soft start current window

[ILCML]

I've seen quite a few topics on SS here, but my question goes unanswered....I have an ABB softstarter with a max motor current rating of 6.1A, and I need to control a motor at 480v with an FLA of 2.8A. I seem to remember being told that the circuit in the softstarter has a current 'window' in which it will operate properly. I have also been told that the current rating on the SS is a max, and it will run at a lower current. The ABB PSR series I'm looking at has the various models rated by current, which makes me think that the former is true....I was just informed that the motor will be run at 480v rather than 230v as I thought when I spec'd the SS, and now I'm stuck....It is currently not compeltely built, and I thought I'd get some feedback before it's built and I test it. Naturally, ABB is apparently closed for the day.

 

[dpc]

I'm not clear on what your actual question is.

 

[ILCML]

Oh, sorry about that.....will the softstarter with the higher current rating (6.1a) control a motor ok that's only running at 2.8a....the smaller model SS max current is 3.4a....but I can't get my hands on one in time.....

 

[jraef]

Maybe yes, maybe no. Only ABB can answer that.

The issues would be with the current limit and motor thermal overload protection. If you cannot turn the settings down low enough, you may not have overload protection if the soft starter has that built-in. If you have a separate external OL relay, then that may not be an issue as long as your OL relay is sized properly.

The other issue is current limit. Not all soft starters provide current limit and those that do may use different ranges of current sensing adjustment. A common range is 2:1 because of the accuracy of the CTs they will use in the sensing circuit. So if your soft starter is like that, it may only allow the current sensing to adjust down to 3A. That still may be acceptable depending on what your application is; in fact you may not even need current limit at all on such a small motor. If your soft starter doesn't even have it as a feature (and many small ones like that do not), then there is no issue again.

 

[ILCML]

FYI.....after speaking with ABB, I'm told that as long as the motor is started under a reasonable load, that although the ramp time may be shorter, it will work. It will work with little or no load as well with a decreased ramp time even still.
I finally ran the thing with a slight load, and did not take any numbers on anything, but there was a very noticable (and adjustable) ramp up and down.

I am using an external overload, sized properly. Thanks for your reply Jraef, I always consider your replies very valuable....

 

[itsmoked]

Thanks for coming back with that ILCML. We appreciate that.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com