Considering switching to VFD from Rotary

[Investigator]

Im in the planing stages of a new shop building at home, just for home hobby use. I currently have a RFC built around a 5hp 3ph idler, it is not balanced just simple direct wired. I built it because at the time I owned 2 lathes, a 16" Southbend and a 12" Logan. I have since sold the Southbend, so the phase converter only runs the Logan, my mill is single phase. In planning for the new building, I'm playing with layout and am considering going to a VFD for the Logan to save the space now used for the converter.

Right now the only advantage I see of switching to a VFD is the space savings, but that is a really big advantage in my mind. The Logan has the Reeves drive as well as a 2-speed motor, so speed adjustments are not an issue. I have infinite speed adjustment from around 20-2000rpm. If I swap to the VFD I would only program it to run on 60hz and either have it on or off, not using the VFD for speed adjustments.

I'm leaning toward switching and keeping the idler motor 'just in case' I run across any good deals on 3phase equipment I can't pass up. Have I missed anything? Is there any reason to not do this?

 

[MikeInOr]

One of the nice things about a VFD is that you can plug your machine into any 220v outlet.

If you are building a new shop and you are planning on using a RPC I would recommend wiring your shop for 3 phase then run the 3ph from your RPC into the 3ph breaker breaker panel. You will then be able to run your 3ph machines where ever you put a 3ph outlet.

It is awfully nice to bring a new machine home, plug it into a 3ph outlet and go! I have a RPC with a 10hp idler... eventually ALL of my machines will be converted to run of VFD's.

 

[cathead]

Yes, a VFD is nice and I own one of them myself. FAST FORWARD 20 YEARS: The RPC will still likely be in running shape but
the VFD will likely be in scrap electronics pile probably in Agbogbloshie. I would hang on to the RPC.

 

[Crank]

I'll put in my 2 cents worth for arguing both ways.

I have three pieces currently set up with VFD's, a 5hp motor in my Takisawa TSL-800D, a 2hp motor for my Schaublin 102 and a 1hp on my Bridgeport. I used to have a 5hp Graziano SAG14 that I ran off of an RPC. When I went to the Takisawa, I found that VFD's were finally available that could produce a full 5hp and by going that route, I was able to strip out all of the contactors and electrical controls from the lathe and consolidate all functions to the VFD panel. I also have been able to program the VFD to ramp the motor to speed and ramp to a stop. I still need to add a braking resistor to have an emergency instant stop, but with the ramp down I programmed, it will bring the spindle to a complete stop in well under 2 seconds. I have absolute control over spindle speed and the ramp up doesn't slam the gear train. The 3ph output is smooth and shows in the surface finish of the parts, with no loss of power. I recently wanted to see how it would respond to a heavy cut and on a 2.5" round of stainless, I wound up taking .100" DOC with a moderately heavy feed and the lathe never slowed at all. The VFD is about the size of an old time lunch box and weighs about 6lbs. Which is much better than an RPC that was over 100lbs and ate up a sizable footprint in my crowded garage/shop.

The Schaublin was a case where I had to replace the motor since the options to run a 380V motor were limited and bulky.

The Bridgeport was my first piece of 3ph equipment and with only a 1hp motor, the VFD's from back then were adequate to do the job.

Pros: Compact, programmable, cost is constantly dropping and versatile.
Cons: Does not play well with switches (if downstream from VFD) control switches must be connected to VFD to prevent confusing VFD (oversimplification but you get the idea). Cathead has a reasonable point, longevity is debateable. You get what you pay for, my 5hp VFD was around $700, but it was designed to do what I bought it for, it wasn't a repurposed industial unit.

As for an RPC, I just sold off mine last weekend, it did a stellar job powering the Graziano and never had any issue other than popping one fuse in my master switch panel on a single leg of the phases. It was not terribly loud and only a minor task to turn it on before powering up the lathe. My Graziano had a raft of contactors, switches and other electrical wizardry stuffed into it and as I tend to harbor ill will towards electrons, the RPC was the simple way to avoid grief. If I had a large shop area that I could leave an RPC stashed out of the way and had multiple machines of various complexity in regards to electrics, the RPC is simplicity and durability epitomized. It just wasn't my ideal option. Personally, I always felt the power didn't allow an ideal surface finish.

Pros: Simple, durable and reasonably understandable for most people to wire up.
Cons: Weight, noise, no adjustability and less than ideal wave form that may or, may not impact final finish. I will admit that the last comment is just a personal observation YMMV.

Each option has it's benefits and if your budget allows you flexibility, you won't be forced to go only one route based on what your stuck with. if you have the opportunity to play with a quality VFD, it might help swing your decision.
BTW, my RPC was a Cedarberg 5hp.
Good luck!

Mark

 

[Investigator]

One of the nice things about a VFD is that you can plug your machine into any 220v outlet.

Yes, a VFD is nice and I own one of them myself. FAST FORWARD 20 YEARS: The RPC will still likely be in running shape but
the VFD will likely be in scrap electronics pile probably in Agbogbloshie. I would hang on to the RPC.

I'll put in my 2 cents worth for arguing both ways.
.......
Pros: Compact, programmable, cost is constantly dropping and versatile.
Cons: Does not play well with switches (if downstream from VFD) control switches must be connected to VFD to prevent confusing VFD (oversimplification but you get the idea). Cathead has a reasonable point, longevity is debateable. You get what you pay for, my 5hp VFD was around $700, but it was designed to do what I bought it for, it wasn't a repurposed industial unit.

Mark

Let me ask a question to clarify.....

