3 Phase conversion for Felder AD741

[63Denied]

Hello everyone. I realize there are lots of threads about 3 phase conversion already but I can’t seem to wrap my head around the specifics of my application. I bought a Felder AD741 Jointer/planer from an industrial auction knowing it had a 7.5 hp 3-phase motor in it. I asked my electrician to wire It for me with a 50 amp breaker going to a static phase converter from North American Phase Converter. This did not work, and I should’ve figured that the $150 solution wouldn’t work. So now I’m researching Rotary Phase Converters and VFDs. There’s a lot of talk between soft start, hard start, heavy load and light load, getting a converter that’s sized 50% larger than motor rating etc.

So my question is, what do you all who know about these things recommend? How do I know if my motor is a soft start? What’s considered a “heavy” load? We’re talking industrial machines here. Is taking a 1/16” off an oak board a heavy load? And if I have a 7.5 hp motor and I’m buying a phase converter designed for that, is the 50% larger than rating already factored into the rating of the phase converter? Thank you all for any answers and advice you might have.

 

[Lightning rod]

What model of SPC did you install?
What do you mean it didn't work ?
Failed to start ? Failed to run under load ?
This is not a difficult rating to size an SPC for
North American recommends this unit

https://www.northamericaphaseconverters.com/wp-content/uploads/2019/04/PL-15.pdf

Maybe your unit is undersized? Or something is damaged on your jointer?

 

[Steve from Socal]

Your planer starts with the knife rotating but under no other load. A soft start would not be needed IMHO. A 10HP rotary would be the right size.

 

[tool_scrounge]

Use you static phase converter with a 10hp motor to make a rotary phase converter.

 

[marinusdees]

Hello everyone. I realize there are lots of threads about 3 phase conversion already but I can’t seem to wrap my head around the specifics of my application. I bought a Felder AD741 Jointer/planer from an industrial auction knowing it had a 7.5 hp 3-phase motor in it. I asked my electrician to wire It for me with a 50 amp breaker going to a static phase converter from North American Phase Converter. This did not work, and I should’ve figured that the $150 solution wouldn’t work. So now I’m researching Rotary Phase Converters and VFDs. There’s a lot of talk between soft start, hard start, heavy load and light load, getting a converter that’s sized 50% larger than motor rating etc.

So my question is, what do you all who know about these things recommend? How do I know if my motor is a soft start? What’s considered a “heavy” load? We’re talking industrial machines here. Is taking a 1/16” off an oak board a heavy load? And if I have a 7.5 hp motor and I’m buying a phase converter designed for that, is the 50% larger than rating already factored into the rating of the phase converter? Thank you all for any answers and advice you might have.

A static phase converter works by splitting off a "dummy" third leg using capacitors to shift the phase from one live leg of the 240v. Since the third "phase" is a phantom to create a rotating field to start the motor rotating, after which it runs essentially "single phasing" and only produces 2/3 of rated power. Do as suggested, and run a (used?) 10 hp three pahse motor in parallel with the planer motor. The 10 hp motor will essentially generate a full third leg, and full power. This is a rotary phase converter.
Or, invest in a VFD rated for 7 1/2 hp.

 

[marinusdees]

A static phase converter works by splitting off a "dummy" third leg using capacitors to shift the phase from one live leg of the 240v. Since the third "phase" is a phantom to create a rotating field to start the motor rotating, after which it runs essentially "single phasing" and only produces 2/3 of rated power. Do as suggested, and run a (used?) 10 hp three pahse motor in parallel with the planer motor. The 10 hp motor will essentially generate a full third leg, and full power. This is a rotary phase converter.
Or, invest in a VFD rated for 7 1/2 hp.

PS Since it sounds like you only have single phase power to feed a VFD, the 50% over rating is required for the VFD to be able to generate the three phase power in sufficient quantity (amperage) to run the motor. Think, 2/3 power since only two hot leads leading to three. As in, the inability of the static converter to produce only 2/3 enough power. Same difference.

 

[63Denied]

Thank you all for the info and expertise. I just got a 10 HP rotary phase converter (unused) on FB marketplace for $500. Once I finish a couple other projects, I’ll be wiring it up and let all of you know the results.

