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

Brooklyyyn

Plastic
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Mar 31, 2024
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Tristsate Area
In the process of working out the logistics of wiring my newly acquired 2 hp Bridgeport Series 1 Mill.

In theory could I just wire the 3 phase output leg of the VFD to a receptacle and plug my machine into that? Thereby retaining use of the manual switch on the machine and not needing any of the variable speed capability of the VFD since I would prefer to do so manually anyway. If such a setup wouldn't work I would love to understand why.

I get that not wiring it directly to the motor could create an additional potential failure point in the wiring/connections along the way. But if the connections are rock solid this setup would work right?
 
most vfd's use a delta connection. If your mill is wired like that it would work. Second point is that the vfd needs to be tuned to the motor. Having it wired to a receptacle is bad practice as someone might plug in a different motor. If you are moving to a lower voltage, the vfd will need to provide more current to make the same horsepower and your machine wiring might not be up to it.
 
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.
 
That will work fine as long as you do not use the existing switches while the vfd is on. Turn off vfd, wait for motor to coast to a stop, throw reverse lever, turn on vfd. Or just use the reverse switch on the vfd while the motor is running.
I wire mine so the VFD has a short cord with a female receptacle on it. Then a short cord on the motor with a matching male twist lock. Makes it easy to do the wiring on the bench.
You can rewire the old switches to control logic to the vfd. Accidentally flipping the old power switches under load may backfeed EMF to the vfd and fry it.
Bill D
 
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.
 
There is a reason why every vfd manual has no switches between motor and drive in large letters more times than there are pages. The do not say do not lick wires even!
 
That will work fine as long as you do not use the existing switches while the vfd is on. Turn off vfd, wait for motor to coast to a stop, throw reverse lever, turn on vfd. Or just use the reverse switch on the vfd while the motor is running.
I wire mine so the VFD has a short cord with a female receptacle on it. Then a short cord on the motor with a matching male twist lock. Makes it easy to do the wiring on the bench.
You can rewire the old switches to control logic to the vfd. Accidentally flipping the old power switches under load may backfeed EMF to the vfd and fry it.
Bill D
Yea something like this is what i had in mind as well. Would this risk of back feeding to the vfd still apply if im only switching the manual switch on the mill from forward ~> off?
 
most vfd's use a delta connection. If your mill is wired like that it would work. Second point is that the vfd needs to be tuned to the motor. Having it wired to a receptacle is bad practice as someone might plug in a different motor. If you are moving to a lower voltage, the vfd will need to provide more current to make the same horsepower and your machine wiring might not be up to it.
Totally get that, but this is a home shop that i will be the only person using the equipment. I plan on doing a multi phase restore on the mill so would need to occasionally move it around the shop. Would be way easier to do if i can just unplug it rather than have to disconnect wiring in the motor housing.
 
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.
Im a hobbyist and would be using it for some damascus steel making applications as well. Likely looking at 1-5 hours a week generally
 
Why not have an auxiliary switch panel to control things remotely? VFD's contain provisions for this. It allows you to continue to use the varidrive for speed control if you want to. Why do that? Some motors aren't fond of frequency changes that go too far outside the normal 60Hz.
 
It's your mill, but why would you not want to use the variable speed capability that the VFD gives you?
The mill already has variable speed capability, so not seeing the benefit of blindly tweaking the vfd speed electronically to unknown spindle speeds when I can have much better accuracy using bridgeports built in system once i tune the vfd settings to match whats listed on the bridgeport controls. Seems like that would be great feature for the step pulley BP mills, but for the ones that are already variable speed im not seeing the upside unless theres some finer details im missing.
 
Why not have an auxiliary switch panel to control things remotely? VFD's contain provisions for this. It allows you to continue to use the varidrive for speed control if you want to. Why do that? Some motors aren't fond of frequency changes that go too far outside the normal 60Hz.
Seems like extra steps just to have an off switch at the mill which is already there, no?

Why would the frequency be changing to begin with? My intention is to tune the vfd to the settings of the motor on this machine, and then just use the machines built in belt drive system for speed adjustment. Wouldnt the motor demands and vfd output remain consistant throughout?
 
Seems like extra steps just to have an off switch at the mill which is already there, no?

