jamesp
Cave Dweller
Member since October 2012
Posts: 36,171
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Post by jamesp on Jun 23, 2016 23:58:07 GMT -5
Nice tumbler. For the sake of argument, if the "load" is 6 amps, hp doesn't make much difference. 1/3 hp will draw 6 amps, 1/2 hp draws the same. Only difference is lower hp may be maxed and larger at 2/3 full load. How does this sound John ? "ESTIMATING HORSEPOWER Constant load: This is the simplest case. Determine the load from the nameplate on the driven unit, or, if this is impractical, measure the torque required to turn the load. Choose a motor for which the load is 75 to 100% of the motor's rated capacity. When the load is steady with a long duty cycle it is safe to load the motor close to its fullload capacity, in the area of 95%. This will optimize efficiency and keep the motor cost to a minimum."
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,171
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Post by jamesp on Jun 24, 2016 8:39:10 GMT -5
Motor manufacturers rarely mention 'no load' amps.
A 1/4 HP motor running no load draws up to half of what a 1/2 HP draws.
But even at no load the motor is still pulling 30-50% of the full load amps.
A 1/4 HP motor has substantially less full load amps than a 1/2 HP motor.
If you are say running one barrel on a multiple barrel tumbler you may be close to 'no load' amps.
There is not much information regarding 'no load' motor operation.
Punch press operations a good example. Many motors running no load till the clutch is engaged. So many motors are on for long periods with out a load. Size motor for 70-95% full load range when loaded.
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Post by johnjsgems on Jun 24, 2016 17:46:12 GMT -5
When I was in HVAC the engineers designed exhaust hoods with fully loaded motors. They made it through the warranty but running 24-7 on the roof over restaurant grills was pretty brutal. A lot of these motors were 1/6 or 1/4 hp. I would replace with 1/3 hp (wholesale cost was less, go figure) and running amps generally ran about 75%. Much longer life than 95%-100%. We had issues with very high ambient temps and extremely low voltages too so that may have factored. I also found but don't know why that severely over sizing motors so they ran pretty much unloaded caused them to overheat. I understand your point about no load motors but I was just mentioning loads are loads. Same load will draw same current. It doesn't take much hp to turn tumblers. My HP 40 lb. tumbler had a 1/3hp. They used same hp motor from 12lb. up to the giant one.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,171
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Post by jamesp on Jun 24, 2016 18:35:26 GMT -5
When I was in HVAC the engineers designed exhaust hoods with fully loaded motors. They made it through the warranty but running 24-7 on the roof over restaurant grills was pretty brutal. A lot of these motors were 1/6 or 1/4 hp. I would replace with 1/3 hp (wholesale cost was less, go figure) and running amps generally ran about 75%. Much longer life than 95%-100%. We had issues with very high ambient temps and extremely low voltages too so that may have factored. I also found but don't know why that severely over sizing motors so they ran pretty much unloaded caused them to overheat. I understand your point about no load motors but I was just mentioning loads are loads. Same load will draw same current. It doesn't take much hp to turn tumblers. My HP 40 lb. tumbler had a 1/3hp. They used same hp motor from 12lb. up to the giant one. Motor design must be a different story in a roof top where the heat punishes them. People have said things about using an 'air over' motor without a fan on a tumbler. One must consider the temperature of the 'air over' the motor. Designed for darn hot air. 1/3 HP do cost less than those 'air over' 1/8-1/6 HP motors. They are tearing buildings down constantly here and scrap yards full of roof tops being scrapped. Lots of fan motors laying around. Fan applications can be brutal, plugged filters and strong winds make for unforeseen load conditions. No load and low load are a similar factor effecting current draw. I found oversized motors to use a lot of current on my tumblers. Have clipped the 1/2 back to 1/3 on the big tumbler and the 1/4 back to 1/8 on the small one. The 1/8 HP turns 35 pounds at 20 RPM, I figured it would get hot and be overloaded, but not so. Current clamp said 70% FL. They have been running over 50 months, half the time with big motors, half with smaller ones. Power meter dedicated in winter months, bill reflects.
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Post by johnjsgems on Jun 27, 2016 10:21:17 GMT -5
Air over is not something you want at any price. Furnace manufacturers save a few bucks by using "air over" motors. They have no built in cooling fan and use the furnace blower air to keep motor cool. You would have to run an external fan to keep motor running.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,171
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Post by jamesp on Jun 27, 2016 20:05:29 GMT -5
Air over is not something you want at any price. Furnace manufacturers save a few bucks by using "air over" motors. They have no built in cooling fan and use the furnace blower air to keep motor cool. You would have to run an external fan to keep motor running. Never had a bit of trouble out of them on my tumbler. Even running in a hot greenhouse all year.
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