VFD for 3 phase table saw

[James White]

I have a 6.5 HP table saws with a 3 phase motor. I am considering a rotary phase converter vs the VFD linked below.

Do VFD converters suffer the same power losses as do static phase converters? Below is the one I am considering. Will it have enough power to drive my table saw? What if the motor is delta wound?

https://www.ebay.com/itm/4KW-5HP-VFD-Inverter-Driver-1phase-18A-220V-for-Air-Compressor-Spindle-Motor/112172111234?hash=item1a1dfa9582:g:yeMAAOSwmRZZ4II C

James

[Darcy Warner]

That won't run it.

[Malcolm McLeod]

That won't run it.

In the practical sense, Darcy is correct. However, if the OP wants to do a deep dive into the VFD's parameters, he can run it. But only within the limits of the VFD!

I didn't read the manual for the link, but taking the item's 'title' at face value, it will handle 18A at 220VAC/1ph. This equates to about 3Hp. And power in must equal power out (ignoring efficiency losses for simplicity), so OP can set the max current for the unit to 18A on the input and ~9.6A on the output (~ 3Hp at 230VAC/3ph). You've just become the proud owner of a 3Hp table saw, no matter what the motor says - or asks for when feeding that 4" slab of KD white oak - the VFD limits the amps, and therefore power to 3Hp.

James, I doubt this is what you want, but with the linked VFD, it is what you'll get.
******************************
Edit: :oAfter reviewing the linked VFD further, I need to revise my 'calculations' above: it seems like this VFD will handle 18A on the output (at 220VAC/3ph = 5Hp). And, since it is (apparently) advertised to produce this from a single phase input, I must assume the input section of the VFD is sized to handle 5Hp (at 220VAC/1ph = 28A).

So, parameters would need to be set at 28A max on input and 18A max on output. ....GOOD NEWS James!! You just upgraded to a 5Hp saw!:cool:

[Adam Herman]

http://www.factorymation.com/CV-2005-H3

The teco CV-2005-H3
would work. this may not be an area to cheap out on.

[James White]

Malcolm,

Thank you for the details. The chart at the bottom of the page shows 27amps for the input and 18 amps for the output. Does that change things? I think my question more surrounds the fact that a regular static phase converter gives you only 2/3 the power of the driven motors rating and only half if it is delta wound motor. Do these VFD's and this one linked in particular have this down side?

James

[John Lanciani]

http://www.factorymation.com/CV-2005-H3

The teco CV-2005-H3


would work. this may not be an area to cheap out on.

That's a 3 phase input drive. I suspect that if the OP had three phase available he wouldn't be looking for a VFD for his saw.

[Jeff Heath]

Just a note to add to your considerations. A "static" phase converter can be very dangerous to a motor. 20 plus years ago, before I knew better, I was running a static converter to start my very first 3 phase machine. It cooked the motor, and the magic blue smoke came out. I kept that motor all this time to show woodworkers that come to my shop the perils of static converters.

You should be considering the correct sized, and derated VFD, or a rotary phase converter. American Rotary makes a good one ( I own 2), and they also sell kits if you're able to follow instructions and do a little bit of wiring. Not difficult. My 10 hp converter from them was from a kit. My 20 hp RPC is CNC balanced and was a complete unit. Quiet running, and starts the bigger machines in my shop very nicely.

I have 2 machines running off VFD's ( for speed control), and the machines that don't require speed control, like table saw, jointer, planer, etc.....I run off the RPC's. What I found, for my own personal experiences going back 20 years, is that having an RPC to create 3 phase in the shop paid for itself very quickly. I find that 3 phase machines, even though they are better quality, are often less expensive than single phase identical machines, because most people shy away from 3 phase, not wanting to deal with it. Having an RPC allows you to run many different machines in your shop, which will allow for future upgrades, as you find them. If you go the VFD route, you will be buying a new VFD for each machine, or re-programming the limits of your existing one each time you want to change machines. That gets time consuming in a big hurry. An RPC allows the motor starter, with it's heaters, to provide your overload protection for your motor. With a VFD, you bypass the motor starter, and the VFD essentially is the motor overload protection. IF you set the parameters of a VFD to maximum settings, so you can use it on a bunch of different machines, you lose your overload protection on the smaller motors of the bunch. A risky proposition, especially for direct drive motors that are not easily replaced if you cook one.

Some food for though.

