All Your Green Blog

...Continued from here.

Bad news. This is not a good method for commuting. For the rush of using no gasoline to get to work on two wheels, I'm sticking with a contraption known as a "bicycle." At least for now.

I didn't get as far this time. Even with a real charge, the scooter only got me to the foot of the last bit of the hill. Recall, I use the word "hill" only because it's shorter than "very small increase in elevation over a couple miles". Kilimanjaro, this ain't. And I only got to the start of it. I was two miles from work this time. Pushing that monster that far is an exercise in will power. I was basically wrestling with an oddly shaped 80 pound opponent intent on not letting me get to work, fighting me for every inch of pavement with its magnetically possessed rear tire.

Well, maybe it was just the charge, maybe we hurt the batteries on that first partial charge or something. Maybe it would be fine on the way back. No sir. Half way. Same deal. And this time, I was checking it every couple of hours to make sure the charger still had a sound connection.

What's wrong here? 2.5 miles is so very much not equal to 18. Well, I did some math, and discovered something interesting. Schwinn didn't. Do math, that is. Here's how it breaks down:

The charger is 36 volts at 1.5 amps, or 55 watts. On an 8 hour charge, that's 440 watt-hours assuming it was at maximum current for the entire time (we'll give them the benefit of the doubt, and round up to 500 watt-hours). Now the motor has a peak output of 1000 watts. Now the scooter is actually very inefficient at full throttle, but we'll pretend it's perfectly efficient for ease of estimates. Let's say it goes at full throttle as far as it can. That's 15 mph for as long as 500 watt-hours would last under the draw of a 1000 watt motor. That's a half hour, or 7.5 miles. That's assuming a rider weight roughly zero pounds, on a flat surface, with all the uncertainties biased in favor of the scooter, except the draw from the motor at full throttle.

And what do you get if you feed in real numbers? Why... just about what I was getting out of it! Based on my estimates, the scooter was performing exactly as one should expect it to.

Well, 7.5 is a lot less than 18, so is Schwinn lying? Well, yes and no. The 'no' is because the motor wouldn't likely be drawing the full 1000 watts with a zero pound rider. The 'yes' is because their pants are on fire, and no rider is zero pounds. There are no conceivable real-world scenarios that would produce anything even resembling their claim of 18 miles. None. I'll be calling the manufacturer soon, and we'll pit my amateur physics, electrical engineering, and arithmetic skills against theirs.

But it doesn't really matter in the long run. I never intended to leave this thing stock. I will find a way to use it as a commuter. The "battery pack" is actually three 12 volt lead-acid batteries zip-tied together, so that's the first point of improvement. With new batteries (recycling the old), I'll probably have to build a charger, but I have friends with actual electrical engineering degrees to help with that. And then.... I'll be unstoppable!