Spindle options electrical math

I’m reading and learning about the various aftermarket spindle options, but I’ve kind of hit a stumbling block. I’ve determined that I don’t want to go bigger than a 1.5 kW spindle, as I don’t see myself using anything bigger than what an ER11 collet set can support. I don’t think I would ever need a 1/2" shank or even 3/8" shank mills.

Because I’m far from living in my forever home, and see several more moves in my future, I can’t guarantee that I will have 220V power available to run a 220V VFD. If I’m renting, its pretty rare for a landlord to allow you to modify the electrical panel to support a 220V feed. So I feel like I’m limited to 110V input for a number of years yet.

My concern is this: a 1.5 kW spindle at 110V could potentially draw 13.7 A at peak power on the output side of the VFD, which I doubt I would hit, but its possible. A standard 20 A breaker is only meant to handle 80% before tripping, which would mean it trips at 16 A. However if I add anything else in the mix on the same circuit like a vacuum, I could easily exceed the 16 A and constantly pop the breaker. I’m assuming that because I’m not stepping up the input voltage from 110, the input current would be the same, no? I believe all the VFD does is rectify the current to DC and then change it to 3 phase so that you get a frequency to run the spindle at variable speed, unless I’m wrong?

So the other option I have read would be to run a 220V VFD and spindle, but I’m not sure if the VFD will step up the voltage from 110V to 220V first, or do I need to run an external transformer before that? And if I do, the same problem regarding current draw possibly exists yes? You can’t change the laws of physics.

So can someone help illustrate what the input side current draw would be for a 110V input VFD or a 220V input VFD running off a transformer?

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Presuming that you are considering a 3-phase, 1.5KW spindle (may be called a brushless DC):

Power is power since energy is energy. (power is energy delivered per unit time). If you use a step up transformer, you actually make it worse, since the transformer will not be 100% efficient.

A 1.5KW unit is going to take 1.5KW (max) no matter what source you use. If you are ultimately plugging in to 120V supply, that supply will need to be capable of about 13.5A (12.5A for the spindle power, and maybe another 120W-- 1A-- for the VFD/driver.

Plugged in to a 240V supply, halve that current.

As to the breaker: a 20A breaker should allow 20A indefinitely. The 80% is a rule that the circuit should be planned such that it will no normally be loaded at greater than 80% by continuous loads, and no single connected device should normally require more than 80% (there are exceptions), not that it can not supply the breaker rating. A continuous load is defined over a three hour period. Lighting, for example, is continuous.

Breakers are sized based on 125% of the continuous load plus 100% of the non-continuous load.

In fact, most breakers will carry more than than the specified rating for an indefinite period, though how much for how long is not certain in general purpose devices (there are several classes of breaker where this is well specified that are used for such things as large motors).

The requirement is that the device trip within a specified time for an overload, based on a specified curve. The greater the overload, the smaller the maximum time to trip. This allows for such things as your vacuum or AC unit to start without tripping the breaker, as the startup current may be several times the running current. The curves are specified based on the fact that the wire will not heat instantly. A 12AWG conductor code rated for 20A (NM cable in a wall, for example) takes time to reach the temperature where the insulation is compromised, and the time will go down as the current goes up (this is non-linear for several reasons, the primary ones being the quadratic P=I^2R and the linear cooling law P=a(Tw-Te) where the constant a depends on the installation, Tw is the wire temperature, and Te is the environment temperature)

The uncertainty comes, in large part, due to the installation-dependent things like environment temperature and heat transfer from the device. The requirements are meant to be conservative.

My suggestion:

Use a VFD that is dual voltage. When you have 240V available (think dryer outlet, for exampl, or electric oven), run on that. When you don’t be careful about what loads are on the same circuit you are plugged in to.


@enl_public, thanks for the knowledge regarding breakers. That was interesting and I learned something new. It has been two decades since I had two semesters of electrical engineering, so while I understand the basics like Ohm’s law and P=E*I, its been far too long for me to remember a lot of it.