Can I run 220 1ph to the VFD, then wire the Logan to the output of the VFD, and still use the mechanical "on/off" switch on the Logan? Could I go to the VFD, turn it on to be just standard 60hz, then go and use the Logan with the manual switches like I do now while the RPC is running?

It sounds like folks are saying that with the VFD the machine is left on and the VFD controls the on and off. Is that correct?

 

[Crank]

Investigator,
In a nutshell, NO!
That's what I meant in regard to "Does not play well with switches ". The key is that you want to run the output of the VFD staight to the motor, not the cord running into the machine because there tends to be a number of bits that all want a piece of the action electrically. It's not a monstrous task, all you do is run your ON/OFF switch and FWD/REV switch to the bank of connections for that very purpose on the front of the VFD. You will disconnect the contactors (if you have them) so that the switches merely pass a low voltage control signal though and "tell" the VFD what you are wanting to do. The VFD handles the rest. I eliminated the contactors (relays) that switched the 220V 3ph to the motor and directly wired the VFD output to the motor. Otherwise, you could bypass the controls entirely on the machine and make them useless and control all functions directly from the VFD panel.

It really is that simple to take 220V 1ph and what comes out of the VFD is 220V 3ph. In their purest form, a VFD works perfect for a driven motor with no form of control (fan motors, pumps, etc,,,), but they have advanced and now work with ouside control signals to start, stop, control speed, E-stop, FWD/REV, etc...

I'm no videographer, but here is what I did. All of the guts you see for wiring in the lathe are now gone and this is before I programmed it.

Here are the runs with the motor for the Schaublin and it running on the lathe.

Hope this helps!

Mark

 

[MikeInOr]

Let me ask a question to clarify.....

Can I run 220 1ph to the VFD, then wire the Logan to the output of the VFD, and still use the mechanical "on/off" switch on the Logan? Could I go to the VFD, turn it on to be just standard 60hz, then go and use the Logan with the manual switches like I do now while the RPC is running?

NO - Definitely not! Rule #1 is there should be no switches or other controls between the VFD and the motor! The VFD IS the controls for the motor. Sorry if I made that confusing previously.

Once you have converted (rewired) your machine for it to be controlled by the VFD it is ready to be plugged into a single phase outlet... any 240v single phase outlet that is handy. You no longer have to have a 3 phase outlet near by or a long 3 phase extension cord to plug the machine into your RPC. For me this makes moving my machines around easier as I wired plenty of 1 phase 240v outlets in my shop... but I did not wire a separate 3 phase infrastructure in my shop.

In contrast one of the pluses for using a rotary phase converter and wiring your shop for 3 phase with multiple 3 phase outlets is you can bring your new acquisition home, plug it into one of your 3 phase outlets, turn your RPC on then you are good to use your new machine with its existing controls, no rewiring required. You don't have to wait until you have purchased the VFD, enclosure, misc switches and wiring items and rewire the machine to use it. The 3 phase shop wiring and RPC give you the instant gratification of using your new machine we all crave! LOL!

I recently bought a used 3 phase mill. I brought it home, unloaded it, positioned it where I want it... then used a 3 phase extension cord to plug it into my 10 hp RPC in the other room. I got to play with my new toy as soon as I got it unloaded. I will rewire the mill to use a VFD eventually so I don't have to have that heavy 4-10g extension cord running through the middle of my shop... I will be able to use a 240v single phase outlet that is right next to the mill.

Does this make more sense?

 

[Investigator]

Ah, I understand now. I'm not liking the idea of motor control via the VFD. I think my best plan will be move RPC to a quieter space and leave things as they are.

Just for giggles, tell me what happens if I try to use the switches on my machine downstream from the VFD

 

[Crank]

You could curve your spine, develop an allergy to whales and your babies will be born naked.

Other than that, it may not work, or you might release the "majic smoke". Never tried and don't want to find out. I think the sudden load change can wreak havoc with the light electronics in the VFD. However, my Bridgeport has a separate factory motor for the table feed and I have used it without incident. I keep waiting for it to cause problems, but so far the little$100 Teco is still holding up.

Mark

Sent from my ONEPLUS A6013 using Tapatalk

 

[mksj]

VFD's in certain modes need feedback from the motor (sensorless vector) to determine the rotational speed of the motor as well as tuning the VFD to the specific motor parameters. When you interrupt this function it can have unpredictable effects (VFD will go into a fault mode and shut down) and can result in failure of the output section of the VFD. The VFD expects and is designed around driving only a motor, and the VFD does not output smooth sign wave 3 phase, so it is not designed to be used with any other load other than a motor. There are phase inverters (Phase Perfect) that basically generate a fixed 3rd wave at 60Hz and can be used with machinery needing 3 phase input from single phase. They are expensive, but work well with shops that have multiple machines/CNC machines.

A properly designed RPC can be very quiet and represent a small space. I recently saw a portable RPC "AMP" from American Rotary Phase Converters, when on you had to be close to the unit to tell if it was even running. Nice that it is portable on rollers, just plug the single phase on one side and your machines in the other side. Not inexpensive, but an alternative for those individuals that do not want to deal with building an RPC/electrical wiring.

AMP - Mobile Phase Converter - American Rotary

AMP Mobile - The AMP Mobile rotary phase converter is plug-and-play ready for a quick and cost-effective installation. Equipped to run 208-250V equipment in three tiers: Tier 1: 1 Breaker and 1 Receptacle Tier 2: 2 Breakers and 2 Receptacles Tier 3: 3 Breakers and 3 Receptacles These...

www.americanrotary.com

My recommendation, as others have also indicated, is stick with an RPC in this setting.