VFD or contactors

I am looking for supporting documentation on using a vfd over contactors. I have a nunch of conveyors starting and stopping all day.
I am sure there is some documentation on ramping up and down instead of across the line. I assume life span increased and peak energy decrease.

There is a lot of literature from the various manufacturers out there but almost all of it deals with pumps and fans.
I do recall seeing a PDF from Rockwell somewhere that covered conveyor drives. You might try searching their site.

Unless you need speed control, soft start drives should be adequate for your application. You could also see a power factor improvement with soft starts versus contactors.

we use contactors in front of vfd's for e-stop purposes only.

did not use to do that until one of the opto inputs shorted in the on state.

luckily, a motor disconnect was within reach of the guy caught in the conveyor when the e-stop was pushed - when i worked for a UK company.

regards,
james

Various truths to consider here.

On something like a conveyor, you will not see a significant change in energy consumption with VFDs or soft starters. Energy is work across time, also power across time. If you lower the power, you increase the time it takes to do the same work, so no energy is saved. Don't fall for that trap. Energy savings from VFDs only applies to replacing other means of varying FLOW in centrifugal machines such as pumps and fans. A conveyor is never a centrifugal load.

Peak demand charges (in the US) are based on sliding windows of time, between 15 and 30 minutes dending on the utility, they are intended to offset the utility's cost to handle RUNNING loads, not starting surges. Soft starting with a VFD or Soft Starter has almost no effect on those charges. Again, marketing messages from suppliers are meant to make you buy them, not make you smarter.

If you can benefit from varying the speed of your conveyor, then by all means use a VFD, because the only other way to do that is to use mechanical vari-drives, and they are horribly inefficient. But if all you need to do is permanently CHANGE the speed of a conveyor, then change a belt or gear ratio, it's cheaper and just as efficient.

A VFD will improve the displacement power factor, which might affect your aggregate power factor penalties from the utility, if any. A soft starter will not. Soft starters are often marketed as "energy savers" using terms such as "power factor control", that is almost always a scam, don't fall for that either. Soft starters cannot improve power factor and besides, improving power factor does NOT save energy in a meaningful way for the end user.

The only possible benefit to using a VFD instead of an across the line starter is if you are beating the motors to death with starting and stopping all the time. In that case, as Bit Bucket 07 said, a Soft Starter will likely suffice, but it should be noted that below 10HP, a VFD may actually be cheaper now. A VFD will however add about 3-5% losses to your continuous energy consumption, a soft starter will not.