“Drive” Down the Cost of Power Transmission

We have seen that high- and premium-efficiency motors can provide dramatic savings over the course of a year's electrical consumption. However, the transmission elements, such as gearboxes, belts, and chain drives are often even more important to conserving energy efficiency."Look what happens when you connect a high- efficiency motor to a V-belt input shaft, a worm gear, and a V-belt out...
By SEW-Eurodrive November 1, 2001
Sections:
Energy and Cost Savings
Recommendations

We have seen that high- and premium-efficiency motors can provide dramatic savings over the course of a year’s electrical consumption. However, the transmission elements, such as gearboxes, belts, and chain drives are often even more important to conserving energy efficiency.

“Look what happens when you connect a high- efficiency motor to a V-belt input shaft, a worm gear, and a V-belt output shaft,” Jan Lindholm, a SEW-Eurodrive Industry account manager, told us. “The motor has an efficiency of 90%. But when you add those drive elements to it, the efficiency drops to 64%. Replace the worm gear with a helical gear, and the overall efficiency rises to over 69%.” (See Comparison chart).

“However,” Lindholm told us, “if you can eliminate the two V-belts, replacing them with a hollow shaft helical gear, you boost the efficiency quite significantly. I like to show our customers that you can use a normal motor with an efficiency of 86.5% in combination with a hollow shaft helical gear and end up with an overall efficiency of 84% (Example #4). That’s 20 percentage points higher than Example #1: the high-efficiency motor that’s attached to the two V-belts and the worm gear reducer.”

Energy and Cost Savings

How do these percentages translate to dollars and cents? Let us say the motors in question are 7.5-hp models running 24 hours per day, seven days per week. Within two years, Example #4 will have saved nearly $2,000 in overall costs over Example #1, including purchase cost and power consumption. (Figure 1)

Comparing energy costs over a 10-year period, Example #4 will save over $9,000. (Figure 2). $9,000 in energy savings from a single-motor drive system represents a substantial return on investment.

Recommendations

“I like to recommend hollow shaft helical gears,” Lindholm told us. “This is a product we have offered for a long time. Worm gears are good reducers but they have much lower efficiency than helical gears. And the efficiency of a worm gear is not constant. A worm gear can have 60% to 65% efficiency at 1700 rpm, but only 40% to 45% efficiency at 100 rpm. Other factors must be taken into consideration, of course. Worm gears can handle shock load better than a helical gearbox. Many times, the selection of the reducer is based on space limitations. For a conveyor, a right angle reducer is preferred because it can be installed without any protruding parts. We can help with those decisions.”

SEW-Eurodrive sales engineers can offer valuable expertise in the integration of all the components in your drive package. Call 1-800-601-6195 or visit www.seweurodrive.com .

Comparison of various reducer types with and without external transmission

Example 1 Example 2 Example 3 Example 4
High-efficiency motor 90.20% High-efficiency motor 90.20% Premium-efficiency motor 91.00% Normal-efficiency motor 86.50%
V-belt input shaft 90.00% V-belt input shaft 90.00% Nema adapter on input shaft
Worm gear reducer 87.00% Helical gear reducer 95.00% Helical gear reducer 95.00% Hollow shaft helical gear reducer 97.00%
V-belt output shaft 90.00% V-belt output shaft 90.00% V-belt output shaft 90.00%
Overall efficiency 63.56% Overall efficiency 69.41% Overall efficiency 77.81% Overall efficiency 83.91%