VFD or Soft Start

The application is a small conveyor that needs to speed up and then speed down so that the part gets moved down the conveyor quickly.

I have looked at both an SMC-3 (BULLETIN 150) and a PowerFlex40.
Conveyor motor is 1.5HP at 575VAC. Part is around 40lbs, conveyor is 20feet long.

There is only ever 1 part on the conveyor.

The price difference on the rockwell site is only 150 bucks, so I think we should get the VFD, but I have to know for sure that the soft start can't do the job properly.

Not sure if I understand you correctly but it sounds like you are looking for complete speed control. If that is the case then only the vfd will work. The soft start can only soft start, current limit start, kick start, soft stop, or coast to rest. The soft start is only meant to softly start a motor and then switch it to a bypass contactor once it's at speed. The vfd will do just about anything you ask from it when talking about speed.

What I need is something that will accelerate the conveyor up to top speed and then slow it down to a stop quickly, so the part makes it from the start of the conveyor to the end of the conveyor as fast as possible.

I just installed a PowerFlex 700

I LOVE IT... its on the Ethernet so I am going to run it in my Redlion G3, I have not got that far yet... just controlling it with a pot for now, but its was easy to set up

I would go with the PowerFlex as you can do a lot later also if you change anything

The fatest response will be an across the line starter and a motor brake.

I prefer the Omron G5 series as its configurable to several drive types
Ie flux control, or v/hz or the equivalent to senserless vector

Tom Jenkins said:

The fatest response will be an across the line starter and a motor brake.

Click to expand...

fatest? wtf, you dissin me?

anyways, I suggested the VFD, cause we may run into something at startup that the VFD will be the only cure and for the price difference, I think much better option.

Tom is right. Going across the line will definitely be your fastest. As far as soft start, with these few details it sounds like it will work. But for the money buy the drive. Sometime in the future you might need speed control or maybe even overspeed the belt or just anything.

VFD. PowerFlex works great. Mine are all on DeviceNet. As boardmaker said, the flexability of the VFD leaves you future options.

mordred said:

I prefer the Omron G5 series as its configurable to several drive types
Ie flux control, or v/hz or the equivalent to senserless vector

Click to expand...

So does the PF 700.

I would say your best option is the VFD. Softstarts generally have a low rating of how often you can start and stop per hour; they're just not designed for what you want to do.

As is so common among technical things, the "best" way is---well, it depends!

In terms of simple and very fast, Tom Jenkin's mag starter and backside brake is "very good". But it might not be the fastest. With sensorless vector, it is possible to accelerate with more torque than across-the-line. And, you don't have to stop accelerating at 60Hz. Just keep increasing the speed until the motor reaches it's hp limit. Then, at the last possible minute, slam on the backside brake to a stop. That might be a little faster especially if the run time is long enough to accommodate the overspeed part. But that is taking "fastest" out to the extreme, a bit.

On the other hand, you could use a heavy duty rated softstart to get a little control of acceleration torque and add DC injection braking to stop. That can also be quite fast but you gain some control over both ends of the run. And, there are no brake linings to replace regularly.

Or, you could use a heavy duty drive with a very short accel time, use the overspeed capability I mentioned above and put a snubber braking package on the drive for stopping fast. This gives you precise control over the accel and decel time with overspeed running in between. You will spend some extra money to do this but you gain precision and future flexibility.

Finally, I hope there is no worm gear with a ratio over 28/1 between the motor and the conveyor or, as soon as you try to slow down, the worm gear will lock up and you will definitely get a "slam stop". At least, until the gearbox case splits open and the gearlube runs out!

I hope I've made you think a bit more about your options.

AB also has a PowerFlex 4 which is a smaller cheaper package than the PF40. I believe they have a 575 volt model. It is more difficult to do a comms option on though.

However, it may bring you more into the price range of the SMC, and still do everything you are asking fo right now and then some.

Sounds like a very simple project..... As much as I am an AB guy, there are a LOT of cheaper drives than the power flex that can do this simple application. It does not sound like there is enough weight to need a DBR so any drive will work