Variable Frequency Drive questions

[etpm]

VFDs are motor dependent. It's not likely you'll be able to have a single VFD for the shop because each motor will have different energy and load specs. However, 3ph motors can run from about 30hz up to 120hz. That's how you change the motor speed. I bought two when I first got my Mill. One was required for the Mill and the other was required for the Table Feed. Obviously, they had to be able to run at the same time, so I needed two VFDs. I've since replaced the 3ph table feed with a modern 120v style and added table lift as well. My VFDs were less than $100 each and used common 240v single phase wiring.

I thought about going with an RPC, but they are large, clumsy and VERY loud as well as expensive. They don't like being turned on and off. And you'll need a lot of 3ph wiring to get it to each machine. The box and breakers alone will most likely cost more than several VFDs.

RPCs are not necessarily loud. I know because the big one I have in my shop is not loud. It just depends on the motor used. If one VFD is used the same amount of wiring and breakers and a 3 phase panel would need to be used as would be needed for the RPC solution. With the single VFD there can be a switch at each machine but this switch must be wired to the VFD. The way most VFDs work require using the on/off buttons on the VFD to control the motor. If a motor is switched off and/or on while the VFD is powered on it can ruin the VFD. I have seen this happen more than once. Several switches can be wired in parallel to the VFD though. And the wire is pretty fine gauge so it is cheap. A potentiometer, like a volume control, can also be wired to the VFD to control motor speed. However, having a potentiometer at each machine, while possible, is not as easy because they cannot be wired in parallel. They must each be switched in and out so only 1 at a time can be used. A less expensive wire and breaker solution is to use one VFD for each machine. This also will lessen the considerable radio frequency noise that comes from long wires between the VFD and the motor. This RF noise can impair WIFI and Bluetooth connections as well as interfere with FM and AM radio. There are ways to ameliorate the RF noise but this just adds cost. I think the best solution for the OP is to use one VFD for each machine. I say this even though I would use the RPC solution for myself. But I am comfortable and competent with electricity and electronics while the OP is not and we want what is best for the OP and not ourselves. 3 HP VFDs can be had for $80.00 each delivered. Link: VEVOR 3HP 2.2KW 10A 220VAC Single Phase Variable Frequency Drive Inverter 245496239798 | eBay
One HP is 746 watts, or rounded it is 750 watts which is also .75 KW. When searching for VFDs it is usually easier, though not always, to search for KW rather than HP. VFDs come in standard wattage ratings so a 3.75 KW, which is not standard would be more expensive than a 4 KW unit. So a few minutes searching can really save a lot of money.
5 HP VFDs can be had for $122.00 delivered. Link: VEVOR 4KW 220V 5HP RS485 Variable Frequency Drive Converter VFD Inverter w/Cable 741754318651 | eBay
Wiring for VFDs would be just two hots and a ground for each machine rather than 3 hots and a ground for the RPC. Machines with lower HP can use smaller wire and breakers. Plus, and this is a big plus, breakers for two conductors are way cheaper that breakers for 3 phase wiring. And 3 phase panels are more expensive too. If a VFD is used at each machine there does not need to be a breaker between the VFD and the motor, just the one breaker from the panel to the VFD. REMEMBER, breakers are only to protect the wires, not whatever is connected to the wires. If the OP already has a panel and it has 12 single breaker spaces free then the OP would not need to buy another panel. Variable speed can be had easily at each machine when each machine has its own VFD. This may not be a big deal, then again it might be nice, especially if a bandsaw is one of the machines. Another advantage of separate VFDs is if one fails only one machine is affected. For me personally I would go with the RPC, but I am a good scrounger and could probably find a 7HP 3 phase motor cheap and I have lots of wire handy and so on. But for the OP I think the cheapest and most simple solution is 6 VFDs.
Eric

 

[dougtrr2]

While you could switch a VFD from motor to motor, keep in mind that you are not supposed to have a switch between the VFD power leads and the motor. The potential exists to "fry" the VFD. Has something to do with feedback to the VFD.

I am currently running a 3hp planer on one VFD and a 1 HP edge sander on a different VFD. I have the edge sander set up with a limited amount of speed control, but I don't like the sound/feeling I get when I approach either limit. You do lose power as you slow the motor down.

Both machines are set up to use the original start/stop switches. Most VFD can be programmed to do so. I didn't want to be struggling to hit a little VFD button if something went south on my machines.

The instruction manuals for VFD's tend to suck. The terminology is confusing, there are a LOT of parameters you don't need to touch, but figuring out which ones are important is tough. Automation Direct has an excellent support staff that walked me through an issue (my fault) without being condescending.

Good Luck,
Doug in SW IA

 

[m1garand762]

Make sure your motors are class f insulation, and I strongly suggest ageis grounding rings on the motors to protect the bearings

 

[5030]

Thanks, I've seen videos of that for years.
But my understanding of electricity includes:
5 volts, like USB, pretty safe
12 volts, like a car battery, be careful
120 volts watch out!
240 volts - mistakes can easily lead to major injuries

Actually, 3 MA across your heart will but you in a pine box... Forever. It's not the voltage that kills you, it's the amperage.

