VFD For 3 Phase Equipment, not just motor

[John Halsted]

I'm looking at a Felder AD941 that is a 3-phase machine. I'm wondering if I can just put a VFD in front of the whole machine, or if VFD's are really only designed for handling one motor. The machine has peripheral electronics like the power planer bed height and digital readout. I do not know if the feed motors are separate or if everything runs off of one motor.

There don't seem to be many "digital phase converters" on ebay, just expensive rotary stuff. But when I search for VFD there are tons of cheap options. I don't see any reason why a VFD couldn't do what needs to be done, unless they're only setup to operate in a load-sensing way where it only works powering a motor directly.

This exact question about the AD941 was actually asked in an older thread but never clearly answered and the OP never came back and said what he did, if anything. The answer would apply to any 3 phase equipment though.

Edit: AD941, not 741 and not 471, woops.

[ray grundhoefer]

A vfd is only meant to be used with an individual motor. I believe It would cause all kinds of problems with your electronics. In this instance a rotary phase convertor is probably your best option.
Ive never done it but its not to hard to make your own with a 3 phase motor. You can probably find out how on youtube.

[John Halsted]

A vfd is only meant to be used with an individual motor. I believe It would cause all kinds of problems with your electronics. In this instance a rotary phase convertor is probably your best option.
Ive never done it but its not to hard to make your own with a 3 phase motor. You can probably find out how on youtube.

I still can't quite understand why a vfd shouldn't be able to act as a dumb phase converter, but let's say that's the case. The next quest is can the Felder AD 941 be setup with a vfd on the cutter motor and a single phase to handle the powered bed and digital readout? I still don't know if there is an independent drive motor for the planer feed.

A vfd would be far cheaper and smaller than a rotary phase converter.

[jack forsberg]

We Have wired your saw with a single VFD a few times . You cannot think of VFD’s as a power source to plug in to. they are motor controls and have to be wired as such. Generally we leave your three phase controls in tact on your saw and run new control wire for the vfd . It is obviously the best to have two VFD’s but just for the scoring saw it’s not a big deal. If you’re interested in our solutions contact me at Jack@jforsberg.ca . All we need from you is a picture of the motor tags

[Van Huskey]

We Have wired your saw with a single VFD a few times . You cannot think of VFD’s as a power source to plug in to. they are motor controls and have to be wired as such. Generally we leave your three phase controls in tact on your saw and run new control wire for the vfd . It is obviously the best to have two VFD’s but just for the scoring saw it’s not a big deal. If you’re interested in our solutions contact me at Jack@jforsberg.ca . All we need from you is a picture of the motor tags

Jack since it is potentially relevant here (since the J/P in question is available with motors up to 10hp) what is the limit on HP (or kW) for single phase in 3 phase out VFDs currently?

[jack forsberg]

Jack since it is potentially relevant here (since the J/P in question is available with motors up to 10hp) what is the limit on HP (or kW) for single phase in 3 phase out VFDs currently?

Currently up to 20 hp 39 amps Three phase out put. but do understand that this requires a 100 amp branch circuit. This VFD is a particularly large at 44 lbs and shipping costs are in the $120 range.

[David Kumm]

There were Felder combo machines sold as single phase that had three phase motors controlled by a vfd and wired internally to handle the various electronics. I'm guessing that what Jack does is similar. Felder used small motors so the vfd could fit inside the machine. Dave

[Malcolm McLeod]

Simply put, VFDs take the input AC (assuming 240VAC, 1ph for you), convert is to DC and use it to charge it's internal DC buss (2 ea. - 1 DC+ / 1 DC-). Then the output section of the VFD rapidly switches the DC buss on and off - injecting what 'looks' like 240VAC, 3ph onto the motor leads. ...not sure this matters to you, but sometimes I just can't resist data vomit.

So in your proposed setup, you power the VFD, and hit 'Run'. It ramps the output electronics to the Hz setting you selected (lets say 60Hz, so full 240VAC). There is absolutely no load on the VFD at this point. Now you go to the Felder, hit the 'go' button for the ?4Hp? saw motor, the Felder starter closes, and the full ampere load hits the VFD. The saw blade twitches briefly and you need a new VFD.

A VFD must be connected directly to the motor with NO switch gear, disconnects, or starters in between. Please don't try what you're proposing. Hope this helps.

...And see what Jack posted. I think what he's saying is they leave the Felder controls 'ON' all the time, then use the VFD controls to 'Start' the saw..? This avoids the magic smoke release. But don't let me put words in his mouth.

Van, I've never seen VFDs claim to handle >5Hp, 3ph motors using 1-ph input power. But nearly, any VFD can serve as a 'converter', IF the input section can handle the amps associated with the 1-ph current draw of the load and can have the "input phase loss" alarm disabled. Just don't shock load it like I described above. And they get really pricey for the average hobbyist!

[Dan Friedrichs]

John,

There is nothing physically which prevents a VFD from acting as a "power source" rather than a "motor controller". The VFD rectifies the single-phase input to DC, then chops it back up (inverts it) to produce 3-phase AC. It could easily do that and operate as you desire. However, no one (aside from you) has that "need" - the large-scale need is to control a motor's speed and provide overcurrent protection. So while a VFD could conceivably be produced to do what you desire, I think it either doesn't exist (commercially), or would be so expensive (due to being such a niche product) that it would be cost-prohibitive.

If you're somewhat electrically-inclined, I'd suggest you do a little disassembly of the machine and see if you can figure how the electronics are powered. I'd bet there is a AC-to-DC power supply in there generating 12V or 24V for the electronics and elevation motor(s). If so, that power supply is almost certainly "universal" input, and single-phase input (you can connect 90-264VAC into it, meaning it would run on 120V single phase, 240v single phase, or from 2 legs of a 3 phase supply, etc).

