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Do VFDs harm non-inverter-duty table saw motors? Powermatic 3-phase 5hp Baldor from 1989.

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Forum topic by Dreban posted 05-17-2018 10:45 AM 7751 views 0 times favorited 34 replies Add to Favorites Watch
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Dreban

41 posts in 212 days


05-17-2018 10:45 AM

Topic tags/keywords: vfd table saw powermatic

Howdy,

I just won at auction a Powermatic 66 from 1989 that has a Baldor 3-phase, 5hp saw duty motor with plans on using it in my home workshop (garage) which is single phase. I just learned what 1 and 3 phase power are, soooooooo I’m having lots of fun trying to figure out an economical way to run it without using a static phase converter. I’d like to keep all 5hp.

I’d like to use a VFD and program it to soft start (although that’s not a necessity).

Money is tight and I see new VFDs on ebay in the area of $130-$230, depending on if they are 4kw or 7.5kw rated.

I can’t afford a new, single phase motor, nor can I afford a 10hp rotary phase converter.

I have a 220 outlet in the garage.

I just read that “An inverter-duty motor is a much newer concept that became necessary as motors began to be driven by VFDs (inverters or AC drives). An inverter duty motor can withstand the higher voltage spikes produced by all VFDs (amplified at longer cable lengths)”

I highly doubt my old Baldor,is an inverter-duty motor.

Any advice is appreciated. Thanks!


34 replies so far

View msinc's profile

msinc

569 posts in 706 days


#1 posted 05-17-2018 11:17 AM

There is no “economical” way to produce 3 phase power if you don’t have it coming into the building. Now that you understand the difference in 1 and 3 phase power the best thing I can tell you is sell the PM66 and buy a saw that is usable in your shop. That is, since you say you don’t want to or cant afford a single phase motor for it. You could always put it on the back burner until you can get the right motor for the power you have.
There are those on this forum that believe and will tell you that phase converters or other devices to change 1 phase into 3 are the “way to go”. There is certainly no harm in a converter and they produce good clean usable power. But the initial cost is not the worst of it. There are no free lunches. There are also those on this forum that believe and will tell you that converted power is cheaper to operate. Make no mistake, it probably is cheaper to run a machine, especially 5 hp, on 3 phase….but throw in the converter and it is very definitely not. You are now powering two machines to run one. Converters are thirsty and will cost you more in the long run that just having 3 phase run to your building. Conversion devices have their place, when you absolutely cannot get 3 phase power to the building….or if the machine you need to operate is not made in any other power configuration, but to just arbitrarily get a 3 phase machine and then go buy a converter because you don’t have 3 phase power? {I understand this was not your intent} Not the worst idea, but not really a great one either.
All that said, I don’t know what you are doing with this table saw either…if I had to cut 2” thick dry hickory or white oak all day long for weeks on end, I might get set up with a 5 hp 3 phase saw. There is no power source nor machine that is out of my reach and I don’t have a 5 hp saw in my shop. 3 phase is one of those things where if you need it there is no substitute. If you don’t then it is really a waste and make no mistake, there is no resale value. When you decide to sell a 3 phase machine you are pretty limited to who can use it. In most cases you will end up just about giving it away.

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bbasiaga

1240 posts in 2197 days


#2 posted 05-17-2018 12:12 PM

Motors are usually self cooled by a fan that is attached to the motor shaft. When the motor runs, the fan runs at the same speed. When you put a motor on a vfd and run it slower (this is a typical method for output control in industrial processes, speed up or slow down the motor to get whatever output from a machine you are after), the fan also slows down. If the motor wiring, insulation and other components are not designed to handle the heat (the fan has also slowed down providing less cooling) then the motor life is reduced.

Since a table saw is single speed and you probably wouldn’t want to slow it down, I suspect the impact of the vfd in your case is less. As long as it provides the right voltage so the amp draw doesn’t increase, I would guess the motor would even know the vfd was there.

Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

View RobHannon's profile

RobHannon

190 posts in 733 days


#3 posted 05-17-2018 12:40 PM

Be careful with the 5hp VFDs. A lot of them are rated for 5hp IF you have 240v 3phase powering the VFD itself. They will still work on single phase 220v, but you have to derate them. As much as %30 from some mfg recommendations. There is not a lot of benefit for a tablesaw running at a slower speed than it was designed for, so putting them on a VFD is not typically seen. The next jump in VFD that will run derated on single phase power is probably going to be a 10 hp and then you are getting into the same price range as a 5hp single phase motor. You may need to do some creative mounting though if you do that.