As an aside, I run my all my 220/3 machines on a Gerhardt Werner rotary converter. It's rated at 5 horsepower but if I need more, I'll idle one of the 3 phase machines to increase the amperage output. Of course the motors have to be Wye wound to do that...

My only 220/3 machine that is the exception is my LeBlond Servo Shift toolroom lathe. It has a built in freq drive.

I have 200 amps of 220/1 in the shop.

I ain't no electrician either and I have a healthy respect for juice and I NEVER put both hands in a live panel either.

My 2 cents for what it's worth.

 

[LD1]

It's not the voltage that kills you, it's the amperage.

As someone who has worked on everything from 5v DC control circuits up to 13kv....I HATE that phrase.
2 reasons....
1. It's impossible to measure the potential amperage across the heart when working on live electricity. Too many variables.
2. It actually takes BOTH.

You have to have sufficient voltage to overcome the bodies natural resistance in order to get meaningful amperage to the heart. But again....no good way to measure or predict.

In other words......it takes BOTH.

You could have 100,000 volts but 1/10mA and it won't kill you. (Think taser)

You could also have 1000A but at a very low voltage and it ain't gonna kill you either. And you probably won't even feel it. (Think car battery).

It takes BOTH volts AND amps to kill. Because without sufficient voltage to get the amps to the heart....you live.

It's like the saying that falling doesn't kill you, it's the sudden stop at the bottom. But you ain't ever gonna get that sudden stop unless you fall...lol.

 

[5030]

Whatever.... Don't play with fire, you could get burned too.

 

[CalG]

around 80 or 90 volts things start getting real for electric shock. There are lots of "devices" that stay under that value just for that reason.

E I and R stuff....

 

[CADplans]

A friend had an entire shop of 3 phase machines, and only single phase coming into the house.

He had one motor that was larger than any of the 6 or 8 machines.
That 3 phase motor created the 3 phase that would run any of the machines.

He simply had a switch that could connect the 2 wires of 220 to the extra motor.
He had a pulley on the extra motor, and would wrap a rope around the pulley.

He would give the rope a good pull, like starting a gas engine.
With the motor spinning, the single phase 220 switch was turned on.

The motor would then run.
While the motor was running, it was inducing the needed voltage into the third leg.

Three wires were connected to the same terminals as the incoming 220.
These three wires would have the 3 phase that ran any of his machines.

What I just described is the poor mans rotary phase converter.
It works.

One cool feature,, wrap the rope on the motor pulley in reverse, then pull.
Once started, the 3 phase output would run the wired equipment backward.

Sometimes, reverse is needed,, cheap, too. (actually, free!!)

This is exactly how a rotary phase converter works,,
instead of a rope, it uses the "kick" of some capacitors to get the extra motor spinning.

One other negative,, it uses a little extra electricity,,
Who cares, this is a one man show,, not a production shop.

When you get to the point that the machines are producing a $6.5 million income per year, get the power company to bring you real 3 phase.

Until then, enjoy the 3 phase that will cost as little as $100 to get you up and running.

 

[LD1]

A friend had an entire shop of 3 phase machines, and only single phase coming into the house.

He had one motor that was larger than any of the 6 or 8 machines.
That 3 phase motor created the 3 phase that would run any of the machines.

He simply had a switch that could connect the 2 wires of 220 to the extra motor.
He had a pulley on the extra motor, and would wrap a rope around the pulley.

He would give the rope a good pull, like starting a gas engine.
With the motor spinning, the single phase 220 switch was turned on.

The motor would then run.
While the motor was running, it was inducing the needed voltage into the third leg.

Three wires were connected to the same terminals as the incoming 220.
These three wires would have the 3 phase that ran any of his machines.

What I just described is the poor mans rotary phase converter.
It works.

One cool feature,, wrap the rope on the motor pulley in reverse, then pull.
Once started, the 3 phase output would run the wired equipment backward.

Sometimes, reverse is needed,, cheap, too. (actually, free!!)

This is exactly how a rotary phase converter works,,
instead of a rope, it uses the "kick" of some capacitors to get the extra motor spinning.

One other negative,, it uses a little extra electricity,,
Who cares, this is a one man show,, not a production shop.

When you get to the point that the machines are producing a $6.5 million income per year, get the power company to bring you real 3 phase.

Until then, enjoy the 3 phase that will cost as little as $100 to get you up and running.

Yup. Poor man's rotary. And yes it works.

But a good RPC has a few advantages.

The poor man's converter (or even using some start capacitors and an electric motor) have a pretty bad balance. 240v/240v and like 180-190v on the "induced" leg.

Ind the phases are symmetrical at 120° apart.

It only becomes an issue if you are working at rated motor power alot. Because the unbalanced phases loose a little.....and as volts drop (like the generated leg) amps go up.

So on a 5hp motor you'd be running about 9 amps on the main legs. But the induced leg of 180-190v starts jumping to 11-12a. Which is even more than a 1.15SF motor is made to handle.

In a nutshell....motor life starts to suffer.

But the GOOD RPC's compensate. They have a few more windings on the generated leg to balance voltage better. And use capacitors to better balance the sine wave closer to 120°

 

[dstig1]

Another plug for Automation Direct VFDs. Their phone support will handle even the stupid questions I had without any problems. Very good support, so if you know nothing about these (Like me) then it is a good source to buy from, and they are not expensive either.