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...MAAOSwmRZZ4IIC

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.
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Edit: After 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!

[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 (....blackmagic 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...able-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