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Motor Starter
- Thread starter dblyle
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Just the motor starter itself? If so, what kind of starter? Electro-mechanical or solid state (soft starter). If it's a soft starter, is there a bypass contactor?
Assuming you meant a basic electro-mechanical Across-the-Line starter with a cheap bimetal overload relay, the only appreciable heat it will produce (if sized properly) is the dissipation of the heater elements, the contact resistance and the coil consumption. Heater elements are typically about 9W per phase, so 27W. Contact resistance is typically no more that .005% of the motor power. So at 40HP worst case (although unlikely) you are at about 30kW, making your contact resistance losses be around 15W. The contactor coil consumption varies greatly between manufacturers as a percentage of each other, but not much anyway so probably a worst case scenario is around 30W there. The aggregate total is going to be probably no more than 80W dissipation if everything is sized properly.
The one big caveat is that the contact resistance varies greatly with loading once you get up to the limits of the device and based on the contact wear over time. So if your contactor is a bit under sized or is getting old it will put out a LOT more heat. That's why we say the contacts "burned up" when it quits working. The heat can get so bad as to melt the contact materials.
Assuming you meant a basic electro-mechanical Across-the-Line starter with a cheap bimetal overload relay, the only appreciable heat it will produce (if sized properly) is the dissipation of the heater elements, the contact resistance and the coil consumption. Heater elements are typically about 9W per phase, so 27W. Contact resistance is typically no more that .005% of the motor power. So at 40HP worst case (although unlikely) you are at about 30kW, making your contact resistance losses be around 15W. The contactor coil consumption varies greatly between manufacturers as a percentage of each other, but not much anyway so probably a worst case scenario is around 30W there. The aggregate total is going to be probably no more than 80W dissipation if everything is sized properly.
The one big caveat is that the contact resistance varies greatly with loading once you get up to the limits of the device and based on the contact wear over time. So if your contactor is a bit under sized or is getting old it will put out a LOT more heat. That's why we say the contacts "burned up" when it quits working. The heat can get so bad as to melt the contact materials.
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