I’ve been looking at the ubiquitous Chinese VFD / Spindle packages that dominate the search results on ebay, Amazon, AliExpress, etc. From what I’m seeing, it appears that the VFDs are dual voltage, but you have to change the parameters accordingly. Of course, its not easy to get a straight answer, and I haven’t found one that is expressly dual voltage. Guess I’ll keep looking. The only real reason I’m considering the Chinese models is the cost. Otherwise, all I find are “professional” grade products that would end up costing me more for a spindle and VFD than I paid for my SO3.

Edit: Its a big assumption, but I figure if the VFD will accept single phase 220-240V input, then it should also work for single phase 110-120V input.

2nd Edit: Yeah, I’m definitely not seeing dual voltage VFDs. Seems like the more I look, that for anything that is going to operate near 2 hp or above (like a 1.5 kW spindle) you need at minimum a 220V single phase input minimum. Which brings me back to the thought of using a transformer. I get that you lose power through the transformer, but I don’t see what other choice I have.

Hey Evan,

Watching this thread intently :smile:

One thing I noticed, and let me preface by saying I am not an electrician. I don’t know if it’s my part of the country, or my home builder, but wall outlets here are typically 15amp circuits with corresponding wiring, outlets and circuit breakers. The 20 amp outlets I have have one slot vertical and one slot that will accept a horizontal or vertical leg. When I wired my garage I did exposed wiring in steel conduit at 20amps. I added one circuit by itself for my dust collector (17.5amps) and another single outlet for my air compressor. Then I have two more 20amp circuits with several outlets each (that aren’t used concurrently). The dust collector runs just fine by itself, albeit I’ve never measured the exact draw, just read the info plate. Chances are if you have standard outlets then you have standard 15amp rated wiring(more copper costs more money), regardless of whatever breaker someone jammed in the box. Be careful what you plug in! Maybe a real electrician, not a hack like myself will chime in and clarify my limited knowledge. Be safe!


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@DanoInTx: Dan you are right on this point. I own the house I’m currently living in, but soon moving due to military orders so renting it out. I wired up my garage like you, following NEC standards and getting a permit and final inspection. As a result, I ran 20A circuits, but did it properly using 12-2 Romex, which is rated at 20A. I have seen plenty of residential circuits that are 15A and 14-2 wire. I’m fairly confidant that no code inspector in the US would let you get away with 14-2 wire on a 20A breaker, but you can never be sure in older homes, or if someone has decided to do some “shade tree” electrician work on their own without a permit. Or used an unscrupulous contractor. I’m not an electrician either by trade, but I know probably just enough to be really dangerous.

That’s why I want to get this VFD stuff correct. It seems from my research that while many folks are buying / running the Huanyang VFDs (the same picture offered on all the ebay and Amazon listings), and they may work well enough, I don’t know if you are getting what you pay for. While its great that you can buy the Huanyang 110V input rated VFDs, none of the name brand folks like Hitachi offer a comparable product. Anything “name brand” that is in the 110V range is only rated for up to about 0.75 kW applications, largely based on the current draw and its effect on components within the VFD. In my reading there seems to be some technical reasons for this, but bottom line I think I’m going to have to stay away from the 110V input VFDs. Which makes it very difficult for me to switch to a spindle that is bigger than 800 W.

Coolness, we’re on the same wavelength so to speak then. My current home is only 11 years old and the electrical from what I can tell looks good. Having said that I grew up in a house that was built in the 30’s and it seemed like every time a fuse popped a larger fuse was screwed into the box. I did some work on that house back in the late 90’s (my mother’s house) and it was like every time I’d pull some wire to change an outlet or replace a fixture the insulation would just fall apart in my hands. Mom finally did a HUGE remodel about 10 years ago and they pretty much ran all new service (thank goodness!). Just wanted to make sure you didn’t cook your walls, but it sounds like you know at least as much as I do, enough to be somewhat safely dangerous!


That is absolutely priceless!! I burst out laughing then had to explain to my wife what was so funny…

I’m following all these spindle threads out of curiousity, but I’m still struggling to determine the benefits given the parameters we work within. It seems, to me anyway, each “benefit” necessitates another mod in order to fully take advantage of the enhanced capability. But I’m learning a bunch. So, party on all


Yeah, I’d kind of like to invert this and derive from it what is the optimum 110V spindle which one could hope for?

