Rat Bastid
Dunamis Metron
Let me see if I’m getting this right.
You are saying the VFD replaced that big green machine or the VFD is running it??
Im a bit slow on the uptake.
VFD
- Thread starter Rat Bastid
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Let me see if I’m getting this right.
You are saying the VFD replaced that big green machine or the VFD is running it??
Im a bit slow on the uptake.
1WildRT
Well-Known Member
A 200 HP electric motor replaced the big diesel... They are using a VFD to control the motor so it's speed can by controlled....
Rat Bastid
Dunamis Metron
Ok, that’s IMPRESSIVE.
I've run both VFDs and Roto Phase set ups for my home shops. I preferred the Roto Phase set up based on an old 5 HP 3 phase motor feeding a small auxiliary 3 phase panel that I ran up to 8 machines; I believe I got closer to rated full power on my machines with the R P.
gzig5
Well-Known Member
This is a bit incorrect, a VFD doesn't generate the third leg. A rotary phase converter generates the third leg. A VFD is typically a two part machine in that it has on the input side a Converter front end that typically uses diode bridges to convert AC to DC voltage and Bus capacitors are used to smooth the DC and eliminate AC ripple. The output side is an Inverter uses some sort of silicon transistor, FET, MOSFET, or IGBT arrangement to convert the DC back to AC at the desired RMS frequency. That frequency along with the motor pole count is what determines how fast the motor spins. 230V VFDs that have single phase inputs can have limitations as to how large a motor can be driven, and that is determined by the size of the converter used in the front end. You need a significantly larger single phase converter section to be able to handle the same current that a three phase bridge can. Three phase input VFDs don't have this limitation, but typically aren't useful to home shop types that are looking for the single phase 230V input aspect.
I can go on and on an on about this VFD control theory topic but won't bore you. I am an engineer for AB in the facility where all of the low-voltage (600VAC and down) VFDs are designed and some of the mid-size drives (50-500hp) are built. I actually work in the motion control Servo business, which is essentially a VFD with a dedicated position feedback input for use with permanent magnet motors in robots and repetitive motion applications like packaging.
We have a Medium-Voltage division that handles drives from 600 - 11,000 volts, with the more common ones being 4160VAC. Those drives essentially fill a room and the motors can be more than 32,000 HP. There are a lot of MV motors around 500 hp too, because the higher voltage allows use of much smaller conductors, and copper costs often drive the decision.
The simple answer is yes. You can use it as a speed controller as well, but don't expect to get any decent torque from a low cost simple VFD and regular induction motor, much below the 40Hz range. Below that the torque suffers and you need more advanced loop control, as well as an auxilliary cooling fan to prevent burning the motor insulation. Still better than nothing, but you will need to use the mechanical speed control in the head for large speed changes.
Rat Bastid
Dunamis Metron
I‘ll just be running the lathe with this VFD. I want a mill so bad I could spit end mills but I just don’t have the space for one.
Unless I hit the lottery and build a bigger shop or I get rid of some of my hoard of CRAP. That hasn’t happened since 1979 so I don’t see it happening now.
gzig5
Well-Known Member
FIY, if cash strapped, you can run multiple motors off a single VFD if the combined HP isn't larger than the rating. The drive just sees a larger load. Often done on large conveyor systems but I don't know how you would utilize it in a home shop.
You can also use a single VFD to control multiple machines one at a time buy switching motors in and out of connection while un-powered. VFDs typically don't react well to switching loads in or out on their output, while they are energized. Bad juju.
1WildRT
Well-Known Member
Find more space... Mills a great to have... I had one of those Rung Fu Mill/drills for 6-7 years, don't waste your time, get a Bridgeport or a clone... The Rung Fu couldn't take a .025 cut on mild steel without chattering... The Jet Bridgeport clone can easily take .100+ without chattering...
Since you don't typically run the lathe & mill at the same time in a hobby type shop one VFD feeding a plug outlet so you unplug the lathe & plug in the mill works fine....
IfItsGotWheels
XS Tech-Anything worth doing, is worth doing in XS
Agreed, when I was ordering a 30HP drive, Danfoss suggested I double the size, not so much because it was undersized but because the load 10 3Hp motors produced on startup would 1.5 times the regular load.
Rat Bastid
Dunamis Metron
I ordered a 4 HP VFD. And of course, after I did that I walked my lazy arse out to the shop to look and I have a 1 HP motor.
Screw it. I’m not cancelling the order or sending it back. If it fails I’ll get a better one.
