Author Topic: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?  (Read 1164 times)

SCLead

Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« on: September 04, 2018, 09:50:52 PM »
Apologies if this is the wrong section..I feel like it counts more as "structural" electrical than the electrical section calls for.

So here's my dilemma. As I acquire more and more tools, I find myself falling into more and more 3P machines. At the moment, I'm up to six. This is in contrast to my one single phase 220v and two or three 120v machines. This is mostly driven by acquiring things in lots, rather than individual machines, and price drives all.

I was able to pick up a new 5hp Baldor motor cheap ($50) with intent to build an RPC out of it. The biggest 3P machine I have at the moment is a 3hp Baldor pedestal grinder (it's a beast!). I'm no electrical engineer, so I'm not even sure a 5hp RPC will run a 3hp 3P machine. That said, I figure 5hp RPC is enough to run any one of my other machines at a time, but certainly no two of them.

So the question becomes; at what point does it make sense to get 3P 220v dropped into my shop? I haven't price shopped at all, aside from some general online browsing, and it's obvious the price varies immensely based on an exceedingly wide range of factors. By having 3P dropped to my property, should I expect to pay a higher premium on my monthly bill regardless of usage?

In contrast, how inefficient are rotary phase converters? Obviously this depends on the motor used and quality of design, but as a rule, are even the best RPCs horribly inefficient creatures that will justify a hard-line 3-phase install in a relatively short timeframe?

Carpenter84

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #1 on: September 04, 2018, 10:20:35 PM »
Having 3ph run to your shop 100% depends on whether 3ph exists on your street. The install cost is typical of a service change, as round here is anywhere from $1000-2500 depending on a pile of factors. IF you have 3ph at your street, call an electrician and see if you can get the ball rolling because (around here) it can take months to get the hydro company to schedule. And that's if you can get permission to drop 3ph at a residential address.
Least you can do is make the phone calls.
I'm not aware of a premium.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Carpenter84

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #2 on: September 04, 2018, 10:22:28 PM »
Someone else will have to chime in on the RPC. I know they are quite inefficient and tend to have a lot of current draw.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

f350ca

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #3 on: September 04, 2018, 11:42:01 PM »
No idea what the costs or availability of getting 3 phase installed where you are but around here its very expensive and
energy charges are based on your peak loads.
I bit the bullet and installed a Phase Perfect converter. It operates at 97% efficiency, runs virtually silent (unless I work it hard enough to turn on its cooling fans), generates perfectly balanced 3 phase and can run multiple loads.
I needed enough power to run my 10 hp lathe, for smaller loads a vfd might work for you. I have one on my drill press, that was easier than running a 3 phase line to it and having walk across the shop to power up the converter when I needed to drill a hole.

Greg

cathead

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #4 on: September 05, 2018, 05:56:17 AM »
I'm running a home made RPC using an old 7.5hp 3 phase motor and have been for years.  The input current on any phase
converter is going to be roughly three times the current on each output leg.  They do have a fair current draw especially
when spooling up the RPC but not a lot just idling.  The electrical energy on an RPC is shuffled into 3 phase inductively. 
If I do a lot of machining in a month, my electric bill might increase up to $20 or so at 10c/KWH  Most of the time, I'm powering up a
5 horse Monarch 14C lathe.  The RPC has only one moving part and if it is kept oiled (mine has oilers with a dip ring)
it is very dependable.  I have a VFD(TECO FM50) on my Enco mill and it works fine presently and provides variable speed
and a lot of other features.  The down side is that it contains a circuit board with many parts including large capacitors
and solid state devices that are prone to fail.  One bolt of lightening could easily render it junk.  From a dependability
standpoint I would tend to think that an RPC would be the more dependable unit.  I do like the features of the VFD though
so I guess one would have to weight the pros and cons for himself.   
     

To install three phase power would likely cost more than one would want to spend at least around here.  Also there
would most likely be a monthly metering charge.  The local utility here charges $40 per month per meter.  Having
thought the subject over my vote goes to the RPC hands down.
 
« Last Edit: September 05, 2018, 06:04:11 AM by cathead »
Cathead @ Catwerks

firestopper

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #5 on: September 05, 2018, 09:10:30 AM »
If you have 3 ph available then ask for an estimate including other questions you posed here.
For me, it would have costed $14k to have the power company bring in 3ph. only because it would have required 1.5 miles of trench as all our power is in ground.
I built my first RPC in 2001 and have been a fan ever since. I'm currently using a 7.5 HP idler to run 9 machines. The system is very quiet and efficient.
In my current shop, I used the same idler from 2001 and purchased a Phase Craft box on Bay for $200. shipped. These control boxes are designed based on your motor specifications and quite affordable. I can tell you my first home made system cost way more than what these control boxed run.

