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Home » Soft Starters Knowledge » What is soft start?
What is soft start?
"Soft start" in reference to when you connect AC and get surge current to charge capacitance:
When AC current is over X amps for more than Y line cycles. X and Y depend on the AC breaker you plan on using. Usually, if you can stay under a peak of 30A for less than 1/2 line cycle your OK to the line (15A 120Vac breaker), but depending on your design that might be way too high and you'll burn up traces or blow fuses and of course cause flicker.
For smaller PFC systems, it is not usually a huge problem as input capacitance is much lower, for non-PFC systems you really need to be careful as mentioned previously. Though if this is for your 10W design (from previous questions), I would guess you'd be fine as long as you didn't over do your input capacitor.
"Soft start" in reference to control system (first few switching cycles):
A lot of this depends on the load requirements, response time of the converter, max power of the converter, and output capacitance.
At max power, how long to charge the cap to required voltage?
Then what's the response time on the control to prevent overshoot? (this is where soft start will help you... to prevent overshoot).
What happens to the load at voltages lower or higher than the specified output? (If it wants 48V, but blows up at 50V, use a soft start).
When AC current is over X amps for more than Y line cycles. X and Y depend on the AC breaker you plan on using. Usually, if you can stay under a peak of 30A for less than 1/2 line cycle your OK to the line (15A 120Vac breaker), but depending on your design that might be way too high and you'll burn up traces or blow fuses and of course cause flicker.
For smaller PFC systems, it is not usually a huge problem as input capacitance is much lower, for non-PFC systems you really need to be careful as mentioned previously. Though if this is for your 10W design (from previous questions), I would guess you'd be fine as long as you didn't over do your input capacitor.
"Soft start" in reference to control system (first few switching cycles):
A lot of this depends on the load requirements, response time of the converter, max power of the converter, and output capacitance.
At max power, how long to charge the cap to required voltage?
Then what's the response time on the control to prevent overshoot? (this is where soft start will help you... to prevent overshoot).
What happens to the load at voltages lower or higher than the specified output? (If it wants 48V, but blows up at 50V, use a soft start).
Why or what causes a brand new starter to burn out. (3 phase, 480V). There is a reset button on starter. I guess this is the overload. It should still be able to reset! It is instantaneous.
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