Buying a VFD is an inexpensive way to get started with 3 phase, and performs its job fantastically. If you start to expand your shop, like I have over the years with 27 different machines (woodworking and metalworking), the RPC is a huge savings long term. No better way, though, to control a woodworking lathe than with a VFD. Infinite speed control is nice to have, and once you have it, you won't want to do without it.

[David Kumm]

A vfd provides full power within it's parameters. I would do some homework though as there are cheap vfds out there that are not worth the effort. $300-400 is closer to what a decent quality unit should cost. Dave

[James White]

http://www.factorymation.com/CV-2005-H3

The teco CV-2005-H3


would work. this may not be an area to cheap out on.
Adam,
I just looked at that. It appears to be three phase input and so is the one I linked to. I need single phase to three phase. Any suggestions? If I can do this for $400 I would be happy as the rotary converters are double that.

James

[Dan Friedrichs]

J

You should be considering the correct sized, and derated VFD,

The OP is getting confused about derating, so let's clear this up.

A 1-ph-input, 3-ph-output VFD needs no derating, and will provide the rated power. So the eBay one that James linked to can do 18A output, and will draw 28A from the single-phase input. James, do you have a >30A single-phase circuit to plug this into? (do you really need this much power?)

A 3-ph-input, 3-ph-output VFD (such as the one Adam linked to) can be used on a 1-ph-input, but needs to be derated.


So, in the context of providing 3-phase power, there are only 2 situations where derating needs to be considered:
1. Using a static phase converter
2. Using a 3-ph-input VFD on a single-phase input

You do NOT need to derate if you use an appropriately-sized:
1. 1-phase-input VFD
2. Rotary phase converter

[Jeff Heath]

Thanks, Dan. I was putting that ^^^^ info in a different post (this one), and saw you already wrote it, so I just deleted and replaced with this.

[Adam Herman]

That's a 3 phase input drive. I suspect that if the OP had three phase available he wouldn't be looking for a VFD for his saw.

oh whoops. meant to link to single phase input. anyhow. teco makes a good affordable drive.

[Bill Webster]

I would always go with a rotary phase converter (RPC) over VFD except for 2 cases.

1. You only have one 3 phase motor to run and it is 3 hp or less.
2. You want variable speed and can use a motor at least twice the normal size for the machine.

There are many advantages to a RPC. You can run more than one motor at a time, where VFD's need to be dedicated to a single machine. With a RPC, you can use the machines original switch or motor starter. You can't cut power to a VFD using the original switch or you can damage the VFD. VFD's uses large electrolytic capacitors, which will fail eventually. A VFD for over 3 hp is very expensive too. RPC's are bulletproof, will last a lifetime and only use electrolytic capacitors to start the RPC, not when running. Also, VFD's can be a challenge to program if you have never done it before.

You should get close to full hp with either a RPC or VFD if properly sized. You will probably never need the full 6.5 hp anyway.

[Malcolm McLeod]

Malcolm,

Thank you for the details. The chart at the bottom of the page shows 27amps for the input and 18 amps for the output. Does that change things? I think my question more surrounds the fact that a regular static phase converter gives you only 2/3 the power of the driven motors rating and only half if it is delta wound motor. Do these VFD's and this one linked in particular have this down side?

James

I got my numbers from standard NEMA motor load charts and your VFD's specs generally cite +/- 15%, so in this case, they're fundamentally close enough to rely on. You can only get 5Hp out, so you would need to limit the current to keep the motor from pulling more than that. I have never run across a delta vs wye wiring scheme that significantly changed the power delivery of a motor, so again you get 5Hp.

Is this what you want? What you need? What you can live with? What you can afford? Not that I need answers, but I'd think you do.

And once again, I'll defer comment on Phase Converters (....black:eek:magic to me).

[James White]

Thank you all for your replies! I'm really getting my moneys worth from the $6/year contribution. I always felt I have!

This is the saw in question. I purchased it used for $3500 http://www.grizzly.com/products/12-6-5-HP-3-Phase-Sliding-Table-Saw/G0674

I have never run a saw with a 12" blade and a scoring motor to boot so I do not know what I "need". I do have a 30A breaker dedicated to this location and this is the only 3phase machine to be ran.

I am starting to think that it may be more cost effective to swap out the motor to a 1phase. That being said looking at the photos of the motor on grizzly web page it looks to be long and slim. There may be clearance issues besides the fact that it is face mounted. Finding a 1 phase motor may be tuff. Would a 5hp motor suffice?

I assume the 1 phase scoring motor would need to be rewired if it currently runs off of three phase power.

