How to balance voltage on 3 phase?

[bherr]

OK, I finally got the phase converter running. Had the 110v leads hooked up to the wrong wires. I'm currently reading the following voltages:
Lead 111 to 112 = 241 volts
Lead 112 to 113 = 211 volts
Lead 111 to 113 = 224 volts

My CNC calls for 230 volts, so how do I balance these out so the CNC works properly???

I had to connect the 110volt leads to 111 and 112 wires. Now that the phase converter is putting out the higher voltages do I then come off these three leads #'s 111,112 & 113 to feed the machine? I know this sounds dumb, but I had to ask. Do I use caps to adjust the voltages so they are all the same and I've read somewhere about one of the legs being like nutural(for lack of the proper word) and how do I know which one that is? Are there any special ways the three leads get attached to the machine?

I know these all sound dumb, but I have no expereince in phase converters or using three phase.

ben

[Jack F]

Put the capasitors between the two powered legs and the 3rd generated leg. look on this site for several plans showing where to connect them and the starting values for your application. the desired result is to be within 10% on all legs.

[tonykart91]

Inside the phase converter control box are a few capacitors. The capacitors hold a will not pass AC voltage, so they build a charge when the AC sine wave is on the positive side and discharge on the negative side of the wave (very simplistic). The MFD rating of the capacitor determines the rate at which it builds and discharges. So by increasing or decreasing the total MFD rating of the capacitors, you can shift the voltage and to some degree the angle of the manufactured leg.
To adjust the voltage, adjust the number or MFD rating of the capacitors. Load will also effect the voltage some. It's pretty hard to adjust the voltage with an adjustable load or no load. You can get it close though.
Motors can handle about 10% voltage imbalance, but electronics like it alot closer.

[Al_The_Man]

Go here http://www.metalworking.com/dropbox/...retired_files/ and look at all the files that start with FRW- They include a schematic and tuning method.
Al.

[Powertoolman]

No, this is not a stupid question. It is refreshing to hear that someone pays enough attention to the concept to even ask about balancing a converter.

Your converter is not that far out of balance, but it can be better. Yes, you tune the converter by changing the capacitors. The best way of doing this is trial and error by changing the capacitance of the two banks of capacitors. The closer you get to all three line-to-line voltages being equal, the better your converter will perform. Here is an image I created for a recent posting on another forum. The values are not the same as yours, but I hope it explains why the voltage balance is important.



The best way to balance the converter is to create a table of the voltage results. As you increase or decrease each bank of capacitors, you can see the results in the table.

My article on building a converter explains this better and shows an example of the table as well as how I chose the best values. I haven't updated my article in a few years, but it is in the works. The graphic above was created for the new re-write.

Building a Phase Converter

Oh, I almost forgot, but you never use the Neutral wire with a phase converter. If anyone ever tells you otherwise, you need to run away fast.

=============
By the way tonykart91, capacitors pass AC and block DC, not the other way around. Changing the capacitance alters the phase angle of the AC signal by tuning the capacitor size to the windings of the motor. This is analogous to tuning a radio because it is tuning an RLC circuit.

Rick Christopherson

[bherr]

Rick,
Thanks for the help. I currently only have the phase motor, no capacitors were included, unless they are inside the motor. I copied your article to read and if I can follow your directions I'll proceed. I have found a local company that builds phase converters so maybe I can get them to balance it out for me, as purchasing different capicators could be time and money consuming. Again thanks for the help.
ben

[bherr]

got the phase converter up and running and balanced to 234 on t1-t2, 233 on t2-t3 and 224 on t1-t3. got the tables moving now I just need to start reading .
thanks for all the help.
Ben

[Powertoolman]

Originally Posted by bherr got the phase converter balanced to 234 on t1-t2, 233 on t2-t3 and 224 on t1-t3

That's a good job on the balance. Your generated leg is only 1-1/2 degrees from ideal. (Or using the diagram I drew previously, the purple line is only 2 degrees below horizontal.)

[bherr]

Rick,
thanks, couldn't have done it without your very easy to understand article. got the machine up and running, all axis moving. Haven't tried the spindle yet as far as turning it on. Had the Y axis locked on the limit and it took me awhile to figure out how to get that off, but finally did. Now I've got to learn this Heidenhain 155B control. It doesn't appear too dificult.

Again thanks for the help.

ben

[precise cabinet]

Hi All,
Powertoolman (Rick)

I have also built a 20 hp phase converter and have it starting and running but my voltages are way off. L1= 120 volts to ground, L2= 121 vtg, and L3= 240 vtg. Also the idler motor starts very loud and vibrates stuff off shelves. I hooked up the idler according to the nameplate for 220 V i.e. L1 connected to motor wires 1-7-6, L2 to 2-8-4, and L3 to 3-9-5. One article I found said to hook op the idler differently. Please Help!

[Al_The_Man]

First, you never read the voltages to ground, the only useful reading is between phases.
You need to make sure the motor is connected in the 220 volt mode if it is dual voltage.
Here is a link to the different configurations of motors, your is most likely a wye connected dual voltage, see B109144 here.
Connections
See the link in post #4 for tuning.
Al.

[precise cabinet]

Thanks Al
Well that didn't work. I was not able to read voltage because the motor made such a loud noise I shut it down. I'm thinking that perhaps I have a bad motor. I bought it from a reputable dealer so I wonder if maybe it was re- wound in the past. Also the voltages that I noted earlier are consistent if you go phase to phase. Phase 1-2 =241, 1-3 = 351, 2-3 =350.
Thanks
Chris