If you use that ebikes.ca calculator, set the controller current limit well above what the motor can handle, you will see maximum power at close to 50% of maximum RPM, this is at full throttle, and current only limited by the motor resistance. At that 50% speed efficiency is also around 50%. Lowering the controller current limit setting shifts the maximum power point and efficiency higher, up to 60 to 75% as you say. So, it all depends on the controller. My "250W" ebike draws 675W at 15km/hr, and on the flat it does 30 km/hr. the 1kw ungeared Hub motors do better efficiency because they are not running at the un- current limited maximum power point. The maximum power allowed here is 300W, Europe is 250W.
-----Original Message----- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV Sent: 31 May, 2017 4:29 AM To: ken; Electric Vehicle Discussion List Subject: Re: [EVDL] Most efficient hub motor for 20" wheel ken via EV wrote: > I have a Bike E with a 20" rear wheel I want to put a 36 volt at 500 > to > 1000 watt hub motor there but I want it RPM effecint for 20 mph. > where do i find such a wheel at reasonable price. I also have a Bike-E, and have thought of electrifying it. But its handling is such that I wouldn't feel comfortable with such a big motor. Keeping it down to 20 mph is a good idea! Note that PM motor efficiency tends to peak strongly near full power. At light load, they are much less efficient, because you have full magnetic losses all the time. So it may be better efficiency-wise to use a smaller motor and gearing to achieve the best speed/efficiency tradeoff. My Bike-E has a 7-speed rear hub, and of course a very long chain. My thought was to mount the motor under the seat, with a freewheel sprocket to the chain. That way, it gets the benefit of the gearing. The freewheel means you're not spinning the motor when it's not being used while pedaling. -- Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius, and a lot of courage, to move in the opposite direction. -- Albert Einstein -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)