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Using a VFD w/ a Sliding Table Saw That Has Independent Main/Scoring Motors?

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Forum topic by Steinbierz posted 06-07-2019 04:28 AM 1587 views 0 times favorited 19 replies Add to Favorites Watch
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Steinbierz

36 posts in 532 days


06-07-2019 04:28 AM

Hello,

I am looking at purchasing a three-phase table saw for my shop but I only have single-phase power. The saws I am looking at typically have two, three-phase motors (a 7 hp main blade motor and a 1 hp scoring blade motor both with independent switches).

I have been reading a lot about VFDs and want to go this route over a rotary unit but a comment I read on Wolf Automation’s website has me confused. Their comment: “Any and all machine installed switches that are on the equipment will need to be rewired to the terminal boards on the VFD for separate external signal control. They cannot be left on the machine as is and be expected to work.” I don’t understand then how I could use a VFD if I have more than one three-phase motor, both operating independently. My understanding is that if you rewire your equipment switch back to the VFD, you are now using that switch to turn off the VFD. If I only had one motor, I could see wiring the main motor switch to the VFD so that I would have local control of starting and stopping the VFD, hence stopping the saw. How to still have independently operating motor switches though has me thoroughly confused.

Thanks for any help that you all may be able to provide.


19 replies so far

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therealSteveN

2876 posts in 969 days


#1 posted 06-07-2019 08:37 AM

My thought whenever I see talk about using some sort of phase converter isn’t about if it can be done. We all know it is done all over.

My question is in a worst case scenario if everything goes up in flames if you will still be covered by your home owners insurance. I always think why ask here, ask you agent.

I’ve had mostly State Farm, and Allstate home owners insurance policies for homes, with a few Farmers, and one Liberty Mutual. So far I’m 0 for 23 saying NO, and showing me in their books, the citation, or in a few cases citations that clearly said No.

This doesn’t just apply to phase conversion, but to a whole host of by gosh, by golly electrical hook ups.

I know I’m a big wuss for bringing this up, but if just one person is saved from loss of the biggest one investment they have, it’s worth it. So check first with your agent, and get it in writing that it is Ok, then proceed forward.

On the other hand a lot of people will be shocked to know that 3 phase is usually available at the road from your power company. Costs a ton to bring it in, and they do the hook ups usually. That is just so they know it’s correct. Then your home owners is A Ok. Weird world sometimes.

-- Think safe, be safe

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GrantA

1512 posts in 1803 days


#2 posted 06-07-2019 11:22 AM

Steve, what are you worried would start a fire? The drive itself? Use a drive from a reputable company (all mine are ABB ACS150 series (I recommend Wistex for purchasing) with proper wiring. Start with the appropriate breaker (mine are all dedicated circuits so I can kill the drive when finished working), appropriate gauge solid copper on the feed side either in the wall or in conduit, to a junction box with SO/SJO cable (and strain reliefs!) to the drive and from the drive to the motor in the appropriate gauge. Or have a pro do it. You may have to make a few phone calls to find an electrician who is familiar with vfds, they won’t be cheap but if you’re unsure it’s worth the peace of mind!

In response to the original question, you’ll need 2 vfds to run the 2 motors. No way around it, that’s the nature of a VFD. In this situation I might steer you towards a rotary convertor. If you’re looking at a slider you may end up with more 3ph tools too! Trust me ;-)

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Steinbierz

36 posts in 532 days


#3 posted 06-07-2019 12:35 PM



My thought whenever I see talk about using some sort of phase converter isn t about if it can be done. We all know it is done all over.

My question is in a worst case scenario if everything goes up in flames if you will still be covered by your home owners insurance. I always think why ask here, ask you agent.

I ve had mostly State Farm, and Allstate home owners insurance policies for homes, with a few Farmers, and one Liberty Mutual. So far I m 0 for 23 saying NO, and showing me in their books, the citation, or in a few cases citations that clearly said No.

This doesn t just apply to phase conversion, but to a whole host of by gosh, by golly electrical hook ups.

I know I m a big wuss for bringing this up, but if just one person is saved from loss of the biggest one investment they have, it s worth it. So check first with your agent, and get it in writing that it is Ok, then proceed forward.

On the other hand a lot of people will be shocked to know that 3 phase is usually available at the road from your power company. Costs a ton to bring it in, and they do the hook ups usually. That is just so they know it s correct. Then your home owners is A Ok. Weird world sometimes.

- therealSteveN

Not saying a fire couldn’t happen but, in my case, at least my house is safe. My shop is detached and approx. 75’ away in a 1500 sq. ft. steel building.

I realize there is probably a difference (and trust me, I am no VFD expert) but, since I started researching this, I am amazed at the amount of equipment that you can buy brand new (a big Powermatic lathe being one) that is manufactured with 3 phase motors with onboard VFDs to run on 240V single phase.

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RobHannon

265 posts in 926 days


#4 posted 06-07-2019 12:45 PM

I think you would either need a VFD with multiple outputs, never seen one but they may still exist, or 2 VFDs. Depending on the mounting type, it may be easier/cheaper to replace the 3 phase scoring motor with a single phase and put the VFD on the main drive motor. In any case you are looking at a large VFD to power that and a rotary phase converter may be a better investment. Particularly if you may end up with other 3 phase equipment down the road.

