De-rating Spindle HP

[AutomatedIngen]

I'm interested in buying a used VMC, maybe something like a Fadal 3016, Fadal 4020 or Haas VF2. For either of the machines I'm looking at purchasing a year 2000 model, hopefully with all working electronics and controller, and eventually retrofit with Dynamotion Kflop. Unfortunately while all of these machines can fit in my height requirements, I think they may require a bit too much power. All three of those machines have 20hp spindles, and if I get a 20hp phase perfect phase converter the required breaker for single phase is 110-125 amp breaker.

I've managed to come up with somewhat of a solution, which would be to use the phase perfect then go to a step up transformer to step up the voltage to 440V instead of 220v, this would allow me to probably half the amp requirements and ultimately install a smaller single phase breaker (assuming my theory is correct). Even still, I think a breaker of 60 amp (assuming) would be too much for my 100 amp shop service, as I still will need some power to run a 5hp compressor (thinking I want 440v 3 phase for that as well), as well as lights and other tools, possibly simultaneously. I do realize that breakers are sized larger and often times these types of machines are not ran at full load.

My question, is it possible to de-rate the hp of a spindle motor? While this may sound crazy, and being i'm a hobbyist with some manufacturing projects in mind, I would like to have instead of 20hp spindle motor something along the lines of 7.5hp, but will go 10hp max. If it is possible, how exactly would I do it? I'm assuming it would be something in the vfd but I have heard that only newer vfd's allow current limiting. How would I de-rate an older style spindle motor for the types of machines I have listed above, if it is even possible?

I've searched all of the web but perhaps my search terms are not correct, I'm sure one of you intelligent individuals would be able to assist me.

Just so we are clear here, upgrading my service amps is not an option. Also I'm sure the easiest work around would be to get a 10hp spindle motor and 10hp vfd, but that would probably be around the $3000 mark. Would like to see if I can do something functional for cheaper.

Thanks

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[Jim Dawson]

Just to clarify, running the machine on 480V with a transformer from a 240V service will only reduce the amps at the machine, the amp draw from your shop service will remain the same. A 20 HP 3 phase motor is going to put about a 70 amp load at full rated power on a single phase service. Starting load is going to be higher than that.

Your only real option is to derate the spindle. The only way I know to do this is to use to VFD to current limit. The other option would be to replace the spindle motor with one of lower HP. I had to do this with my router, it had a 12 HP spindle and I went down to 2.5 HP.

A 5 HP single phase motor (compressor) will draw about 23 amps at 240V. As long as your service is single phase 240V, the service is still going to see a 23 amp draw even if you are running a 3 phase, 5 HP motor with a VFD.

Another option might to be get a 30 KW, 3 phase generator. I saw one the other day for $3000, I've thought about doing this.

[AutomatedIngen]

Just to clarify, running the machine on 480V with a transformer from a 240V service will only reduce the amps at the machine, the amp draw from your shop service will remain the same. A 20 HP 3 phase motor is going to put about a 70 amp load at full rated power on a single phase service. Starting load is going to be higher than that.

That makes perfect sense now that you say it. If that is the case even if I put a 220v-440v step up transformer before a rotary phase convertor (phase perfect only do 220v), I'd still be utilizing the same amperage, correct? If that is the case than in my situation, there would be no benefit to stepping up voltage to 440v?

Your only real option is to derate the spindle. The only way I know to do this is to use to VFD to current limit. The other option would be to replace the spindle motor with one of lower HP. I had to do this with my router, it had a 12 HP spindle and I went down to 2.5 HP.

I have read somewhere that current limiting can affect output speed too, which is something I'd definitely not be willing to sacrifice.

As I figured, replacing the motor definitely be the easiest solution, initially I was thinking that I would have to replace the vfd as well, but if I'm correct it should be perfectly fine to use the 20hp vfd for the 7.5-10hp motor.

I suppose I can recoup some of the money spent on a spindle motor by selling the 20hp spindle motor.

The biggest problem I see here for replacing the spindle motor is fitting it to the original supports. I'd like to avoid manufacturing supports for a smaller hp spindle motor, but I suppose if this is the easiest way I will do what is necessary.

Another option might to be get a 30 KW, 3 phase generator. I saw one the other day for $3000, I've thought about doing this.

I wish this was an option. Where I live we cannot by law run a personal generator if service to the grid is available. The only time we can run a personal generator is if there is a power outage. The electrical company has a huge advantage because they generate and distribute so they can make those sorts of rules. Not to mention you don't want to know the cost of gas/diesel where I live.

[Jim Dawson]

That makes perfect sense now that you say it. If that is the case even if I put a 220v-440v step up transformer before a rotary phase convertor (phase perfect only do 220v), I'd still be utilizing the same amperage, correct? If that is the case than in my situation, there would be no benefit to stepping up voltage to 440v?

