VFD question

I would like to speed up my 1940's LeBlonde 13" lathe. Right now it is 500 RPM maximum. I run it on real 3 phase (supplied by my power company) and it is a 1 HP
motor.
Since I am not interested in phase conversion do I buy a special 3ph input VFD or do they all accept 3ph input. Also, do I oversize the VFD for the 1hp motor? I do have a large mill, 2 hp, but see no reason to ever hook it up to a VFD. It already handles 40 to 3500 RPM. Convince me otherwise. I also have an old surface grinder that has a 3hp motor. Will I ever want to change speed on that?
All advice appreciated.
Ivan Vegvary
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All the surplus ones I've seen accept 3 phase input. You probably don't have to oversize the VFD for normal operation, but it would give you a safety margin, with more ability to dissipate heat, etc., and I imagine more ability to withstand sudden load changes. The Allen Bradley 1305 series have good documentation and are available used on ebay at pretty decent prices.
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On Mon, 16 Apr 2007 22:52:48 -0400, "ATP*"

Be aware that the older A-B drives are unfiltered and electronically noisy. If you have a lot of electronics, thermocouples around, chokes are available which help. I had to install a bunch on some older drives to stop my ContolNet network from glitching intermittently. The Powerflex family are well filtered, except maybe for some of the 120 V. input Model 4's.
Pete Keillor
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There's no electronic stuff in my garage yet, but I'll keep that in mind. I do have a speed control for my Bridgeport feed that I plan on wiring in at some point.
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I just bought two VFDs from Dealer Electric ( they have a new name now, can't think of it), also patronized by people in this ng.
They told me (I think) that most--or at least the ones I got-- VFDs will take either single phase or 3 phase input. The difference is, with 3 ph input, you no longer have to de-rate the VFD by 1/3. But sometimes, the rating of the VFD, anticipating single phase hookup, is * already* derated for you.
A 2 hp VFD is not that much more expensive than a 1. My 2hp was about $250. I would go 2 just for the margin, and for the unforeseen, like using the VFD elsewhere, or changing the lathe motor, etc.
If the VFD doubles the speed of your motor (I'm not sure it can, haven't really done much with mine), you'll still have only 1,000 rpm on your lathe, not very fast for a 13", imo. You can also have your motor rewound, for two-speed operation as well, for more speed latitutde. Or put in a higher rpm motor, which would raise your lower range as well. Some re-winding houses charge very reasonable rates, while others ask for the deed to your house.
Mebbe you should put your SG motor on yer lathe!
I've been curious about the pros/cons of varying grinder speed myself. Less of an issue than say a lathe, but still might be useful for differing materials.
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wrote:

It's your call, you can certainly do it. If it were me, I guess I'd think about the 1940's spindle bearing design and what speed it could handle when deciding how much to speed it up.
Also, electric motors have a max speed. Modern motors (especially inverter duty) usually have it on the nameplate. At some speed above max, the rotor will come unstuck due to centrifugal force, or whatever you want to call it, and expand, wrecking the motor.
If you have an old motor, I'd at least try to find some max speed data. If none can be found, I'd be conservative. Hearsay on this group suggests older motors may generate more torque. They are usually a larger frame size for the same power. A larger diameter rotor might have a lower max speed.
Good luck.
Pete Keillor
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Ivan Vegvary wrote:

Generally one VFD per machine, so mill & grinder are irrelevant. Generally VFDs take single phase input, but many take 3 phase. It's a good idea to somewhat oversize VFDs if you can afford it.
You may have some issues ($$$) if you go more than 20% faster than the motor was designed for. Not necessarily in the motor, but maybe in the lathe.
GWE
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Grant Erwin wrote:

Yes.
No, not sure where you got that idea. Nearly all VFDs take three phase input, many will also accept single phase input, some will not. Remember that VFDs were developed as motor speed controls for industrial applications, not as substitute phase converters for home use.

