Static converter problem

I had the exact same trouble with a static converter many years ago. I'd suggest you get another three phase motor, just for trial.

As to voltage. One leg will be ground. Two of the legs are your 220 VAC from your one phase supply. The last leg is your "wild" leg. Voltage between this and either of your one phase supply legs can vary considerably and tends to run high. I know I've seen 250.

FWIW, I ended up converting my static converter in to a three phase idler motor converter to give more power and better starting on my equipment.

Karl

I have Stop/Start buttons which I suspect are "magnetic"? can they cause a problem?

You haven't provided enough information for any sort of definitive answer. Look at some of the articles on phase converters in Metal Web News. One of them has a schematic diagram of a static phase converter. It may/may not be similar to yours.

Does the motor hum?

You should have 240v between at least two motor terminals.

You really need to provide more details.

Most likely, but not certainly, the pushbuttons are bringing in and breaking a start relay. Are you hearing a click (relay closing) when you push start?

It might be time to pull the cover and see what you can see. You might get lucky and have an electrical print.

I'm sure others will chime in with more advice.

Karl

If there is any kind of control circuitry in the grinder, e.g. switch/relays operated by 220v single phase, the 2 hot leads must go there. The generated third leg would go to the other connection on the grinder.

Wayne D.

According to Wayne :

Exactly. The generated third leg is *only* present long enough to spin the motor up, and then it goes away.

And a "static" converter only works with a certain motor horsepower range -- which varies from converter to converter.

So -- if your control circuits are on the phase between the generated leg and one of the others, they won't see voltage to pull in the relay to convince the motor to start.

And also -- be warned that the surface finish from a surface grinder powered from a static converter will be poorer than that from a real three phase. (As will the finish if you replace the three phase motor with a single phase motor.)

You will be better off with either a rotary converter (which you can build using a spare three phase motor and your static converter, but you will get a better finish -- especially if you take the time to tune the rotary converter to your grinder) or with a VFD. You don't really need the variable speed from the VFD here, but you will benefit from quieter operation than you would with the rotary converter.

Good Luck, DoN.

I have Start/Stop buttons on my grinder. They are not just a simple switch. I guess they are "magnetic"? type. Can they be an issue?

There's not enough information to be sure but your "magnetic" starter button may be the cause of the problem.

Although all three phase wires are fed to the starter, the operating coil is only uses two of them, connected to it via the start and stop button contacts. When operating from true three phase it doesn't matter which pair are used.

With a static converter, at the moment of switch on, the "three phase" output is wildly unbalanced and the"wild" leg phase to low voltage may be less than half normal. If the operating coil happens to be connected to this phase it will not operate correctly and the motor will buzz and fail to start.

The wild leg output can be identified by a continuity check. The wild leg is the one that does NOT show almost zero ohms to either of the single phase input wires.

Ideally you should check out the connections and be sure that the coil is fed from the two outputs that show continuity to the single phase input. However, the quick and dirty way is to experimentally rotate the three output connections. At least one, and possibly two of the three possible re-arrangements should allow the motor to start normally.

Jim

short answer, "yes" = you must ensure that the power supply to the relays is across the 220, and that the capacitor goes only to the "other" motor leg or the relays won't energize.