yadams said:
Hello everyone, this is my first post on this forum. I was hoping to get some advice on a motor and controller pairing for my CB750 conversion. The bike needs have a top speed of 80mph and a range of 80mi. So far the only component that is locked in is the battery because I already have it which is 72V 105Ah with a 100A discharge and a 3c rating. Hopefully this battery can meet the aforementioned requirements.
Due to packaging constraints and simplicity I also want to go with a hub motor. I was planning on going with the 17in 8000W QSmotor from aliexpress.
The main thing I'm lost on is the controller since I am reading so many mixed things. The Kelly KLS-H Series QSKLS7245H seems like a good option but I don't know if it has good enough field weakening to get the 80mph top speed. The BAC 4000 also looks interesting but it seems like they are hard to get and a nightmare to tune. Honestly I feel like I'm just not aware of all the options so if anyone has suggestions for the motor or controller I would love to hear them.
80 miles of range at what speed? Without extreme aerodynamics 80mph chews thru battery capacity in a hurry.
If the BMS of your battery limits you to a maximum of 100A, then you can forget about 80mph. Not only is that not enough power from the battery to get to 80mph without some kind of aerodynamic shell, but 72Vx100A max power draw from the battery will result in craptastic performance with such a heavy bike. Hell my son's sub 100lb ebike draws a peak of 125A at 74V nominal, and while it has quite respectable acceleration, it's geared (via wheel diameter as are all hubmotors) to a top speed of only about 60mph.
Fun acceleration that meets or beats that of smoke belching transport with our home built electrics is fairly easy, but matching the top speed or range of a high performance ICE machine is difficult, especially starting with a frame that's not designed specifically around your given battery.
Before giving good advice we really need some more information such as:
- What cruising speed for your range requirement as noted above.
- Terrain and type of riding. Flat, hilly, or mountainous, along with lots of steady-state cruising or more stop-n-go city use.
- What kind of all up load do you expect (weight of donor bike without motor, battery weight, your weight, expected cargo)
- What is your goal? Something fun to ride...an around town errand runner with good range...an economical long commuter that save you a bunch of money and outright performance is unimportant.
One last thing. Start preparing yourself for a smaller diameter wheel on the rear, and how to make it look good on your bike. The reason is that even the biggest hubmotors perform better and more efficiently in the smaller size wheels. That's why it's relatively easy to find scooter shaped electrics running 13" tires that have top speeds of close to your 80mph desire, but very difficult to find one (if not impossible) running a hubmotor in a 17" wheel as set up from the factory. I have multiple bikes that meet and exceed your performance desire, but all run a 13" scooter rim, so the 5" wide tire has an outside diameter of less than 20". I have only one running a 16" rim that does better than 80mph, but that's on a sub 150lb bike including the battery. With a big 273QS motor you can probably get away with a 16" rim as long as you look for the lowest profile tire that will fit, but your motor will still be happier and more efficient in a 13" rim.