View Carl10's profile

Carl10

109 posts in 659 days


#4 posted 05-17-2018 12:53 PM

Dreban,

Do a search here on VFDs and you will see plenty of articles talking about using a VFD. As previously stated, not sure why you would ever need 5HP. I too had looked at auctions for a solid cabinet saw and many were 5HP 3PH and much cheaper than the 1PH counterpart. That is when I saw Mr Unix (Brad) talking about using a 3HP VFD on a 5HP motor. It saves you significantly in cost and if you exceed 3HP (which would be odd in normal use) it would act like a breaker and reset. From my understanding, the inverter duty is to handle varying the frequency of the motor with the drive to change speeds (not applicable in your case). Your other concern about noise on longer cable lengths should not be an issue assuming your VFD is attached to the cabinet right next to the motor. You can also buy shielded cables just for that concern.

Hope this helps,

Look for Brad’s comments.

Carl

View TheFridge's profile

TheFridge

10744 posts in 1688 days


#5 posted 05-17-2018 12:56 PM

Unless you want want to buy a rotary phase converter, static phase converter, or new motor, VFD is your only option.

They are used all the time with great results. A motor that is going to run full speed all the time will probably see little to no effect of running off a VFD.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Sludgeguy's profile

Sludgeguy

43 posts in 325 days


#6 posted 05-17-2018 02:10 PM

Our electrical engineer at my place of employment indicates the following.
1. An inverter duty motor has the ability to address higher temperatures and some of the electrical issues associated with VFD.
2. Since you will be operating the motor at full speed and only intermittently there shouldn’t be any problems using a VFD to create 3 phase power.
3. Your amp draw will probably not approach the full draw of a 5 HP motor unless you are cutting very thick and very hard material. This means that excessive heat buildup is highly unlikely.
4. Using a VFD to create 3 phase power from single phase is pretty common especially for small pumping applications.

In summary, he thinks you will be fine and that you should enjoy your saw.

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TheFridge

10744 posts in 1688 days


#7 posted 05-17-2018 02:27 PM

Ditto. This isn’t going to be a continuous duty motor.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Dreban's profile

Dreban

41 posts in 212 days


#8 posted 05-17-2018 03:03 PM

Thanks, all. Truly appreciated. I’m just a casual woodworker at home doing my projects and I currently have a Makita 2705 contractor saw. A fine saw in it’s own right, but I got the 3-phase, 5hp Powermatic 66 for $300 and couldn’t pass it up, as I thought I’d never be able to afford one. I learned quickly why my impulse bid of $300 at the beginning of the auction turned out to have legs and win it. ha.

I looked into getting 3 phase at my house since my electric company said I have it at my transformer. Wow. Spendy. That idea went out the window.

I do want to do my garage cabinets in hickory someday, but I’m not using this saw all day, by any means. I’ll use it a few times a month, depending on the project (why I also don’t care about how much it costs to run it). I think the most work I’ve put my current saw through were beaded faceframe cabinets and shaker doors made of eastern white maple. Someday soon I’d like to begin processing my own rough sawn lumber to S4S for projects, but I’m not doing that for more than my project’s needs.

Grizzly sells a single phase, 5hp motor for $400, however. I need to look into how difficult it would be to mount it, as I’m sure the mounting holes are proprietary.

I know this saw is more than I’ll ever need, which I actually like. No matter what I do in woodworking the rest of my life, this saw will do it. It’s heavy, there’s no vibration, it cuts smooth, it cuts fast, the table is larger so it’s easier to cut sheets, it’s got looooong fence rails I can incorporate a side table into and the fence is rock-solid. And I really look forward to having a weekend to myself down the road where I can completely take it apart, clean it, lube it and put it back together. I’ve seen posts about changing out the bearings before problems begin and I guess I could read up more on that someday, too.

View Sludgeguy's profile

Sludgeguy

43 posts in 325 days


#9 posted 05-17-2018 03:28 PM

For $300 you stole it. Congrats and enjoy it.

View RobHannon's profile

RobHannon

190 posts in 733 days


#10 posted 05-17-2018 03:34 PM

Does the existing motor have a frame type on the tag? Looking at some other threads on PM66s folks have directly bolted a 145tc frame motor, but I have no idea if all years of the PM66 would use the same mounting setup. It is certainly something that has been done before.

Also, don’t completely discount a 3hp motor. That is more than sufficient for most work and you may have an easier time finding a good priced decent motor. Look around for Leeson, Marathon, Baldur motors with whatever frame type is correct for that saw.

