Variable Frequency Drive questions

[newbury]

I might have posted this before -but-
I've 6 pieces of used 3 phase woodworking equipment (up to 5hp) I bought at a auction. Our son (a maintenance/electrical type) was going to help me build and hook up to a rotary phase converter. He never got around to it. At that time VFD's in the power range required were running about $1K and up. And I was told that I would need a VFD for each machine or have to go through a pain of reprogramming the VFD.
VFD prices seem to have dropped.
Is there some way I could just hook up a VFD big enough for the maximum size motor and plug the equipment in one at a time?
I'm a 1 person shop so running 1 thing at a time is fine.

 

[etpm]

It depends on the VFD. They generally don't like running a large range of loads. But some will. So you really need to check. There are all sorts of cheap VFDs on ebay. If you have a 7hp 3 phase motor kicking around you can easily build your own rotary phase converter. They are simple and there are plenty of plans online available for free.
Eric

 

[ponytug]

I'm a fan of VFDs, but they aren't the easiest items to get up and running sometimes. I think that some VFDs are easier to program than others, and some have the ability to store several different profiles. Often times buying a cheap VFD gets you a manual that is tough to decipher and has errors in it. (BTDT) I really like the many options of VFDs, like soft start and braking options that I think have value for reducing the wear and tear on equipment.

However, if you have a wide range of HP motors, using just one VFD isn't going to be optimal, and you are likely better off with a rotary phase converter, but you will miss out on things like variable speed control. As @etpm writes above, you can certainly build one yourself, but the cost really depends on what you have lying around. (E.g. I don't happen to have a 7HP 3 phase motor lying around, so it would be pricey for me.)

Whether you could switch several similar HP motors on one VFD without reprogramming it gets a bit into whether they are all the same motor, and what their driven loads look like. Not always simple.

Of course, there's another option which is to just replace the motors with standard 240V motors, but you may not want to do that if you are trying to restore old machines to OEM condition.

All the best,

Peter

 

[mikester]

Phase Perfect | 3 Phase Power Anywhere With Our Digital Phase Converter | Variable Frequency Drives and Digital Phase Converters | Phase Technologies

www.phasetechnologies.com

I have one of these for running a 60A machine, quieter than motorized phase inverters. Relatively expensive. You can run multiple machines with these.

Small VFD's are cheap these days can easily power a small manual mill, drill, or lathe. Just get one per machine and you get digital motor speed control for each machine. Prices start around $120

https://www.automationdirect.com/adc/overview/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)

 

[newbury]

Small VFD's are cheap these days can easily power a small manual mill, drill, or lathe. Just get one per machine and you get digital motor speed control for each machine. Prices start around $120

https://www.automationdirect.com/adc/overview/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)

Your link shows that it would be $635 for one VFD to drive my 18" planer (5HP). The other 5 machines would be $200 to $300/ machine.

I think that some VFDs are easier to program than others, and some have the ability to store several different profiles.

Could you provide a link to some that store different profiles?

And could someone provide a link to explain why it seems I could set up a 3 phase line with a RPC to provide power for all my machines but I can't set up a 3 phase line with a VFD to provide power for all my machines.

/edit - I thought I had the problem solved when our son was going to build me a RPC, even got a 10HP 3 phase motor. But I don't work well with electricity.
When I was about 5 years old I grabbed some bare 120V wires and darn near fried myself.

 

[mikester]

Your link shows that it would be $635 for one VFD to drive my 18" planer (5HP). The other 5 machines would be $200 to $300/ machine.

Or you could spend $3K on a single 1ph to 3ph converter that provides 3ph output to run all three.

No free ride anywhere. I guess you could buy the $635 one and move it between machines...

 

[ponytug]

Your link shows that it would be $635 for one VFD to drive my 18" planer (5HP). The other 5 machines would be $200 to $300/ machine.

Could you provide a link to some that store different profiles?

And could someone provide a link to explain why it seems I could set up a 3 phase line with a RPC to provide power for all my machines but I can't set up a 3 phase line with a VFD to provide power for all my machines.