It's a bad idea trying to over speed a non inverter duty rated motor by more than a few percent, particularly if it's a fairly old motor.
On VFD ratings and derating, you *never* have to derate a VFD when operated with a three phase input unless there is a separate derating factor such as a high temperature environment. When operating a VFD on a single phase input you *may* have to derate the VFD, but you need to read the manual for it to find out for sure as some VFD ratings already take single phase input into account.
As for overrating the VFD for the heck of it, if there is a reasonable probability you might eventually want to use the VFD on a different machine and the cost difference is not more than 25% higher, purchasing the next size up is reasonable.
Pete C.
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Ivan Vegvary wrote:

Wouldn't it be cheaper to upsize the motor to perhaps 2hp and change the pulley setup to speed up? Your model was supplied in a 750 rpm version as well as 500 rpm.
Tom
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check out automationdirect.com you can download the manuals for the units they sell
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Gunner Asch wrote:

How much current do you need? A simple buck transformer will do the job, as long as it's secondary can handle the current.
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wrote:

Are the transformers center tapped or do they just have 2 terminals for input and two for output.
If the latter they are simply 10:1 ratio transformers. If you stick 120 in you will get 12 out the secondary. Stick 240 in and you'll get 24 out.
If they are centre tapped, without seeing them I'd guess you put 240 across the full input winding or 120 across half the input winding.
Having said all that, I'd do it myself but I'm not sure I'd advise anyone else to try it.....
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Dennis wrote:

The only stupid question is the one you don't ask. :-)

I've seen transformers with two 120V primaries that you wire in series for 240V input, or parallel for 120V. This one might also have two secondaries, that would be used the same way; I'd have to see the tranny.
(it seems I'm about the third one so far to suggest the buck transformer.)
Cheers! Rich
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Gunner Asch wrote:

If you do a search on "buck boost wiring" you will find references for how to wire one of your transformers to "buck" your 249V down to 225V. Basically, the 24V secondary goes in series with the feed to your RPC, and the primary just connects to the line. The secondary amp rating at 24V has to be enough to handle the load of your RPC/machine.
http://www.jhlarson.com/ind_tables/GET/ge_buckboost01.htm
If your transformers are large enough to handle the single phase load see single phase diagram A and you'll need only one transformer.
http://www.jhlarson.com/ind_tables/GET/ge_buckboost03.htm
If the transformers are only large enough for the three phase load you'll need to use three of them after the RPC. See diagram F, which is really the same as the single phase setup in triplicate.
Do plenty of voltage checks before trying to run anything to ensure you have it wired correctly to "buck" to 225V rather than "boost" to 273V.
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As an example, I run three 450 Watt Metal Halide high-bay lamps in my barn. They were surplus, thus inexpensive, but designed to run from 208V.
I purchased a "0.25KVA" (250-"watt") buck-boost transformer that has a 240V primary, and a 32V secondary. The secondary is rated at just a little under 8 amps at full load.
The three 450 Watt fixtures draw 6.5A total at 208V. So the 250 VA rating of the transformer is sufficient. ('been running them every night for 12 years off that same little grey box)
LLoyd
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NOOOO !!
Never put a transformer in the Output of a VFD! It is variable frequency... Those transformers are NOT going to be amused with 20 HZ !!
Keep the Buck transformers in the Line side, where they get 60 hz. just the way they like it..
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Gunner Asch wrote:

Except we're talking about an RPC, not a VFD.
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Maybe YOU are talking about an RPC, but the subject of the OP is " VFD question "
" Ive got a 5hp PC3 vfd running my Gorton MasterMill. The top end voltage it is supposed to run on..is 230vts + about 5 volts It will run down to 200 volts. Im running it on single phase, been doing it for years. "
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Cross-Slide wrote:

It doesn't matter, since the transformer goes before anything else. It operates at line voltage, and in Gunner's case at a constant 60 Hz.
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"Michael A. Terrell" wrote:

It does matter, a set of transformers can most certainly come after a RPC, if you only have buck transformers large enough to handle the three phase current, not the single phase current.
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