novembersierra28 said:
Unfortunately 20Ah is not how much current you intend to pull, it is simply a capacity rating of a particular battery, cell, or pack.
What you need to know is how much current will be pulled out of the battery, both maximum and average. Without that info you might or might not get the performance you want out of a battery pack, or possibly even damage the pack if it's not sized large enough to safely supply that amount of current.
Worst case you can assume the (I think) 300A your controller can pull at maximum, for however long it's spec'd to do that (probably 10 minutes or less), and then whatever it's sustained current rating is. That is, assuming your controller will shutdown at overcurrent or over temperature.
It also depends on what speeds you expect to get to and maintain, because that will determine part of the power demands, as well as how long you have to maintain those demands and how long your pack has to last (assuming you get no chance to recharge at the other end of any particular trip--if you can always recharge at the halfway point, you can size the pack for 10 miles).
So if you were to use cylindrical A123 cells to make the pack, lets assume 5C for them as max output current (I can't recall what they actually can put out safely, so all these numbers are rough guesstimates), and that they are 3Ah each. That means that each cell can output 15A max (but could only do so for about 12 minutes to total depletion (which might damage the cell). Maybe 8 minutes to a safe LVC.
Even just saying that you needed it only for 8 minutes, assume you need the ability to put out 300A, you'd need at least 20 cells in parallel. If you need that current for longer than that (in total, not necessarily all at once), you need to double (or more) that number.
Then 3.3V for the unloaded cell voltage. That's 11 cells in series.
So at minimum you'd need 220 (20 x 11) cells. You might need 440 or more, depending on the actual current consumption of the system in use as you travel, to get your desired range.
Because the Cell-man prismatic versions have a much higher c-rate and capacity, you don't need nearly as many of them.
You face similar issues with any pack you wish to build out of small cells. Larger cells simplify things somewhat.
but first, I gotta fix this freewheel sprocket problem. There's no turning back. it still partially works without any bearings inside the freewheel, but for how long is anybody's guess....I need a tough freewheel with a 7/8 bore and 3/17 key, I'm charging the batteries up and will test everything this evening when all three are charged up.
i think I need to machine the Etek's shaft down to 5/8, as this opens up a lot of options to fit on freewheels...etc... would you agree?
The freewheel sprocket on the motor shaft just allows you to pedal without the motor turning, right? So if you needed to, you could indeed fix the freewheel into a single piece, as long as you do not need to pedal without motor power.
To remove the freewheel, you might see if you can find someone you know (or a hardware store) that will let you use a 3-jaw puller.
