[Matt@RFR]

I know there's a few guys here that have their machines running on phase converters. My utility bill each month is between $500-$600 and I only run the machine after work and on the weekends. Maybe 40 hours max or so per week. There's been many weeks that I didn't even start the thing too. The machine is an '07 VF-2ss running on a 50hp American Rotary phase converter.

The majority of my work is prototyping and very small runs (max of 10 parts on average) so the machine is sitting idle quite a bit, and the biggest cut I take for the most part has the spindle at 50%.

I took some amp readings today and will share the results. I'm no electrician, so hopefully I did everything correctly. The way I measured amperage is with a clamp-on amp probe clamped onto one of the wires coming from the main panel into the phase converter.

At idle, it pulls 14A per leg.
Starting spindle from 0 to 12k rpm pulls 140A per leg (200% spindle load).
12k rpm steady state pulls 18A per leg (3% spindle load).
12k rpm, 50% spindle load cut pulls 27A (50% spindle load).

I used this formula to come up with Killowatts:
Amps per leg x 2 legs x voltage (240) /1000 = killowatts.

We get charged roughly $0.20 per kwh. So worst case scenario, if I roughed something out at 54A for 40 hours/week that would cost me $415 over and above our regular house usage. That works out to taking up $11 of my hourly rate. Not bad, but I don't use the mill like that. A big chunk of its time is sitting idle while messing with programs, changing offsets, etc. That, and the majority of the tooling I run is 1/4" and smaller, down to very small endmills. I'll see 3-5% spindle loads for hours on end.

What are your thoughts? Is this in line with what everyone is seeing?

[gar]

080323-1604 EST USA

Matt@RFR:

First, you doubled your current, and second you do not know your power factor. Also you are assuming the current is a sinewave.

Your cost sounds high.

Let us assume your $0.20 cost per KWH, then $600 = 3000 KWH. Assume your house base average load is 1.5 KW and a 30 day month, then 30 * 24 * 1.5 = 720 + 360 = 1080 KWH. This leaves 1920 for your shop. Divide by 160 and you have an average load of 12 KW or 12000/746 = 16 HP. Does not seem to compute.

Even if you assumed the idle load of the phase converter was resistive that is a load of 14 * 240 = 3.36 KVA . Actually it is probably about 2 KW of power, or slightly under 3 HP.

Use your service entrance watt-hour meter to measure the actual power input at idle load and then at your 50% machine load. Also try to determine the average base load for everything except your shop.

.

[Donkey Hotey]

I second the idea about checking the meter. In fact, I tracked usage on my house many years ago. I read the meter daily and tracked it in Excel. It was an interesting exercise in learning just how much power a refrigerator costs per month (!!!) or a waterbed heater (!!!!).

Take a reading before you leave in the morning, mark the time. Take another reading when you get home and mark the time. You can figure out roughly what your home's parasitic load looks like from that. Then fire up the shop and do a 'typical' evening of work. That'll give you some indication of the real power consumption.

Somewhere in there, you're running a good sized compressor to keep up with the spindle. With that kind of money tied up, you probably treated yourself to a bunch of big florescent lights. Do you have a TV running out there while you're working? A gas furnace (fan)? An electric heater? They all sound insignificant but they add up quickly. Especially if you've got a family and the rest of your house is still running 'normally' while you're outside (other TVs, lights, cooking, etc).

After all of that, your bill does still sound high. How often do they really come out and read your meter? Has this been a couple of months? One of the reasons I started tracking usage was they misread one of the dials on my bill and sent me a huge bill one month, then didn't read it for two more (estimated). It caught up on the fourth month but that didn't matter: I had to pay it.

[davereagan]

50hp sounds like major overkill. I don't think you often use more than 15hp on that mill. For reference, 15 hp will cut over 20 cubic inches per minute of mild steel with a good face mill. Example: .15" depth of cut, 2" width of cut, 65 inches per minute.

[gar]

Another perspective.

If you think your phase converter is the cause of high electric bills, then it has to get very hot.

A phase converter is a relatively small package and suppose from my above assumptions that you take 1/2 of the 12 KW figure or 6 KW and dissipate this within your converter package and imagine how hot it will get. You can judge this by what would happen if you put 6 1 KW heaters in side the converter package.

