Will a Static Phase Converter Work For Two Motors?

MatthewL · Apr 10, 2019

I have just about finished up cleaning and repainting my VN no. 16 mill. Because it is just a home shop machine, and I won't be machining anything to aggressive, I decided to use a static phase converter. However, there is one 2HP motor for the main driving, but there is a small motor that drives the table power feed. Reading up on static phase converters, I understand that a phase converter is required for every individual machine. Would that apply here for two motors? It still all goes to one receptacle. Also, I know a static phase converter only supplies single phase and just starts the motor with capacitors, but there is a whole electrical panel and switches that control speed of the power feed motor. Will the static phase converter work for all of that too? I haven't bought the converter yet, by the way.
I have a separate question about getting 220, but I will make another thread.

Thanks,
Matthew

dalmatiangirl61 · Apr 10, 2019

As long as only 1 motor is running at a time, I think it will work. Do not think it will work running both at same time, but might be wrong. Do yourself a favor, buy or build a rotary phase converter, static converters suck.

MichaelP · Apr 10, 2019

I guess as soon as the first motor starts running it becomes a rotary phase converter.

Froneck · Apr 10, 2019

No not really. The static converter is designed to operate the motor after is started it. Most likely it has a run capacitor and possibly a balance capacitor. Any additional motor will be looked upon by what ever circuitry it has as a change in load by the main motor. Then the reverse will happen if your mill operates like mine in that if I stop the main motor and remove the feed the feed motor continues to run now putting a static converter connected to a motor it was not intended to operate.

TDegenhart · Apr 10, 2019

I am not an expert but I think you will find that the function of the static convertor is essentially a continuously rated start panel. In other words, the motor once started, runs single phase and will produce an unbalance but usable 3 phase. This would be true for any other motors connected. Any balancing is incidental to getting the motor rolling.

This is similar to how my RPC works. It has no separate start circuitry. The balance caps get the motor started (usually). Occasionally I do have to spin the motor shaft to get it started but once running, runs fine.

Tom

Froneck · Apr 10, 2019

I use RPC in my shop so don't bother with static. However I went to an auction that was equipment in a garage used by a retired Tool and Die maker being sold by his widow when he passed. I purchased a Surface Grinder that had a static converter installed. I then connected it to single phase, being interested in it's function I found that it did have a run capacitor. Not sure if it had any balance Cap. but did not drop the 3rd phase after start-up and allow the motor to "single phase". It worked quite well looked to be top quality had I more time I would have looked more at the circuitry so as to possibly design one for my use. But having 2 other Surface grinders and it being a Harig hand surface grinder needing room I sold it to a friend. Furthermore the Balance Capacitor is not for starting, it's connected to the wrong side of the line. In my RPC I remove the Start Cap. after start-up nor have Balance Cap. Yet the RPC 3rd leg is connected to the shop motors and provides part of the run current. The fact you have starting problem might be caused by the balance Cap. Plus Start Cap. being too small. If I were to use a balance Cap. I'd have it disconnected during start-up and connected after Start Cap. is disconnected.

dalmatiangirl61 · Apr 10, 2019

I know a guy that put together a crude RPC using a static converter, 220 1ph into static box, static box outputs into a 5hp 3ph idler, and to use the medium size lathe the 5hp idler outlet was fed to a 10hp idler, then to lathe motor. Other than saying it worked, I do not know more about it.

Froneck · Apr 10, 2019

dalmatiangirl61 said:
I know a guy that put together a crude RPC using a static converter, 220 1ph into static box, static box outputs into a 5hp 3ph idler, and to use the medium size lathe the 5hp idler outlet was fed to a 10hp idler, then to lathe motor. Other than saying it worked, I do not know more about it.

What your describing is a start circuitry used to start an RPC. I do that too, start a smaller RPC motor and if a larger motor is required add a larger one being started by the smaller running RPC. Static converter has no revolving components like a motor and provides a means to run 3 phase motor from single phase usually thru the use of capacitors and electronic switching.

RustySparks · Apr 10, 2019

MatthewL said:
there is a whole electrical panel and switches that control speed of the power feed motor.

Since this is a mill, you will want accurate control of feed speed. Although it seems likely that the power feed motor would at least attempt to run while the main motor was running, You will want something better to supply 3 phase to the mill than a simple static converter, so you will have more predictable feed rates.

TDegenhart · Apr 10, 2019

Doing a google search for static phase convertor diagrams yields only one conclusion. The is no rotary element with a static unit. Some are simple starting caps only, some have both starting and running caps, some have both starting and running caps with the starting caps switched out. Some have a lot of solid state circuitry.

Tom

Froneck · Apr 10, 2019

As I was saying there are quite a bit of Static converters and I'm sure they are called Static simply because they have no rotary action. Unlike an RPC. The OP must determine what type he has. He must understand that if he has the type that simply starts the motor and does not add any run energy either from capacitors, inductors or electronic circuitry and that the motor is running at at a much lower rating. Single phasing a motor intended for higher loading will soon burn out the motor. Furthermore most static converters are rated for the motor being driven adding anything to the load is not good. In my Toolmaster mill the feed motor runs at one speed and gears change the feed rate but in my Gorton Mastermill it has a DC motor that RPM are changed to change feed rate. That type of application might allow using a static converter for 2 motors.

dalmatiangirl61 · Apr 10, 2019

Froneck said:
What your describing is a start circuitry used to start an RPC.

