3ph Shopbot run on a rotary Phase Converter

[Randy Bogardus]

I've contacted Tech Support about this and haven't got hold of the resident electrical tech expert there yet so thought I would put in out here. The phase converter I have is a good one with plenty of size but it put's out at 230V. The initial response from Tech support is that this isn't recommended but would probably work ok and that the spindle may not last as long as it otherwise would have. Has anyone ever done this? Thanks for any opinions on this and I won't be firing up the unit based only on responses here on the forum. I just trying to find out what kind of trouble I have created for myself. Thanks, Randy

[Brady Watson]

You can get a single phase VFD and omit the RPC completely...unless you have other things to run.

-B

[Randy Bogardus]

I run other 3ph tools in my shop, I had 3ph tools when I moved out to the "sticks" where I don't have 3ph coming off the grid, so I need the RPC anyway. If I did "backtrack" to single phase on the cnc only, then the VFD would be the only device I would have to change....even though the spindle says "asynchronous 3-phase motor"? I appreciate the input.

Randy

[Ajcoholic]

I've contacted Tech Support about this and haven't got hold of the resident electrical tech expert there yet so thought I would put in out here. The phase converter I have is a good one with plenty of size but it put's out at 230V. The initial response from Tech support is that this isn't recommended but would probably work ok and that the spindle may not last as long as it otherwise would have. Has anyone ever done this? Thanks for any opinions on this and I won't be firing up the unit based only on responses here on the forum. I just trying to find out what kind of trouble I have created for myself. Thanks, Randy

Randy,
I run my whole shop (many pieces of woodworking equipment, from 5HP to 25HP+) off of a large RPC. )my shop is 4km off the main power line so 3 phase supply wasnt happening).
When I bought my Shopbot, I was planning to get the 4HP HSD spindle on three phase - but was told the same thing, that it was not a great idea due to the imbalance (however slight) in the three legs of the 3 phase power (generally the two generated legs are lower voltage than the supply).

I went with the single phase VFD and it hasnt posed me any issues - just costs a little more initially. Not worth the gamble, if it will lessen the life of the spindle and/or VFD. I believe the spindle itself (which is three phase) is the same, and it is the VFD that is larger - it generates the three phase for the spindle digitally from the single phase supply. At least thats the way I understand it.

[Randy Bogardus]

Thanks, Andrew....good info. Guess I should have asked a few more questions, and this just illuminates my limited electrical expertise. Sounds like swapping out the 3ph for single might be the way to go. Nate at Shopbot suggested that might be the case but also said, "talk to Scott"....just hoping Shopbot will take returns on unenergized electrical parts if it comes to that...
Thanks Andrew and Brady!

Randy

[mark_stief]

I've been running mine on a phase convertor since 2006 not one single problem just make sure it's balanced between the 3 legs and you won't have any troubles with it but I also know there will be alot of on here than will disagree with me also Good Luck with it talk to your electrician he should be able to balance it if he is familar with covertors

[Randy Bogardus]

Thanks, Mark. Perspective appreciated!

Randy

[Ajcoholic]

I've been running mine on a phase convertor since 2006 not one single problem just make sure it's balanced between the 3 legs and you won't have any troubles with it but I also know there will be alot of on here than will disagree with me also Good Luck with it talk to your electrician he should be able to balance it if he is familar with covertors

Mark,
The thing is, there are a lot of companies making rotary phase converters, of various levels of quality and varying amounts of voltage difference on the generated legs. I forget exactly what the imbalance is on mine (I have a 75HP total converter, will run up to a 25HP single motor but up to 75 HP combined) but it is somewhere around 10 to 15V lower on the generated legs VS my 240V feed.

Do you know how close each leg is on the output of your RCP, under load? I'd be curious. I'm no electrician - and I hate to take chances when someone tell me I shouldnt.

I know on the big iron CNC's, they suggest if you are using a RPC it should be one with a very clean filtered supply where each leg is pretty much identical, voltage wise.

AJC

PS I do know that balancing isnt as easy as you suggest - as the generated legs will drop in voltage as you increase the load (I was there when he was measuring the output of each leg, as I turned on my central DC, my 10 HP compressor, spray booth fan, etc - it is one thing if all you are running is the CNC, but in most working shops you will have several other pcs running or turning on and off at the same time - kind of the point of having a CNC, ie, its running while you are doing other things. At least that's the way it is in my shop.

[Randy Bogardus]

Thanks everyone for getting me up to speed on this. I can see where the issues are after your inputs and doing some of the homework I should have done prior to ordering as I did. I'm pretty certain the RPC I have is a good one so it sounds like if I don't back out of three phase it is mostly a matter of balancing the output voltage. Thanks again, all. I'll be in touch with SB tech support first thing tomorrow morning.

Randy

[zeykr]

I helped set up a shopbot in a friends shop with rotary phase converter. We had trouble with braking on the spindle with his converter. We tried an external braking resistor and several other things, but ended up going back to the single phase vfd which fixed all problems. His other tools ran fine on the rpc.

[Randy Bogardus]

Thanks, Ken. It seems I may be heading the same direction unless I were to upgrade my RPC.

[mark_stief]

Andrew I have mine set up to be +or- 5% the last one that I set up is 2-25hp motors and was easier to balance than my single motor ones it takes some time to balance but it was just a matter of adding run caps of the right size

[Ajcoholic]

Andrew I have mine set up to be +or- 5% the last one that I set up is 2-25hp motors and was easier to balance than my single motor ones it takes some time to balance but it was just a matter of adding run caps of the right size

Yes we also added 4 large caps to the unit I have. I think iirc mine is within 5% or so as well. But no one could definitely say what was needed.

I have a 10 hp ingersoll rand compressor that is a power hog, and I know my V's drop temporarily as it gets running.