Convert a 3phase surface grinder to single phase?

Hi all.
I saw this http://www.gumtree.com.au/s-ad/picton/miscellaneous-goods/surface-grinder/1071972077
and can't resist it.

Only problem is I don't have 3 phase power. Will this be hard to convert to single phase or uselessly expensive?
If I touch wires I tend to make sparks, catch on fire, explode, that sort-a-thing. When it comes to knowing anything more then using a multi-tester, i'm boned.
Any advice appreciated. Always wanted one!

You need a Variable Frequency Drive (VFD) or a Rotary Phase Converter (RPC). Not that hard to do, in fact, there is an entire forum devoted to it: Transformers, Phase Converters and VFD

I believe the prevailing wisdom is that converting a 3ph machine to single phase introduces oscilations in the motor waveform, leading to waves in your finish (as I read about with lathes, I imagine it'd be the same, if not worse with a surface grinder), the RPC is the way to go, methinks.

Hi; This is a bit more difficult as you did not mention the voltage rating of the machine. If it is a 230volt 3phase then a rotary converter would likely be a good choice, if it is a higher voltage that makes it more complicated and expensive but still doable. A lot will depend on how good the deal is and how badly you want/need a surface grinder. Checkout the forum on VFD's and phase converters on this board.

How many horse motor?

VFD or if more than 3 hp you'd probably want an RPC

The VFD will be cheaper, and limited to only one machines, but it is a muchhhhhhh more versatile device. Being that you can fiind tune your motors performance to your likeing whenever you wish using the VFD's user interface. Im not an electrician... when I bought mine, I was extremely intimidated, but I assure you, it isn't rocket science.

VFD is likely to be your cheapest route: converts 220v single phase 50-60Hz to 220v 3phase at any Herz from 1 to 200+. In your application you would set it for 50-60Hz and use it as the motor
drive. I would stick to quality VFD mfg: Hitachi, Teco, Toshiba and avoid ones with "chinese" names. The 25-40% lower price of the latter is reflected in high infant mortality and longevity
problems. The suggested ones are only nominally higher price and meant for heavy duty industrial use. In theory an RPC can be "cheaper" but most posters that do these have multiple
3ph machines or access to inexpensive or free motors, capacitors, relays, switches and boxes. If you have to buy all this a VFD is cheaper.

For a list of other VFD candidates this site has a list, but you will have to see what is available in Oz, avoiding the 'chinese' ones: Variable Frequency Drives - VFD - In Stock

One other aspect, unlike other metal working machines, grinders have high precision spindle usually directly driven by the motor and changing the motor is Bad Idea. Runout on these will be measured in microns
not tenths. Single phase motors have subtle pulsations apparent in grinding that 3ph motors do not.

Before everyone recommends a VFD., make sure there is only ONE motor that needs power.
Depending on the surface grinder, there may be pump motors, or a Z axis jog motor.
Plus all the electrical controls.

If there is more than the ONE spindle motor, then an RPC is the way to go, it will happily supply all the motors.
For a Single small motor, no other loads, then an RPC is dead simple.

A rotary phase converter may be a wise choice from a safety standpoint as well. If you over-rev the motor, which can be done with a VFD, you may risk running higher than the recommended speed of the grinding wheel. Limits can be set on the unit though, as far as I know.

In my home shop I run a 15HP RPC to power my 2HP mill, 2HP surface grinder (which also feeds a 1/4HP coolant pump and 1/3HP dust collector) and 5HP lathe. Every once in a great while, it's all three at once.

shamanj said:

Hi all.
I saw this Surface Grinder | Miscellaneous Goods | Gumtree Australia Wollondilly Area - Picton | 1071972077
and can't resist it.

Only problem is I don't have 3 phase power. Will this be hard to convert to single phase or uselessly expensive?
If I touch wires I tend to make sparks, catch on fire, explode, that sort-a-thing. When it comes to knowing anything more then using a multi-tester, i'm boned.
Any advice appreciated. Always wanted one!

Click to expand...

The grinder in the link has a spindle motor and a hydraulic pump motor. The electrical box has four pairs of pushbuttons and an emergency stop. This sort of machine needs a rotary phase converter, which makes the wiring simple and easy. You can use a VFD for each motor, but the wiring will get very complex. It will not be practical to replace the motors, especially the special spindle motor.

Larry

in addition to more pronounced torgue cogging with single phase, another reason for staying 3 phase is that the motor on a quality surfce grinder is likely properly balanced (this helps to get a good finish, it is very easy for imperfections to show up in the finish)....that's not going to be the case with a run of the mill replacement motor

L Vanice said:

The grinder in the link has a spindle motor and a hydraulic pump motor. The electrical box has four pairs of pushbuttons and an emergency stop. This sort of machine needs a rotary phase converter, which makes the wiring simple and easy. You can use a VFD for each motor, but the wiring will get very complex. It will not be practical to replace the motors, especially the special spindle motor.

Larry

Click to expand...

Actually Larry, to be more precise it appears to have the spindle motor, plus an external coolant pump & tank, and internal hydraulics. And it looks to be a good quality machine, tough to find over there!

Ken

PixMan said:

A rotary phase converter may be a wise choice from a safety standpoint as well. If you over-rev the motor, which can be done with a VFD, you may risk running higher than the recommended speed of the grinding wheel. Limits can be set on the unit though, as far as I know.

In my home shop I run a 15HP RPC to power my 2HP mill, 2HP surface grinder (which also feeds a 1/4HP coolant pump and 1/3HP dust collector) and 5HP lathe. Every once in a great while, it's all three at once.

Click to expand...

Mind telling us how you make a 15 HP motor run, the one that runs the RPC ??The motor that turns the RPC.... where do you get enough power?

The 15hp motor doesn't "turn" the RPC-it IS the RPC....

To get 15hp thru it, a bit more than 50 amps would be needed at 220V.

With only a 10 hp or so max load(with all machines running) current required would be less.

Thanks heaps for the knowledge input guys. Really really appreciated. I think this is a craptonne more bang for buck with a VFD or RPC then a chinese one. I'm looking at RPC's now and getting a shipping quote.
Cheers ya-all i'll post when it arrives!