Soft-start motor switch

[Mark Gibney]

Can someone recommend an appropriate soft-start switch to use with a 3-phase 5 hp 1750 rpm motor?

It's going on a band saw, if that matters.

Thanks, Mark

I don't know why the two sideways photos of the nameplate are below the post. I also cannot remove them. Sorry for the duplication.

483174

[Malcolm McLeod]

What is your operating voltage?
Safe to assume you already have 3-ph power available? (manufactured or grid?)

Allen-Bradley is my go-to for all MCC gear, but Telemechanique is 2nd.

Traditional soft-start requires 2 contactors, timer, CB, and O/L - - and can get pretty expensive. Never used one, but I recall sales pitch of some 'packaged' electronic soft-starts that are simpler - but still more expensive. If you NEED reduced current start, a VFD is more versatile and about the same cost in 5Hp sizes. (End of VFD sales pitch.)

[Mark Gibney]

Malcolm, I have 240 volt 3-phase from the utility. I'm in a rented shop in a manufacturing zone, so all good in that respect.

[Malcolm McLeod]

Some links for info, if you need such:
https://www.rockwellautomation.com/en-us/company/news/blogs/why-choose-a-soft-starter-instead-of-an-ac-drive-.html

https://www.rockwellautomation.com/en-us/company/news/blogs/why-are-drives-easier-to-apply-than-soft-starters-.html

https://www.rockwellautomation.com/en-us/company/news/blogs/inside-the-delta-vs--wye-delta.html

I haven't looked at the wiring for that motor, but it becomes important for soft-start selection. You'll also need to make some decisions about what control voltage you want to use for a soft-start. I can't offer any specific part numbers w/o that.

[Malcolm McLeod]

Link to the 'electronic' style soft-starts I referenced. Never spec'd, installed, used one of the 'flex' versions - available for 240VAC power.

https://www.rockwellautomation.com/en-us/products/hardware/allen-bradley/motor-control/soft-starters--low-voltage/smc-flex-smart-motor-controllers.html

I had forgotten, but I have integrated a couple of the SMC-3 electronic soft-starts (long time ago). They're all 480VAC, so won't work for you.

[Malcolm McLeod]

One more....

I realized it has been a long time since I have done anything with soft-starts, so I've been reading - - call it professional development.;)

483175
^ The right hand of the schematic is what I'm calling traditional; a 6-lead motor needs a total of 9 relay contacts. As you might imagine, these contactors, their interlocks, extra wiring, and controls can get expensive. This took me several minutes to find, presumably because nobody does this anymore and EVERYBODY offers electronic soft-starts now.

And this is typical electronic soft-start -
483176
...and shows why control power decisions are important for selection; the control terminals must match the provided signals' voltage.

[mark werline]

You could also consider a Variable Frequency Drive over a soft start switch that has the capability to ramp speed upon start and is configurable.

ESV402N02TXB LENZE 5HP NEMA1 IP31 SMVector VFD (electricmotorwholesale.com) (https://www.electricmotorwholesale.com/LENZE-ESV402N02TXB.html)

Acceleration/Deceleration Profiles
Two Independent Accel Ramps
Two Independent Decel Ramps
Linear, S-Type
Auxiliary Ramp(or Coast)-to-Stop

[Bill Dufour]

Due to demand and the numbers produced I would think a VFD may be cheaper then a soft start switch. Espically since you already have three phase input and do not need to oversize the VFD.
A generic china made 5hp vfd is around $150.
Bill D

[Mark Gibney]

Malcolm, the info you provided is way above my pay grade. I don't understand it well enough to use it in my decision making, but I'm sure it's great info! So thank you.

Mark, from what I gather, VFDs are a little more complex, they do more than what I need, so maybe staying with a soft start is better.

Rockwell Automation recommend a particular soft start switch that comes out at about $750 before shipping. There's a "refurbished" one on the Bay for a little over $200. Shipping from India. I contacted the seller to ask in what way it has been refurbished.
Any opinions here about refurbished electronics like this?

Here are two photos of it -

483213 483214

[Aaron Inami]

Any opinions here about refurbished electronics like this?


I don't know about industrial stuff like these soft-starts, but "refurbished electronics" in the audio industry is really a misnomer. It just means the original manufacturer tested it and it performed "to specification". Then they just recycle it out to the used buyer crowd. It actually costs them too much money to tear it apart and replace degraded parts such as capacitors (which definitely have a finite lifespan). For $200, I would bet they didn't do anything with it. You're basically looking at a minimum $100 for some engineer to pull apart a device and "look inside". To actually fix/replace parts, the actual cost to manufacturers could be anywhere from $300-600 dollars (you're better off buying it new at this point).

[Warren Lake]

whats the point to the soft start? Im using machines up to 60 years old original switches and motors. Used by people full time before I bought them, I press a button the machine runs. Just another internet I need thing? Do have one machine Griggio jointer that starts in Delta and switches to Wye I think it is. Other stuff just snaps on and is running full speed in a split second.

[Bill Dufour]

My Dad's story about soft starts.... They had a large motor driving a vacuum pump. It was hard to start and would trip overloads for the motor. Probably 200-400hp. It was belt drive with 10-12 belts so they cut off one belt at a time until it slipped enough to get started. Sinc ethey use dthis pump only a few times a year it lasted just fine.
Bill D

[Rod Sheridan]

Can someone recommend an appropriate soft-start switch to use with a 3-phase 5 hp 1750 rpm motor?

It's going on a band saw, if that matters.

Thanks,

I don't know why the two sideways photos of the nameplate are below the post. I also cannot remove them. Sorry for the duplication.

483174

Hi Mark, why would you want to soft start a motor that small?

Regards, Rod.

[Mark Gibney]

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.

[Rod Sheridan]

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.

Makes sense Mark, you’re probably going to find that with the inertia of the saw you won’t need soft start……Regards, Rod

[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