 

[63Denied]

Well. Not great news. I wired up the 10HP rotary phase converter. It will start up and run no problem. But when I wired it to the motor on the planer/jointer, it started the blades spinning (slowly it seems) and then popped the 40A circuit breaker after a second. I can spin the motor and the blades by hand, so they move freely and there’s no drag. Anyone have any ideas on what else I can check? From everything I’ve read it seems like it should work. When I put in my motor requirements to the American Rotary calculator they recommended a 15HP Rotary Phase Converter. But even if it’s undersized, my current 10HP model should turn the motor just at a slower speed, right?
Any ideas appreciated. Thanks.

 

[Tundra1]

Have you verified the motor winding leads are properly connected? Usually there are a few different ways they can be wired depending on service voltage. Possibly something got swapped around.

 

[American Locomotive]

An undersized rotary phase converter will not run a motor slowly. It will often cause machinery to have trouble starting, which will then trip a breaker. It should still probably start the machine with no load though.

 

[micromind]

A 40 amp two pole circuit breaker will not support a 7 1/2HP 3 phase motor. 80 would be about minimum, 100 would be better.

 

[63Denied]

A 40 amp two pole circuit breaker will not support a 7 1/2HP 3 phase motor. 80 would be about minimum, 100 would be better.

Really? Because a single phase 7.5 HP has a 31 amp rating. Do I need to double that because I have the two motors running on the same line at the same time? Or do 3 phase motors draw more amps?

 

[micromind]

Really? Because a single phase 7.5 HP has a 31 amp rating. Do I need to double that because I have the two motors running on the same line at the same time? Or do 3 phase motors draw more amps?

It's not running current, it's starting current.

A typical AC motor will draw 6 - 10 times the running current while it starts. Even the code recognizes this and allows for a larger breaker for motors.

According to code, the smallest wire for a 7 1/2HP single phase motor is #8 copper if you're using THHN in conduit. If you're using some sort of cable, like NM-B then it's #6.

The largest breaker is 100 amp.

It's perfectly compliant to have #8 and a 100 amp breaker in this case.

 

[wyliesdiesels]

Really? Because a single phase 7.5 HP has a 31 amp rating. Do I need to double that because I have the two motors running on the same line at the same time? Or do 3 phase motors draw more amps?

thats running current NOT starting IN-rush current, which as said above, can be very high. this momentary (200ms) current can trip lower rated breakers.

 

[alfredeneuman]

Motors are required to have supplemental overload protection in the form of temperature sensors embedded in the motor windings, or heat sensors in a motor starter.
The breaker just protects the wire.

 

[wyliesdiesels]

Motors are required to have supplemental overload protection in the form of temperature sensors embedded in the motor windings, or heat sensors in a motor starter.
The breaker just protects the wire.

In the case of larger motors The breaker only protects the wire from ground fault and short-circuit. The overloads in the motor or starter protect the motor and wire

 

[tool_scrounge]

Really? Because a single phase 7.5 HP has a 31 amp rating. Do I need to double that because I have the two motors running on the same line at the same time? Or do 3 phase motors draw more amps?

one comment: for a three phase motor that uses 31 amps, the equivalent single phase motor with the same HP rating, voltage and power factor would use 1.71x more current (52 amps) at full load. As previously posted, You also have the current spike on power up. That is one advantage of a VFD, - the slow ramp up in speed on power up greatly reduces the current spike.

 

[micromind]

31 amps is about right for a 7 1/2HP single phase motor operating at 230 volts. For a 3Ø model, I'd expect to see a bit less than 20 amps.

 

[wyliesdiesels]

one comment: for a three phase motor that uses 31 amps, the equivalent single phase motor with the same HP rating, voltage and power factor would use 1.71x more current (52 amps) at full load. As previously posted, You also have the current spike on power up. That is one advantage of a VFD, - the slow ramp up in speed on power up greatly reduces the current spike.

a 3Ø 7.5hp 230v motor has an FLC of 22a not 31a. 31a is the FLA of a single phase motor. The FLA of a 3Ø 7.5HP motor would be less than 20a

 

[tool_scrounge]

a 3Ø 7.5hp 230v motor has an FLC of 22a not 31a. 31a is the FLA of a single phase motor. The FLA of a 3Ø 7.5HP motor would be less than 20a

Thanks, misread that.

 

[theoldwizard1]

Your planer starts with the knife rotating but under no other load. A soft start would not be needed IMHO.

I agree with the first statement. Very light starting load.

IMHO, a GOOD/TRUE soft starter, would further reduce the starting current with no negative impact on running performance.

 

[63Denied]

Thank you all for the info. I’m working on upgrading wire, circuit breaker and magnetic start stop switch.