Regarding ratings of a relay to power 3HP pump

[Embedded_Geek]

HI,

What should be the ideal rating of a relay so that I can power 3 Horse Power pump without any problem?


Thanks in advance,

 

[phobos1]

lets assume it to be a single phase pump so 3hp = 746*3 watts therefore current is (746*3)/230V A ten amps or over than than relay will do the job

 

[Embedded_Geek]

I did the same calculation and even purchased one. But it seems that the pins are quite thin (diameter). So, my doubt is whether it can hold that much current through it. I am doubting due to the inrush current during starting of pump.

 

[phobos1]

r u starting the pump directly or by a starter

- - - Updated - - -

if not using a starter the starting current will be 6 to 8 times of full load current

 

[Embedded_Geek]

r u starting the pump directly or by a starter

I am not using any starter. My microcontroller controls the latching relay, which inturn switches ON the pump. Could you please give my some link in India where I can obtain the starter. I basically have only little idea regarding the starter.

Thanks,

 

[schmitt trigger]

In the current calculation, you forgot to include efficiency and power factor. The actual current will be higher. According to the Reliance Electric website, a good rule of thumb for single phase motors at 230 v is 5 amps per HP. Therefore you require a continuous rating of 15 amps.

Also..The starting amps of an induction motor are 3 to 5 times the running current.. A normal relay's contacts will fuse after a few starts.

For that reason, power relays, in addition to its voltage/current ratings, show a HP rating.