James

[Darcy Warner]

It will cost more to switch it to single phase.

[Dan Friedrichs]

Odd that they used a 1-ph motor for the scoring motor, and a 3-phase motor for the main motor...

The main motor is 16A, so the ebay VFD you linked would work. For $200, give it a shot.

[Malcolm McLeod]

I would always go with a rotary phase converter (RPC) over VFD except for 2 cases.

1. You only have one 3 phase motor to run and it is 3 hp or less.
2. You want variable speed and can use a motor at least twice the normal size for the machine.

There are many advantages to a RPC. You can run more than one motor at a time, where VFD's need to be dedicated to a single machine. With a RPC, you can use the machines original switch or motor starter. You can't cut power to a VFD using the original switch or you can damage the VFD. VFD's uses large electrolytic capacitors, which will fail eventually. A VFD for over 3 hp is very expensive too. RPC's are bulletproof, will last a lifetime and only use electrolytic capacitors to start the RPC, not when running. Also, VFD's can be a challenge to program if you have never done it before.

You should get close to full hp with either a RPC or VFD if properly sized. You will probably never need the full 6.5 hp anyway.

I have seen VFD's fail for sure, but they are suitable for daily, industrial pounding, for hours on end. I deal mostly with Allen-Bradley, and would bet in a light industrial (10-hr/day) or home shop their VFDs out-live me (maybe 1-2% failure rate in a given year??). Also, you'd typically install the VFD upstream of the existing controls, or better yet re-wire the tool's controls to operate as inputs to the VFD (and use braking), and rarely only cycle VFD power.

The import VFDs have similar function, and industrial user base would abandon them in a heartbeat if they regularly crashed a multi-million dollar process. I see no such angst among this user group...?

As for proper size, you are correct, Bill. For full rated power, you'd have to jump the next size up - - and I don't remember ever seeing a 7.5Hp VFD in stock - - so if you need/want 6.5Hp from motor, you gotta look at 10Hp VFDs. And again, set the 'limit' parameters to match the nameplate FLA of the motor.

[Bill Dufour]

With a VFD do not set too fast a deceleration time for a saw or grinder. If you do the nut can spin off and the let the blade or grinding wheel run off. Use at least 3 seconds or more to stop the motor. I use 3 seconds for both accelerate and decelerate on my drillpress.
Bill D

[David Kumm]

Are you comfortable with wiring, understanding schematics, and programming? Multiple motor machines with multiple stop start and limit switches usually have a bunch of electronics. You will need to bypass the main motor and reroute the switches to the vfd for the main motor. The power will still need to enter the machine to energize the starter for the scoring motor. If the scoring and main motor can be started together, you will need to separate them so the scorer is started on the machine and the main motor from the vfd. If there is a braking module you will need to disconnect it . I'd also want a separate braking resistor added to the vfd so as to not overload the vfd when starting and stopping repeatedly in a given time period. A vfd is great in many applications but the more complicated the machine electronics, the more complicated the conversion to using a vfd. A RPC may be easier to get running if you are new to this stuff. Dave

[Jeff Ramsey]

I'll second what Jeff said.

Jeff, what model AR RFC do you have?

[James White]

David,

The scoring motor only works when the main motor is energized. Would it not continue to work in the same fashion whether powered by a VFD or RPC? Those are the only two controls on the machine. Start and stop for the main motor and same for the scoring motor.

Does anyone have a recommendation for a VFD under $500? Most of the 1 to 3phase seem to stop at 3hp.

James

[CPeter James]

I don't think that running two motors off one VFD at the same time will work. Also, one rule that MUST be followed is NO switching beyond the VFD. The VFD controls starting and stopping. No other switching allowed. As much as I love VFDs (I have 9 installed), this sounds like the case for a high quality RPC. You got the at a good price. Feed it the correct power. Also messing with the controls on this sould like a recipe for disaster.
CPeter

[Dan Friedrichs]

James,

The scoring motor is a single-phase capacitor-start motor. And it looks like it has it's own, independent, on/off button? If so, just plug it (via its switch) into your single-phase circuit.

Then, buy that eBay VFD (it is correctly-sized for your main motor), and use that to control the main motor. Note that you can't use the on/off buttons on the saw, any longer - you must control the main motor using the on/off buttons on the VFD. But, you could re-wire the saw's on/off buttons to act as remote buttons for the VFD on/off buttons.

The only caveat is that there may be some goofy electronics to deal with in the saw (for instance, something that only lets you turn the scoring motor on if the main motor is running). You may have to bypass or otherwise deal with those.

