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| Is a single NTC thermistor enough for motor soft start? |
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| analogo:
I would like to limit the inrush current of a water pump. It is working fine up to now, but I can hear how violent the initial impulse is. Reading around I have found that the most basic way to implement a soft start is a NTC thermistor. But I haven't found any application note that deals with simple cases like mine. Here is the my trivial circuit: https://crcit.net/c/38a809a8be3c4096a4255481784daee1 (The capacitor is there to block EMF.) Would such a trivial circuit be OK? How can I determine the right Ohm value for the thermistor? |
| Benta:
It must be an extremely small pump with a 4.7 k NTC. As such, start current should not be an issue. ??? |
| analogo:
Benta, that was just a diagram, I have no idea which value the NTC should have. :) The (el cheapo) motor is consumes ~ 1A (24V) in steady state, and about 1.5A when it starts up. Is there a rule of thumb for which Ohm value the NTC should have for such a motor? In addition to the inrush current, I would like to use the soft start to avoid the initial transient wave of water that violently shakes the pipes. |
| Kasper:
Not sure how to use a thermistor for this but you could connect switch through RC delay circuit to transistor to slowly turn it on. |
| TimFox:
When using a NTC thermistor to limit starting current, you must remember that it may not cool off sufficiently between power-ons, if you need to start and stop the load repeatedly. |
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