Soft-start motor switch

[Bill Dufour]

From those quotes a VFD will be cheaper and it has soft start capability and other useful features like variable speed and braking as well.
Bill D

[Aaron Inami]

I have seen braking done on a table saw (Felder K700S for example), but the saw blade is a very light item. If you do braking on a bandsaw, those wheels are extremely heavy and have a LOT of momentum. Would this be too hard on the VFD/capacitors to handle? There was another thread on capacitors in a Perfectphase unit being stressed from CNC spindle braking.

[Warren Lake]

I liked that thread, made me aware of a thing ive never needed and saved me from putting extra wear and tare on the roto. Internet good thread for me at least.

[Rod Sheridan]

I use braking on my band saw mill via the VFD

Works fine as long as you don’t exceed the VFD rating.

Regards, Rod

[Bill Dufour]

Probably need to add a braking resister sized to the load. make sure that the braking terminals are actually connected internally in the VFd. Many are not, they are just for show. A stove heating element can be used.
Bill D

[Michael Schuch]

Rod - maybe I don't!
This thread has educated me a lot on this topic. My initial interest is because several of my machines with 3-5 hp motors SLAM into action, and while I'm putting this bigger (to me) band saw together I got interested in a soft starter.
I'm within a couple of weeks of firing up the saw for the first time and I'll see how it goes.

I have a 5hp 12" Powermatic table saw that does this. I had to tighten the belts considerably to keep them from slipping on startup. I currently run the saw off my rotary phase convertor. Some day I will switch it to a VFD. I have no need to vary the speed on a table saw but the soft start would be nice and also allow me to plug the saw into any extra 220v 1ph outlet.

My recommendation would be to go the VFD route. VFD's were originally designed to offer speed control of 3ph motors running on a 3ph supply. The only down side to a VFD is that it will take some extra wiring to integrate with your saw which might be intimidating if you are not comfortable with AC wiring.

[Aaron Inami]

One thing that you should know is that VFDs need to be wired directly to the motor. This means that you cannot use any existing power switch (especially magnetic switches). Any emergency stops built into the switch/saw cannot be used either. If you do use a VFD on a saw, you need to make sure the VFD is configured to NOT run the motor upon VFD boot-up (in case of a power outage). If you want an emergency stop with a VFD, it may be possible using a special switch and the VFD option terminals on the communications bus, but you need to make absolutely sure the emergency stop operates as intended.

[John Lanciani]

One thing that you should know is that VFDs need to be wired directly to the motor The output of a VFD has to be tied directly to the motor, but that doesn't mean that you must control the motor directly from the VFD control pad. This means that you cannot use any existing power switch (especially magnetic switches) This is not true. Its relatively straightforward to use the existing start/stop on most machines to seamlessly control a VFD. Any emergency stops built into the switch/saw cannot be used either. Again, this is false. Most (all?) VFD's have programmable inputs that can be configured for E-stop functionality If you do use a VFD on a saw, you need to make sure the VFD is configured to NOT run the motor upon VFD boot-up (in case of a power outage)I've installed more than a few VFDs and I've never seen one configured out of the box to run on power up. You'd have to go out of your way to enable that command If you want an emergency stop with a VFD, it may be possible using a special switch and the VFD option terminals on the communications bus, but you need to make absolutely sure the emergency stop operates as intended. No special switches needed, just some low voltage wiring and a basic understanding of simple circuits

Comments in red above.

[Bill Dufour]

Make sure to lockout reverse for a saw.
Bill D

[Aaron Inami]

My understanding of a magnetic switch is that you enable the magnet and the power output by pressing the "ON" button. The current flowing through the switch keeps the magnet powered and keeps the switch "on". When you push the OFF button or have a power outage, you lose current and the spring-loaded magnet is released to cut off connection to AC. I don't know how you could successfully use this with a VFD. Maybe you can tell me how? If you use it on VFD output, you would always have to keep the "ON" button pushed down as you hit the "RUN" button on the VFD. If you use the magnetic switch on the VFD power input, does the VFD use enough current at idle to keep the magnet enabled?

I have not played with VFDs enough to know how to do the emergency stop. I suppose you can use a push/pull switch for RUN/STOP on the VFD. Essentially, you "pull" the switch to run the motor and "push" the switch to stop the motor which gives you a type of emergency stop.

[Rod Sheridan]

If you wanted you could use a contact from the starter to operate the run input on the VFD.

I’ve done this on several machines using a control relay and multiple start and stop push buttons……Regards, Rod