For the cost of that VFD vs a correctly-sized RPC, this is a no-brainer. Get it and try it out.

As David said, you'll need to be comfortable wiring switches, relays, etc - these are industrial electronics, not consumer products - but to an extent, that's true of the RPC, as well.

[Dan Friedrichs]

I don't think that running two motors off one VFD at the same time will work.

For some reason, the scoring motor is 1-phase, so I think he can just "ignore" that part of the problem and wire it directly to his supply.

[David Kumm]

My controls are likely more complex but here is an example of what you are taking on when rerouting wires for a vfd. Not saying it isn't possible, but also not nearly as easy as with an old single starter machine.381352381353 Dave

[Malcolm McLeod]

I don't think that running two motors off one VFD at the same time will work. ...


For some reason, the scoring motor is 1-phase, so I think he can just "ignore" that part of the problem and wire it directly to his supply.

I don't own the saw, never worked on one, and don't have the electrical schematic in-hand, so take this with the ignorance with which it's offered - - common sense is that the OEM intends the scoring motor at 240V/1ph, be powered from 2 of the 3-phase legs...?

Also, Peter with regard to my 'snip' of your statement, a VFD can drive multiple motors (I've seen cases of up to 50-some-odd motors from 1 VFD), but the O/L protection gets increasingly complex to say the least. The total power consumption of the motors just has to stay within the power limits of the drive. Regardless, in the OP's situation, I think Dan's advise is practical and sound. The VFD and re-work of the saw's control wiring seems to be the least expensive option.

The RPC may be more expensive, but require no modification to the saw's wiring...?? Name your poison.

*******
Edit: Reading a couple of the other posts, it occurred to me that the interlock on the scoring motor is fairly easy to duplicate with a VFD: Most, if not all VFDs will have a relay output. You can program the VFD to close this relay when it is 'at speed' (main motor running). Then simply route the scoring motor 'start' signal (wire) thru the 'running' relay. Now you need both the operator start request via pushbutton, as well as the main motor running, in order to start the scoring motor.

[James White]

David,
I usually don't shy away from technical challenges within reason. I bet I could come here for advise if needed.
I did pass on an Altendorf F45 for $1800 where all of the electronics where "bypassed" because of "probably just needs a switch" so that the main power button controlled the main motor only. It also had .030" of sag in the cast iron table!

To say I am on a shoe string budget is an understatement. I had to barrow $1500 from my wife to take advantage of the deal on the saw. I have thought of building an RPC. However I don't like the idea of an extra motor idling all day or having a two step starting process for using the saw. Do the off the shelf RPC's start on demand from the saw?



Also, one rule that MUST be followed is NO switching beyond the VFD.

Thank you for that info! Super important to know going in.

Dan,

I may go with the one from ebay. I also like the idea of going thru Amazon for there guaranties. Here is one being sold by the same manufacturer as the ebay one. Many of the seller reviews say great support, supper responsive to technical questions, return shipping reimbursed etc. However they are three phase input or single. How do you derate them? Is the one below big enough?

https://www.amazon.com/Variable-Frequency-Inverter-Converter-HUANYANG/dp/B077KSN4C5/ref=sr_1_2?ie=UTF8&qid=1521030779&sr=8-2&keywords=Huanyang+Variable+Frequency+drive

James

[Dan Friedrichs]

James, the Amazon one doesn't have current specs, so I don't know.

The formula is that you take the phase current of the 3-phase load (the motor) and multiply by sqrt(3) to get the equivalent single-phase current. If the VFD is rated for at least that much on the input, it would work.

So in your case, the main motor is 16A, multiply by sqrt(3), and you need 27A from the single-phase supply. The eBay one is rated for 27A input, so it would work. If the Amazon one is rated for >27A input, it would also work.

FWIW, I think eBay's protections, etc, are as good as Amazon's, these days. But the Amazon one is actually "rated" much higher HP than the eBay one, so it might be a better deal - might be worth asking the seller for a spec sheet or current ratings.

All that said, the motor will only draw full power if you call for it. Even with a 12" blade, you'd have to be pushing pretty hard to need 6.5HP from that saw. Either of these would work fine, and we're really quibbling over a corner case that you'll probably never see.

[James White]

Dan,

Thank you for being so helpful. I was concerned that the EBAY offering was $60 in shipping so if there where any issues I lose $60 off the bat. Where as the Amazon offering has free shipping.

