairable damage been done? I used the ohm meter to test each lead for a short to the motor housing; none were. I printed out a two-delta wiring diagram (is this correct for 220v?), and have now connected:

L1-1&6&7&12
L2-2&4&8&10
L3-3&5&9&11

I closed the start cap switch, closed the disconnect switch, the shaft started to turn (without any obnoxious noises).... and then nothing. Apparently I blew both 20a "general purpose" fuses, on L1 & L2. Are my fuses just too small, or is there something else going on?

Thanks for the help (and patience)

Robert