Best case, you might find that you can power the digi-drive electronics from single-phase with zero modification, then put a VFD on the main motor.

(Jack - the machine the OP is talking about is a jointer/planer, not a saw, so there is no scoring blade motor...)

[John Halsted]

The AD 941 jointer/planer I'm looking at is 4hp.

Malcolm, from your explanation it sounds like you're saying VFD's are undersized or overrated for their labeled motor hp, and the way they can get away with this is by soft starting the motor, thereby skipping the high-draw moments of the starting sequence. Ok fine, but then I I should just be able to get a much bigger VFD, right? Even one rated for 10hp is only $200.

[Van Huskey]

I hadn't seen more than 5hp rating for a 1>3ph VFD but I had heard Jack had options for more, apparently a lot more. Not surprised about the amperage necessary for a 20hp drive, I think most 20hp (starting) RPCs need even more than 100 amp service.

[John Halsted]

John,

There is nothing physically which prevents a VFD from acting as a "power source" rather than a "motor controller". The VFD rectifies the single-phase input to DC, then chops it back up (inverts it) to produce 3-phase AC. It could easily do that and operate as you desire. However, no one (aside from you) has that "need" - the large-scale need is to control a motor's speed and provide overcurrent protection. So while a VFD could conceivably be produced to do what you desire, I think it either doesn't exist (commercially), or would be so expensive (due to being such a niche product) that it would be cost-prohibitive.

If you're somewhat electrically-inclined, I'd suggest you do a little disassembly of the machine and see if you can figure how the electronics are powered. I'd bet there is a AC-to-DC power supply in there generating 12V or 24V for the electronics and elevation motor(s). If so, that power supply is almost certainly "universal" input, and single-phase input (you can connect 90-264VAC into it, meaning it would run on 120V single phase, 240v single phase, or from 2 legs of a 3 phase supply, etc).

Best case, you might find that you can power the digi-drive electronics from single-phase with zero modification, then put a VFD on the main motor.

(Jack - the machine the OP is talking about is a jointer/planer, not a saw, so there is no scoring blade motor...)

All of that makes sense, except that since VFD's are programmable, I don't see why designers wouldn't include a "dumb converter" mode. As far as demand, people do sell and want phase converters - why is anyone using rotary anymore when the hardware needed to do it solid state is so cheap?

I'm actually an electrical engineer, so I am inclined to rewire the machine. I just wish I knew a bit more about what needed to be done before buying it.

Any AD941 owners here that can look under the hood and tell me what it's got?

[jack forsberg]

Simply put, VFDs take the input AC (assuming 240VAC, 1ph for you), convert is to DC and use it to charge it's internal DC buss (2 ea. - 1 DC+ / 1 DC-). Then the output section of the VFD rapidly switches the DC buss on and off - injecting what 'looks' like 240VAC, 3ph onto the motor leads. ...not sure this matters to you, but sometimes I just can't resist data vomit.

So in your proposed setup, you power the VFD, and hit 'Run'. It ramps the output electronics to the Hz setting you selected (lets say 60Hz, so full 240VAC). There is absolutely no load on the VFD at this point. Now you go to the Felder, hit the 'go' button for the ?4Hp? saw motor, the Felder starter closes, and the full ampere load hits the VFD. The saw blade twitches briefly and you need a new VFD.

A VFD must be connected directly to the motor with NO switch gear, disconnects, or starters in between. Please don't try what you're proposing. Hope this helps.

...And see what Jack posted. I think what he's saying is they leave the Felder controls 'ON' all the time, then use the VFD controls to 'Start' the saw..? This avoids the magic smoke release. But don't let me put words in his mouth.

Van, I've never seen VFDs claim to handle >5Hp, 3ph motors using 1-ph input power. But nearly, any VFD can serve as a 'converter', IF the input section can handle the amps associated with the 1-ph current draw of the load and can have the "input phase loss" alarm disabled. Just don't shock load it like I described above. And they get really pricey for the average hobbyist!

no generally we leave the old motor controls in tact but do not use them this is only so the Machine can be converted back to a three phase with little work . There is actually no problems with my drives bringing Motor’s online as long as the VFD is sized properly. It’s more prudent to start both motors at the same time as disconnecting the motor is not as harsh . Overload is a little more complicated but not impossible. Generally what prohibits this type of installation is the larger VFD’s get the more expensive. generally two smaller ones are cheaper. If you’re looking for generated electronic inverter electricity phase perfect is the way to go. Basically a VFD without variable frequency. Although I feel I can provide far more horsepower with individual VFD’s and you’re not reliant on one power source and therefore cannot have a catastrophic failure.

[David Kumm]

John, are you sure the motor isn't 4 kw rather than 4 hp? Felder generally spec'd their single phase motors at 4 hp and the smallest three phase was 4 kw or 5.5 hp. Dave

[Malcolm McLeod]

The AD 941 jointer/planer I'm looking at is 4hp.

Malcolm, from your explanation it sounds like you're saying VFD's are undersized or overrated for their labeled motor hp, and the way they can get away with this is by soft starting the motor, thereby skipping the high-draw moments of the starting sequence. Ok fine, but then I I should just be able to get a much bigger VFD, right? Even one rated for 10hp is only $200.

Again, simply put - you are correct. VFDs can be under-sized, compared to line starters, because of the relative soft start. But the devil is in the details:
- What is the 1-ph FLA for your 4Hp motor? This is approx 1.7 times greater than the nameplate. A VFD must have its input sized so that each input leg can support this current.
- Make sure you have a start scheme that avoids the high in-rush of a line starter. My guess is you'd smoke even the 10hp in the scheme I outlined above.
- If the VFD doesn't support disabling the phase loss alarm, it just sits there 'faulted' and won't run.