phase converter questions

[dave abbott]

:confused:Hello all fellow creekers,
I recently purchased a Time Saver wide belt sander. It has a 20 horsepower Lesson motor and a 3 horsepower belt feed motor. The sander also has a vfd. The motor has 53 amps stamped on the plate. I also have a 10 horsepower 3 phase table saw. I would like to know how many horsepower rotary phase converter it would take to operate these adequately with the option of adding more 3 phase machines.
Thanks in advance for all your help,
Dave

[Chuck Saunders]

Is the VFD a 3ph input or a single phase input that generates the 3rd leg? If it is 3ph input, it appears that 20HP is your design load. Based on the driven load being 2/3 of the converter, you are looking at a 30HP motor for the converter. Are you sure you can't get 3PH to your location?

[dave abbott]

chuck i could get 3phase power if i had about 220,000 dollars i live out in the country and elect co would have to run it about 7 miles .

[Rob Russell]

Dave,

Is the VFD for the feed belt? That's what would make sense to me - so you can speed up and slow down the feed speed.

A rotary phase convertor (RPC) to run all that is going to be big - I agree with the 30HP sizing Chuck mentioned. One issue with RPCs is balancing the legs. You need pretty well balanced power to feed into a VFD or the VFD's electronics may shut it down.

One option to consider is a Phase Perfect. It's a digital phase convertor that produces 3-phase power that's balanced to within 1% leg to leg. The drawback to Phase Perfect stuff is price. A good 30HP, CNC-quality RPC will run around $2K - the 30HP PP is $6K+.

[Rob Russell]

Another question - what do you have for dust collection? A sander like that really needs a serious sucker to pull out the sanding dust. That's gotta be a 5 - 7.5HP DC system. They talk like 1000s of CFM for a big sander like that.

[dave abbott]

:confused:Yes I think the vfd is for the infeed table. Someone told me that if I could fasten the wild leg to L-3 that I could get by without the digital rpc.

I have a 18 inch blower with an 8 inch inlet for my dust collector then I reduce it down to 6 inch. My sander has one 6 inch dust port.

p.s.
My sander says it draws 53 amps does anyone know how many amps it takes to start up under no load.

Thanks again,
Dave

[Rob Russell]

Startup on the 20HP motor will still spike above 53 amps because you're trying to get the rotor spinning. How much - I can't answer that - maybe one of the professional sparkies will chime in.

The reason I was suggesting a digital phase convertor is because it will allow you to run 3-phase motors of all sizes without worrying about the balance between phases. Be careful - there is a big difference between the Phase Perfect, a static convertor and other digital convertors. If you buy a rotary phase convertor and size and balance it for a 20 HP load, if you try to run a small load (3-5 HP) - the legs could be way out of balance for a load that small. Just be careful about making sure that whatever you buy will work for ALL of your needs.

[Mike Thomas]

Have tried over at QWWM? You can read for hours on this topic over there.

[James A. Wolfe]

I give. What's QWWM?

[Chip Lindley]

That's OWWM....not Q! Old Wood Working Machinery http://www.owwm.com/

[James A. Wolfe]

Thanx,
Jim.

[Rick Christopherson]

Startup on the 20HP motor will still spike above 53 amps because you're trying to get the rotor spinning. How much - I can't answer that - maybe one of the professional sparkies will chime in.First off, it is important to note that the 53 amps (56 by my calculations) is the 3-phase current draw. When sizing the single-phase supply circuit, you need to convert this to the equivalent amperage by multiplying by square root of 3 (1.73). This means he will need a 100 amp single-phase circuit feeding his RPC/VFD/etc. (plus whatever power the converter will consume when idling).

The inrush current for the motor will be very high, but you do not size the electrical circuit for the inrush current, only the running current.


The reason I was suggesting a digital phase convertor is because it will allow you to run 3-phase motors of all sizes without worrying about the balance between phases. A digital phase converter is simply a specialized version of a VFD, and simply has a more robust AC/DC converter on the front-end, and might have sinusoidal filters on the output.

If you buy a rotary phase convertor and size and balance it for a 20 HP load, if you try to run a small load (3-5 HP) - the legs could be way out of balance for a load that small. Just be careful about making sure that whatever you buy will work for ALL of your needs.No, when balancing a rotary converter, it is balanced according to the size of the idler motor, not the load. It is the static converters that need to be balanced for the load, because the load is serving as the rotary portion of the converter. A large rotary converter can operate a small motor without any problem, but a large static converter will not operate a small motor without frying the motor.