A phase converter only supplies 1/3 of the power to the 3 phase load, the rest comes directly from the single phase lines. View the load as a three phase Y connected resistor bank and you can see why. If a 50 HP converter is only supplying 50/3 HP and if the converter is 75% efficient, then the losses in the converter at full load would be about 50/(3*4) or about 4.16 HP or 3.1 KW. But you will never run at full load. A converter will not be as efficient at light load as full load, but my guess is that you might expect that a 1 KW average load from power loss in your converter. Thus 160 hours is 160 KWH or $32 per month for your converter. These are wild guesses but illustrate an analysis method.

Cross checking this with your 14 A at idle and 240 V we have 3.36 KVA and I do not think my 1 KW figure for average dissipation is too far off.

(edit) Get a wattmeter and an appropriate current transfomer and measure actual power input to your phase converter. Maybe better get an electronic wattmeter that uses a clamp on Hall device current sensor. Note: ordinary transformer type current transfomers are a serious problem if the secondary is not connected to a low impedance. With the secondary unloaded it can produce a destructive voltage. (end edit)

.

[bob1112]

When we tested converters, it seemed they pulled between .2-.3A/HP of the slave motor. This could be 10-15A just sitting there on the single phase side. Rotary converters are pretty efficient "when" loaded between 20-90%. The SS can easily pull 10A of three phase just sitting from the servos being fired up and all the fans and such running. The SS also does not have a counter balance and has to hold more power on the Z servo to keep it in position. I can't remember what they do under power down.

Our other shop has 2 of them and they love power but even with 2 of those and three others, the bill does not exceed 600. I would guess the reason you have a 50HP is because of the amperage?? I know the breaker in the SS is 100A! They really do not need it. You could sneak by with a 25HP converter on that machine for what you are doing.

We almost had to run the SS machines with converters so this is interesting. The only thing I can recommend if you only need control functions, you can add a circuit to only power the 120V control of the machine until you are ready to fire up the rest of it. You may also try testing with the estop on to see if that can drop consumption a bit.

If you wanted to back up to a 25HP converter, just find a slave motor and retune the caps a bit. My self or others here could walk you through it. I am interested to see what happens here because this could be a scenario for me soon. I have a lower HP Haas on a converter right now but need to get an SS.

[gar]

080324-1906 EST USA

Our 20 HP VF-0E uses the Z servo for counter balance on Z.

With servos off the input lines read about 1 A for the pair supplying the single phase load and the wild leg reads near 0. With servos on and no motion the said 2 legs are about 1.2 to 1.3 A and the wild leg is about 0.8 A.

Not very much power consumption.

.

[bob1112]

Wow, that is much lower than ours. That might mean he has a problem with the converter slave motor or mill. Maybe a meter issue??? Never heard of it but 600 bucks sure seems high. I did notice he said 20cents/kw. I think ours is around 9 cents here.


Gar, just curious what meter you used for that test? Hell, my old machine has three cooling fans in it that pull more than that! Now I have to go test my VF1.

[Matt@RFR]

Thanks for the help guys. What I'm going to do is track my electicity useage via the meter and see if that brings any light to the subject. I think that will take a couple weeks to get a good average, so I'll update this thread when I feel I have something decent to post.

The reason I have a 50HP phase converter is simple: When I bought this mill, I had literally never touched a CNC machine before and didn't know exactly what I was getting into. I had no customers (it was bought for another business venture that failed) so I didn't know how I was giong to use it, and there's allways the possibility of getting a CNC lathe at some point. It made sense at the time, anyway.

And just to clarify, I never refered to all this as a problem. I just wanted to get an idea of whether my electicity bill was inline with what others were paying in similar situations. Ofcourse, if there IS a problem I'd love to get it solved because these electricity bills are a much bigger portion of my shop rate than I initially figured.

Our other shop has 2 of them and they love power but even with 2 of those and three others, the bill does not exceed 600.

Do these machines run on a phase converter?

[gar]

080324-2019 EST USA

Matt@RFR:

We think your bill is excessive and therefore we think you have a problem.
But obviously part of it is the CA high cost of electricity.

I have assumed this is at your home and you have some other average base load that is part of your cost.

