Soft Starters for Single Phase Submersible Pump

[natkingcole]

Hi Everyone,
Has anyone ever encountered an undersized start capacitor (from manufacture) for a single phase pump???

I would like to integrate some sort of soft starter for my submersible pump which pumps rain water to a tank. Is this possible??....

Thanks,
NKC

 

[Lucien Nunes]

Presumably the pump is intended to start direct-on-line. Is there an actual problem with doing so, that you want to overcome by using a soft start? What size pump is it?

I am not sure I have seen an incorrect size capacitor fitted to a motor (I have on some PSU modules) but low capacitance is a known failure mode of some types of film cap. I suppose it's possible for a new or apparently new cap to be significantly out of tolerance by the time the motor is commissioned.

 

[natkingcole]

Presumably the pump is intended to start direct-on-line. Is there an actual problem with doing so, that you want to overcome by using a soft start? What size pump is it?

I am not sure I have seen an incorrect size capacitor fitted to a motor (I have on some PSU modules) but low capacitance is a known failure mode of some types of film cap. I suppose it's possible for a new or apparently new cap to be significantly out of tolerance by the time the motor is commissioned.

I just want to minimize stress on the pump...Start the pump slowly i.e....The pump size is 850W.....My calculation for capacitance came to 17.8microF (Minimum) However, fitted cap was 16microF.....I could be wrong....I used Capacitance energy formular...

 

[Lucien Nunes]

The ideal run capacitor for a given motor depends on a number of compromises. You can make a good estimate from the requirement in VArs but the manufacturer is likely to have selected the value after testing for various parameters including operation over a range of load torques, line voltages, temperatures etc and possibly included effects such as minimising torsional vibration and harmonics.

A soft start might reduce mechanical shock load but is it really that serious on a small submersible pump? I'd keep it simple personally and stick to the original capacitor value.

 

[natkingcole]

The ideal run capacitor for a given motor depends on a number of compromises. You can make a good estimate from the requirement in VArs but the manufacturer is likely to have selected the value after testing for various parameters including operation over a range of load torques, line voltages, temperatures etc and possibly included effects such as minimising torsional vibration and harmonics.

A soft start might reduce mechanical shock load but is it really that serious on a small submersible pump? I'd keep it simple personally and stick to the original capacitor value.

ok.....Noted...Thanks bro....

 

[DPG]

I just want to minimize stress on the pump...Start the pump slowly i.e....The pump size is 850W.....My calculation for capacitance came to 17.8microF (Minimum) However, fitted cap was 16microF.....I could be wrong....I used Capacitance energy formular...

With the tolerances of those types of cap I wouldn't be worrying about accuracy to that degree.

 

[natkingcole]

With the tolerances of those types of cap I wouldn't be worrying about accuracy to that degree.

ok...is it better to use plastic-packaged capacitor or the metal one?

 

[Marvo]

ok...is it better to use plastic-packaged capacitor or the metal one?

Often run capacitors are in a metal can because it aids with their cooling but in many cases it doesn't really matter as long as the voltage and duty cycle specs of the new capicitor are same as or better than the original spec. It's easiest to just stick to a similar form factor as the original so you don't need to worry about it physically fitting in the enclosure or under the retaining strap.

 

[natkingcole]

Often run capacitors are in a metal can because it aids with their cooling but in many cases it doesn't really matter as long as the voltage and duty cycle specs of the new capicitor are same as or better than the original spec. It's easiest to just stick to a similar form factor as the original so you don't need to worry about it physically fitting in the enclosure or under the retaining strap.

Ok...The original was was in a plastic package...And it expanded a bit..and then probably burnt....What could be the cause??...what is the the typical lifespan of such capacitors when used in this application??....It is the reason why I am resizing it....Deploy one thats a bit bigger....Your thoughts???

 

[Lucien Nunes]

Capacitor life varies widely with temperature, working voltage and voltage spikes that can cause progressive damage. Premature failures of motor-run caps are quite common and they are often the first component to fail in a machine. A good insurance policy to increase the useful life of a cap is to specify a higher voltage rating than needed, although it will tend to be physically larger.

 

[Marvo]

Also short cycling (rapid and prolonged on/off cycles) of the pump could drastically reduce the run capacitor lifespan.