Screw it. I’m not cancelling the order or sending it back. If it fails I’ll get a better one.
Ordering oversize is not a bad thing at all, because now you have reserve power for other items you may want to run in the future. If @gzig5 has anything to add as far as other benefits, I would like to hear about it, although I have seen firsthand the torque loss associated with the 66% or lower speed reduction. That was on large Winsmith double worm reduction mixer (treatment plant flocculator) drives with 1-1/2 HP VFD specific motors.
1WildRT
Well-Known Member
FWIW lot of machinists types use the VFD to overdrive the motor as much as 50% (90 hz) which is where I've heard the non VFD rated motors tend to fail...
Rat Bastid
Dunamis Metron
Well that’s bad news because I need a bunch more RPM to make using different tooling easier. I need more SFM for most everything I do.
1WildRT
Well-Known Member
Exactly... Older machines don't spin fast enough for carbide insert tooling... Might consider a motor pulley change, you lose torque but gain SFM & as long as you don't take huge cuts it works pretty well... My small lathe can still take .120 cuts without showing any sign of being overloaded..
The big lathe will take .400 without much trouble... I rarely take more than .125 in a single pass...
gzig5
Well-Known Member
Being a bit oversize isn't a bad thing and our sizing software tends to build in and recommend a little margin. For example lot of customers will buy a 5hp drive model to run all the 1-5 hp motors on a machine. Imagine how many conveyors and motors are in a UPS or Amazon facility and you'll understand the benefit. Allows them to carry fewer spares at the slightly higher initial expense. I've run 1hp motors on 75 HP drives and they work fine for a low dynamic application. The current sensor feedback is down in the mud and you wouldn't do that big of a mismatch in an idustrustrial setting, but it works for the testing that I need to run. There is a tipping point for where you start to loose signal fidelity on a large mismatch, but I'd expect a 1hp to work on a 4hp drive just fine.
I wouldn't expect the speed on a lathe to be a problem unless you are running a 100yr old one with plain spindle bearings and then the limiting factor is the bearing design. On a mill, if you know you are going to be running higher speed with small diameter tooling most of the time, I'd suggest changing the pulley system or if possible go from a four to two pole motor (1800 ->3600 rpm). If you have a quality US made motor, it may live at the higher frequency settings, but they do make inverter duty motors for a reason. Regardless, I'd figure out how to add a cooling fan to the motor if you are concerned. You can spend some money on a industrial quality drive an a motor with encoder and significantly enhance your speed/torque control, but seems like overkill on a Bridgeport spindle and a lot of people make a lot of good parts with a standard VFD setup. If you do jack the speed range up, keep an eye on the spindle bearings.
Rat Bastid
Dunamis Metron
Ok, so I ordered a VFD. Was going to be here Friday. Got an email this morning that said they didn’t have any and it got cancelled.
Unreal.
So in looking again I see there is a VFD I like (I think I like but I’m guessing) but you can get two different models.
One is what they call a “general” VFD and the other is a “vector” VFD.
Is one better than the other for a manual lathe?
Unreal.
So in looking again I see there is a VFD I like (I think I like but I’m guessing) but you can get two different models.
One is what they call a “general” VFD and the other is a “vector” VFD.
Is one better than the other for a manual lathe?
gzig5
Well-Known Member
Sensorless Vector control is a little more sophisticated than the V/Hz output of a basic drive, but unless you think you need more precise velocity control I don't think it makes much difference on a manual lathe. Might have some benefit on lower rpm torque but I can't say for sure. I'm much more familiar with tuning Servo drives than the open loop VFDs. Wouldn't hurt to have in your back pocket if the price difference isn't too big.
Sensorless Vector Control of AC Drives
Sensorless Vector Control of AC Drives
MopaR&D
Nerd Member
How fast is "fast enough"? We got a Clausing lathe at work built in 1975 and it's a tank, weighs 2500 lbs and has a 10hp (I think) motor with a hydraulically-controlled variable speed (basically like a CVT) along with 3-speed gearbox in the head. I think it maxes out around 3600 RPM but I've never run it anywhere near that fast, generally 200-1000 RPM for turning most parts which are generally 1-2" diameter and most of the tools we have are the replaceable-carbide-insert type. I've gotten pretty good at using it but I'm not a machinist, basically taught myself using YouTube videos and a couple books.
When researching this lathe it seems most people who have had the hydraulic variable-speed system fail just locked out that part and added a VFD to control the motor. Replacement parts for the drive system are long gone and it's kind of a PITA to work on.
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