New Toys, Planning Power...

JimDawson said:
A few random thoughts on VFD vs. RPC on a mill. I have both a VS head and a VFD, and for most operations have the VFD set to 60Hz and use the mechanical speed control.

Soft motor start vs. instant on. Less shock on the mechanical system
Controlled breaking/deceleration vs. coast to stop
Nice for drilling & tapping. Change the speed with a knob vs. crank speed down or or even go into back gear for tapping speed.
If converting to CNC, spindle speed can be controlled by the program vs. manual speed change.
In a CNC conversion, wiring is simplified for FOR/OFF/REV vs. rather complex and expensive contactor controls.
Motor overload protection vs. no overload protection on most mills.

Even if I had 3 phase power available, I would probably install a VFD on the mill just for convenience.

On a lathe, the VFD is less advantage, but all of the above applies. I am running a static phase converter on my lathe but have been thinking putting a VFD on it just to be able to fine tune the spindle speed between the geared speeds.
.
.
Click to expand...
I totally agree with everything Jim presents here. I also have a variable head BP knockoff with a vfd
& I wouldn't have it any other way.
 
We use an RPC to run our CNC mill (controller on separate 1-phase circuit) and bandsaw. Lathe is old Monarch 10EE on single phase. RPC's tend to be a little simpler to setup than VFD's. If you need an RPC, you might want to check out Southern Phase Converters. They are cheap (relatively), appear to be well built, and Larry Dalton (the owner?) is very friendly and very helpful.
 
I posted some pictures of a VFD I installed that I use for two machines. The VFD is large enough so I don't have a motor problem. I installed two receptacles in the door, one for each machine, HOWEVER, I put a large sign on it to not plug both machines in at the same time. What I have been told and read from the manufacture is that you should NEVER use a drum switch. Like everyone above has stated, it needs to be connected to the motor directly. I had a DRO on my mill and I put a remote switch from the VFD and mounted it there so the VFD is in a box with a fan for cooling and I never mess with it as my mill has adjustable speed on it. I'm not sure what I called the photos but they shouldn't be too hard to find.
 
I've installed VFD's on a Bridgeport Step Pulley Mill, Bridgeport Variable Speed Mill as well as my personal Lagun Variable speed Mill, Precision Matthews PM1128LB lathe and 16" Southbend lathe, and have not been disappointed.

As a side note, I replaced static phase converters with VFD's on the first two mills mentioned and they seemed to work fine but the owner wanted the versatility of the VFD's.

Static Phase Converters are the cheapest solution of all and but probably the least robust and flexible.
 
Just remember that static phase converters are hardest on your motor because it's not really supplying 3 phase to the motor. It means your motor is also running at about 2/3 of its rated power.
 
SRDC said:
Just remember that static phase converters are hardest on your motor because it's not really supplying 3 phase to the motor. It means your motor is also running at about 2/3 of its rated power.
Click to expand...

Resulting in higher motor operating temps.
 
I added a VFD to my lathe. I had to rip out all the wiring. I got extra parts like 2 contactors and some switches. I was able to add a variable speed knob and a low speed Jog Forward and Reverse. I added a E-Stop which stops the lathe in 1 second. The minimum RPM has dropped from 70RPMs to 9RPMs and the top speed increased by 30%. I just can't run at low RPMs for too long, The Oiler doesn't work at 10HZ. I will be adding a external lubricating pump soon. If you do go VFD, make sure you get all the features you need.
 
A digital phase converter though initially a little pricey is another option for running multiple machines. It functions the same as a RPC but is solid state and supplies balanced 3 phase with no noise and 97% efficiency.

Greg
 
Hopefully he's got it up and running sometime in the past 8 months. ;)

Tom
 
I believe a lot of people get scared off from rotary phase converters because there are so many poorly designed and built home made versions. I faced the same issue when setting up my shop. I wanted to plan ahead for any future machines or bigger machines as well as what I currently had. I investigated the better quality VFDs and rotary phase converters. I went with a factory built American Rotary brand phase converter based on favorable reviews on Practical Machinist. I got a AR series 7.5 HP model. Push button start and extremely quiet. I can stand right next to it and only hear a low hum. Well balanced legs for the 3 phases. The electrician I hired does a lot of commercial work and he said it was the nicest phase converter he'd seen. American built with a warranty and components easily accessed and replaced if a capacitor ever goes out. Try that with a little Chinese puzzle box VFD. If one of those needs repair it probably would be cheaper to replace outright. With the American brand phase converter I can run all 5 of my 3 phase machines easily at the same time. After it was installed I turned on each machine one at a time until all where running. Absolutely no strain or change in the output. Full power and torque. As I add or upgrade machines it will easily handle anything up to a 5-6 HP 3 phase motor. I've been running it on a regular basis for the past three years. Best $600 I ever spent.
 
You must log in or register to reply here.
Back
Top