Torque Vs. HP required for ST head

[Doug]

Its not realy fair to compare old electrical equipment to new stuff and the touch test for heat doesn't actualy reflect how efficient something is.

I recall about 15 years ago I installed a a group of large electric pumps in a local hospital. These were ne high efficiency type motors replacing some very old Nema U frames. The pay back in efficiency VS initial cost of the new equipment cost effective. Trouble is modern high efficiency motors run very hot to the touch and create a lot of electrical noise. These motors were later replaced with cooler running, quieter less efficient T frames because the Hospital maintinance staff just didn't trust or believe me this was normal.

An ST head has a massive cooling fan and ability to move a lot of air.
The core is sized relative to its cooling capacity and rating.
Wire size is what the maker could get away with based on hot spot temperature of its insulation type.

An ST is what it is a head built on the cheap. If the air gap was tighter and the maximum use of availlable slot fill was made it would probably make a noticable difference.

Oversizing a head thinking your going to be more efficient is wrong. As your load decreases the rest of your non copper losses remain the same. A fully loaded 5 kVA unit would probably be more effeicient than a 7.5 only loaded to 5000 watts.

Doug
 

[Andre Blanchard]

Its not realy fair to compare old electrical equipment to new stuff and the touch test for heat doesn't actualy reflect how efficient something is.

Just to be a PITA, the amount of waste HEAT created is a very good reflection of how efficient it is.
The temperature of that heat however is not, like you say below it all depends on how fast the heat can be dumped.

I recall about 15 years ago I installed a a group of large electric pumps in a local hospital. These were ne high efficiency type motors replacing some very old Nema U frames. The pay back in efficiency VS initial cost of the new equipment cost effective. Trouble is modern high efficiency motors run very hot to the touch and create a lot of electrical noise. These motors were later replaced with cooler running, quieter less efficient T frames because the Hospital maintinance staff just didn't trust or believe me this was normal.

An ST head has a massive cooling fan and ability to move a lot of air.
The core is sized relative to its cooling capacity and rating.
Wire size is what the maker could get away with based on hot spot temperature of its insulation type.

An ST is what it is a head built on the cheap. If the air gap was tighter and the maximum use of availlable slot fill was made it would probably make a noticable difference.

Oversizing a head thinking your going to be more efficient is wrong. As your load decreases the rest of your non copper losses remain the same. A fully loaded 5 kVA unit would probably be more effeicient than a 7.5 only loaded to 5000 watts.

Doug
 

The oversized unit is not going to be as efficient as a properly sized unit but I hope given the quality of the ST units that the lower stresses will make it more reliable.

[dweber01]

My genset is for standby, a few lost watts don't bother me like it would if I was running 24/7, I never suggested oversizing the head was more efficient, just better at starting a heavy load. I wonder what percent of efficiency I pay for that?  To be honest I bought the 12KW head because I wanted to be sure it was large enough in case I find the time and a used turbo to play with, thanks to somebody who did that already for the idea.

Dan