Need help setting up a large lathe (air interlock)

[ignator]

Also, you do have to make sure the drive is for 220VAC input, I see lots of the 440AC input units on eBay, but they will not operate at 220VAC input, and will show an error code of low line input. To bad, they are lower cost as folks like me only want the 220 input models.

 

[Entropy455]

Today I called and spoke with an engineer at Teco - specifically about purchasing a 40 horsepower VFD, and running an external bridge rectifier, with extra capacitor bank - and jumpering it into the VFD. Here's what he said (in no particular order)

Most, if not all, Teco VFDs sill require an AC input to drive the electronics (small stepdown transformer tapping off the AC input). This design is preferred over trying to switch a 330 plus volt DC bus down to TTL voltage. Thus I'd need to electrically lift, or otherwise power this transformer with AC, while also separately feeding the DC bus (an internal modification to lift the input rectifier).

The DC bus terminal connections are taps, and are not intended to carry the full bus current. Thus I need to hard-wire/jumper the external power supply directly into the internal bus bars.

The typical weak link in the design (the reason for derating) is the DC ripple, and not necessarily the diodes. More specifically, the capacitor bank is too small to filter a single-phase ripple. I might be able to simply jumper in extra capacitance, and use the stock rectifying diodes - depending on the VFD unit I select.

He recommended against using a variable-torque drive for a lathe, with the assumption that I'd desire the ability to slow the motor and still make cuts.

A constant-torque VFD is a harsher electrical load on the DC bus, compared to a variable-torque mode - again, with DC ripple being the ultimate performance limiting variable - where the VFD is trying to switch power that simply isn't available.

Needless to say, the context of our discussion was clearly reiterated - in that Teco doesn't advise or condone ANY of the above modifications. This was purely a could it be done hypothetical discussion.

I still haven't made a decision as to what I'm going to do. . . . I suppose the next step is to price out a bank of electrolytic capacitors, and a heavy-duty bridge rectifier.

 

[ignator]

The typical weak link in the design (the reason for derating) is the DC ripple, and not necessarily the diodes. More specifically, the capacitor bank is too small to filter a single-phase ripple. I might be able to simply jumper in extra capacitance, and use the stock rectifying diodes - depending on the VFD unit I select.

As I've indicated before, my large lathe has a 7.5HP motor, with a 10HP VFD. I've never tripped it from DC bus voltage fault cause from excess DC ripple. I've done a turning cut in low carbon steel 0.5 inch depth, with a .004" feed per turn. No problems. The same can't be said with my small lathe with a 1HP motor where I can overload it easy.
I do believe you are overrating your real 40HP needs. With a VFD, if you over do it, it just shuts down, and the worse thing is damaged carbide tooling.
I can only say from my past engineering days, when management would say "better is the enemy of good enough". Your making the full load 40HP capability requirement, beyond any possible use.

So I asked the Aliexpress seller about the manual earlier in the afternoon, and just received 8 PDF files for the drive. You can set the drive up for vector or V/f control. Also the DC bus has terminals for external power, if you still want to go that route.

I'm guessing you want to go with TECO name brand. Curious what their price is for a rated drive.

 

[ignator]

Entropy, if you are still considering the import drive, I would go the eBay route because if there are any issues, you have their and PayPal protection.
A quick look at the manual, I'm impressed by the readable text. Only issue I see is chapter 1 page 4-5 with Chinese page numbers.
I'm confused by chapter 1 page 12 general precautions, about converting to 2 phase input. That can be a real thing with a Scott T connection. So I don't think they implied this to be single phase. But ?.
I don't see anywhere in the manual that this large of a drive is supported by single phase input. Chapter 2 page 15 has a table. Other locations indicate single phase for the 2.2KW and smaller.
Chapter 7, Table 7-1 page 228 does not seem to have model V8-G 2S 30R0G listed. So I assume the single phase models are not in this manual. There may not be a custom manual in English for this model number.

 

[Entropy455]

I'm not stuck on any particular brand. I called Teco simply because their number was easy to find.

The e-bay seller sent me the manual also. The fact that the model number is not contained within is problematic. The capacitor bank required for single-phase 40 HP operation is gigantic (more than double a 3-phae unit). I'm not sure everything required for single-phase would fit inside that box. . . .