/edit - I thought I had the problem solved when our son was going to build me a RPC, even got a 10HP 3 phase motor. But I don't work well with electricity.
When I was about 5 years old I grabbed some bare 120V wires and darn near fried myself.

The reason a rotary phase converter would work with any/all of your machines is that it is making a fixed frequency into whatever load it faces. A VFD responds to the motor/load characteristics to try to provide the requested frequency/motor speed. While you can unbox a VFD set the voltage/frequency/HP and connect it to a motor, the VFD will do a better job of speed/frequency/voltage control if it "learns" about the specific motor, and its load.

The often not talked about item with VFDs is whether or not the motor is "VFD ready" or "inverter ready". This means a motor that has better than normal insulation (F/G/H), and usually windings and rotor that are designed for the high-frequency harmonics that can occur with VFDs.

https://library.e.abb.com/public/fec1a7b62d273351c12571b60056a0fd/voltstress.pdf

Vintage motors are not inverter ready, so I recommend babying them when using VFDs. Mine have input and output filters on them and are tuned to one particular motor per VFD.

The high frequency harmonics (voltages) from a VFD can damage the windings in an older motor. The farther the VFD is from the motor, the bigger the chance of getting damaging harmonics. VFDs located at a distance from their motor (not recommended!) usually have load reactors to reduce the harmonics to try to attenuate the problem. (VFDs may have line reactors to damp harmonics going back out toward the voltage supply. Not normally an issue for home users, but if you have five VFDs powered up, it might be an issue.)

One final item: VFDs need to be powered up regularly to keep their capacitors working; somewhere between monthly and yearly depending on who you believe.

How to Protect VFDs in Long Term Storage

Keeping a Spare VFDMany applications that utilize a variable frequency drive (VFD) are critical and can’t afford to have extensive downtime. One option that many opt for is to keep a spare VFD on the shelf, ready to switch out if the need arises. If you are not careful, however, that VFD may not...

vfds.com

TL;DR if you connect a VFD to an older motor, you are likely to get a longer life out of the motor if you "tune" the VFD to that particular motor. That means that one VFD per motor is your best bet. (Or go for a phase converter.)

All the best,

Peter

 

[LD1]

There is no reason you cant use a VFD sized for the biggest motor on any of the smaller ones.

As said.....you can literally unbox it....set it at 60 hertz, and set the voltage and use it. It would be just as good (actually better) than a RPC.

What makes a VFD nice is you can custom taylor some of the settings. Like accel/deceleration....to start something slowly if it has high inertial load. OR even braking.....and you can also set things to protect the motor. Like over-current, or frequency limits, etc. But you would have none of this with a RPC anyway.

I have both. A VFD that currently is only used on an electric motor we bolt to a logsplitter when we want to split indoors. (5-min swap to go from gas to electric or vice versa). The VFD is wired with a female 3ᴓ plug. And I have ran other 3ᴓ stuff off of it without swapping any parameters. But currently its just for the splitter.

I also have a RPC that runs the mill and lathe. But sometimes if others are helping me in the shop I am using both of them at the same time. And that is the biggest drawback to the VFD. Swapping it from machine to machine and only able to use one at a time.

 

[newbury]

<snip>
The farther the VFD is from the motor, the bigger the chance of getting damaging harmonics. VFDs located at a distance from their motor (not recommended!) usually have load reactors to reduce the harmonics to try to attenuate the problem. (VFDs may have line reactors to damp harmonics going back out toward the voltage supply. Not normally an issue for home users, but if you have five VFDs powered up, it might be an issue.)

<snip>

Peter

What's "located at a distance from their motor" 10 feet? 50 feet? Any good links for further reading?

 

[etpm]

Your link shows that it would be $635 for one VFD to drive my 18" planer (5HP). The other 5 machines would be $200 to $300/ machine.

Could you provide a link to some that store different profiles?

And could someone provide a link to explain why it seems I could set up a 3 phase line with a RPC to provide power for all my machines but I can't set up a 3