There is no reason to use the original VFD for the feed conveyor, except to be able to vary the speed of the feed. If the TimeSaver has its own built-in speed control for the conveyor (a VFD), then using an external VFD would serve no purpose. This of course assumes that you power the entire sander from a rotory converter. If you wanted to power the conveyor from a separate, smaller circuit, then the VFD will provide that function.

I guess where I am going with this comment is that you would not necessarily want to power the VFD from your rotary converter. Nevertheless, if you did power the VFD from your rotary converter, the VFD wouldn't care about any moderate imbalance in the converter because the VFD simply rectifies the incoming AC to DC.

As for the size of a rotary converter, you size it to your largest single load, and you don't need to worry about how many smaller loads you add to it, because each of the smaller loads will tend to share some of their excess current as though they were an additional idler motor. I am hesitant to suggest what size converter to use for a motor of this size without doing some calculations, but a rough ballpark should be in the 30 hp range. The same stipulation holds for sizing your electrical circuits. It will depend on how you configure the system, but I wanted to point out the 1.73 factor I mentioned above, that most people forget about.

[dave abbott]

Thanks for the reply Rick. This is what i'd like to do. Let me know if you think it will work. I want to come from a 100 amp circuit breaker in my single phase panel and from there i'd like to go to 30 hp-rpc? Then go to a 3 phase panel breaker box and run each machine off of an individual breaker.
p.s. the vfd is built in the control panel so that won't be an issue.
Thanks,
Dave:confused:

[Rollie Meyers]

Another place besides the OWWM forum www.owwm.org (http://www.owwm.org) is here at Practical Machinist.http://www.practicalmachinist.com/vb/forumdisplay.php?f=11 I don't always agree with what some say over there, but there are some folks who know phase converters there.

[Rick Christopherson]

p.s. the vfd is built in the control panel so that won't be an issue.That's what I had suspected from the get-go, and the reason why I went off on a tangent about the VFD not caring very much about the RPC balancing. :)

This is what i'd like to do. Let me know if you think it will work. I want to come from a 100 amp circuit breaker in my single phase panel and from there i'd like to go to 30 hp-rpc? Then go to a 3 phase panel breaker box and run each machine off of an individual breaker. What you want to do is feed the RPC from its own circuit, and send only the new generated leg to your 3-phase load center. The two other legs for the 3-phase load center should be fed from their own circuit breaker from the original main load center, and not run through the same breaker as the RPC.

It has been a while since I sat down and figured out breaker sizing for a large RPC, so I am not confident in my numbers. I am "thinking out loud" so someone else may be able to spot any mistake in my thoughts. The basis for my thoughts is from "conservation of power"--what ever gets consumed on the 3-phase side must equal what goes in on the single-phase side.

The breaker size for the RPC needs to be based on 50% of the RPC motor rating and 100% (an additional 50%) of the generated leg (an idling motor draws 50% of its nameplate rating). Thats 40 amps times 3, plus 40 amps (=160 amps) divided by 1.73, which equals 92 amps at single-phase. So yes, a 100 amp breaker is needed to drive the RPC.

Your 3-phase panel needs to be set up as a standard subpanel from the main panel, except you do not carry the neutral into this panel (it MUST be ONLY 3-phase, Delta, not wye). Phase A and B come directly from the main panel, and phase C comes from the output of the RPC.

The main breaker size of your 3-phase subpanel needs to be sized according to the total power consumed by all running 3-phase motors. This is where you need to take into account all of your other 3-phase motors that might be running simultaneously. The RPC doesn't need to account for this, but this main breaker does.

Below I have a picture of a Square-D, 3-phase, Main Lug load center. (Yes, only an absolute geek would have one of these sitting on their desk on a Saturday morning to take a picture of it.)
http://www.woodworkforums.ubeaut.com.au/images/smilies/smilie%20signs/sueme.gif
Connect phases A and B directly from the main load center (either the lugs or a main breaker), but to protect the windings in your RPC idler motor, connect the generated phase-C by back-feeding a smaller circuit breaker which is rated for the maximum nameplate rating of the idler motor. For a 30 hp idler motor, this should be the 3-phase rating, which is 75 to 85 amps-or whatever you can find in this range.

