ECN Forum Forums General Topics of the Trade General Discussion Area Single Phase to 3 Phase converter questions

Just started a butcher shop renovation and found that their bandsaw is 3 phase, fed with a Hass phase converter, which is on a 220v 20 amp breaker at the panel.
Converters ratings are 220v 3hp 11.7 amps

If I read the literature correctly it states that the motor to be connected's FLA is not the FLA the converter will "see" you take the FLA of the motor and multiply by 1.41 to find the converter's true load. Which makes sense with it not being true 3 phase.
So... this guy wants to use the existing phase converter to supply not only his 6.2amps 3 phase bandsaw but also his 4.8 amps 3 phase grinder which will be relocated in the walk in cooler.
The converter can't handle both at the same time so I'm looking into whether it's possible to have some sort of starter contact interlock so it's one load or the other.
Am I correct about the converter? Any suggestions as far as the starter?
Thanks

Odd to have such a small convertor...

Easy/cheap way to only allow one load would be a double throw switch, relay may be expensive and hard to find. However without knowing.... I would warn about how each unit is started. If both require power to start through a relay, well OK then. But if one or both are started by a switch, you may be creating a dangerous situation where an operator wont be present for the starting of a grinder or bandsaw. Or worse someone else is present for it starting remotely. Anyway, for the price of doing it with a contactor, for a little more, you could just add another convertor. (Not including the additional circuit if required)

Pick up any standard three phase reversing contactor/switch. Remove the load side jumper wires and viola you have an set of interlocked of contacts. You will need to add individual overload relays because each motor has a different FLA. Then you need to add interlocking to make sure the VFD is "off" before switching any motor "on" (VFDs do not like it when they are up-to-speed and a motor is "slammed" on).

After installation it may be less expensive to simply purchase a second VFD.

Do both the bandsaw and grinder already have contactors. If so, both probably have N.O. aux. contacts to seal in across the start button. Some contactors already have unused N.C. aux. contacts built in. If not, you should be able to add a N.C. aux. contact block to most. Wire the N.C. from one in series with the N.C. stop (and any N.C. E-STOPS?) of the other. Then it's a matter of first come, first serve. One won't be able to start or stop the other, just prevent it from starting while the other is running. If you are using 120VAC coils with a neutral, you're safer running the START/RUN first, then the STOPS, Interlocks, and any E-STOPS. That way, the interlock contact is usually not energized by the opposite circuit. But I would put signage at each starter, mentioning the interlocks amd the possibilty of being energized...
Let me know if you want me to put up a ladder .
Joe

Is this a rotary phase converter or a static phase converter?

If this is a rotary phase converter, then it may very well be capable of operating both of these motors at the same time; you will need to find the literature for that particular converter. See, for example http://www.phase-a-matic.com/RotaryApplicationNotes.htm for a competitor's product.

-Jon