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Wiring a VFD to a receptacle a viable option? (Bridgeport)

What would be considered oversized? I've seen people elsewhere online mention going for something that is 1.5-1.75 x your motors running amperage. I think the one I ordered is just under 2x the rated amperage of my motor.
Starting current is 5 to 8 times the running current, typically.

However, most VFDs have a short term overload rating. If that rating is at 150% for several seconds, then you can use that rating to help.

With 5 to 8 times running current, I'd round it to 9x. Then, using the 150% short term overload, the minimum over-sizing would be to 6x the motor rating for the largest motor.

Mind you, that is NOT just to run the one motor. For that you can do maybe 120% of full load as the VFD current rating and be fine.

The 6 x rating (minimum) is if you want to just use the VFD to make 3 phase, and keep using the on-off switches on the machines. And, it pre-supposes a 150% overload capability for the VFD. Personally, I;d go a bit larger, but that is the minimum to function.

If the overload is different for the particular VFD, then the minimum size would change accordingly.
 
Starting current is 5 to 8 times the running current, typically.

However, most VFDs have a short term overload rating. If that rating is at 150% for several seconds, then you can use that rating to help.

With 5 to 8 times running current, I'd round it to 9x. Then, using the 150% short term overload, the minimum over-sizing would be to 6x the motor rating for the largest motor.

Mind you, that is NOT just to run the one motor. For that you can do maybe 120% of full load as the VFD current rating and be fine.

The 6 x rating (minimum) is if you want to just use the VFD to make 3 phase, and keep using the on-off switches on the machines. And, it pre-supposes a 150% overload capability for the VFD. Personally, I;d go a bit larger, but that is the minimum to function.

If the overload is different for the particular VFD, then the minimum size would change accordingly.
This is excellent information, thanks JST !!
So, if a shop had a 10 hp lathe, a 5 hp compressor and a 3 hp Bridgeport clone, all 3-phase, what would the necessary rating for the VFD to run the whole shop, with switches between the VFD and motors ?
If I understand correctly, 6x 10 hp, 60 hp rating, assuming 150% short term overload rating.
Does this take into account the de-rating for single phase supply ?

I have used several Fuji VFD'd with great success. They have a 60 hp 230 volt 3-phase input one for $4,284, see attached link.
This shows an input power rating of 58 kVA, or 160 amps with DCR. That's enormous !
So I guess it would be drawing this sort of power during a motor start up - which is the point I guess. Using a VFD like this doesn't allow use of the motor slow ramp up feature to minimize starting current.
Bob
 
A few suggestions to make everything simple. Hardwire the motor directly to the VFD outputs, put a plug on the VFD so you can move it if needed. Use a power disconnect switch on the VFD input power to turn it on/off. Use a 3 way switch with 2 wire control, basically Forward - Stop - Reverse, you can add an E-Stop to disconnect a run command, but you would not want the VFD to restart if the E-Stop is released (alternative would be 3 wire control or a latching relay or power contactor), this depends on the VFD. You most likely do not need a speed pot with a Reeves drive, best to use the mechanical speed adjust as you well get better power delivery below 60Hz, and not wear the Reeves drive at one speed if it was used at a fixed speed. You do not need to oversize the VFD, you are not starting the motor across the line. The VFD inputs are low voltage and VFD controls the motor current/volts. If you tune the VFD to the motor you would need to do it statically unless you can remove the drive belt which is unlikely. Autotune would be more significant if you were using the motor over a wide speed range.

Using a VFD as a shop power source, there can be issues with electronic circruitry not being happy being fed a VFD output which is PWM as opposed to sinsodial output. The phase Perfect simple is not a bad option either, and you could use a plug and socket on the mill with no modifications. At the cost of the FRN060F1S-2U, you are in the same price range of the 15Hp Phase Perfect which will provide a cleaner output.
 
That does NOT take single phase into account. If it needs derating, that has to be handled separately.

To make things really simple, do not use a VFD for "shop power".

Get a "Phase Perfect". They are made for the purpose, and are very easy to size, since most of them will start a motor of the same rating as the "PP". No programming to mess with, they pretty much just work.

They have a simple version available up to a 7.5 HP, for $1400 as a basic model. That's not bad for a 3 phase converter off-the-shelf. It's not the max duty industrial version.

Far cheaper than most large power VFDs unless you get the VFD surplus.

There is a member here who goes by "thesjg" or something similar, who works for Phase Perfect, and can give better info. Or just go to https://www.phasetechnologies.com/products/phase-converters/phase-perfect
 
I have a static phase converter (linky). Works fine. Spindle starts and reverses normally (rigid tapping).
Please forgive the hijack.
I am running an (admittedly much cheaper) static phase converter for almost 6 years.
It has been just fine. The thing I notice is that, when tapping, the spindle will not reverse until it has stopped. If I throw it into reverse before it stops, it continues to rotate in the same direction. Are you able to reverse before the spindle has stopped?
 
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If you have a way oversized VFD, you can switch the motor in and out while the VFD is running. You can't do that with a VFD that is rated only for your motor's horsepower. As I understand it, they won't take that kind of abuse.
A VFD with output reactor would handle some of that abuse.
 
