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# Thread: MORE HP for PCNC

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## Re: MORE HP for PCNC

Originally Posted by SCzEngrgGroup
I've never seen a VFD with single-phase input that was rated more than 3HP. And if there is one, it'll require about 50A input current...

Regards,
Ray L.
Good point, you know what happens when we assume =)

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## Re: MORE HP for PCNC

Originally Posted by SCzEngrgGroup
I've never seen a VFD with single-phase input that was rated more than 3HP. And if there is one, it'll require about 50A input current....
(I know Ray knows the stuff below, this is aimed at the OP):

You can use a 3 phase input VFD, and power it off of single phase. You just need to derate the VFD by a factor of 1.73 to account for only a single phase of power.

Or to put it in more useful terms, you need to buy a more powerful VFD to accommodate your 5 HP motor, using the formula of (5 HP)* 1.73 = 8.7 HP.

This doesn't mean you are drawing 8.7HP worth of current. The current max current draw off of 230 V single phase for this inverter is approx I=(5 HP)*(746W/HP)/(230V * 0.85 * 0.85)= 22A (last two 0.85 factors account for the inefficiency of the motor and the VFD). Powering 5 HP off a single phase 230V circuit is doable, and since the VFD is acting as a soft-starter, and limiting the starting surge, it is much less problematic than powering a 5HP cap start-run straight off the same circuit.

http://www.dartcontrols.com/wp-conte...hase-Power.pdf

This is a common practice, and the VFD manufacturers usually provide instructions about doing this.

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## Re: MORE HP for PCNC

Originally Posted by tmarks11
You can use a 3 phase input VFD, and power it off of single phase. You just need to derate the VFD by a factor of 1.73 to account for only a single phase of power.
Not always true. In fact, I suspect it's rarely true. Many VFDs will not work at all if not fed with 3-phase. In fact, a while back I was mistakenly sent a new VFD that was a 3-phase only model. It would do nothing but sit there with a fault indication on the display - it would not power the motor at all. I had to return it for the same model WITH the single phase input option.

Regards,
Ray L.

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## Re: MORE HP for PCNC

Originally Posted by tmarks11
(I know Ray knows the stuff below, this is aimed at the OP):

You can use a 3 phase input VFD, and power it off of single phase. You just need to derate the VFD by a factor of 1.73 to account for only a single phase of power.

Or to put it in more useful terms, you need to buy a more powerful VFD to accommodate your 5 HP motor, using the formula of (5 HP)* 1.73 = 8.7 HP.

This doesn't mean you are drawing 8.7HP worth of current. The current max current draw off of 230 V single phase for this inverter is approx I=(5 HP)*(746W/HP)/(230V * 0.85 * 0.85)= 22A (last two 0.85 factors account for the inefficiency of the motor and the VFD). Powering 5 HP off a single phase 230V circuit is doable, and since the VFD is acting as a soft-starter, and limiting the starting surge, it is much less problematic than powering a 5HP cap start-run straight off the same circuit.

http://www.dartcontrols.com/wp-conte...hase-Power.pdf

This is a common practice, and the VFD manufacturers usually provide instructions about doing this.
My newer inverter welding machine is connedted like that too, you just use the two 230 single phase leads and leave the third lead unconnected that would be used for three phase, it is derated some though.

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## Re: MORE HP for PCNC

Originally Posted by SCzEngrgGroup
Not always true. In fact, I suspect it's rarely true. Many VFDs will not work at all if not fed with 3-phase.
So it does pay to read the manufacturers spec sheet. But I would bet that it is more common then not for a three phase model to work on single phase. Certainly not "rarely true".

Teco-Westinghouse three phase models work on single phase.
Yaskawa three phase models work on single phase.
Lenze three phase models work on single phase.
Hitachi three phase models work on single phase.

All the above manufacturers provide instructions for derating their VFDs for work on single phase.

What brand were you using?

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## Re: MORE HP for PCNC

Most of the machines we build are 3 phase supplied and driving 3 phase motors. I would think in industry this is the norm since most manufacturing uses 3 phase power plant wide even lights.

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## Re: MORE HP for PCNC

Originally Posted by tmarks11
So it does pay to read the manufacturers spec sheet. But I would bet that it is more common then not for a three phase model to work on single phase. Certainly not "rarely true".

Teco-Westinghouse three phase models work on single phase.
Yaskawa three phase models work on single phase.
Lenze three phase models work on single phase.
Hitachi three phase models work on single phase.

