Thread: Hercus 3 phase lathe, single phase supply

Originally Posted by PhaseChangeConv

Do you have a step down transformer to correct this 480V?

No. I was planning to, but during testing I found that it didn't cause any overheating of the motors. Also only being 15% over-voltage, it shouldn't over-stress the insulation of the motor's windings (and I use good quality motors).

If you are using your static to start say your 3hp motor can you then start your 7.5hp motor after this?

Yes.

I do not think that we can call this a rotary system because with a normal rotary converter you could not have a 3hp pilot motor starting a 7.5hp motor.

I still think that once running an SPC is effectively an RPC. However, I do understand your point about the 3hp RPC not starting a bigger hp motor, but isn't that because the RPC would be setup to start a 3hp motor and therefore would not cope with starting the 7.5hp. As I said my SPC is setup to start the 7.5hp so can easily start the 3hp. If the 3hp is already running then it is already generating the 3rd phase and this together with the overall capacity of the SPC allows the 7.5hp to start.

Either way we look at it the system "sharing" you refer to will be far less efficient in your static converter then it would be with our rotary converters.

Agreed - my setup although effective is a bit "rough and ready" and certainly doesn't produce the most efficient output (especially compared to a good commercial unit).

If all your motors are contributing to creating the '3rd' phase they will still all loose power output. Any rotary converter becomes less powerful, less efficient and unbalanced when you apply a physical load to the pilot motor.

I agree that the more load placed on the "system", the less efficient and more unbalanced it gets. I think it applies equally to SPC's and RPC's. The capacity of the RPC is more to do with starting a load motor, rather than keeping it going. It seems logical to me (knowing how RPC's in general are configured electrically) that once running, the load motor would share a proportion of the 3rd phase "generating" with the pilot motor and the more motors that are running, the better the whole system performs (i.e. more spare capacity it has). I guess as the RPC pilot motor is unloaded it is able to provide a fair bit of that spare capacity.
This is an area I would love to find out more about.

Originally Posted by Vernonv

I personally think the vibration issue is a bit of a furphy (even with metal working machines). Most decent machines use a lot of cast iron and are heavy. The vibration caused by the (relatively) slow speed of the motor would have minimal (if any) effect of the accuracy of the machine.

I'm not so sure that's true when talking about high accuracy work. While setting up the lathe to which the VFD mentioned in this thread was fitted, I noticed it was cutting a noticeable cam on the work when using the leadscrew. Turns out the gear on the spindle contacting the gear train had a ding in it which was enough to push the spindle ever so lightly off and create a noticeable ridge. For someone like myself from woodworking it was eye opening into how unforgiving metal is and even seemingly insignificant faults can produce poor results. I certainly wouldn't rule out "pulses" from a single phase motor degrading the work, particularly if they happened to be a harmonic of the spindle speed ie they fell at the same spindle position with each rotation.

Pete

Originally Posted by Big Shed

Hare & Forbes have a 3.2hp 240V motor on special at $209

I just had delivered up a 3hp 240 motor from Royce Cross Agencies in Adelaide ,for $231.00 which include freight to Katherine ,its a 28mm shaft 1410rpm , just what the doctor ordered.

Its second hand ,but has been serviced and has a 3month warranty.Just a few scratches on the paint around the foot mounting holes other wise it looks brand new and no marks on the shaft .

Just need to bore and key the pulley and alter the mounting plate on the saw.

Kev

Good one Kev, hope that completes the project

Originally Posted by Vernonv

Hi Pete,
I also responded in your other thread in the reno forums. I assumed the VFD outputted 3 x 240V (240V phase to neutral) and Fossil is assuming it's 240V 3~ (240V phase to phase). I'm not sure who is right, but I think you will need to check out the VFD specs a bit more closely to determine what they mean by "3 x 240V".

If my assumption is correct then the motor will work without modification. If Fossil is correct then it will need to be modified as he mentioned.

As an aside (and as everyone else is mentioning phase converters) - I built a static phase converter for my workshop that cost much less than $100 (I had a lot of the parts). It runs off 240V split phase (480V) and can run my saw (7.5HP) scriber blade (1HP) and dust extraction blower (3HP) all at the same time ... and I didn't need to reconfigure the motors to run 240V 3~.

Hi, just wondering if you have any info on building a phase convertor, as i need to run a panel saw (7.5HP) from a single phase supply, and can't warrant spending $5,000 on a bought one. cheers luke.

Originally Posted by Turner2608

Hi, just wondering if you have any info on building a phase convertor, as i need to run a panel saw (7.5HP) from a single phase supply, and can't warrant spending $5,000 on a bought one. cheers luke.

Hi Luke,
The converter I am using is running off 240V split phase i.e. 480V, and not 240V. If you only have 240V single phase then you need to either run a 240-415 step up transformer or configure your motor to run 240V Delta (that is if your motor will allow it).

Static phase converters are pretty simple to configure - all you need are some motor run capacitors and a contactor (and a few other minor bits and pieces).

I gleaned a lot of info from the net and also these forums (I think Fossil posted about his build). So your best bet is to do a bit of reading and research first, so that you have an understanding of what your options are and what best suits your situation.

Let me know if you need more detail on anything.