I guess you could say it that way too, but it was a popular name brand static converter, little grey 3" square box with an LED style. He had it all shoved into a closet wired helter skelter with romex and multiple disconnects that had to be engaged/disengaged depending on what machine you wanted to run. I have no idea of how balanced voltages would be on such a system, I was not there to check that, just needed to borrow some machine time.

MatthewL · Apr 10, 2019

Well, I have decided to go with a VFD now. I found a 2hp VFD from Temco that runs off 120 single phase (SKU V02203). Considering I don't even have a 220 outlet yet for a SPC, the VFD seems best.

Matthew

Froneck · Apr 11, 2019

dalmatiangirl61 said:
I guess you could say it that way too, but it was a popular name brand static converter, little grey 3" square box with an LED style. He had it all shoved into a closet wired helter skelter with romex and multiple disconnects that had to be engaged/disengaged depending on what machine you wanted to run. I have no idea of how balanced voltages would be on such a system, I was not there to check that, just needed to borrow some machine time.

Simply put being it was connected to an idler motor his set-up was no longer static. Actually most RPCs use a rather simple static converter as a means to start the RPC. Those with run and possibly a balance Capacitor have a static converter in line with the RPC. The problem comes with trying to operate multiple motors of different HP ratings and the possibility of running more than one at the same time.

Froneck · Apr 11, 2019

MatthewL said:
Well, I have decided to go with a VFD now. I found a 2hp VFD from Temco that runs off 120 single phase (SKU V02203). Considering I don't even have a 220 outlet yet for a SPC, the VFD seems best.

Matthew

If you didn't get it yet you might open a thread on connecting a VFD to your mill. Your mill probably has contacters, transformer and as you stated another feed motor. You might have problems connection to all that and they should probably separated from the VFD output.

neilho · Apr 11, 2019

MatthewL said:
Well, I have decided to go with a VFD now. I found a 2hp VFD from Temco that runs off 120 single phase (SKU V02203). Considering I don't even have a 220 outlet yet for a SPC, the VFD seems best.

Matthew

Each motor requires a dedicated VFD, so 2 VFD's are needed to run your mill. The machine will have to be totally rewired so that the machine controls are wired to the VFD, not to the motor. (Switching VFD outputs are a sure way to trash them.) Dunno what's involved in running 220 to your shop, but rewiring your machine and setting up 2 VFD's is a lot more work than setting up a crude, yet effective RPC.

IMO, if you're planning to have more than one 3 phase motor in the shop, you're much better off with an RPC. Advantages are easy expansion, versatility, wiring, troubleshooting, component replacement and expense. Some self-education is required (PITA when just wanting the damn thing to work, IMO) but it's like any other education - once you have it, everything's easier.

In it's simplest form, you could have a 220V extension cord to a 3 phase motor sitting on the floor. Wrap a lawnmower pull cord around the shaft, plug it in, pull the cord, presto, RPC. They can be much fancier, but an extension cord and a used 3hp 3 phase motor would get your mill (and future machines) running for well under $100.

Neil

mmarquette · Apr 11, 2019

I run my 7 1/2 HP Cincinnati #2 that has a seperate feed motor driving the table functions on a 8 HP static. Run it plenty hard enough for me. Havent seen any issues. The static sure was cheap. even run a 10HP motor on my 24" lathes. Dims the lights for a few seconds but a .200 depth of cut at a pretty decent feed , speed is no problem. I think the statics are under appreciated the rotary ones are overrated

Froneck · Apr 11, 2019

mmarquette said:
I run my 7 1/2 HP Cincinnati #2 that has a seperate feed motor driving the table functions on a 8 HP static. Run it plenty hard enough for me. Havent seen any issues. The static sure was cheap. even run a 10HP motor on my 24" lathes. Dims the lights for a few seconds but a .200 depth of cut at a pretty decent feed , speed is no problem. I think the statics are under appreciated the rotary ones are overrated

The fact that your lights dim for a few seconds indicates you are dragging down the single phase line. It's odd that the contacter don't drop out when starting. I can easily cut .700 depth cut at heavy feed rate with fast RPM cutting Stainless steel on my 24" lathe while my K&T mill is also taking a heavy cut while the 2HP cut-off band saw is cutting and my lights don't even flicker! All by using a simple home made RPC! I'm willing to bet your motors are running hot if used for a long time. What you are simply doing is using the Static converter as a way to start your motors and running them essentially single phase! What you should try is start your lathe, let it idle then try running your mill, the lathe motor will be acting like an RPC.

mmarquette · Apr 11, 2019

Ive run them for hours. Nothing super heavy but plenty none the less.

Will a Static Phase Converter Work For Two Motors?

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