Then you can connect all of your 3-phase tools to this load center using standard 3-pole breakers. (Note that circuit breaker positions for phases A and B above the back-fed phase-C breaker will not be available for use, so do not remove their cover plates in the deadfront of the load center.)

Oh, for calculating the main breaker size in the 3-phase load center, you do not need to use the 1.73 conversion factor. Simply add up all of the 3-phase motor nameplate ratings for all motors that will run simultaneously.

P.S. As I was re-reading my posting I realized that some people may not understand why I suggested backfeeding phase-C with a smaller breaker than the main breaker that phases A and B go through. This is suggested ONLY when you have multiple motors driven from a single RPC, and it is because each new motor will help contribute some of the phase-C power. This contributed power does not flow through the phase-C breaker, so the phase-C breaker needs to be sized only to the size of the motor windings of the idler motor. If you are going to smoke an RPC, it will be the C-winding, so this breaker prevents that from happening.

[Rollie Meyers]

The manufactured phase should be on the "B" or center lug, as it should be treated like a 240 Volt delta & the power/high leg is required the be the B phase per NEC 2005 110.15,also the high leg is required to be orange colored per same quoted section...

[Rick Christopherson]

The manufactured phase should be on the "B" or center lug, as it should be treated like a 240 Volt delta & the power/high leg is required the be the B phase per NEC 2005 110.15,also the high leg is required to be orange colored per same quoted section...NEC 110.15 (2008) is applicable only to color coding and only when the GROUNDED conductor is used, and is not applicable for a non-neutral Delta system (such as a phase converter), nor does it dictate phase number. You will note that in my previous posting that I specifically noted that an RPC-based system CANNOT use the neutral.

This color coding is required to prevent someone from using the high-leg, expecting 120 volts from phase-to-neutral, and actually discovering 208 volts phase-to-neutral by mistake. This is not applicable to motor circuits, because they do not have the neutral. NEC 455.6.2.B indicates that the manufactured leg should be identified, but does not specify how this is accomplished.

As for the presumed requirement of the generated phase being on the B-phase location, I cannot find any NEC reference to this, nor can I fathom any electrical need for this. Please cite the NEC reference, or recind the statement. I am reasonbly confident that the NEC does not make this requirement, because it would dictate phase-rotation, which is not an NEC directive, and would make life miserable for anyone dealing with motors driven from RPC's. Your reference to a phase number "B" comes from a side-note out of a non-NEC document, and has a 0% effectivity for enforcement.

[Rollie Meyers]

I used 110.15 as a example (but did not make it real clear :mad: my bad)you are correct about it is only where a grounded is conductor present, but is still a good way to identify manuf. leg, & black,red,blue is standard trade practice for 208V.(it is not a NEC mandate*) It is also true that nothing to mandate any color code, but properly identifying the manuf. leg makes it EZ to comply w/ 455.9. And on useing the center or"B" for the the manuf. leg since it is req. for 240/120 3Ø & keeping it the same for similar systems is wise,but it's not required....

*Nor is the BOY, Brown,Orange,Yellow used on 480Y/277V.

[Chuck Saunders]

Dave, I assumed that 3PH was out of reach for you, but it doesn't hurt to dream.

Rick, Thanks again for sharing on this topic. I may one day start to understand.

[Larry Edgerton]

Question:

I am running a 50 Hp RPC with the intention of eventually running a wide belt, although I do not have one yet. My question is ......

I would like to come up with a wireless remote control for my phase converter similar to what I use on my dust collector so I do not have to walk across the shop every time I use it. The noise annoys me when it is idling. 100amp load at startup.

Has anyone done this?

[Jim Becker]

Larry...think contactor. You need one rated to switch the supply side of your RPC with the secondary compatible with how you want to switch it. You can use a simple cheap Christmas tree light remote with a 120v secondary or even go low voltage if you prefer. This is the same technique many of us use to switch our dust collection systems on and off...contactors are your friend!

[Chip Lindley]

I did just this, but on a smaller scale. I have a 5hp ARCO type A RPC. Walking across my cluttered shop to turn on the breaker was almost always *too much*!

I used a Size 2 Square D three-pole, magnetic starter with 220v coil, and an old 220v remote control from MLCS, all in its own metal enclosure. The remote switch is wired to engage the starter coil and close the contactors. When engaged, the RPC runs until the remote stop button is pushed, turning off power to the starter coil.

