MikeSSS
1 kW
Geared hub is a front Bafang G311 on a 24" Townie. G311 is small and light, it has 11:1 gear reduction, helical cut gears, it's very quiet but provides surprising thrust, especially for its size and weight. Speed is limited to about 15 mph for the G311, by the possibility of throwing magnets, because of the 11:1 reduction. Controller is a Grinfineon 20A sinewave. Battery is 10s, 4p, 36v, 10ah, 360wh. Rider weight is 120 lb, water bottle is steel and weighs a couple pounds.
The direct drive is a Aotema brushless front hub, sensorless, capable of about 25 mph. It's not a really big DD hub but the front wheel weighs about 25 lb, with tire. Controller is whatever came with the used ebike I bought. It has an off and on switch on the controller. Battery is 13s, 4p, 48v, 13.5ah, 648wh. Bike is a Jamis Hudson, it's sort of like a Townie. Rider weighs about 190 lb, chain, cable and steel water bottle add a few pounds.
The ride was slow, 8.4 miles at an average of 9.4 mph. At this slow speed, the geared motor should be more efficient than the direct drive. Total weight was almost 100 lb less for the geared hub bike/rider and that bike had lower drag tires than the direct drive bike. There were several mild climbs and descents on the ride. Watt hours use were determined by timing the charge for both batteries, the 36v charged at 2 amps, the 48v at 3 amps. Both batteries were charged to less than full charge, so balancing time did not happen for either battery. The 48v battery was charged to 4.0 volts per cell, the 36v to 4.08 volts per cell.
Result: based on charge data, the geared hub bike used 80 Watt hours of charge, the direct drive bike used 96 Watt hours.
Yes, it's sort of apples to oranges comparison, because of the difference in weights, riding styles and tire rolling resistance. But, it seems to me that the geared hub is more efficient but probably not by a lot. Sadly I thought the iphone was left home, it wasn't, anyway I didn't use Strava so I don't know the elevation gained, but think it was about 200 ft. Using that elevation gain and estimated total weights of bike + rider + stuff, gives 12.4 Wh and 19.6 Wh of elevation gain for geared hub and direct drive. So, the direct drive bike used about 7.2 Wh more in climbing. That narrows the 16 Wh difference to 8.8 Watt hours. Consider the lower rolling resistance tires on the geared hub bike and the difference in Wh use is even smaller. Hmmm, perhaps these hubs are pretty close in efficiency. Close in efficiency even at low speed and low power use. More hmmm.
BTW, 2655 ftlb of elevation gain, gravitational potential energy, is about 1 Watt hour of energy.
The direct drive is a Aotema brushless front hub, sensorless, capable of about 25 mph. It's not a really big DD hub but the front wheel weighs about 25 lb, with tire. Controller is whatever came with the used ebike I bought. It has an off and on switch on the controller. Battery is 13s, 4p, 48v, 13.5ah, 648wh. Bike is a Jamis Hudson, it's sort of like a Townie. Rider weighs about 190 lb, chain, cable and steel water bottle add a few pounds.
The ride was slow, 8.4 miles at an average of 9.4 mph. At this slow speed, the geared motor should be more efficient than the direct drive. Total weight was almost 100 lb less for the geared hub bike/rider and that bike had lower drag tires than the direct drive bike. There were several mild climbs and descents on the ride. Watt hours use were determined by timing the charge for both batteries, the 36v charged at 2 amps, the 48v at 3 amps. Both batteries were charged to less than full charge, so balancing time did not happen for either battery. The 48v battery was charged to 4.0 volts per cell, the 36v to 4.08 volts per cell.
Result: based on charge data, the geared hub bike used 80 Watt hours of charge, the direct drive bike used 96 Watt hours.
Yes, it's sort of apples to oranges comparison, because of the difference in weights, riding styles and tire rolling resistance. But, it seems to me that the geared hub is more efficient but probably not by a lot. Sadly I thought the iphone was left home, it wasn't, anyway I didn't use Strava so I don't know the elevation gained, but think it was about 200 ft. Using that elevation gain and estimated total weights of bike + rider + stuff, gives 12.4 Wh and 19.6 Wh of elevation gain for geared hub and direct drive. So, the direct drive bike used about 7.2 Wh more in climbing. That narrows the 16 Wh difference to 8.8 Watt hours. Consider the lower rolling resistance tires on the geared hub bike and the difference in Wh use is even smaller. Hmmm, perhaps these hubs are pretty close in efficiency. Close in efficiency even at low speed and low power use. More hmmm.
BTW, 2655 ftlb of elevation gain, gravitational potential energy, is about 1 Watt hour of energy.