3 phase converter problems

[shawn_t]

I am almost done building a home machine shop, learning all the necessary skills as I go on. My two lathes, a shaper and a vertical Clausing 8520 are single phase. I got the last machine I thought I needed for the shop in April, a Clausing 8540 horizontal mill with a 1.5 HP 3 phase motor.

I followed excellent instruction by George Carlson from home metal shop club of Houston to build a rotary phase converter with a 2 HP idler motor. It isn't working right. I don't know where else to turn to get some help in debugging the converter. Any help would be greatly appreciated.

Here is a link to his article:

http://www.homemetalshopclub.org/pro...nv/phconv.html


Mr. Carlson's schematic shows the potential relay switch in the wrong position which caused me to wire up the switching side of the DPDT relay wrong as seen in the picture. That problem has been corrected now.

The box is 10 by 10 and contains wiring coming in, going to a third box, to the idler, to the mill, fuses for L1 & L2, magnetic starter circuit with a DPDT relay and on and off push buttons, start circuit with potential relay and DPDT relay, a start capacitor (161--193 MFD Rating with a 2 watt, 16k resistor across the terminals) and two run capacitors (30 MFD rating each).

The phase converter idler motor starts up and runs great. As soon as the mill is turned on, the relay starts chattering like crazy. The mill is 1.5 HP and the idler is 2HP. I have checked my connections two or three times and disconnected the run capacitors but can't figure out what is wrong.

The design includes a potential relay that senses the voltage build up in the idler motor's generating third phase line and disconnects power to the coil of the DPDT relay used to switch between the start circuit and run circuit.

Is it possible that when the mill is started up, the voltage in this line drops enough that the potential relay energizes the coil again and the cycle of chattering repeats? Is 2HP idler too small for such a set up? Could there be a wiring problem causing this symptom? The box becomes a machine gun when the mill is turned on so I can't go near it. Is there any voltage measurements while just the idler is on that could help in figuring out what is wrong?


Here are a couple of pictures of the box:

http://i79.photobucket.com/albums/j1...converter1.jpg

http://i79.photobucket.com/albums/j1...econverter.jpg

Thanks in advance for any help or suggestions.

Shawn
Phoenix

[Al_The_Man]

I notice there is a lack of tuning caps in this design, I went with push-button start and no potential relay, If you do a search here, I have posted details and article sources for tuning a RPC.
If you cannot find it I can repost it.
I also used a contactor with 230vac coil so I did away with any control transformer.
Al.

[shawn_t]

Thanks Al:

I referenced the relay coils to netural. I have a start capacitor and two run coapacitors in there, no tuner caps.

A search for "tuning a RPC", "tuning caps" turned up nothing. A search for your user name brought up over 500. What term should I search under?

Thank you,

Shawn

[Al_The_Man]

This is one post 3 phase with idler and draw string only I also posted my schematic can't find it, I will repost if you need it.
Al.

[shawn_t]

There is nothing wrong with the circuit. I had just set up the mill after it had traveled 2000 miles. When the relay started chattering, I would freak out and shut it off immediately. I played with it tonight and after moving the hydraulic variable speed drive around a little, the mill motor came up to speed and the chattering stopped. Once the motor warmed up and I oiled everything, it would only chatter a little and the motor would come up to speed.

It seems that indeed the idler motor is too small. I am going to have to replace it with a 3 HP.

I checked voltages with the mill running, with, and without the run capacitors hooked up.

Ph1 Ph2 220V
Ph3 Ph2 206V
Ph1 Ph3 238V (Primary Lines)

With 30 MFD each, run capacitors:

Ph1 Ph2 224
Ph3 Ph2 224
Ph1 Ph3 239

Should I just replace the motor and worry about changing capacitors later if there is a problem or should I plan on changing the start capacitor for sure?

The start capacitor is rated at 161_193MFD.

Shawn

[Karl_T]

2 hp. idler should be a big enough indler for a 1 1/2 horse mill. Assuming you have it wired correctly, I'd suspect you have a potential relay with too high a cut in voltage. The little voltage dip caused by starting a motor is tripping it out. Replace the potential relay, or consider two other options: 1) use a push to start button that you just hold in until the motor is running or 2) use a delay timer to hold the start cirucit in for a second or two.

If you do go to a larger idler, the start cap should be larger also. i tried too small a one once; the motor comes up to speed slowly, then all the smoke comes out of the start cap with a bang.

Karl

[shawn_t]

Karl:

I sure hope you are right. The 2HP is so quite and vibration free that I can't even tell it is running in my small shop. Changing it out would involve a lot of hassle, a new box to hold additional caps, dismantling a very complicated installation and wiring, etc.

The potential relay was suggested in a right up by George Carlson on Metal Web news site. I am assuming it is suitable for most RPC's since they are generally 3HP and higher.

It is Grainger part number 6X550 with these specs:

Potential Relay, Contact Break Current 35 Amps, Coil Drop Out Voltage @ 60 Hz 100-70, Coil Holding Voltage @ 60 Hz 332, Coil Pick Up Voltage @ 60 Hz 166-180, Single Pole, Normally Closed .

The only lighter duty one they sell is 6X549 with the same 35 Amps contact break current but with lighter voltage numbers:

Pick up 139-153
Drop out 55-20
Hold 168

I think I get what pick and drop out designate, but I am not sure about hold.

I think I should try it. Worst thing that happens hopefully would be that it trips out the start circuit too soon and the idler would have trouble starting. Depending on how it behaves, decide if I can live with this system or to switch to a 3HP idler. What do you think?

Thanks to all that have helped out with their suggestions. I really appreciate the guidance.

Shawn

[Al_The_Man]

I don't quite see how the potential relay can work as it should in this application, normally the relay works in series with a cap in A/C systems (detects the charge time) , your circuit shows it connected across 120 and neutral. There is normally no neutral current produced in the creation of the artificial phase.
Al.

[Karl_T]

I can't get your circuit to download for some reason. But the relay goes from one hot wire to the "wild" three phase leg. here's another article for you to look at:
http://www.homemetalshopclub.org/pro...nv/phconv.html

I see it calls for the same relay you have. I suspect you haven't got something wired quite right.

Karl