View Full Version : 30 hp spindle motor on 240 single phase?

02-24-2008, 09:26 AM
Recently purchased a fairly large cnc lathe which I need to operate on 240 single phase, the machine was originaly wired for 460v 3 phase , here is a pic of the motor and drive along with data plates , what would be my most cost effective way of opperating this motor ? motor is GE 30 hp dc



02-24-2008, 10:39 AM
This is a very large motor to be operating off a residential service, if this is what you intend to do.
At 240v you will need a 100amp service to feed it. On acceleration & decel, these motors pull alot more current than the normal rated.
And you would also need to allow for the very large RPC to accommodate it.
You will need to ensure proper wire sizing on the feeder to avoid voltage drop.
The drive is most likely 3 phase SCR which poses problems with using an RPC due to keeping the phases balanced, with a PWM/IGBT drive with a DC power supply may be slightly better.
If this is in a industrial building, then you should have access to 3 phase.
I would be leery at using it residentially.

02-24-2008, 03:29 PM
Thanks, I am in a commercial building (light industrial) about 2 miles and $19k from three phase power and I am looking for the most cost effective way to power up my new lathe. I have a 400 amp single phase service so I dont think that will be an issue . I am just trying to detirmine if there is any way possible to use this existing drive and or motor. I am not against the possibility of having to replace the drive and or motor to be able to operate this machine at my current location .
Do you think I might do better to find a 3phase AC motor and use one of the VFDs like this one


thanks for any input

02-24-2008, 04:03 PM
I can tell you from personal experience, if you want to replicate this DC spindle motor, especially on 1 ph, it is not going to be easy or cheap.
Supposing you obtain a suitable RPC or Phase perfect 3 ph conversion.
You will need a VFD spindle drive that has the same options and characteristics as the original DC controller.
The best option is a motor and drive that is geared toward spindle application as provided by the likes of Mitsubishi etc, the motors have pulse generator feedback for precise rpm control, they have suitable braking features that duplicate the original DC motor.
I have even used ordinary flux vector style VFD's for these conversions, and it usually results in the owner/operator being disappointed in the outcome in performance.
And these were on 3 phase supply.
You are not going to get a VFD of this size that operates on 1 ph, WEG do make some for larger sizes, but the cost is extremely high, and I do not even know if they go up to 50HP.
So some kind of pseudo 3 phase is going to be need in the form of RPC etc.

02-24-2008, 07:38 PM
Not to mention the cost of electricity used in actually running it.

Would be about 3 dollars an hour here in Ohio.

I hope your area has cheaper electric service. :D

02-24-2008, 07:39 PM
I see single phase in 3ph out 30 hp constant torque drives for aprox $2500 and I have a line on a new old stock 3400 rpm reliant 30hp 3 phase ac motor for $700 but If it wont fit the bill I will put that out of my mind.

I see RPC rated for 30hp around $1700 which doesnt seem to bad. So forgetting cost and assuming I buy an RPC thats larger than needed , where should I go from there?
Am I correct in assuming that even with an RPC that I will not be using the existing drive? WIth an RPC is there a drive that will be usable with my existing motor or do I need to look at replacing it also?
forgetting cost, what would you do in my sit? I am far enough along I am not going to worry about a few bucks. Thanks

Everything else on the machine is single phase so the spindle motor is my only concern

02-24-2008, 08:41 PM
I have never run that large a machine on a RPC, but if you are bent on using this size of machine, you are most likely going to need a RPC anyway, so initially you could try the machine with the existing drive, and then go to plan B with AC spindle if it does not work out.
Do you know if the machine is configurable for 240v down from 460v?
There are other motors to consider, for example, the spindle cooling fan is probably 3 ph, is it configurable from 460 to 240?

