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Discussion Starter · #1 ·
bought a fairly antique 20" Monarch bandsaw. It came with a gigantic (~16" diameter) 5HP electric motor. I'm not sure a bandsaw of this size needs this much motor, but since I have it, I'll try to use it.
The motor appears to be 5HP 3Phase, and probably 1730RPM. It is old enough that I can't find information about it on the 'net. In the US, power is supplied to residences in single phase, so I would like to size and buy an appropriate VFD/Inverter/starter to run it from 240VAC 1-phase at 220VAC 3-phase. It would be great to choose the run speed, have soft start so there's not a huge inrush current, and possibly use dynamic braking.

I've seen less expensive Chinese manufactured VFD's on ebay, but there's typically no consultation with the vendors, and caveat emptor. I have seen recommendations for sizing at multiples of up to 6 or 8 times Full Load Amps. Also I've seen it said with 1 to 2 HP motors that 2 x FLA is sufficient. The label is faded enough that I can't be sure about the listed FLA (12? 12.68? 12/6.8 at 220/440?) nor the motor efficiency.
645121

One formula I found online shows to use ((HP x 746watts/HP) ÷ Efficiency) x √3(for 3phase) to get the KW required to size the VFD properly. It sounds right, but I can't read the necessary info from the motor badge so I wondered if anyone is familiar with this gear enough to make a recommendation?

Thanks

Antique GE Induction Motor, 5HP - 3PH - 220VAC
 

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Table 430.250 will give a typical full load current of a 3 phase 230 volt motor as 15.2 amps. Then multiple 15.2 x 1.73= 26.3 amps. Look for a VFD in the 5 hp rating that has a single phase input of at least 26.3 amps. They make them just for what you are trying to do.
 

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Those nameplates have the legends embossed, and the entered numbers punched in. So they are meant to be readable even if painted over (evenly).

I don't see on the nameplate where you think the motor has any 440V ability. Some motors provide a set of jumpers you can move around (dual fields that can be wired in series or parallel) but not every motor.
 

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Discussion Starter · #5 ·
The OP was 7 months ago, so he's probably long gone, but-

I highly doubt a motor of that vintage is inverter rated.
It would probably have a very short lived life on a VFD.
Actually still around. I've learned a lot since posting. The name-plate shows amps as "12 6.8" so it was natural to wonder if it may have a dual voltage intent that was mismarked or else omitted. I found no specific info about this motor.

Table 430.250 will give a typical full load current of a 3 phase 230 volt motor as 15.2 amps. Then multiple 15.2 x 1.73= 26.3 amps. Look for a VFD in the 5 hp rating that has a single phase input of at least 26.3 amps. They make them just for what you are trying to do.
That's illuminating, thanks. Another approach I found gives a close result:
~746 watts/hp x 5 hp == 3730 watts.
Uprate by (~√3) △ 3730W x 1.73(factor) == 6460
Test: (W ÷ V == A) 6460W ÷ 240V == 26.9A.


This motor is absolutely not inverter rated. It might be possible to use it safely with proper load reactance, but I don't have a recipe for that.

Anyone?
 

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Unless you are going to run it at half speed under high torque, don’t worry. In almost 40 years and hundreds of VFDs I’ve been involved with, I have seen only one motor that was made specifically for a VFD. None of the rest had any problems. My experience spans small hp motors to large several hundred hp motors. VFDs half the size of a loaf of bread to VFDs larger than three phone booths.
 
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