To The Soft Starter Experts

BobB

Lifetime Supporting Member
Join Date
Jun 2002
Location
Sydney
Posts
4,548
I hardly ever use VSDs in my business but do use quite a few soft start/stop units up to 18.5kW. Babies. They are used on pumps and there are no real issues here but, as Terry pointed out in a previous thread, soft starters can be fairly useless when starting heavily loaded conveyers, for example.

I normally use the Sprechur & Schuh soft starters as they are the same width as the S&S contactors and fit in line quite well. They are also inexpensive, have thermal protection and automatic bypass contactor built in etc etc. Quick and easy - saves heaps of time. I believe AB sell them also. They own S&S these days. I believe the range has now been extended to 45kW but would expect the larger ones to be a bigger size. Have not looked yet.

I have just had a sales rep in selling the new range of ABB soft starters. They are definately not as easy to mount in switchboards, take up more space etc but, they have a class 30 soft starter for heavy duty. As I hardly ever use these things I am unaware of class 30 soft starters and their advantages. They do list long conveyers as a suitable application for the soft starters.

Do any of you know about class 30 and the advantages of them on heavy duty loads?

Are they configured and/or work any differently to class 10 or are they just heavy duty in the sense that they use larger heat sinks or something?

I also notice that they sell specialty delta in line soft starters. Could be interesting.
 
I have found if you can start it DOL then (if the soft starter is large enough) you can start it with a soft starter no matter what the load. To achieve this you have to wind up the current limit to max which totally defeats the purpose of a soft starter. I would be very dubious about claims of soft starting heavily loaded conveyors.
Soft starting is vastly different than starting with a soft starter.
Regards Alan
 
Bob, the Classes referred to in the softstarter descriptions is the same as the Classes for overload blocks. Class 10 is for easy starting, fast accelerating loads, Class 20 is for average loads, and Class 30 is for hard starting and especially high inertia, long accel time loads.

This impacts softstarters principally in the available accel time and the heatsink size. Typically, these small softstarters are Class 10 because the available accel ramp is limited to 30 seconds which permits a smaller (cheaper) heatsink. A Class 30 softstarter will typically have available accel times that run out to maybe 5-10 minutes and the heatsinks have to be much larger deal with the SCR conduction heating for the long ramp and high currents. Of course, once you are up to speed, the bypass contactor closes and conduction heat is no longer an issue but, getting up to full speed is.

The extent to which you can softstart a load is entirely a matter of the nature of the load. You then have to pick the type of softstarter that meets your needs. For a change, these claims aren't snakeoil but real issues you need to think thru before buying.
 

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