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I’m using GWizard which has become “lite” as my initial subscription ran out and at least with the cutters i use and the materials I cut I haven’t come close to the 1hp limit. The advantages of using a SuperPID with slow 5000 RPMs has been a much bigger plus for me than anything I can see with using a bigger spindle than the Dewalt. I honestly never come close to the 1hp limit, but I mostly cut wood, plastic and a few small aluminum pieces with 1/4” tooling or smaller. The monster spindle upgrades I see look really cool, and I love seeing the mods everyone does, but so far I don’t have any use personally. Modding for the sake of modding is fun though :smile:


@WillAdams and @DanoInTx, so here is what I am learning as I go along. The Dewalt and Makita routers are listed as 1.25 hp routers, as you both know. That is peak hp I believe, which is tough to achieve, mainly due to the fact that they do not compensate for the load being placed on them. In other words, you can set the dial to “3” but the router won’t maintain that speed depending on the cutting forces applied. The advantage of a VFD, or so I believe, is that it maintains the speed you are set at by applying more or less current as required. Which I believe means that you can get away with less hp for the same cutting force, because it is much more efficient. So you don’t need a 1.25 hp spindle to achieve the same result as a 1.25 hp compact router.

1 hp = 745.7 watts, so if you have an 800 watt spindle, thats 1.07 hp. From what I can tell, an 800w spindle would be a nice equivalent to a compact router, but with the advantages of being more quiet (regardless of whether air or liquid cooled), more efficient, and capable of much longer run times and life spans without worrying about heat, brush life, etc. Plus you gain the use of ER collets, although like I said originally, you can’t go bigger than 1/4" ER 11 collets unless you go with a 1.5 kW or bigger spindle. Coincidentally, among the name brand manufacturers like Hitachi, Teco, etc., the biggest 110V input VFDs I can find are rated for up to 1 hp. Since you aren’t likely to run your spindle up to the max horsepower limit and current draw, I believe you could run an 800W spindle off one of these 1 hp / 110v VFDs. For 800W, at 110V output, you are drawing about 7.3 A of current, not accounting for losses in the system, if I understand the math correctly. So that would run on a standard US outlet.

Some of the Huanyang adverts are offering the ability to run 110V input and power a 110V 3-phase 1.5 kWspindle, but it should be noted that the spindle is not the standard ones people are selling which are 220V 3-phase models. And at 1.5 kW and 110V, as noted above you are drawing over 13 A of current. Some other folks in other forums claiming to be EE types or in one case a VFD designer did a tear down on the Huanyang VFDs and were very much against running 110V through those VFDs. My non technical understanding is that they are using low-grade capacitors and other components, which are stressed by the process of taking 110VAC, rectifying it to DC, and then changing it to 3-phase VAC which shortens the life of the VFD overall, and because they are not UL approved, run the risk of fire or more severe problems.

From my spying in the Inventables forums, the 800 W seems to be a popular option, and XCarve owners admit that anything bigger than 800W is probably too heavy for their rails. Sucks to be them.

The most popular spindle sizes I see are .5 kW, .8 kW, 1.5 kW, and 2.2 kW for the hobbyist set. Also, many of the round-body 800 W spindles seem to be conveniently able to fit in a 65mm mount, which I believe is the same size as the Makita.

Gents, I caveat everything I say above with the fact that I am just a guy who falls down too many rabbit holes on the internet. If I am wrong in any way, please someone correct me so I can learn too.


That my friend is excellent info!!!

One small thing worth mentioning. With a SuperPID it is a closed loop speed control and will also apply more “juice” to maintain spindle speed (as I’ve witnessed watching the tach on the SuperPID board). I am not sure on this bit, but I also think the Dewalt is a closed loop type speed control and will do the same (I suspect the Makita is the same). Part of the SuperPID install is disabling the board on the Dewalt and installing a speed sensor which reads off of the armature of the Dewalt. With the Dewalt I still have to contend with brushes of course, but I have a couple sets of spares for when the need arises, and I can’t say if it’s any quieter than a standard Dewalt, although at low speed I can’t hear it over the cutter noise or even the air being pulled through my dust boot (I’ve forgotten to shut it off when bringing it forward for a tool change because I couldn’t hear it).