Why would the frequency be changing to begin with? My intention is to tune the vfd to the settings of the motor on this machine, and then just use the machines built in belt drive system for speed adjustment. Wouldnt the motor demands and vfd output remain consistant throughout?
If your VFD is remotely mounted, you'll need to go to its panel to tell it to start, you can't just turn power to it *on*, you have to tell it to start, and which direction. In addition, you'll need a means of shutting off power to the VFD. Someone suggested using the variable frequency ability to change speed, I use the VFD to create 3ph 60Hz power and set speed via the original varidrive. Keep in mind that using the drum switch to reverse motor rotation won't do good things for the VFD, another reason to use an auxilliary switch panel to use the VFD to change motor direction. If you elect to reverse via drum switch, be sure motor is stops rotation before switching. Don't forget to look if your VFD uses an external braking resistor to handle motor direction reversals if you elect to do reverse with the VFD.

You can't wait for inspiration. You have to go after it with a club.
-Jack London
 
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In the process of working out the logistics of wiring my newly acquired 2 hp Bridgeport Series 1 Mill.

In theory could I just wire the 3 phase output leg of the VFD to a receptacle and plug my machine into that? Thereby retaining use of the manual switch on the machine and not needing any of the variable speed capability of the VFD since I would prefer to do so manually anyway. If such a setup wouldn't work I would love to understand why.

I get that not wiring it directly to the motor could create an additional potential failure point in the wiring/connections along the way. But if the connections are rock solid this setup would work right?
Doing this will switch the output. Not something that is recommended. I would never do that with a manual switch.
I don't see the problem with a receptacle and plug. But you can't turn on the vfd unless the BP motor is plugged in. Etc.
 
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Im a hobbyist and would be using it for some damascus steel making applications as well. Likely looking at 1-5 hours a week generally
Yeah, you don't need anything more than that static phase converter I linked. No messing around with settings or new switches or anything else. The machine is an appliance. Walk out, reach for the switch on the head and turn it on, reverse it, whatever. Nothing else to turn on or off. $277 plus shipping and you're done.
 
Doing this will switch the output. Not something that is recommended. I would never do that with a manual switch.
I don't see the problem with a receptacle and plug. But you can't turn on the vfd unless the BP motor is plugged in. Etc.
Got it, so basically all good on receptacle but ditch that manual switch and have the power cord go straight from motor to the vfd output receptacle right.
 
Got it, so basically all good on receptacle but ditch that manual switch and have the power cord go straight from motor to the vfd output receptacle right.
My experience with three phase plugs are that they are not as reliable as a straight connection.
Sometimes I get a stall and find a loose screw for a wire connection point.
 
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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.
This is correct.

With a VFD that is matched to the motor amperage, there is no reserve to handle an "across the line" start (turning on a power switch). With a larger VFD, which can handle more than the start current of your largest motor, that problem is not an issue.

There are folks on this forum who have powered their shops with a large VFD used simply to make 3 phase power.

And, remember that the "Phase Perfect" devices are essentially exactly an oversized VFD, although most only supply voltage to the third phase wire, not all three as a VFD does. It is all about having enough current capacity to handle the motor start.

There is often discussion of the transients that a switch produces. VFDs produce the same sort of transients at their 8, 16, or 32 kHz carrier frequency. Any reasonably well designed VFD has to handle that.

I've designed VFDs to do across-the-line motor starts, and switch-off operations. It's mostly a matter of being sure to provide the current capability.

A long time ago, before MosFets and IGBTs, early VFDs were pretty fragile, using ordinary old-time power transistors. That was decades ago.
 
This is correct.

With a VFD that is matched to the motor amperage, there is no reserve to handle an "across the line" start (turning on a power switch). With a larger VFD, which can handle more than the start current of your largest motor, that problem is not an issue.

There are folks on this forum who have powered their shops with a large VFD used simply to make 3 phase power.

And, remember that the "Phase Perfect" devices are essentially exactly an oversized VFD, although most only supply voltage to the third phase wire, not all three as a VFD does. It is all about having enough current capacity to handle the motor start.

There is often discussion of the transients that a switch produces. VFDs produce the same sort of transients at their 8, 16, or 32 kHz carrier frequency. Any reasonably well designed VFD has to handle that.

I've designed VFDs to do across-the-line motor starts, and switch-off operations. It's mostly a matter of being sure to provide the current capability.

A long time ago, before MosFets and IGBTs, early VFDs were pretty fragile, using ordinary old-time power transistors. That was decades ago.
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.
 








 
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