That is correct. 20 HP is 20 HP, the voltage and current are relative. Power = Volts x Amps.

I have read somewhere that current limiting can affect output speed too, which is something I'd definitely not be willing to sacrifice.

I'm not sure about this. I think the max motor speed might be the same, but the torque would certainly be less.

As I figured, replacing the motor definitely be the easiest solution, initially I was thinking that I would have to replace the vfd as well, but if I'm correct it should be perfectly fine to use the 20hp vfd for the 7.5-10hp motor.

Yes, that would work fine in most cases. I have a 15 HP VFD that is soon to be installed on one of my 5 HP compressors.

The biggest problem I see here for replacing the spindle motor is fitting it to the original supports. I'd like to avoid manufacturing supports for a smaller hp spindle motor, but I suppose if this is the easiest way I will do what is necessary.

The best option might be to look at a machine with a smaller spindle motor. I have 2 knee mills in my shop, one with a 3 HP motor, the other with a 4 HP motor. Both have a work envelope of 32x14x12. They both do anything I ask of them. The 4 HP has a 24 tool changer also.

[AutomatedIngen]

The best option might be to look at a machine with a smaller spindle motor. I have 2 knee mills in my shop, one with a 3 HP motor, the other with a 4 HP motor. Both have a work envelope of 32x14x12. They both do anything I ask of them. The 4 HP has a 24 tool changer also.

I've thought about this and I do have some other options in mind. For me it was mostly about maximizing the size mill I can get. Sure 20hp would be nice, but I think for the most part I will be milling aluminum, but may venture into titanium. The other thing I was thinking was the fadals and haas vmc that I referenced allows me to do a retrofit. While I am sure there are other vmc's out there, I am finding it difficult to find ones with the table size, and part availability that I see is available with fadal and haas. I know I can purchase a vmc brand new and somewhat solve all of my problems, but that increases the cost and decreases the fun factor.

As with everything, there always has to be some trade offs.

[Jim Dawson]

As you say, there is always trade offs. Really your only limitation seems to be the available power, but that is a biggy. I paid $1000 for my 3 HP machine, and the 4 HP was $2500, both mechanically perfect. Just had bad or no controls at all in the case of the 4 HP. I have about $7500 in each of them after extensive controls upgrades.

[NIC 77]

Automated,

I'm glad you posted. I will be "derating" the spindle I have for my build, but I'm going about it a different way. It's a 380V spindle, but I will run it on 220V at the normal amps.

Can you find a power curve for the specific spindle you are thinking of buying? That's where to start. In the constant V/f (Volts / frequency) range of the graph, the lower input voltage will give you the exact same performance up to the point where you reach the voltage limit. But it won't if you limit the amps.

I think running it on lower amps (as opposed to volts) might be problematic as you need a certain number of amps just to run it without load. I think you could do it, but it depends on how much. I'm not an expert but I have put alot of thought into this.

I'd ditch the thought of a phase converter and use the VFD to do the phase conversion. My understanding is that all or almost all VFDs will do the phase conversion for you, but unless it specifically says single phase input, you have to over size the VFD input amp rating by a factor of 1.73, most people just say 2. There is some talk that there can be an inrush current to the VFD capacitors on start up and that this is larger for an oversized VFD. I don't know how much this is, but most manufacturers don't even mention it, so I don't know if it's even an issue, it's just some advice I've read. The VFD converts the AC input to DC and then back to AC three phase.

Also, you can get single phase input 220V to 380V three phase output VFDs. Some of these have large power outputs. So really, I'd ditch the thought of a transformer as well. Search for "220v to 380v vfd" on Aliexpress, you will see some. I'd avoid the Huanyang or whatever it's called 220v to 380v VFD because if you read the fine print, they are not honest about the output specs, but there are some other manufacturers.

The other option is to run it on a single phase input to three phase output 220V VFD or an oversized three phase input 220V VFD.

Find some info and hopefully a graph for the spindle in question. You really need to see what your V/f curve looks like for the spindle motor in question.

Also, please read through a post, and look at the graphs on a site that rhymes with mractical pachinist called "Questions about motor performance and voltage on 3 phase induction motors"

Of course, I haven't done this myself yet, but I will in the not too distant future. If anyone out there has done something similar, I'm sure both the OP and I would like to hear how it worked out.

[NIC 77]

Of course, what I've suggested means that you'll need a new VFD. I have no idea how hard or easy it might be to integrate a different VFD into the existing controls. I have to hazard a guess and say it would be easier than replacing the spindle and less expensive than the phase converter, transformer, etc.

