Small Steps

Battery Woes
I called the battery warehouse and asked about what models might be available with a higher maximum discharge rating. I had to describe a couple times what exactly I was asking for. The gentleman on the other end of the call only knew that batteries were usually rated by a 20 hr amperage. He suggested I check out the SLA 1185/1175 and DCM0075. I did, and as expected, they are for far more A-hrs than my current battery, and cost almost twice as much too. I don't think he ever quite realized what I was asking him. I doubt I will call and ask again, because I always get that guy.

Making matters worse, I rechecked the spec sheet for the DCM0035 I bought a week ago. It shows a small table that compares discharge time to A-Hr capacity. Discharging the battery at a continuous 1.7 amps will yield 20.1 hrs of power, while a continuous draw of 17 Amps will yield only 1 hr of power. Of course, if I'm cruising at, let's say, 45 amps, I'll have about 15 minutes of that kind of power.

Seriously
Distance: My commute is 3 miles one way.
Time: It usually takes me 12 minutes (.20 hrs) to get to work.
Velocity: I usually travel at 45 mph (which might pull only 45 amps on the Lifan)

I can find my average velocity with:
Velocity = Distance / Time
My velocity is then 3 miles / .20 hrs = 15 mph.
This is my average velocity over the course of the entire commute because the time variable includes the time spent at a stop, accelerating, cruising, and decelerating.

I can find my theoretical minimum commute time with:
Time = Distance / Velocity
My minimum commute time is then 3 miles / 45 miles / hour = 3 hours / 45 = 4 minutes.
This assumes no change in velocity, though, which is why it is theoretical only.

I can find a theoretical maximum range with:
Distance = Time * Velocity
A 45 Amp draw implies a discharge time of 15 minutes = .25 hours.
My maximum range is then .25 hours * 45 miles / hour = 11.25 miles

These are just estimates. If I later find that the bike actually only draws about 38 amps at 45 mph, then the numbers instantly change. A 38 Amp draw implies 30 minutes of power for the DCM0035. Thus, I would instead have a maximum range of .5 hours * 45 mph = 22 miles! Considering it is a theoretical value, 22 miles isn't bad if you ask me.

Likewise, if I were headed up a hill, into the wind, and gained 50 pounds overnight, the motor might pull 70 amps, just to maintain the same 45 mph. This would give me a cruise-time of 10 minutes, and therefore an estimated minimum range of 7.5 miles. This means I could make it to work and back fairly easily, I think. Maybe there isn't anything wrong with this battery after all. Later on, I'll be able to charge my batteries at work, so that will help in extending their life and my actual range.

The point:
One simple formula can tell you a lot about the performance you can expect from such a machine. Even if some results are theoretical, it doesn't hurt to know absolute minimums and maximums because at least it can't get any worse than that. =) No matter what you're trying to calculate, it's important to treat the values correctly and consider closely what each variable you've specified really includes or excludes.

Question:
I wonder how much regenerative breaking really does help. I mean, how much can it really "re-charge" the batteries, based on speed and regenerative efficiency? I wonder if exceeding the maximum charge rate of your battery pack when using regenerative breaking is analogous to over-revving your manual transmission when down-shifting. =0

-Colby