I have a brand new Wilo 25hp submersible pump that will not run on a square D soft start. The motor ramps up but will not hand off to the bypass contactor when it reaches speed. Emu 25hp pumps run great. What could be the problem. Softstart settings are the same, impellers are very close to the same. Has anyone else experienced this problem?
A weird quirk of soft starters with bypass is this:
The soft starter "knows" when to turn on the bypass contactor based on two criteria:
1) The current had exceeded a certain threshold
2) The ramp time is done OR the current has stopped increasing
Criteria #2 is the obvious one, but most people don't realize that it is an OR condition. The reason is, if the current limit is set, it will override the ramp time, so if the current stops increasing for a certain amount of time, that means the motor has finished accelerating.
But hardly anyone knows about condition #1. The REASON why it is in there is because without it, the load on the motor may hit a point where it is accelerating, but not pulling any more current, i.e. "
the current has stopped increasing" which is one of the OR conditions in criteria #2. So to discriminate, the current has to RISE ABOVE a threshold and then DROP and settle down to know that the motor is finished accelerating.
Unfortunately, if your load is TOO LIGHT on the soft starter, the current never rises above that threshold and the soft starter does not recognize that the motor is finished accelerating. This often happens when a soft starter is over sized for the application. You are describing this quirk to a tee, my guess is that someone bought a 50HP soft starter because "bigger is better". Either that, or the Current Limit is set actually BELOW the threshold current level! I have never understood why a manufacturer would even allow that, but I have seen it many times. I'm not sure if the Altistart is like that, but it would not surprise me at all. Regardless of the fact that they are a competitor now, I have never had a high opinion of Altistart soft starters. When I had my contractor and panel shop business, their poor quality cost me a butt load of money and the loss of a huge project contract at Chevron. I will never forgive them...