02-24-2008, 08:58 PM
I am def bent on using this machine it is bought , payed for and was moved into my shop yesterday.
The hyd pump is 3/4 hp 3 phase and seems to run fine on a static converter, the blower motor on the spindle motor is 2 hp 3 phase. Other than the drive for the spindle motor everything else can run just fine single phase 230v which brings us back full circle to the original project of how to go about turning the spindle with my avail single phase 240 v 400 amp service. The spindle motor drive is the only thing I am unsure about operating at 230 v, I have no problem springing for a larger than neccesary RPC if thats the best way to go , do you think this GE drive and spindle combination will be able to operate at 240v 3 phase?

02-24-2008, 10:40 PM
This is something you may have to look into further, it is unusual to have that high an input directly into a Spindle amplifier, but I doubt it will run on 240, which means you will have to set up a 240/460 transformer, a 460/240 model can be used in reverse, you need to find out if the supply to the spindle is 3 phase only or 3 phase with star (wye) common tap required.
If you have the manual, it should show it.

02-25-2008, 12:27 AM
Maybe this is a bit out to lunch, but to get the thing running I would be tempted to look for a used 75KVA 3 phase diesel genset. I think most big generators can be configured for a large variety of voltage output. And if I found it was not possible to get an RPC big enough I would then start looking for a used 50 hp single phase motor to hook up in place of the diesel.

03-03-2008, 11:06 PM
Make sure that if you get this thing running that you get the electrical authority to aprove this . I d hate to see all your efforts and hard earned cash being spent on fines ,
or calming down waiting customers .

03-10-2008, 11:58 PM
The easier route, and the only way I see of ever running this machine successfully, is to pay for a 3 ph service or move to a location with it. There are no single phase motors of the size you need and phase converters in this range will be an expensive failed experiment.

You'll have further needs for 3 ph. Almost any industrial grade equipment will require it. It's far more efficient, cheaper to run, instant reversing, low cost motors.


05-16-2008, 11:41 AM
If I may chime in.....My shop is also only a few miles from the 3 phase utility...and like you they want nearly 20k to run the line to me....NOT GONNA HAPPEN. I would rather spend that money on equiptment that I own and can take with me. My suggestion is 1...dont run your hyd motor or any other heavily loaded motor on a static converter...you'll be buying new motors in short order. I would go with a pair of rotary converters in the 25-40 hp range and a good 3 phase transformer ...look around you may be able to find a variable tap transformer that will get you very near the 460 vt output. My experience in this is to expect Higher than expected output when you run a step-down in reverse. I have a ton more info but dont want to go on too long. With the greatest respect to Al and the others hear this will require some out of the box thinking ....you can get the results you want and be safe doing it.

05-19-2008, 10:30 PM
We use drives like that @ work 5 to 500 hp you will need true 480 v 3phase power to run it to achieve 500 vdc. If ANY phase is less than 5% from 480 volts or or 5% from ABC phases you will get a linesync fault

09-05-2008, 06:29 PM
I would like to know if you ever got it going?
I also am several $$$$$$ from 3 phase bliss.
I spent $3600.00 on a 45hp rotophase and $2400.00 on a multitap transformer.
As I get at times 257 ac v.(perfectly normal they say at Hydro Quebec).
It all has to work like this.In comes 220 v more like 257v, thru rotopase out comes 3 phase then into 220v to 600v custom multitap copper x0 transformer.
Custom because no one has multi super duper multi tap transformers for perfectly normal hydro power....
This power then runs my colchester storm total hp rating25hp.Which has a 600v step down to 220v transformer?
I tried going 220v direct but the fanuc control would crash when I turned on the comet mill which is rated at 25hp also.
After fiddling with the taps I finally got it all stable.
I can run both the lathe and mill and a 5hp angle roll at the same time without crashing anything.
But last week the spindle drive in the lathe malfuntioned(Quit).....
I hope its not from the roto setup I have.
The power going into the power pack 229,230,235v should be correct.
I suspect hydro ,as not long before the malfuntion the lights in the shop dimmed a little!?
Can power surge protection be fond in this power range?
So many questions so little time.