hub motors for power

[macka]

Brad,

you had mentioned that hubmotors make great generators, how would I go about hooking one up to be a part time generator part time power unit? I was thinking that 4 wheel drive would be cool on my buggy, but I don't need it all the time, just for certain terrain. I'd like to increase the range of the buggy if I go electric only.

[AtomicZombie]

Unless more than half of your trip is all downhill, adding regen to such a vehicle would not be of any use. You would also need lithium batteries for that.


Brad

[macka]

So even though the front wouldn't be powered full time, it would be spinning all the time. I can't harness that by having a switchout of some sort? Sorry for being aggravating I can't get my head around it.

[AtomicZombie]

Sure, you could harness the power of a generator, but at much more cost than it would be worth on a human powered vehicle.

Think of it like this...

Let's say you worked at NASA and could get your hands on a generator and battery pack that would put at least 75% of the power used back into the batteries. Let's also say that you are an elite athlete that can ride around all day producing 300 watts.

Now you drop on your NASA built hubmotor and battery pack that can propel your cycle for one hour using 500 watts to the motor. As long as your battery pack is healthy, you can wizz along delivering 800 watts to your vehicle under electric and human power.

All of a sudden, you realize that your trip was too far and your batteries are depleted. No problem you say? You can flip the switch into generator mode, right?

Wrong.

What would be the point? You will now have to pedal against the drag of the generator, which at best will put only 75% of the power back into the battery bank. Why not just switch off the motor and deliver all of your 300 watt human power to the wheel?

Even if the motor/generator was 100% efficient, you would still be wasting your time as it would be nothing more than a delay in power transfer. Pedal twice as hard to get 1/2 in return.

Regen is another story though. On super long commutes with a lot of hills, the tiny gains over a few hours could start to add up as energy saved, although it will be a VERY small amount.

So basically, pedaling a generator for gain is completely pointless unless exercise or pure output is your goal. If a wheel/generator could actually put work back INTO a system, you would have invented the holy grail...

Free Energy!!!

This will never happen. Well, not unless you sneak an extension cord into your neighbors outside outlet - this could be considered free energy.

Brad