A good way to evaluate your base average load would be to record your watt-hour meter reading on a day that starts a number of days, maybe a week, when the shop will not be used, and record at the end and see the difference. Divide this by the number of days of the measurement, and multiply by the number of days in a billing period.

Do additional measurements when the shop is running.

If you keep all other loads constant and monitor the meter rate, seconds per rotation of the disk, or disk rotations in a longer time, then you can measure short time average power. Next keep the base load at the same level and run your phase converter only and see what the increase is. Then load the machine with a heavy cut and again do the measurement.

Note: the rate of rotation of the meter disk is a measure of power, and the integral of its rotation is watt-hours. It may have a calibration constant on it, or you may need to calibrate with an electric heater.


viper6383:

The SS may keep fans running because you can expect that in use more power will be dissipated in the cabinet. My mentioned measurements were with the coolant pump off. I will have to check Z load when in this state. However, I do not expect your fans are very high power.

My meter was an Amprobe, about 50 yrs old. I have a Hall device 3 phase power meter, but it is too much trouble to remove the wires to run an actual power test. I also have a Fluke Hall device clip-on probe. It generally correlates with the Amprobe.

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[bob1112]

Matt, Sorry, the SSs are on Delta 240V 3ph. I am headed out now to see what the VF1 pulls at steady state. I use a Fluke 336 for this and it has yet to lie to me. I would agree that something may be using some serious power like your wife left the hair dryer on for a month! I would really want to find the source of that draw if my bill hit half of that here. You may not have a problem but you will need to get a food meter and a pad of paper to figure it out.

[little bubba]

No Haas, but RPCs, a 10hp and a 20hp. The 10hp runs a 5hp machine and a 2hp machine and stays on at least 100 hours a week, a lot of times it runs 24/7. The 20hp runs a 15hp Fadal and a 25hp at 30minutes, mazak. Both can't run at the same time. The 20hp is off as often as it can be.

At around 15 cents per KWH, we are running about $400-$500 a month. Add in a 5hp compressor, air dryer, metal halide lights, heater fan, frig, stand up freezer, 4 computers that never get turned off, mercury vapor light that is on 24/7 outside.

I don't think its too bad.

On the 50hp converter. I think you are at a little bit of overkill. With a 20hp converter, on the Fadal, I was comfortably running at 18+ cubic inches of 1018 a minute. I hit 23 cubic inches, but the spindle started to bog.

For what its worth, the Mazak lathe has a tough time with the 20hp converter. We can only run it in low gear(1360 rpm max), and had to set the spindle ramping for 5 seconds instead of 0.3 seconds.

We just borrowed a 25hp converter so we can run both big machines at once. 3 phase is coming soon, also shouldn't be a problem running all 3 converters at once, 400amps of 220 coming in, used to be a welding shop.

[bob1112]

Remember the SS machines have a 30HPcont spindle drive and require more surge for the 1400ipm rapids. I just tested the VF1 and it was at 1.7A of 3ph and my single phase side was 5.5A per leg. Not to bad. Now the friggin Mori is another story. How about a whopping 15A of single phase at idle! I need to get some more caps in that thing to balance it better so it will calm down. The converter is pulling over 10A with no load. That will prove costly when I start running it daily.

[Matt@RFR]

Viper, your Mori sounds like it's pulling about the same idle amperage as my mill, and your phase converter is about the same as mine as well. Considering your last comment, are you thinking that my bill isn't so high afterall? I'll still do the testing...just curious what your overall thoughts are at this point.

[bob1112]

Well the Mori is pulling 5A and that is because the japs like to over build and decided to put 10 fans on it that sound like a freight train at idle. I am sure if I knock off a few fans, I can get it down a couple amps. It also has a hydraulic turret instead of air so the motor has to stay hot all the time. Guess the really nice thing with the Mori is they use absolute position encoders so I can literally just hit the on button and then hit go. No homing.


In another shop, we ran two Haas VMCs, 2, 50 HP RPCs, a router, a 25HP vac table, an AC, and lights and I want to say it hit 600 in the summer. You are running one machine. Now we may not be comparing apples to apples either. We are talking cost when we should be comparing KWs. Maybe you just pay MUCH more for power their. I think we were 7 cents at the time.