And what the heck is 2-phase? There is no such thing - unless they are describing a center-tap transformer - which is technically 180 degrees out. . . I guess. . . . I want to purchase the V8-G 2S 30R0G model, but my gut is telling me this is really a 40 HP 3-phase unit. There is some shade-tree advertising going on. Every performance variable is clearly specified, yet the input power is implied.. . . .

Teco said I could probably get away with running a 75 horsepower VFD on single-phase, without any modifications - pointing out that I will rarely (if ever) push the motor beyond 30 HP - which I agree, is likely a fact. . . .

 

[ignator]

From seeing the quality of the manual, I think this China manufacture probably got its start manufacturing namebrand USA/EU products. And they have the intellectual property transferred to them to make products of their own (copied) design.

I'm curious what the input power is to a 40HP motor with no load. That probably is 70% of the power you will ever supply to the machine, as the cutting power needed will in my mind always be small in comparison. A quick search finds no load current to be 30-40% of max load. It has been a long time since my engr'ing school on AC machines, and from memory the only useful thing I learned was about a RPC, the subject of this thread.

I messaged back the Aliexpress seller to see if they can provide model number specific data to show this model was designed to support single phase input. If I get any useful reply I'll post this here.

From the manual provided, table 7-2 is missing any VFD box size data for models 11Kw and larger. Makes me wonder how much of this manual is plagiarized from namebrand products.
Someone took the time to make the artwork diagram showing this VFD powered from single phase. I can't imagine that is a 'shade-tree' seller, as they typically have no technical knowledge for this. This model does appear to be labeled a phase converter (found at different web sites), that just happens to be a VFD.

 

[ignator]

This was what I got from the Aliexpress seller;
Hi, thank you for your information.

The model V8-G 2S 30R0G.
220VAC, single phase 40HP 30KW is the customized VFD. It's NOT the standard VFD .The manual is just for the standard VFD . But it's the same to set parameters .

please understand.

 

[Entropy455]

Hi, this model is NOT standard VFD, we need customize it . But the manual is only for standard VFD .

Above is what I just got from the e-bay seller.

I understand the language barrier. Nonetheless, they need to be able to answer a simple question, like "will this VFD power a 40 HP motor with 220 volt single phase input power, or must the unit be de-rated operating on single-phase power?" If they are smart enough to modify the unit for 40 HP @ single phase input, then they "should" be smart enough to tell me so - when asked directly. . . .

The cryptic answers are frustrating. The internet is loaded with complaints about other Chinese manufactured VFDs that fail to perform on single-phase, as advertised (requiring derating). I don't want to make that same mistake.. . .

 

[ignator]

Unfortunately, your not talking to the manufacture, but a sales clerk. They have no technical knowledge.
I have one of those Hungwang VFDs I purchased from eBay 5 years ago. They had to replace the first one. The problem with them is they cheapened the quality of the components, mainly the capacitors, as that was the failure I experienced, and what I see from the various negative complaints. I think I paid $115, and it sits on the shelf, as I got a used namebrand for the same price. I have 8 machines now powered with VFDs (all dedicated to each machine). Most are TECO, but two Hitachi, one WEG. I do not purchased used VFDs, unless I can find the manual online, and get a pdf copy. Rockwell automation (was Allen Bradly) is one such brand I've never found manuals for.

I believe they (Vantrend) have made a model that is capable of single phase input. The AliExpress and eBay pages do not have any dimensions for the unit. The size of the 3 phase input unit vs this one "custom" designed for single phase input would be a deciding comparison, as you've found the filter is huge.

I know that I would trust this machine to do what the sellers are showing it was designed for. I would purchase through eBay and connected it immediately and verify operation of the lathe, so if there is failure, you have eBay's money back guarantee.
If you can get the dimensions and validate in your mind this has the filter size needed for single phase operation, that may give the "warm fuzzy".
So I looked up eBays "not as described" return policy, and found this;
A buyer must request a return no later than 30 days after the actual (or latest estimated) delivery date, or, if the seller's return window is longer, within the return window
The cost of return shipping for an item that is not as described is the seller's responsibility, same is true for any custom duty or other fees.