https://www.ebay.com/sch/i.html?_nkw=rotary+phase+converter+panel

The 7.5 hp system I use powers a 51 Ton iron worker (5hp) with out issue. Most of the machines I run are 3 hp or larger.
I did add two VFD's to the Lathe and to the plate roller for speed and other fine control. These VFD's are 3 ph. in and have been happy with the balanced power supply. That said, use a quality idler motor and you should have a reliable,quiet and efficient RPC system.
« Last Edit: September 05, 2018, 09:20:28 AM by firestopper »
Turn and Burn,
Paco

SCLead

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #6 on: September 05, 2018, 08:42:06 PM »
Thanks for the input so far! I'm aware cost to install could vary tremendously, so I didn't really intend to inquire in that regard - more interested in the running costs of true 3P install vs RPC. The $40/mo surcharge for 3P is what I was curious about, and sounds like that may vary from one utility to the next as well. That would be a deal breaker to me, since I'm just a hobbyist - no way I'd run out $40 worth of efficiency lost in an RPC every month.

VFD's are a definite option, but I'm not really concerned with them since they tend to be machine specific in most installs. I'll probably put one on the lathe, and possibly the wet belt grinder, but I'm not sure how to reconcile the coolant pumps on each with variable speed input. Actually, now that I'm thinking about it, I suppose more than a couple machines could benefit from a VFD, but I'm not exactly sold on the idea of buying and installing a half dozen VFDs  ;D

One question for you folks running multiple machines on an RPC; how do you distribute the power to each machine? I'm kind of envisioning one or two outlets, and swapping plugs as needed, but that's a PITA. Do you hardwire your machines, or have an abundance of receptacles on the RPC box to leave them all hooked up, or something else?

firestopper

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #7 on: September 06, 2018, 08:53:33 AM »
To distribute the generated 3 ph., I ran conduit to each machines location with the exception of two machines. The plate roller and the profile roller both can be rolled around the shop for a specific job and both machines have long cords. The power distribution also includes overhead drops to machines like the band saw and Iron worker that are located away from walls. I purposely ran much heavier gauge wire in the event I wanted to continue to add more receptacles.

This is the RPC permanently mounted on its own circuit. The conduit takes off down the North wall and feeds two mills and a lathe, conduit then runs vertical to three overhead drops (center of building)  and down the West end of shop to the last receptacle. In total I have well over
100' of conduit/wire with room to add more. The Machines run smooth and the idler just hums away. I would do it the same way again.







Turn and Burn,
Paco

f350ca

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #8 on: September 06, 2018, 09:55:21 AM »
Because of the large difference in loads I wanted to add protection for each machine and didn't want to run heavy wire for the light loads. Couldn't find a small 3 phase breaker box so I made an enclosure with fuses. From there I ran conduit close to each machine terminated with a plug in.

Greg

firestopper

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #9 on: September 06, 2018, 10:24:34 AM »
Because of the large difference in loads I wanted to add protection for each machine and didn't want to run heavy wire for the light loads. Couldn't find a small 3 phase breaker box so I made an enclosure with fuses. From there I ran conduit close to each machine terminated with a plug in.

Greg

Good point Greg,
The feed is just that, our machines are fused independently.
Turn and Burn,
Paco

SCLead

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #10 on: September 08, 2018, 12:32:59 PM »
To distribute the generated 3 ph., I ran conduit to each machines location with the exception of two machines. The plate roller and the profile roller both can be rolled around the shop for a specific job and both machines have long cords. The power distribution also includes overhead drops to machines like the band saw and Iron worker that are located away from walls. I purposely ran much heavier gauge wire in the event I wanted to continue to add more receptacles.

This is the RPC permanently mounted on its own circuit. The conduit takes off down the North wall and feeds two mills and a lathe, conduit then runs vertical to three overhead drops (center of building)  and down the West end of shop to the last receptacle. In total I have well over
100' of conduit/wire with room to add more. The Machines run smooth and the idler just hums away. I would do it the same way again.

Beautiful shop, and beautiful FJ40! Not sure which I want worse  ;D Thanks for sharing.

PJB

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #11 on: September 09, 2018, 04:19:34 PM »
Other than the noise factor, SC you won't be sorry you went with a RPC.    Post up pics when you get it all set up.
I want what yooz gots

jpigg55

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #12 on: September 10, 2018, 08:11:05 AM »
Depending on need, location, and restrictions, I wonder if it would cheaper to get a 3 phase generator vs install 3 phase ?
Not practical for a commercial business, but for a limited use shop ???
SB 9A, Clausing 8520, Sanford MG 612

Machinists Gazette

Re: Cost/Benefit of Rotary Phase Converter vs. Real 3P Upgrade?
« Reply #12 on: September 10, 2018, 08:11:05 AM »