Just remember that any remote starter setup must be sized according to your own RPC. Someone mentioned you need a 50hp RPC! This would need a very LARGE mag. starter (at its single-phase rating) to carry its full amp load. HUGE! for 50hp!

I beg to differ with the need for a 50hp RPC!! The literature that came with my ARCO 5hp RPC states that up to 15hp can be run off it, if motors are started one-at-a-time. I have successfully run a 5hp shaper and 3hp DC together off the 5hp. RPC. You should read further on good industrial-grade RPCs and see if you cannot get by with a 20-25hp unit to run your WBS and DC together!

There are lotsa bargains on eBay on used mag. starters. Just receive a guarantee they are not DOA! Good Luck, HappyNewYear!!!

[Larry Edgerton]

Chip, I already have the 50hp RPC, its the wide belt I don't have yet. I was looking at a 42" SCMI two belt when I bought the RPC, and wanted to be able to run my 11 Hp planer and 5hp jointer at the same time, thats why the large RPC. The market fell apart here so I never got my wide belt. Someday though......

Actually I just bought a 2675 drum sander from a friend that is just too crippled to work any more, and the way work has been here in the worst little state [economically]in the union, I'll be making that work for me for a while.

Oh Ya..... I dug back in the archives, and I read until all the words started to run together and I have decided.....

I will have to hire someone. I just have a hard time with anything electric. My brother says its simple, he wires up computors in race cars all the time, but to me ......

It just bores me to tears and I fall asleep reading. I have always been this way.

I'll try some more reading in a couple of days.

[Steve Jenkins]

Larry, why don't you give a call to the mfg. of your phase convertor. I have a 75hp Kaye and have spoken with the tech.support people and have found them very helpful. I've also found that phone calls are generally much more productive than emails in most cases.

[Larry Edgerton]

Ok, I called in an electrician, and I can not afford their proposal right now. Can anyone recommend a book that would deal with this sort of thing, but be geared for an electrical midget. Say..... Shop wiring for dummys.:)

[Chip Lindley]

Larry, does your 50hp RPC use a magnetic starter to actuate it, OR do you throw a knife switch on the fuse box? This is where we will start!

[Larry Edgerton]

Knife switch.

[Jacob Szajkowski]

The breaker size for the RPC needs to be based on 50% of the RPC motor rating and 100% (an additional 50%) of the generated leg (an idling motor draws 50% of its nameplate rating). Thats 40 amps times 3, plus 40 amps (=160 amps) divided by 1.73, which equals 92 amps at single-phase. So yes, a 100 amp breaker is needed to drive the RPC.


I am new to this post but not to the subject. I was following until I read this and wondering Rick if you can elaborate?

[Rick Christopherson]

I am new to this post but not to the subject. I was following until I read this and wondering Rick if you can elaborate?That posting was made a month ago so I don't recall the details, and I don't really want to go through the whole thing again tonight. However, in a nutshell, the concept pertains to conservation of power (or current) in that what ever power you get out of the converter on the 3-phase side (including power consumed by the converter) is required on the input, single-phase side. What confuses this is that the tool motor can (and should) be on a separate single-phase breaker for the non-generated legs, and drawing power only from the generated leg of the converter.

[Art Walker]

It seems at first like Rick's scheme of backfeeding only the generated leg to a three-phase breaker panel has a number of advantages - including being able to size the conductors and contactor in the RPC panel according to merely the idler full-load requirements, rather than the combined load motor demands (for a many-simultaneous-load-motors situation, the big conductors are the non-generated legs from an upstream single-phase panel to the three phase distribution panel).

The catch is that if the backeed breaker trips, or the idler overload relay trips if included in the RPC panel design, or the RPC panel is inadvertently shut off, or its single phase supply breaker trips in a load center upstream, the load motor(s) soldier on with a third leg which is anywhere from nonexistent (1 motor running) to unbalanced (small n>1)...until/unless they trip their overloads on the heating through the good legs as a result of running unbalanced, or trip their 3ph breakers, or the main breaker.

I guess the question is, is this more xor less desirable than having the load motors shut down abruptly in the case of an RPC fault, in a design wherein all three legs of the three phase load center are downstream from the RPC and therefore under its control regime?

And it seems like the scales tilt yet again, if one is trying to use one subpanel for both 3ph and 1ph client circuits - excluding positions over the wild bus for the latter, of course.

Art