So you have 30 days of test time from date of receipt to complaint through eBay's system. I've never failed to get a refund when their system is used. I've purchased many items from China, I've learned the only items not to buy are HSS endmills. I never received, any endmill that passed my rockwell hardness test. They are all soft as butter (HSS=Rc >64, non were harder then 25, some less then 4, but I bought cheap, don't even try it if SWT brand). I tried to get metric size endmills, still don't have any. I've had good luck with ceramic tooling, boring bars both indexed and brazed, R8 spindle tooling has been good.
Do you have any tooling and large scrap to turn and face and prove the converter will perform to your satisfaction? Your only out your time if this fails early and purchased from eBay.

 

[Wizard69]

Guys, one of the bigger factors in successfulrunning of a VFD on single phase is the size of the input rectifier. Obviously single phase currents are much higher for a given amount of motor power so the rectifier needs to be able to handle this extra current.

This is where talking to an applications engineer can save you a lot of grief. They have access to the documentation that details the component size. The topology of VFD’s is largely the same from manufacture to manufacture for low end drives. That is the AC input is converted to DC via a rectifier and filter. That DC voltage is thenfeed to the rest of the drive for conversion to AC. That input section needs to be robust enough to be reliable and maintain that DC bus voltage.

 

[Entropy455]

If I ever buy a new place, it will have 3-phase power in the shop. . . .

 

[mcostello]

I have a small home based machine shop. Usual equipment. 20-30 years ago 3 phase power was about 2 miles away and the cost was around $2000 to get it here. Now They have put in new lines with 3 phase power to balance the load. It is along the road 150' from the shop. I asked the cost expecting to make the change now that it is close. More than $2000 with a commercial account to go with it. Think I'll keep what I've got.

 

[Entropy455]

If 3-phase were running along my property line, the decision to bring it into my shop would be instantaneous. The problem is that the 3 phase power is 2 miles from my house. About half that run would require adding the second feeder-wires to the telephone pole(s). The last mile however is where the cost balloons out-of-control. Power lines in my neighborhood are required to be underground. The underground wire (7200 volt coaxial direct-burry) is 12 dollars per foot (I'd need two wires) - that's 125 grand just to purchase the last mile of wire. I have no idea how much the above ground portion would cost, or the cost of the 3-phase transformer. I pretty much gave up at 125 grand. . . . .

When I built my shop, my property had a single 200 amp service (to the house). I had the service upgraded to 320 amperes, with a 185 foot run of 350 x 350 KCML x 4-0 feeder wires - which will support a 200 amp panel on the house, and a 200 amp panel on the garage. The bill from the power company for the upgrade was just under 700 dollars. That was with me digging the ditch, purchasing & installing the panels, and also purchasing & installing the below-grade conduit (required for low-voltage feeders).

 

[ignator]

When I built my shop, my property had a single 200 amp service (to the house). I had the service upgraded to 320 amperes, with a 185 foot run of 350 x 350 KCML x 4-0 feeder wires - which will support a 200 amp panel on the house, and a 200 amp panel on the garage. The bill from the power company for the upgrade was just under 700 dollars. That was with me digging the ditch, purchasing & installing the panels, and also purchasing & installing the below-grade conduit (required for low-voltage feeders).

"You bloom where you're planted", looks like you built a superduty large shop, and did everything for the machine shop power.
I'm guessing your back to 'plan A' of building your own RPC. Sorry for the divergent path.

 

[Entropy455]

There is more than just cost at play here.

I purchased a 1.5 horsepower VDF & motor kit from dealerselectric - for my little lathe (1800 rpm fully enclosed motor, constant-torque 230 volt VFD). I'm going to install this unit, and see how much I like it.​

My goal was to keep the 80 horsepower rotary phase converter project below $2500 (which includes the cost of bringing in the additional 200 ampere panel to assist powering it). The problem is that the contactors cost five times more than anticipated. By the time I'm ready to push the start button on my phase converter (with all the hidden costs), I'll probably be within a grand of a VFD.

If I purchase a VFD for my large lathe, it will be this one: https://dealerselectric.com/EQ7-2125-C-SRPLS.asp I'm not happy about the cost, but it's the proper size for my machine. The units cost what they cost. . . ..