All the above manufacturers provide instructions for derating their VFDs for work on single phase.

What brand were you using?
It may well be more common than it was a few years ago. But, that means buying a VFD of almost twice the needed capacity, to get full output from the motor. So, a 5HP motor would require a 8.5+HP VFD to safely deal with the much higher input current. Going over 3HP is usually quite a large cost hit. And, like the one I got, if its not specifically advertised as working single-phase, it may not. How would you know for sure before buying?

Regards,
Ray L.

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## Re: MORE HP for PCNC

Originally Posted by SCzEngrgGroup
How would you know for sure before buying?

The VFDs may be setup to monitor each phase and fault out on loss of a phase (since it would result in the other two phases drawing more current, potentially exceeding the ratings of Boost circuitry and MOSFETS/DIODES used in the front half AC->DC conversion circuitry). To work on single phase, you would have to disable the monitoring of the unused phases. If that is not possible (as it wasn't on yours), than it isn't suitable for single phase use.

Alternatively, the VFD monitors the draw of each phase and faults out on overcorrect in a single phase. If it is setup like this, then it will work on single phase with no tweaking of any settings.

But back to the OP, I would agree that anything over 3 HP on this machine is going to be pointless, as surface finish is going to suffer from lack of rigidity at those cutting forces. Even a full size Bridgeport only rocks a 3 HP motor (apples to oranges, I know).

Bottom line, though, is if you are shopping for a 5 HP inverter, and it says "Single or Three phase input, 5 HP" then be very careful: it is telling you that it can be operated on single phase IF you derate it. Which means it won't work with your 5 hp motor. A 10 HP VFD will run you \$600-700 (vs. \$300 for a 3 HP). Is it worth paying twice the cost to get to 5 HP?

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## Re: MORE HP for PCNC

I noticed while fiddling with eBay VFDs that even models that claimed to error on input-phase-loss mostly didn't if fed single-phase from the start. Perhaps they'd throw an error if a phase disappeared while in operation.

Especially 400+V VFDs where there's not really single phase available unless you work at it.

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## Re: MORE HP for PCNC

Can a derated 5hp VFD run a 5hp motor? In other words, if the OP bought a "5hp" 3-phase VFD and hooked it up to single-phase power, could they assume they would get roughly 2.8hp out of the 5hp motor? If the OP is only looking for a little more power, that 2.8hp might be about perfect.

Plus, I imagine they could run a 5hp motor at 2.8hp for longer periods without worry of overheating it.

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## Re: MORE HP for PCNC

Originally Posted by SCzEngrgGroup
How would you know for sure before buying?
Regards,
Ray L.

Phil

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## Re: MORE HP for PCNC

yes, you have to use a VFD that allows single phase input and yes you must buy one of a higher rating because not all three diodes for the input are being used, that is what I've read in my research anyway.
motor is on its way, now I have to try and find a deal on the VFD

jh

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## Re: MORE HP for PCNC

and as far as finishes, yes, pushing the rigidity of the frame could give rougher finishes, but who cares? because that would be on the roughing cuts . hence the "rough" finish
then come back with the proper finishing cuts, no problem. I don't know a machinist that doesn't do that when a lot of material has to come off first.

jh

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## Re: MORE HP for PCNC

Originally Posted by Hirudin
Can a derated 5hp VFD run a 5hp motor? In other words, if the OP bought a "5hp" 3-phase VFD and hooked it up to single-phase power, could they assume they would get roughly 2.8hp out of the 5hp motor? If the OP is only looking for a little more power, that 2.8hp might be about perfect.
That is another way to go, hadn't thought of it that way.

You could, but you need to make sure you set the FLA (Full Load Amps) setting to be 1/1.73 of the normal max limit of the VFD.

But take that thought one step further: just run your 5 HP motor on a 3 HP VFD with single phase input and save a little money, as it would essentially be the same thing. Over current limiter in the VFD should keep you within the capability of the VFD. Just make sure that you verify FLA (Full Load Amps) is set in the VFD appropriately for the VFD capability (it should be by default), and then set the ramp up speed longer to limit the start-up surge of the motor.

Of course, if you really think you need 5 hp....

I guess if later on you feel you need more power, you can swap your 3 HP VFD over to your lathe, and pay the extra bucks to get a 10hp 3 phase VFD....