View MrUnix's profile (online now)

MrUnix

7050 posts in 2401 days


#11 posted 05-17-2018 03:42 PM

Another ~$200 for a VFD and you are up and running easily without any fuss on your existing single phase 240v household power. Swapping the motor out would be more expensive and more hassle since you would also have to address modifying the starter for the new motor. With the VFD, you can sell the starter (it will not be needed) to recover a bunch or all of the expense. Add another $100 or so for new bearings, belts and blade and you have a lifetime saw.

As for being ‘non-inverter-duty’ – don’t worry about it. People are running motors that pre-date inverters by decades without any trouble, and in a weekend warrior environment, there is no issue you need to be concerned about. “Inverter Duty” motors are geared towards commercial environments where they are running all day long.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View TheFridge's profile

TheFridge

10744 posts in 1688 days


#12 posted 05-17-2018 03:44 PM

Changing bearings in a 3ph motor is easy. A 5+ inch 3 jaw puller will do almost everything you need. The arbor is a little more complicated but not much. Just take a pic of where the spacers and load springs go (wavy washer. Motor will have one or 2 as well) and put it back together in the opposite way you took it apart.

Don’t beat on the outside race when trying to get a shaft to seat in the inner bore. Or the inside race when seating the outer race in a bore. The balls can deform which pretty much kill your bearing. 90% of the time I use a short piece of 3/4 pvc. Just don’t beat up the shields or seals.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Steve Peterson's profile

Steve Peterson

394 posts in 3285 days


#13 posted 05-17-2018 04:31 PM

Great score at $300. The saw might have been used heavily in a production shop, but there isn’t much that wears out in a table saw other than a few bearings. The only other thing is the motor itself. It would be unfortunate if you find out that the motor is fried after spending money on the VFD. Take the belts off and check the motor for smoothness. If it feels rough, have a motor shop check it out before buying a VFD.

I like the idea of adding soft start on a tablesaw. My soft start routers are much nicer to be around at startup than my tablesaw.

-- Steve

View Dreban's profile

Dreban

41 posts in 212 days


#14 posted 05-17-2018 05:53 PM

The Baldor motor is a 184C frame and I have yet to look it up to see what that mounting pattern is in comparison to the new, single phase, Grizzly motor, which says is a NEMA 56 frame. I don’t know if Grainger or someone has a motor mount adapter for that.

Honestly, it’s still on a pallet in the back of my truck. I took the wings and fence rails off but it still weighs a ton. I need to get a neighbor to come help me lower it into the HD Grizzly mobile base I just bought for it so I can roll that baby around.

I read that after I wire a VFD directly into the motor (I have yet to see how labor intensive that is) I can hook up the table saws existing power switch upstream from the VFD in order to act as a kill switch should I need it. The Powermatic 66 power switch from 1989 isn’t exactly a large paddle switch I can hit with my knee if need be, so I might look for some other option down the line for safety purposes. IF what I read is correct and that I can put a power switch between my 220 single phase outlet and the VFD.

And then I’m worried the sawdust will harm the $240 VFD since it has now dust shielding. The NEMA 4x VFDs are $800+ and enclosures for the cheap ones are almost as much as the VFDs. Between my sanders and miter saw putting dust in the air in my garage, I’m afraid I’ll damage the VFD.

I guess that takes me back to, if the new $400 5hp Grizzly motor has a similar/workable mount that might be my best bet.

View MrUnix's profile (online now)

MrUnix

7050 posts in 2401 days


#15 posted 05-17-2018 07:15 PM

Wiring the VFD is trivial and you can use your existing switch to control it. The hardest part is figuring out where to mount it. A switch between your wall power (240v) and the VFD is not going to shut the machine down – you use the VFD for that, and there are lots of options, including wiring an emergency off switch if you want. As for dust protection – it’s pretty simple to build an enclosure to keep it out of direct contact to sawdust (for example, see this recent thread for some ideas). Others have used large junction boxes or even old army ammo cans as well. No need for a NEMA enclosure.

Also – you will get a ton of benefits with the VFD that you can’t get anyway else – soft start, controlled braking, torque control, multiple speed options useful for stuff like cutting plexi or sheet metals where full speed tends to melt rather than cut clean, etc… plus, a three phase motor is more efficient and robust, with bearings being about the only maintenance item needed since there is no start circuit to deal with (centrifugal switch, capacitors, etc..).

Cheers,
Brad

PS: Getting it out of the back of the truck is easy… let gravity assist. Get some 2×10’s or similar to use as a ramp. I’ve move plenty of similar machines single handed in a similar fashion.

PPS: Don’t forget that you can sell the starter on the saw now (it is a NEMA starter, right?) to offset the cost of the VFD, making it basically a wash on cost.

-- Brad in FL - In Dog I trust... everything else is questionable

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