 

[ignator]

I think I mentioned that I purchased many VFDs from Dealers Electric. Fast delivery, and seems to be the best price that I've found.
Also I wrote in many threads the ability to have a conversion constant to display spindle RPM, as I find I never need to change the belts on the small lathe (or drill press, milling machine). The motor is a 1800RPM model, and I set the max Hz to 120 which gives a very wide speed range. It is just very handy setting the spindle RPM directly.

I started with a V/f model on the lathe (TECO flux master 100), and it 'cogged' at low RPMs, so just last year put a Hitachi that I picked up NOS from eBay for <$80, this is a sensorless vector drive.
The big lathe I run at 60Hz and use the gear head speeds. However when threading I typically slow it way down.
I recall somewhere in this thread your mid size lathe came with a VFD, but that may be some other thread I'm recalling.

That 100Hp unit is $. They have a soft charge circuit, so the surge current during power on is reduced. I see the spec sheet indicates single phase operation for your power of motor.
Apology's if I'm repeating myself from short term memory.

Back to the project of installing solstice lights.

 

[Racene]

I'm constantly amazed that everyone is hooked on VFD's in my opinion not worth the money (into someone else's pocket ) or effort,take a look at the DC option using 4 -5 hp tread mill motors,results are surprising and cheap,motors can be sourced from local verge side collections for free or purchased very cheaply from the distributors (of fitness equipment treadmills)you don't need to use the TMs electronics if you don't want too as everything to get you running is availible off flea bay,look up You Tube under DC Treadmill motor for machine tool application ,Lathe ,milling machine, drilling machine ,
every AC powered machine tool in my shop has been converted to DC treadmill power,lathe ,mill ,table saw,bore pump,thicknesser to name a few,look into it an save $$$$$$'s. all vairable speed controlled and another bonus no loss of power from high speed to low or vickey versea

 

[Entropy455]

Standard DC motor voltages are 90 volts, and 180 volts. The majority of off-the-shelf DC motor controllers are the same. Treadmill motor voltages however are normally anything but standard (voltage ratings vary widely between manufacturers). This is why surplus treadmill motors are dirt cheap - because standard controllers won't work. If the treadmill's controller is integral to the display, then your lathe will display in mph. That's ok, I guess. The biggest problem is that they turn freakishly fast (between 4000 and 7000 rpm), and have very heavy flywheels attached. It's the only way to get the required inertia/momentum to dampen out the impulse events of a heavy human foot jamming into the belt.

Consider that I just purchased a 1.5 horsepower 1800 rpm totally enclosed VFD rated motor, with a constant-torque VFD controller (a package deal), for less than 300 bucks. It's practically a bolt-in within my little lathe. Whereas a 7000 rpm treadmill motor would require custom mounts, a flywheel guard, with an additional jackshaft to slow the input speed way down. The headache is simply not worth it - even if the treadmill were free. . . . (just my opinion). A standard industrial 1.5 horsepower DC motor with PWM controller would easily cost between 600 and 900 dollars.

My large lathe is 25,000 pounds, with a 40 horsepower drive motor (the problem at hand. . . .)

 

[Entropy455]

Rotational power is equal to torque times angular velocity.

DC motors have constant torque, therefore there's very appreciable loss-of-power at lower rpm. The DC motor rpm is also heavily dependent on shaft load. The main advantage of DC motors is that they make torque over a wide rpm range, in lieu of simply stalling out (like AC motors).

However enter the modern VFD - where AC induction motors may operate over a wide rpm range, at a constant torque - with the fantastic advantage of stable shaft speeds with varying loads. Plus no brushes to replace, and no carbon dust to clean between windings. In many ways, VFDs are vastly superior to DC drives.

 

[DJP]

I have been following this discussion with interest and after debugging the variable speed controller of a mini-mill with DC motor I have come to the conclusion that simple is better. A 3 step pulley and belt works well enough for my needs and as for the mini-mill I directly connected leads to the motor to supply 90 VDC in the event that the speed controller failed during an important job that I needed to finish. Luckily I found a few poor solder joints and a defective (not too robust) speed control pot to make the mill run again. For my Bridgeport I have a single phase 240VAC motor and it also suits my needs.

For hobby use I like simple machines although 3D printing needs some investigation.​