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## Re: MORE HP for PCNC

I'm not sure I'll have the volume in the current electrical cabinet for the larger VFD!
The chain reaction begins.
Keep you posted.

jh

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## Re: MORE HP for PCNC

I'm open to recommendations on VFD's,I have a line on an Emerson Commander SK that will fit the bill but it is HUGE!!

jh

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## Re: MORE HP for PCNC

So what HP VFD are you looking at? Still trying to get all 5 HP out of your motor?

Any VFD in the 10HP range is going to be large, as it has to deal with heat from the MOSFETs, and (at full load) could be pushing out 900W of heat.

If you can't mount this inside the Tormach Controller Cabinet, maybe you could mount it in the base underneath the mill. If you do, make sure you add a fan to draw heat out of that compartment.

Emerson Commander SK is a very good choice.

Again, if you "down rate" your motor by using a 3HP VFD, that will be much more compact.

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## Re: MORE HP for PCNC

I have to wonder how long you think your Tormach will last under a 5 horse motor. You are asking it to deal with a 330% increase in power. Under roughing, which is when the structural integrity of the machine sees the most stress, I doubt it will hold up. My first concern on a stock Tormach, is the spindle bearings will go in no time.
If it was as simple as bolting on a higher horse power motor, then why do most 5hp mills start at 4000lbs?

You would of been way better off learning HSM toolpaths and increase the spindle speed and by using smaller cutters you would have the same MRR as a hogger, but with less stress on the head and column which is what I think your 5 horses will mangle up. Plus you could of made use of your higher ipm.
Just my thoughts.........I'm not trying to discourage you and I'll be watching this thread with interest.

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## Re: MORE HP for PCNC

Originally Posted by G59
I have to wonder how long you think your Tormach will last under a 5 horse motor. You are asking it to deal with a 330% increase in power. Under roughing, which is when the structural integrity of the machine sees the most stress, I doubt it will hold up. My first concern on a stock Tormach, is the spindle bearings will go in no time.
If it was as simple as bolting on a higher horse power motor, then why do most 5hp mills start at 4000lbs?

You would of been way better off learning HSM toolpaths and increase the spindle speed and by using smaller cutters you would have the same MRR as a hogger, but with less stress on the head and column which is what I think your 5 horses will mangle up. Plus you could of made use of your higher ipm.
Just my thoughts.........I'm not trying to discourage you and I'll be watching this thread with interest.
If you were to put a 5 HP motor on your PCNC 1100, you would render your TTS tool holders useless when used with an end mill. You have to use them lightly as it is, but with 5 HP, you're gonna have tool pull out like you have never seen before. If you really feel the need to destroy your machine with a 5 HP motor, then I strongly suggest you switch to the BT30 spindle.

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## Re: MORE HP for PCNC

He, He. Well, my machine is a first gen and I'm will to find out. It has more than made its money back over the years which is a testament to Tormach. Tormach you can quote me.

Destroy? pretty extreme guess maybe? As far as what "last" means? I highly doubt I'm going to crack a casting, keep my ways adjusted more often, most likely. Spindle bearing wear, sure, bearings are cheap and so is a backup spindle for that matter waiting for a quick swap out if needed.

The machine shop I'm in now has way more HP available in their 5 axis machines and they pretty much use 3/8 cutters for roughing SS with the latest tool paths available and they feel they get the best cost benefit ratio of cutter cost vs material removal, I've found 3/8 is a good balance also for this machine and that size isn't going to put the stress into the machine like some big rougher.
I just want to spin it higher and increase the IMP. I'll be really surprised if I can't achieve an easy "solid/high double digit increase.

It's going to be a fun project, without the HP reserve no will know what the limitations are right? until it is done it's all educated conjecture me think. There are many types of mechanical things out there that have withstood some serious excess energy throughput and my experience says this machine has some reserve to play with.
That empirical statement aside, I still want more head room to see how far I go. More fun and cheaper than plunking down 10k for someone else's clapped out FADAL

Last thing I want to do is go 3hp and find out I could have pushed it more after all that expense because I'm not doing it twice

I don't have a auto tool changer and I agree the TTS stuff will more than likely give up holding in the R8, and as I wrote earlier in the post, BT30 will probably be in its future. This machine had a power drawbar before it was available and that worked out great for the TTS so if I go BT30 I'll have to engineer my own new drawbar setup for that tool holder.

On the VFD, for the ease of plug and play and 1 phase in vs cost, the PolySpede is looking like a front runner for the 5hp. Anyone had any "nightmare" experiences with that brand?

jh

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