Current of 1HP Motor

Thread Starter

shivaaa

Joined Jan 5, 2011
55
what happens if i connect two -12V DC Coil, 250VAC - 10 A- in parallel? Just for a thought?

The current rating wil be added right?
 

jpanhalt

Joined Jan 18, 2008
11,087
It's the starting current that is the problem. Your single-phase motor is running a water pump, so it presumably is starting under load. Relays in parallel will not open and close at exactly the same time.

You need a contactor rated for 1HP single-phase at 230V. If you don't have that and need to make do, I would put the two largest relays you have in series. That is not to carry more current, but rather as a safety back up. If the contacts on one weld shut, you may still be able to interrupt the circuit with the other.

John
 

Thread Starter

shivaaa

Joined Jan 5, 2011
55
Understood and thanks..

Can you give me some more idea how can i do this? as u mentioned i dont have a contacter. any other way to do this?
 

jpanhalt

Joined Jan 18, 2008
11,087
I have used circuit breakers (from a distribution panel) in a pinch. They are not for routine use in this type of application, though.
John
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
For single phase, if you incorporate both efficiency and power factor into the calculation, the results come out pretty close, except for the case of no load. Using the Leeson data for a 1 HP motor, one gets:
Rich (BB code):
Output HP, W(HP)      Actual A     Efficiency    PF           Calc. A   
     187 (0.25)             3.95         0.491      0.426         3.87
     373  (0.5)             4.44         0.635      0.583         4.37
     560 (0.75)             5.13         0.685      0.694         5.12
     746  (1.0)             5.99         0.705      0.766         6.01
    1119 (1.5)              8.28         0.684      0.839         8.49
John
Code dictates that one shall use nameplate data, or calculations for the specific motor, failing those, one shall use code supplied data.
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
from the Above table, it seems i can use 10A, 230VAC Relay. is it right?
Motor starting currents can be 6 x FLA, so to answer your question, absolutely not. You need a dedicated motor starter which is comprised of a suitable contact and overload protection. Along with that you will need additional overcurrent protection and branch circuit isolation.
 

Thread Starter

shivaaa

Joined Jan 5, 2011
55
Here are my exact Motor ratings I got from the Name Plate,

Max Current - 3.5 A

Volt - 240V

Fr-50Hz

0.37KW

0.5 HP.

also the Motor has a Capacitor rated 10Mfd

Please tell me wat Relay is suitable.

As they mentioned the Maximum current is 3.5A, still i need to have everything mentioned in last message by GetDiviceInfo?

Thanks.....
 

Thread Starter

shivaaa

Joined Jan 5, 2011
55
Thanks.. I will try to buy only Relay Rated 1HP, but last time when I went to buy relays i could not see any relay rated in HP except one 6v relay rated 1/8 HP.
 

jpanhalt

Joined Jan 18, 2008
11,087
Here are my exact Motor ratings I got from the Name Plate,

Max Current - 3.5 A
Volt - 240V
Fr-50Hz
0.37KW
0.5 HP.
You may also want to take not that your motor is 0.5 HP, not actually 1 HP. At least that is what the nameplate says according to this post.

John
 
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