Please forgive the hijack.
I am running an (admittedly much cheaper) static phase converter for almost 6 years.
It has been just fine. The thing I notice is that, when tapping, the spindle will not reverse until it has stopped. If I throw it into reverse before it stops, it continues to rotate in the same direction. Are you able to reverse before the spindle has stopped?
Mine does but I'm also bumping it, letting it coast down and then reversing. It's still rotating when I hit it but, not full speed. I never thought to try it from full RPM. I try to not do it much because I know it's hard on the capacitors and the contactor. The machine has a variable speed head so even if someone gave me a VFD, it probably wouldn't be worth the trouble to set it up.

The only thing I had that was a little flaky was my 1640 lathe. The phase converter had to be sized for either the spindle or the coolant pump. Obviously not possible so I had to always start the spindle first.
 
A VFD with output reactor would handle some of that abuse.
Nope.....

Problem with a matched rating of motor and VFD is current limit. The VFD probably will not start the machine, because it is current limited, and just cannot supply the full start current. It will likely just trip off and sit there.

The motor wants maybe 6x the full load current, the VFD can only put out 1.5x full load current, and even that is only for a short time. Torque in an electric motor is directly related to current. So the available torque is very low compared to what is wanted.

Some VFDs will continue to put out current at the limit value for some amount of time. It's hard on them, and may run into a temperature limit. It also may not start the motor, because the low, limited, torque is not enough to move the motor plus those parts of the drive train that are always connected to the motor.

if it actually can move the motor, it will accelerate only slowly, and may time out, or trip on overheating before reaching full speed.

That is why serious converters, like the Phase Perfect, are rated for full start current and can produce that long enough to start dessentially any motor of the same rating as the PP nominal rating. I am not sure that the economy home shop type, or even the "enterprise" versions of Phase Perfect are as robust in that way as the industrial versions
 
if it actually can move the motor, it will accelerate only slowly, and may time out, or trip on overheating before reaching full speed.
That is the symptom of weak storage capacitors.
That is why serious converters, like the Phase Perfect, are rated for full start current and can produce that long enough to start dessentially any motor of the same rating as the PP nominal rating. I am not sure that the economy home shop type, or even the "enterprise" versions of Phase Perfect are as robust in that way as the industrial versions
My reactor comment was made in light of protecting the VFD from spikes on output disconnects.
 
That is the symptom of weak storage capacitors.

My reactor comment was made in light of protecting the VFD from spikes on output disconnects.

Uhh, not really. It's a symptom of not enough current capability and sagging voltage on startup. Capacitors discharge pretty quickly. You'd need an awful lot of capacitance to make it through instant motor startup with a VFD that's rated for the motor capacity if it was switched on mechanically at the VFD output while the VFD was running. JST has quite a lot of expertise in this subject.
 
And, it doesn't matter much anyway, since the issue is really the start current available, vs what is needed. You are putting a heavy load on the VFD, a load maybe 4 or 5 times even the short term overload capacity of the VFD.

The VFD is probably adequately protected against that, but it is protected against it by a current limit. The VFD may just shut down and give an overcurrent error message.

Some VFDs have a mode where they will put put their max current instead of shutting down. Those likely just will not start the motor if there is any significant load, maybe even just some belts and a shaft or two. Even if the motor will start, it is likely to be a very slow start.

So the main reason for not trying to start a motor like that with a matched VFD is that it just does not work.

The other reason is that depending routinely on an "emergency" overload protection circuit is bad practice. Kind of like the airline not making a stop at your airport, but handing you a parachute instead.
 
The only thing I had that was a little flaky was my 1640 lathe. The phase converter had to be sized for either the spindle or the coolant pump. Obviously not possible so I had to always start the spindle first.
Similarly, my SB Heavy 10 has a 1 hp motor which doesn't want to play well with the SPC, even when the SPC is configured for 1 hp instead of the 2 hp for the mill. Instead of digging into it, I just start the mill with the spindle disengaged and let it run as an RPC when using the lathe.
 
A few suggestions to make everything simple. Hardwire the motor directly to the VFD outputs, put a plug on the VFD so you can move it if needed. Use a power disconnect switch on the VFD input power to turn it on/off. Use a 3 way switch with 2 wire control, basically Forward - Stop - Reverse, you can add an E-Stop to disconnect a run command, but you would not want the VFD to restart if the E-Stop is released (alternative would be 3 wire control or a latching relay or power contactor), this depends on the VFD. You most likely do not need a speed pot with a Reeves drive, best to use the mechanical speed adjust as you well get better power delivery below 60Hz, and not wear the Reeves drive at one speed if it was used at a fixed speed. You do not need to oversize the VFD, you are not starting the motor across the line. The VFD inputs are low voltage and VFD controls the motor current/volts. If you tune the VFD to the motor you would need to do it statically unless you can remove the drive belt which is unlikely. Autotune would be more significant if you were using the motor over a wide speed range.