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ibewjon

604 posts in 3188 days


#5 posted 06-07-2019 12:59 PM

Even our front load washer that just died was a 3 phase motor and vfd. Mechanical problem killed it, not motor or vfd. I do not like rotary converters because you are running a motor to run a motor. With my power company, 3 ph is not available in most areas, except for open Delta with a high leg. And there are continuing monthly charges for the service. I would be using a vfd or buy new motors. Most people do not know that the electrical and other codes, like gas, have a lot of input from insurance companies, as well as manufacturing and installers.. An experienced electrician is a must for these installations. An insured contractor is the best choice. That should end any insurance problems.

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Steinbierz

36 posts in 532 days


#6 posted 06-07-2019 02:03 PM

I talked to an electrician friend of mine who admittedly does not work with VFDs but he was wondering out loud if starting and stopping a 1 HP scoring motor while the VFD was energized would be as much of an issue as it would be using the table saw switch for the bigger main motor. He was thinking that with the main motor running, turning on-and-off the scoring motor might not slam the VFD…all WAGs at this point.

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ibewjon

604 posts in 3188 days


#7 posted 06-07-2019 03:40 PM

Shutting down a motor while the vfd is running can burn out the vfd. A disconnect for a motor on a vfd has extra contacts that shut down the vfd if the disconnect is opened. That is why the switch on the saw can not be used directly to the motor. The vfd must be shut down.

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AlaskaGuy

5284 posts in 2704 days


#8 posted 06-07-2019 03:48 PM

My slider is 7.5 hp for the main blade, 7.5 for the shaper and a 1hp scoring motor, I when with a rotatory phase converter and couldn’t be more happy. Since I went that route my dust collector, power feeder, band saw and jointer/planer is all ran off the rotatory phase converter. I don’t see a big + to VFD’s other than they may be cheaper. My RPC is over 20 years now, it been never miss a lick. One down side is when it comes time to sell 3 phase equipment it be more difficult.

BTW, I can run a total of 21 hp worth of motors at a time as long as start the motors one at at time.

-- Alaskan's for Global warming!

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Steinbierz

36 posts in 532 days


#9 posted 06-07-2019 08:00 PM

Thanks to all who have given the technical answers I was looking for.

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ibewjon

604 posts in 3188 days


#10 posted 06-07-2019 08:30 PM

If you have the vfd’s, check with manufacturer. I have never seen more than a single motor simultaneously running on a single vfd.

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Steinbierz

36 posts in 532 days


#11 posted 06-12-2019 12:03 PM



If you have the vfd s, check with manufacturer. I have never seen more than a single motor simultaneously running on a single vfd.

- ibewjon

From just about everything I have read i’m certain you are correct. The only exception might be if both motors (and they are not in my case) are the same HP and I only say that based on an answer that I got from Wolf Automation…”The normal method is a 1 VFD to 1 Motor relationship. Two motors can be run off the same VFD so long as the motors are of the same HP and specification because what happens to one motor will happen to the other, a combined load size would be utilized when connecting two motors to one VFD, you also would need separate thermal overloads when running two motors off of one VFD.”

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Steinbierz

36 posts in 532 days


#12 posted 06-12-2019 12:23 PM


My slider is 7.5 hp for the main blade, 7.5 for the shaper and a 1hp scoring motor, I when with a rotatory phase converter and couldn t be more happy. Since I went that route my dust collector, power feeder, band saw and jointer/planer is all ran off the rotatory phase converter. I don t see a big + to VFD s other than they may be cheaper. My RPC is over 20 years now, it been never miss a lick. One down side is when it comes time to sell 3 phase equipment it be more difficult.

BTW, I can run a total of 21 hp worth of motors at a time as long as start the motors one at at time.

- AlaskaGuy

Great info! What size is your RPC?

I contacted American Rotary and gave them a list of my equipment and the motor HPs. I also mentioned that I would almost always have NMT two pieces of equipment running at the same time, one being the dust collector. They took my biggest combination (table saw at combined HP of 8.5 and a 5 HP dust collector). The rep recommended an ADX/AI-40. To be honest, I was floored that they would recommend a 40 HP RPC. Further, the MSRP for that unit was a shocker as well. I found from further research on other websites the frequent recommendation to size your RPC 3 to 4 times your biggest load.

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ibewjon

604 posts in 3188 days


#13 posted 06-12-2019 12:35 PM

Thank you. Glad to help. I am certainly no expert on vfd’s, but I have hooked up a couple hundred designed by engineers. The largest ran 5000 HP motors, on 13,800 volts.

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ibewjon

604 posts in 3188 days


#14 posted 06-12-2019 01:56 PM

I see a price of about $4000 for that machine. VFD might be a money saver, especially if the saw is the only 3 phase you have. And if a vfd fails, it will probably be cheaper to replace than repairs on a rpc. And a power surge or lightning can definitely cause damage to either one. Good surge protection is a must, and not expensive.

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Steinbierz

36 posts in 532 days


#15 posted 06-12-2019 02:08 PM



I see a price of about $4000 for that machine. VFD might be a money saver, especially if the saw is the only 3 phase you have. And if a vfd fails, it will probably be cheaper to replace than repairs on a rpc. And a power surge or lightning can definitely cause damage to either one. Good surge protection is a must, and not expensive.

- ibewjon

The only real reason I am considering a RPC is for possible future purchases of 3 phase equipment so that I can get away from single phase motors as much as possible. However, the cost to do it right (or at least how I would prefer to do it) appears to not be cheap so I may need to reevaluate what I really need for my situation.

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