[Grayling]

We have a small shop where there is no dedicated 3 phase power available. Our 3 phase power is generated from two RPC's. One is a homwmade with a 20hp idler and the other I think is a 10hp from a local electrical shop. The 20hp is dedicated to our Haas SL 2 and the 10hp runs an EZ Trak and another Bridgeport. Everything is 220v 3 phase. The problem we have is when the Haas spindle is accelerating and the air compressor kicks on it will give an error to the effect that there is a loss of power on one or more of the legs and the machine will shut down. The compressor is 220v single phase BTW. Does anyone know if there is a way to fix this? I also get over voltage errors on the Haas, also. Usually when the rapid is at 100% and it has been running a while. It seems if I turn the rapid down to 50% it won't happen as often. Let me know if I should post in the Haas forum, too. Thanks.

Steve

[Al_The_Man]

You should not experience a sever drop on the two main 240 feeds as these are direct from the service supply, if they are wire sized correctly.
Make sure that any 1 phase circuitry on the machine is fed from these two main feeds, it is often caused by the artificial phase feeding the controller circuitry, this is the phase that experiences the drop.
Al.

[cjmerlincnc]

Hi, Just a thought, Does the compressor have a slow start device on it.

Where I live the supply is notoriously bad as I'm surrounded by farms and frequent brownouts and under-voltage. My compressor just has the pressure cutout and when it comes on all the lights dim a bit and my 3 phase converter noticably suffers too.

Also a mention, maybe check the pressure cutout poppet valve that vents the pressure on the compressor pump. If there is still a bit of pressure between pump and tank the motor will find it harder to start, drawing more supply current than it really needs to.

Another thing is, is the compressor plugged in near to or on the same supply circuit as the RPC. Try using a different socket further away. I had a small compressor that used to crash my cnc computor until I changed where it was plugged in and had no further problems.

As Al the Man mentions, check that the legs of the phases on the RPC that are fed from your supply also supply all the electronics on the machine and the generated leg only supplies motors. There are always larger voltage fluctuations on the generated phase. Some machines won't even run properly unless they are connected that way as I found out after alot of head scratching.

Cheers
John

[Grayling]

Thanks for the replies Al and John.

Can one of you tell me the easiest way to check which legs are which. Like I said about the RPC, it is a homemade one and I am not familiar with how it was put together. Not too familiar with 3 phase power anyway. Can I check the legs on the machine with the RPC off and get power on two of the three legs and do it that way or will that not work?

John, our lights do the same thing as you described when the compressor kicks on. Haven't noticed if the RPC does anything or not, though. I would say our compressor does not have a slow start device. I will check how the power is connected to see if I can isolate the compressor a little bit more and check to make sure the pressure bleeds off when it shuts off, too.

Steve

[Al_The_Man]

Can one of you tell me the easiest way to check which legs are which. Can I check the legs on the machine with the RPC off and get power on two of the three legs and do it that way or will that not work?

All three are probably switched in at power up, if so you would have to trace which is which by meter before the RPC is powered.
The 240v pair would be switched straight through to the load.
It then should not be hard to identify the 240v supply pair.
Al.