Like I said, get a meter and a piece of paper and we will know soon enough if you have a problem. I will tell you this from building RPCs, if they are not tuned right, you WILL pay!! on that 50HP, I would tune the 1-3 and 2-3 to 250V for your loads. Find out what it pulls by it self. At the prices you are paying, you may be able to afford a digital rig soon. I plan to build digital units soon if I cannot get 3ph in my next building. I am sure I can save about 20K by building my own

[Mark Hockett]

My power bill is around $130 a month. I have a Fadal 15-XT, Milltronics VK3, Haas TL-1, BP mill, a couple of manual lathes and a surface grinder all running on 1 Phase Perfect DPC-A10 digital phase converter, except the Haas. I wouldn't even think about running a CNC machine on a rotary but thats just my opinion. My Haas salesman told me they wouldn't warranty a machine that was running on a rotary when I was looking into a VF. The PP is more energy efficient and has cleaner power than the rotary, even cleaner than you get from most power companies. The efficiency of the PP is around 97% where a rotary is 80%-90% which results in higher energy bills, so the PP can pay for itself over a rotary in lower power bills.
The PP also helps protect my equipment something a rotary wont do, here is a quote from PP,
"Sophisticated software in a digital signal processor (DSP) controls the phase conversion process and continuously monitors load conditions. It balances output voltages, and shuts down in situations that can damage the electrical phase converter or the load being operated. Rotary and static converters are electromechanical devices that have changed little since they were invented in the middle of the past century. They cannot respond to changes in the load and input voltages or make decisions to protect your equipment."

Another way I lowered my power bills was move my shop from CA to WA, my power bills used to be in the $500 a month range in CA.

Mark Hockett
Island Tech Enterprises
Clinton, WA
http://www.islandtechent.com/

More chip less lip

[SORCHEROR]

the pahse converter is running even if your machine isnt,50 hp rotary uses alot of electricity,even unloaded,you are paying a higher rate in CA then i do in NY,when i ran my 50hp converter my bill was always higher,alot higher

[gar]

080326-0913 EST USA

If you are going to make usefull comparisons, then you need some quantative data.

As a residential customer what you buy from the power company is energy, not current. A current input measurement to a device may not be a good predictor of power consumption. Note energy is the integral of power over time.

Consider the 50 HP converter that has been discussed. Unloaded this is nothing more than an unload motor. The primary power consumption of an unloaded motor is core losses, friction, and windage (really part of friction). All input power in this case goes into heat. It is not unreasonable to assume these losses represent 10% of the motor rating. Thus, 50 HP would be 5 HP = 3.73 KW. If this motor idled for 40 hours per month that is 149.2 KWH and at 0.10/KWH this is $14.92 per month, or double that at 0.20/KWH. This is not a large figure in comparison with a normal residential bill.

What you need to do is put a wattmeter at the input of the unload RPC and see what is the actual power input.

.

[bbrown01]

This is a very interesting topic. I just installed a 25hp rotary converter for a yet to be installed VF-2SS. The company claims it has a starting capacity of 25hp but a running capacity of 50hp. Unloaded, the converter draws 55 amps at 248v. That's a whopping 13,640 watts without the machine connected! All the literature on the product claimed the converter didn't consume any power. I feel like I've been duped.

This particular model has circuitry that measures the voltage and current of T3 and switches in and out a set of capacitors to maintain the voltage of T3 to within 5% of L1 and L2. This point is settable and it is called low and high modes. The unloaded current is 55 amps in low mode and 35 amps in high mode. High mode is what the converter should be running in while SS is cutting.

The problem is (other than my future electric bill) just having the SS powered up is not enough to switch the converter from low to high even at it's lowest setting. It requires something like 20% of the converter's rating to switch it and the set point is adjustable after that. It takes the spindle to be turned on to switch from low to high. I'm not sure what the effects (current spikes) of switching low to high and back will have on the machine.

Should I be concerned? I don't want to risk damaging the machine. Even though I just spent $5k plus shipping on this I may rip it out and install a Phase Perfect.

[davereagan]

How are you measuring the 55 amp draw? That is enormous. It sounds just as high as the FLA rating on the nameplate. If the motor is not doing any work, that all turns to heat. What happens when you run the converter for even a half hour unloaded? I'd be worried about it burning up. Have you called the company and asked for guidance or an explanation?

Dave