I put in a question to HuanYang the manufacturer regarding there VFD offerings. Ill see what they say.

Here is a video where they compare there VFD to similar looking clone.
https://www.youtube.com/watch?v=tjhPwYVSSz8&feature=youtu.be

James

[David Kumm]

Just for information, take a look at the electrical section of the practicalmachinist forum. They have some really good electrical guys and refuse to even discuss that brand of VFD. Not saying good or bad, but read about VFD before spending. A mistake is costly. Dave

[Chris Parks]

Just for further information purposes Powtran VFD's have the ability to have different profiles for different machines programmed into them so the same VFD is easily used for multiple machines, I think it can have 10 different profiles put into it from memory.

[Tom Bender]

My table saw has variable speed. It is great, easily worth the extra cost and effort. I normally run it at a tip speed around 2000 fpm.

[James White]

Can anyone tell me what this board is for? It powers the third leg of the main motor. It gets it's power from the third leg off the relay output and is labeled R3 in the photo. However the board also gets feeds from legs two and three up stream of the relay. What is labeled M3 goes to the motor.

My hair brained plan was to take single phase 220 from legs one and two post relay and feed that to the VFD. Then the VFD would be wired direct to the motor. However this board complicates things since it gets power both post and pre relay.

It would have been an ideal solution since it powers the scoring motor with the house fed 220v single phase and also powers the VFD post relay. This would allows use of emergency stop buttons on the saw.

Could I power this board entirely off of the VFD?

Now tell me why I am dreaming and I overlooked....


James

[James White]

The wiring diagram can be seen in the manual on page 59.

http://cdn2.grizzly.com/manuals/g0674_m.pdf

[Rod Sheridan]

It looks to me like a DC braking injection board for the main motor. In the EU, blade braking is required to meet a time parameter to stop the arbour in under a given length of time.

If that's what it is you won't need it with a VFD, you'll program the VFD for the correct braking. In that case the board and main motor contactor can be removed.

You'll have to connect any limit switches on the machine (such as door open) to the VFD as well as the stop and start buttons, including and E-stop buttons in other locations......Rod.

[James White]

Rod,
Thank you very much! I was able to remove the board for the most part. There is a fuse on there that is being used to supply the relay of the scoring motor. I wanted to leave the board in position anyway. Then I will not to loose it.
The saw is working great with the 7.5kw VFD from Amazon. I can slow the blade down to loose the burning I was getting in maple. The saw has a general purpose/sheet goods blade in it and it turns out 8/4" maple burns. Not anymore!
James

[Dan Friedrichs]

Yay! I'm excited you got it running!

If the VFD didn't come with one, you can add a braking resistor so the blade can be brought to a stop very quickly. A nice safety feature (that the saw originally had), but that you can create with the VFD, too.

[James White]

It has a built in braking resistor. What is a good stopping time in second? The saw does not have the two post to prevent the blade from spinning. The washer is keyed to a flat on the shaft. So there is no issue with loosening the nut. But I don't want the blade slipping either. I was unsure what to make the stop time.

James

[Dan Friedrichs]

My SWAG is that my Hammer stops a 12" full-kerf blade in about 2 seconds (it would vary based on the inertia of the blade). That's probably fast enough that even the most impatient person wouldn't be tempted to reach to grab an offcut (or whatever) too quickly. I probably wouldn't set it to stop too fast, though, as you'd be putting some unnecessary torque (and wear) on belts, etc.

[Bill Dufour]

I have seen 3 seconds recommended but with no gears to strip you can safely stop faster. I would not go below 1 second. On some cheap VFDs the acceleration is the same as the deceleration time. I would not accelerate less then 3 seconds.
If the decelerate is set too fast it can overload and switch to coast down mode. But you have a resistor to dump the braking energy into so that should not be a problem.

For a lathe with a heavy log you would have to take more time to change the rpm.
Bill D.

[Bill Dufour]

My SWAG is that my Hammer stops a 12" full-kerf blade in about 2 seconds (it would vary based on the inertia of the blade). That's probably fast enough that even the most impatient person wouldn't be tempted to reach to grab an offcut (or whatever) too quickly. I probably wouldn't set it to stop too fast, though, as you'd be putting some unnecessary torque (and wear) on belts, etc.

Is that coast down time or a controlled braked stop time?
I

[Dan Friedrichs]

Is that coast down time or a controlled braked stop time?

It's braked via DC injection (not a VFD), so it's not coasting down, but it's also not controlled :)