You mentioned you might want to venture into cutting things other than aluminum. If you want torque at lower RPMs, you are better to use a lower voltage and keep the amps. At the lower RPMs where the voltage has not yet reached the input voltage on the V/f curve you should have the same performance IMO. Take a look at the thread I suggested, and in particular, the graphs.

Also, if you buy a different VFD you'll need to make sure the frequency is sufficient for the number of poles in the motor to get you to your max RPMs.

If someone would like to disagree with me, I am happy to hear your comments, I won't be offended and might learn something in the process.

[AutomatedIngen]

Hi Nic, thanks for the reply.

I do not have any data on the specific spindle I am thinking of buying or anything like that at the moment, I am still in the research phase, and probably will remain there until I find a practical solution to my problem.

I'd imagine I would do what Jim said and just replace the spindle motor or buy a smaller sized vmc, that will suit my needs. I have always liked the thought of "buying the most expensive quality component that is within your budget". I do not like going back and purchasing something I know I should have purchased the first time, and will certainly attempt to avoid that scenario here.

On your thoughts of using a VFD to do phase conversion there are a few reasons I can think of that I wouldn't want to do that. The primary reason though is that I would like to run multiple pieces of equipment off of one phase perfect, the vfd would not allow me to do so.Also I have read about some disadvantages of using a VFD as opposed to a phase perfect, but none of those are worth mentioning.

Post your findings back here when you derate your spindle, so I/we have a better understanding of your findings.

[skrubol]

I'm thinking of doing something similar to what Nic suggested for a large router spindle I'm looking at. It's a 380v that I plan to run on 240v (single phase.)
I do have an HP/torque curve for the spindle, so I stuck it in Excel to estimate what the curve would look like at 240v.

Does my math look right to you guys?
Thanks.

[NIC 77]

Hi There,

So long as the VFD will output 240V (instead of 220V) it looks about right to me. 380/240 = 1.58, 1.58 x 10.1 = 16, so limiting at 10 should work (a little below 240V).

Is this an HSD spindle? HSD tells you what the amp draw will be at max power. You would need to limit the max amp output of the VFD to the same as it would use at 380V. What is the max amp draw for your spindle?

Past 15000 RPM, No need to reduce the power more on 240V. If the 380V curve came down at a sharper angle to intersect the grey line, then yes, but past 15000, you could maintain the grey line flat and it won't touch the blue one.

I haven't done this yet. I believe up to around 7500 RPM you will achieve the exact same performance that you would running at 380V because obviously, below this RPM, the spindle would be getting less than 240V regardless if you had a 380V VFD or not.

Are you going to use a single to three phase VFD? I understand that three phase to three phase also works on single phase most times but you need to oversize the input current specs by a factor of, I believe, 1.73, but most people say two. What kind of power do you have available, as in max amps, single phase, etc?

I'd really like to see how this works out for you, so please let me know your results when you have it set up. I have yet to find a suitable inexpensive VFD for myself, but it is still my plan to derate in this manner.

Is this a two pole or four pole? What frequency is needed for the 24000 RPM?

[skrubol]

Pretty sure I've got a bit over 240v at the wall, so 230-240 should be around what I can get to the motor. Some VFD's will do trapezoidal commutation when you go above the bus voltage, gets you more RMS voltage, but more harmonics (noise, vibration, maybe heating?) At worst I'd be at 9 HP, but full torque below around 7000, still overkill for what I'd be doing. The spindle maxes at 28A up to 15000 RPM, and 24A at 24k RPM. Again, not too worried about getting anywhere near 8HP past 15k RPM, don't see myself pushing a 1/2" end mill that fast in Al, and don't think I'd push a 3/8" that hard.

The spindle is coming with a 20HP 220V 3-phase VFD. Nameplate only shows up to 400 Hz though, and it's a 4-pole motor (so needs 800 Hz to get to 24k.) Enough to get started on if I can make it behave on single phase. If I can use that VFD, I'll just run the motor in delta (220V, 48A,) and just limit the power on the VFD if I can (I know it's possible to limit the current, not sure if having an HP limit is common though.) I'll probably need to limit it closer to 5HP until I can get a new circuit put in for it (going to be running it off the 30A dryer plug for now.) Hopefully I won't trip the breaker when applying power to the VFD from the inrush.
Once I get it all up and running I'll be stalking Ebay for a 7.5kw/10HP + 800Hz VFD. I've found that 10+kW 800Hz single phase VFD's are nonexistent, save Chinese models (and I'd rather avoid those.) Might end up with one though.

Don't hold your breath on hearing about my results.. I've got a few projects queued up before I get to this one (finish remodeling my living room, finish my little router, build a proper stand for my mill with a full enclosure in mind, convert mill to servos I've already got, then will be upgrading the Z axis to take this monster. Then I'll need to finish that enclosure.) My goal is to start on the spindle sometime around Christmas.