ECN Forum Forums General Topics of the Trade General Discussion Area How hot should motors run

Yes it is. If the motor is not overloaded. Have you checked the current? Rolled steel motors like yours get hot. They are supposed too. The thin rolled steel gets much hotter than a cast iron frame. Marathon makes a good motor. Have a beer and enjoy your pool.

What makes you think your motor is not efficient?

It can't be that efficient in pumping water if that much energy is coming put as heat.

Current is around 4.8 @ 251v

Greg, don't confuse the motor casing temperature with electrical losses due to inefficiency. The emissivity of a smooth-drawn steel motor casing will be very low, so that the amount of heat energy actually radiated will also be low. Small motors have proportionally much lower surface areas per hp than larger models, leading to higher surface temperatures as the motor sheds the inevitable electrical and mechanical losses as heat. Cast-iron shells do run slightly cooler because the surface is rougher, emits better and can have cooling fins easily cast-in. At 1 hp brake, on a pump = near constant torque, you should be getting losses of around 40-75W, perhaps 90-95% efficient. 4.8A at 250v looks about right/a tad high for a 1 hp motor, and I'd expect a sealed type [ no venting] to be fitted in a pump application, for obvious reasons.

The thing to look out for is that the water flow through the system is not restricted unduly, such as by partly closed valves, choked filters etc., as this can overload the motor and damage the turbine by cavitation.

The best test is to use your nose. If it ain't stinking of burning plastic, don't fix it!

Alan

Several irrigation pumps I have (5 hp - 240V) all run 190F in enclosures baking in the sun.

I replaced the filter and balanced the system again. That improved the head and I may have actually dropped the temp a degree or two but I still don't like things running that hot.

Greg, a friend of mine in Jacksonville contacted me two weeks ago with a similar problem. The motor ran OK, but was so hot to the touch that he burned himself. He had recently replaced the motor and it turns out that it had a shorted winding to ground, right out of the box. Half of the field became a great big heating element while there still managed to be enough of a field to allow it to run.

I'd check for continuity from L1 and L2 to the frame ground with everything disconnected. Depending upon where the shorted winding is, it may not offer enough resistance to overload the circuit. It might provide for a nice heater though. Of course, an Amprobe on each leg should tell you the story as well. If both readings aren't identical, then you have a leaking winding.

My friend took his motor back to the pool supply place and they replaced it promptly and stated that they've had quite a few of these returns lately. Maybe you got one of these outdoor heaters too?

That should trip the GFCI but I will still look.

There was no current on the EGC or the pool bonding wire.