Shoeshine wrote:...If I got a scooter off of CL and wired in my 12v battery bank, The motor controller from the scooter would just feed in voltage from 0-12v in the lower range of the throttle?...
The motor would be fine, but not necessarily the controller.
The controller will be expecting to be supplied with the specified supply voltage. As the battery depletes its charge, its voltage drops, according to its performance curve. Different curves for different types of batteries. Controllers are designed not only for a target voltage & current, but also for the type of motor they'll be driving and the type of battery supplying. Each controller will have a minimum voltage it must have for its circuits to work, and enough over that to provide a voltage to the motor. So if your controller expects a supply of 36 VDC, but needs a minimum 24 VDC for the controller to work, then it will not run with a 12 VDC battery, even though the 36 VDC might be controlled down to 8 VDC for driving the motor at lower speeds.
And, as Gyre points out, although it will work, each motor has its best efficiency point. So using a motor that will drive the scooter to say 30 mph, but moving that same weight at 5 mph, will use more power than an optimal motor at 5 mph but with a top speed limit of 7 or 8 mph. But it will work.
That said, a motor designed for a top speed of 20 or 30 mph, geared down using bike gears to a top speed of 8 to 10 mph, would put you in the ball park of good efficiency at 5mph, with the bonus of likely being able to pull a good load.
And I don't know of any systems designed for 5 mph, except for some golf cart types, which are usually actually designed for 20 mph, but with a limiter added on the controller for sale in certain markets or applications. Many e-bikes are not efficient in the speed range they actually used in for the same reason: they're limited by the controller (set to meet laws in that jurisdiction) to a given max speed, but the most efficient speed for the motor is above that. But the good ones are efficient enough, just not optimal; so your battery pack may provide a range of 24 miles instead of 30 miles. Although the high-end battery packs are expensive, buying more pack is cheaper than a very expensive motor & controller optimized to your exact application.
Shoeshine wrote:... I was just hoping that the collective wisdom here might give me a shortcut. I'm all about trying shit.
Was also hoping that I might get a few pointers from folk who had tried these things before me. eliminate the dead ends. save myself afew bucks in prototyping....
It's just that there are so many ways to do it and many variables for each.Gyre's explanations are just barely touching the top of the various subjects you'd have to acquire knowledge of in order to predict a successful outcome.
So, you're faced with possibilities of:
- go and acquire a lot of knowledge (way more than one would think)
- buy/copy something known to work at that speed & weight range that has already been engineered by someone else
- grab something cheap and easy, and hook it up and see what happens (I'm assuming you have enough knowledge of electricity to properly wire & manage these drive currents safely).
I used a cheap brushed motor with a variable range controller to ensure that the voltage curve of my battery pack stayed fully within what it will work with, so I can limp home if I'm pushing the limit. viewtopic.php?f=286&t=54678&hilit=bike+motor#p812180
This is not
the best solution, but for many applications it is a working solution.
I see the controller I got is up in price, but it comes with a throttle twist grip.http://tncscooters.com/index.php?route= ... uct_id=188
They have the motor at 24 VDC and 36 VDC, both at 250W and 450W.
Bracket for mounting on a bike. http://tncscooters.com/index.php?route= ... uct_id=499
The 24 VDC motors would have the best chance of working well with 12 VDC.
I'm running 48 VDC from my LiFePO. I should see what that controller does when supplied with 12 VDC, and what voltage the motor is getting at 5 mph and when towing.
It's very easy to spend a lot of money on the quality parts. But, before you do, make sure they're the parts you need, or you'll just end up buying something else later.