Sorry I assumed you were planning the dual voltage setup for a dual motor bike. It’s a good question if dual motors would benefit a long-distance bike. However there are plenty of discussions about dual motor vs. single motor bikes on the Endless Sphere forum so I won’t go into that. As for dual voltage, it’s not true in my experience that a low voltage setup has higher torque. A higher voltage setup has both higher torque and higher speed, but is less efficient. Also with a high voltage setup one tends to go faster because one can, and so uses more wh per mile and also incurs more wind resistance.

So if you were to make a dual voltage system it wouldn’t be low voltage for hills, high voltage for flats. It would be low voltage for long-distance trips and high voltage for carrying groceries back from the grocery store down the hill.

A switch for changing voltages on the fly would be fun to make, but it might be easier to just re-wire your battery pack before each trip after deciding if you’re going on a long low wh/mile trip or a short high wh/mile trip. I use two 36v batteries that connect either in series or parallel depending on my needs. I use special Anderson harnesses I created as described in this post:http://bikes-as-transportation.com/my-diy-sla-trip-batteries/. When you change the voltage of your dual-voltage system it is also a good idea to change the low voltage cutoff using a Cycle Analyst. If you forget this step and leave the LVC at 32v when using 72v batteries you risk draining the batteries too far and damaging them. Some batteries have a battery management system that might prevent such damage.

Let me know how it works out!

-Laurence

A 100 miles in 5 hours is an amazing achievement. At that speed, I suspect that there was not much assistance by human power. In my case, my 90 mile trip (150 km) was done at about half your speed (8 hours) with an estimated electrical consumption rate of about 8.4 wh/mile (800 wh charge) which is less than half your rate. However, I forgot to mention that I probably added another 500 wh of pedal power and cheated by adding another 150 wh of charge during a lunch break where I could plug in for an hour and half. If I factor this into the equation, I get a total consumption rate similar to yours, about 16 wh/mile. Of course, there are other factors in the comparison not considered like: wind friction, total mass of bike and rider, and terrain. In my case, more than half the trip was done on old British railway lines built in the 1800s, converted to very flat bike paths which really help reduce the consumption rate..

Back to the dual battery pack versus dual motor options, I prefer not to add a second motor to the front wheel because: a) it adds more weight without adding more energy, and b) my front forks might get bent with the extra torque unless I go with a smaller wheel size. It’s easier for me to just add battery packs and switches which I will do over the winter.

Another idea for adding a second motor would be to start with a recumbent bike that has 3 sprockets (pedal, intermediate and rear wheel sprockets). You could replace the intermediate sprocket with a second motor by fixing the hub and allowing the motor to spin the sprocket in the same direction as the pedal sprocket, The second motor could then assist the rear wheel motor at the appropriate selected gears, In this way, you still would have your pedal sprocket and the recumbent still qualifies as a bike.

Any thoughts on this?

Al

Sounds like you have quite the setup. I recently converted an old touring bike to an ebike and took it around the lake here (about 100 miles) in five hours. I was packing 2,160 watt-hours but only used 1,839. Average speed 20.7mph, 18.1 wh/mile.

Higher voltage batteries can give you more acceleration and speed, so you’re right that if one of the motors in a dual drive bike can handle a higher voltage you might consider two battery packs. What might be simpler though is using a single battery pack and choosing two motors that are similar in size or limiting the power of the smaller motor.

Paragraphs.