I have rabbit holes all over my backyard (no joke), and I fill them in with dirt (if no bunnies are present) all of the time so I don’t twist an ankle while mowing…they can be exciting for sure! I am in no way trying to dissuade anyone from doing mods, whether they help or not. One look at my motorcycle (that has many mods) and it’s obvious i believe in “making things my own”, whether that improves performance or not. Just my motorcycle headlight assembly/mounts cost as much as a standard SO3, and I can’t honestly say I can see the road any better now than with the stockers…but man it’s cool!!! What I have found in my efforts is that I get great enjoyment when some change I make really works, and I mean if it even turns on after I’ve had my grubbys all over it. These machines are a hobby themselves for many of us, not just the stuff we make with them, and that is why I bought one. I mean, how much fun is a Mori Seiki to watch after the initial set up, yawn!!!


My understanding is both the Makita and DeWalt have electronic speed control — it’s listed as a feature for each, and the latter having it is what makes it possible for the SuperPID and VFD to be so affordable (they avail themselves of the circuitry is my understanding).

Correct, the Makita is 65mm.

I would like to distance the discussion from what’s commercially available, and take up the question: Provided with a 110V power source and typical 15 amp circuit (probably/possibly shared with the machine and a laptop) what is the best electrical motor setup one could work up to spin and endmill, and using available ER collet sizes, what is the largest ER collet which one could avail oneself of using the smallest diameter housing, and if possible, a brushless motor?

Would it be possible to make something better than the Kress 800 FME P? Is that (or the Makita RT0701) the best option commercially available? The bullet points:

  • 110V
  • narrow diameter
  • two models with two different collet options (FME is Kress-proprietary, FME P is ER-11)

But we’re missing on:

  • brushed motor — what would be involved in building a similar unit with brushless motor? Where does the price shift to?
  • larger collet — is that actually an advantage? A lot of times I find myself re-working a design down to 1/8" endmills, finding 1/4" too large. A 3/8" collet was just posted to the unofficial Facebook group, and Elaire has had an 8mm option for a while now

So, the question becomes: What would a custom run of spindles which were:

  • 110V
  • brushless motor
  • ER-20 collet
  • designed for the narrowest possible standard housing

cost to make a reasonable size batch? What would be the demand for them? (I am not asking these questions as a Carbide 3D representative) If it’s so simple, why isn’t such a unit available?

It’s pretty obvious that the trim routers are intentionally limited to 1/4" tooling so as to keep folks from overloading them when using by hand or putting them in a router table — what is the actual upper limit on what they can spin?

Two things on my wish list for a new spindle, as mentioned by @WillAdams above, ER collets and brushless. More power, not so much (now that statement is totally out of character for the guy with 455 hp Camaro :grinning:).

Otherwise my modding urges have been satisfied by @Luke’s new Z, SuperPID and upgrading to XL. Of course mods are fun so if that’s your thing, mod away.

Just wait until you need to figure out the regulatory on what kind of power plug you need…
Rule of thumb: Stay below 920W draw on a low line (100-120v) cable, or 1850W on a high line (200-250v) cable, or suffer the delayed wrath of governments worldwide.

There is a reason pretty much everything takes a C13 or C15 cable on the device side if it consumes any significant power and has a removable cable. C19 shows up with the really high power high line stuff (20A, 240V = 4.8KW) with removable cables.

This is likely why you don’t see “name brand” low line VFD’s at higher power - there’s no demand by “name brand customers” for a low line VFD > 900W because they can’t power it “in the rules” with a single removable cable.

Anyway, you clearly can come up with a connector combo that would get you above 920W on low line, but the losses get high unless you’re using pretty large conductors (copper has gotten expensive…and better connectors can be a lot cheaper), the cables wear out rather quickly (heat), and can be hard to source off the shelf at a reasonable price ($2-$3). Get above that 920W number and it’s cheaper to use multiphase or high line so you just don’t see it in commercial gear unless someone made a mistake early in the design process with power sizing. Probably the only reason I know this is because I’ve made that mistake…


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