What size phase converter do i need?

[tcalef]

I'm looking to buy a rotary phase converter for my Boss 4 CNC. Its the 2HP model, what size do I need? Some phase converter guys say double, some say same hp, some say 50% extra.

Any one running one of these on a phase converter?

[Sparky_NY]

Originally Posted by tcalef I'm looking to buy a rotary phase converter for my Boss 4 CNC. Its the 2HP model, what size do I need? Some phase converter guys say double, some say same hp, some say 50% extra. Any one running one of these on a phase converter?

I ran my bridgeport off a rotary converter until I retrofitted the controls all over and went with a VFD at that time.

The reason you see a variety of size recommendations for rotary converters is due to how starting the load is. In our case, the mill motor starts with very little load. The bridgeport motor is a super heavy duty motor and sometimes you see the 2hp also rated for 3hp for 30 minutes. It can also put out much more HP for shorter times. Because of the heavy duty nature of the bridgeport motor, I would go with a 5hp converter. I made my own, as many have, it is very easy and pretty cheap. Another benefit of a 5hp is that you could run a second similar sized machine at the same time should the need arise.

I am sure you noticed how bridgeport 2hp motors are as large, or larger, than 5hp motors you see out there.

[tpmx57]

I use a 7.5 hp American Rotary CNC grade converter to run a TC-22 and a series II cnc with no problems.
Can run both together plus my drill press

[John Bennett]

Have run a Bridgeport R2E3 Boss 8 mill on a rotary phase convertor for over ten years with no problem. When looking for the phase convertor, I oversized to 10HP for future equipment needs. It should be noted that the bridgeport needs three phase, to the spindle motor only, as the cnc part is single phase. (look at wiring diagrams). This, then would allow you to run a phase converter with say a 3hp rating (for short peak spikes) with the wild leg to the spindle motor and run straight single phase 220 for the rest of the machine.

[jeffblack1968]

Have you considered using a A.C drive (VDF. variable frequency drive) they cost less and you can have veritable speed on your motor. They are fairly easy to set up

[Sparky_NY]

Originally Posted by jeffblack1968 Have you considered using a A.C drive (VDF. variable frequency drive) they cost less and you can have veritable speed on your motor. They are fairly easy to set up

All true BUT in this case it would not interface into the existing Boss controller for speed control. In a case where the control is retrofitted then this is indeed the hot ticket.

[tcalef]

My aim is to get this machine running with Mach3 for hobby milling (no plans on servos)

1) I've ordered a 5hp rotary phase converter, but it looks like VFD may be the way to go. On eBay, the VFD's look like $200, so I think I could get one of those and 3 drives for the same cost of the RPC.

2) It looks like most people build their own power supply to give the steppers the right DC voltage. What voltage are the stock steppers supposed to run at? I am assuming that the power supply needs to convert 220 VAC to that voltage, but at what current?

[jeffblack1968]

You can get a VFD that uses 110 or 220 single phase input.
The stock steppers you are looking at should list the DC power they require. I purchased my DC power supply from Ebay it was very reasonably priced.

[tcalef]

What specs should I be looking at for a VFD? There are a ton of cheap ones, but sometimes you get what you pay for

[jeffblack1968]

First make sure AC Drive is single phase input. and then if you need 2 hp you only have to buy the size you need you don't have to buy a larger on like you do with a phase converter. I have 2 of the 3hp Chinese models you see on Ebay they work fine. I have had one for over 3 years and I use it 3 to 4 days a week. I also have 3 Hitachi AC drive the SJ200-015NFU series they are very well made and they have constant torque so you can have heavy start loads and lower running speeds. The Hitachi comes with a good manual to help with the set up. I got the Hitachi from driveswarehouse.com There number is 1-888-476 5944 They also sell them on Ebay. Driveswarehouse has tech support to help if you need it.