upgrade from router to 10 hp spindle

[David Buchhauser]

I had a question from a fellow member about sizing his supply circuit to match his potential upgrade from router to air cooled spindle. Here are his specs below. Based on his specified VFD with the potential for 35 amp current draw, and adding in a 25% safety factor, I recommend a 40 amp breaker with #8 wire size from his 220/240 Vac supply to his VFD. Typical 10 hp motors draw around 30 amps at full load. I'm not sure if this applies to 3 phase spindle motors. The specs for the spindle show 15 amp current draw.

He responded that he intends to run this new spindle from a 20 amp circuit using #12 wire. What are your thoughts? I would be particularly interested to hear what Gary has to say about this.

Thanks,
David

VFD 7.5KW,Variable Frequency Drive 35A,CNC VFD Motor Drive Inverter Converter 220V,for Spindle Motor Speed Control (1or 3 Phase Input, 3 Phase Output)
I am hoping this is the correct unit for the spindle below , the 380 v is a concern to me as no output voltage is mentioned



Specification
Rated power
7.5 KW
Voltage
380 V
Current
15.0 A
Frequency
300 Hz
Collet
ER32 (6 mm)
Rotating speed
1-18000 rpm
Runout off
0.01 mm
Connection of spindle end
ER32 Φ4-Φ20
Bearing model
6005 x 1,7008 x 2
Torque
3.98Nm

[Jim Becker]

I think that there is going to be an issue with a circuit that small. Your recommendation is in line with what I would expect to be required.

[Michael Burnside]

7.5kW at 240V is a peak current of 31.25A (7500/240). A 20A circuit is woefully underrated for the task.

Edit: I'm also a little confused by the specs with 380V and 15A. That just doesn't make a lot of sense given the 7.5kW power rating. Also 7.5kW is pretty insane. I have a 3kW and I can't think of my HSD spindle being the weak link with my setup.

[Gary Campbell]

Some random thoughts on this:
#1... if you dont have 380VAC power, walk away, unless the motor is dual voltage
7.5kw (10.2hp) What kind of machine and cutting process requires this much horsepower? An industrial router table?
Personally, I would never drive a motor over 5hp on single phase
In most cases a VFD powering a 3ph motor rated at 7.5kw will require 1.73 (sqrt 3) times that when single phase input is used by the inverter to generate the 3 phase for the motor. (laws of physics) this means means that for ~32 amps to the motor, ~55 amps may be required to the VFD.

[Matthew Joseph Rogers]

These spindles are going to be rated at both a maximum instantaneous power rating (7.5kw) and a maximum continuous power rating (5.7kw).

What you sent shows that the VFD is rated for an input amperage of 35 amps which is about 1.5 times the rated amperage of the spindle (assuming it is actually a 240v spindle that you are getting and the rated amps are based on the same power as the 380v unit - 23.75A @ 240v). This is the minimum recommended size for a single phase supply VFD with 1.73 times the desired figure. It will work, likely without any issue since a CNC router will rarely be cutting at maximum continuous power for any length of time.

The 380v spec could be a problem for you, so that is the most important thing to check as a VFD can not usually convert 240v power up to 380v.

There is no problem running any size motor or spindle on single phase power through a properly sized VFD, so that is not an issue. I have a 25hp liquid ring vacuum pump running on a 100a single phase supply to a 40hp VFD and it works great. It is barely enough supply (125 amps would be better but not available - it is currently sized at 90% of the load where 80% is the desired spec). But the VFD acts as a soft start so there is no large inrush of current and I can also turn down the vac pump to save electricity and adjust vacuum level.

[stan kern]

I have not done anything yet , the spindle arrived and its 380v 3phase 15 amp ,
still checking(VFD) on wire size for the 220volt single phase I can go either way 20amp or 30 amp
the VFD specs are 220v single phase to 3 phase 40a 0-400 HZ, the 40amp is the maximum
I have a lot more work to getting the spindle plate and its 17lbs my router is 8lbs
all bearing are heavy duty

[Matthew Joseph Rogers]

A VFD will magically create 3 phase output from single phase input, but it won’t magically create 380v output from 240v input. Unless that spindle is able to accept 240v input as well (seems doubtful), you need to stop and figure that out first.

[David Buchhauser]

I was kind of wondering about that 380V spec. for the spindle. My largest spindle is 4KW (about 5 hp) and I run it from a 30amp 220V circuit with #10 wire size. Same for my smaller air cooled spindle, which I seem to remember is around 3 hp. For hobby work I'm not sure why one would need more than 5 hp or so, and as was mentioned 10 hp would most likely be way overkill.

David

[Gary Campbell]

I can go either way 20amp or 30 amp

I have a lot more work to getting the spindle plate and its 17lbs my router is 8lbs

I can go either way 20amp or 30 amp......This is not very likely

I have a lot more work to getting the spindle plate and its 17lbs my router is 8lbs..... Make sure you add or increase the size of an air counterbalance AND install a larger stepper/servo on the Z axis to accommodate the extra mass

[stan kern]

hoping I have all this right , wouldn't be the first time to make a mistake
but before anything happens I will bench test this setup and take current readiing
specs attached
and matching VFD ordered

[David Buchhauser]

Stan - maybe you could tell us what sort of work you intend to perform with this new 10hp spindle. Do you think you really need that much power (and associated spindle weight) for your router table. Are you intending to do full production work with thick materials, or just your normal hobby stuff like the may projects you have posted here?
I still don't understand how a 10hp spindle motor will only draw 15 full load amps as indicated in your spec sheet.

David

[David Buchhauser]

Stan - I assume you are looking at something like this.

https://www.ato.com/7-5kw-air-cooled-cnc-spindle-motor

vfd.jpgspindle 1.jpgspindle 2.jpgspindle 3.jpg

[Matthew Joseph Rogers]

That’s really cool to find VFDs that are able to also acts as a voltage transformer and convert lower single phase voltages into higher three phase voltages. That really opens up a lot more used industrial machinery for use in smaller shops that don’t have access to a three phase service.

My shop is located down a road with only single phase utility supply, so I would have to pay $40k just to have the utility pull a third wire if I wanted 3 phase service. Then I would still have to run new supply wires and new panels. So thanks for posting that link.

[stan kern]

yes this is good if it will work as shown, wish this equipment existed years ago as my shaper motor was huge and heavy and lots of current to start it
and run it

[stan kern]

David
Thats it waiting for the VFDas I got sent the wrong one (wrong 3 phase voltage )(now i have to see if i can sell it)