Using a VFD as a shop power source, there can be issues with electronic circruitry not being happy being fed a VFD output which is PWM as opposed to sinsodial output. The phase Perfect simple is not a bad option either, and you could use a plug and socket on the mill with no modifications. At the cost of the FRN060F1S-2U, you are in the same price range of the 15Hp Phase Perfect which will provide a cleaner output.

For the power disconnect on the input side are you referring to something like this? https://www.homedepot.com/p/Siemens...-Indoor-Safety-Switch-RBPU-GF221NAU/309777794 .... And then during operation I would cut the power to motor via the VFD controls, and then once that is off cut power to the VFD via the switch if im understanding correctly.

Where exactly are you suggesting I put the plug on VFD in this scenario since you suggested I hardwire the motor to the VFD output
 
A power disconnect can be as you have shown or a rotary style power disconnect. The latter you can get one that mounts to an enclosure/machine or comes with an electrical box. Convention is to have the VFD output directly wired to the the motor, in some industrial settings they may have a disconnect for motor replacement purposes. There also can be issues with plug and socket rating should it be used as a disconnect or become disconnected. When the VFD is powered on, you then use the VFD low voltage inputs to turn on/off the motor which is done electronically by the VFD. This can be done with what is called 2 wired control which requires a sustained ON command, or 3 wire which uses momentary switches to turn on/off the run command, reverse is typically a sustained ON switch, but some VFDs a separate momentary button can be used. My mill and lathe use a plug on the power cable that goes to the VFD, you are limited to the rating of the plug and socket ratings vs, hard wiring. That being said it is usually not a big deal to remove the power connections to a switch like you linked to in order to move a machine if it is occasionally done.
 
"In theory could I just wire the 3 phase output leg of the VFD to a receptacle and plug my machine into that? "

Short answer: yes.

Long answer: be aware of the risks of doing this, and avoid them.
 
Short time overload for a VFD is typically about 1.5-2x rated continuous output.

Starting current on an induction motor is typically 6-8x rated continuous input.

You end up needing a VFD rated at least 4x the largest motor, and it goes into overload and delivers twice that - 6-8x the motor rating.

Note the requirement for 'largest motor'. If you're using a VFD to run a bunch of small motors started in sequence, you may barely need to oversize the drive at all. That works great for e.g. 8x condenser fan motors on a big chiller, but not so great for running a couple of machines in a machine shop.
 
If you have controls on the mill now that are just Across-the-Line starters, when you energize those motors, they will want to pull 600% oif their rated current on startup. A VFD, if sized for the motor HP, is only capable of around 200% current for a few seconds. So to allow it to function with the existing downstream controls, the VFD must be AT LEASE 3x larger than the motor. In addition, your VFD, when used as a phase converter, must already be 2x the motor size, so to do what you are wanting, you are looking at 6x. You have a 2HP motor, they don't make a 12HP VFD, so you would have to buy a 15HP VFD to pull this off.
 
If you have controls on the mill now that are just Across-the-Line starters, when you energize those motors, they will want to pull 600% oif their rated current on startup. A VFD, if sized for the motor HP, is only capable of around 200% current for a few seconds. So to allow it to function with the existing downstream controls, the VFD must be AT LEASE 3x larger than the motor. In addition, your VFD, when used as a phase converter, must already be 2x the motor size, so to do what you are wanting, you are looking at 6x. You have a 2HP motor, they don't make a 12HP VFD, so you would have to buy a 15HP VFD to pull this off.
Is the math based on the HP or the current draw of the motor?
 
Is this for heavy use? Like 8 hours a day for a business? Hobby: 3-4 hours a month? Repair shop: 4-5 hours a week? I have a static phase converter (linky). Works fine. Spindle starts and reverses normally (rigid tapping). It's been on that thing since 2000. No issues. You're going to only get about half the power out of the motor. That's still a bunch unless you're doing really heavy work. I've never stalled the spindle.

If you're going to really use the machine hard, or all day, a rotary or a VFD would make life easier on the motor but, you may well not need it.
Certainly seems like the simplest and most straight forward solution without breaking the bank. I see some folks in other forums pounding the table about rotary phase converters being the online viable solution in these kind of situations. Are there some undesireable effects on the motor life with static phase converters? I get the output HP will be reduced which is fine by me, I have no reason for the the full 2 HP anyway
 
Certainly seems like the simplest and most straight forward solution without breaking the bank. ... Are there some undesirable effects on the motor life with static phase converters? ...
Can't answer your motor question directly.

My previous step belt B'port ran on a static for the 18 to 20 yrs that I owned it with no problems other than the Phase-A-Matic failed after about 16 yrs. I have been using a WYN static since (both on the previous mill (till I upgraded) and my current step belt B'port mill. A few yrs ago I added a 3 hp idler to the mill (sits on the floor behind the mill as a poor boy rotary for the mill using the static to start). The 3 hp motor is unfortunately a bit undersized for the 1.5 hp B'port to be able to instantly reverse. I also have a 10hp WYN static on my 7.5 hp Summit 14 lathe (which has a whole bunch of electrical stuff like a transformer, contactors/relays,etc) and it has been working fine for the past few years that I have owned it,
 








 
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