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Wednesday, December 9, 2009

Power Usage and Traffic Patterns

After the repair in the last post, I took off all the suspension stuff to take a trip and pickup some stuff posted on, about 8 miles away from the house. Round trip of around 16 miles should be no problem as long as I help by pedalling and don't go too fast, so I'll have plenty of power to get back with a little to spare.

It didn't quite work out that way, though, as there were almost 3 miles of detours. Twice on the way there I ran into construction that wasn't going on when I last was in the area, where large areas of streets were blocked off that I needed to go thru to get to where I would cross to the next area.

Because of the layout of the city, there are often places where the grid of streets does not continue normally--it is broken up by parks, walled-in apartment complexes and housing areas (that have only one or two inlet/outlet roads, and seemingly never in the direction I must pass thru), and acoustic walls on some streets that have a lot of traffic next to residential areas. Those walls have few breaks for roads or paths so it can be tough to get around them without significant detours.

I plan my trips so that I won't encounter any of those areas, wherever possible, but when I'm forced to detour I may end up having to go around more than just the original detour area because of these other large "blockages". Sometimes I may be able to get around them a shorter way by going on a major road instead, but those roads (due to the traffic constraints of these blockages, primarily) are usually quite congested with traffic at 45 to 50 MPH (even when they are marked 40 or less), and are usually only two narrowish lanes each way, with no room for a bicycle to ride to the right of traffic--I'd have to ride *in* traffic, and would almost certainly
cause someone enough frustration along the way that they'd do something irrational and stupid, and both of us would regret it (assuming I lived to do so).

So I go the long way around when forced. If it is not that far on one of those major roads, and there are gaps in traffic, I may be able to get most or all of the way around before traffic catches up, but that is unusual. If it's really short, 1/8 mile or less, I'll walk the bike on the sidewalk, if there is one. Almost never is it that short.

Thus I end up with detours such as that tonight, using up more power than anticipated. This time it was a serious problem, as I had a car battery and some other stuff to haul back with me, and needed the power to move it all. I'd also planned to stop for some other things along the way, but ended up not being able to due to time (had to ride MUCH slower than usual, around 9 to 10MPH for most of the trip after the first detour, so I could save power).

All in all, the trip was 19.069 miles, and took 2 hours and 5 minutes of actual travel time, not counting several long stops I made on the last 1/4 of the trip to let the batteries rest and get a little more power. I'd guess it actually took more like 3 and a half hours, all told.

I did hit 20.0 MPH at one point in the trip, probably on the downhill of one of the canal tunnels. 9.1MPH was the average, though. The odometer hit 931.0 miles as I pulled up into the driveway.

When I left, the batteries were at 40.5V resting, and 34.9V resting when I got back. 31.0V under half load, and 28V if I put it at full throttle, with almost no pull. The lowest voltage noted by the meter was 23.77V! Hopefully I haven't damaged the pack too badly.

I used 14.239Ah on the trip for the motor (not counting lights or turn signals, which are still not wired thru the meter. I'd guesstimate around 1Ah more for the lights, since I did not turn them off during any part of the trip, even the stops, and they take around a third of an amp including the laptop ac adapter and the intermittent use of the turn signals and brake light.

I probably could have gotten more power from the batteries in warmer weather; it was around 50F when I left a bit after sunset, and it was not much above 40F by the time I got back. Three hours later as I post this, it's just at the edge of freezing outside, at 33F. I keep the bike inside so the batteries don't get really cold, but it's often down to 50F in that back room once it gets this cold outside.

The batteries did not feel warm at all during any part of the ride, but I can't tell their internal temperature. Even feeling the post terminals just felt as cold as the rest of the bike. I kind of wish I had had the DMM with the thermal probe with me, but I didn't.

494.3Wh total, for an average of 29.52Wh/Mile. Still in the same ballpark as the short trip measurements with and without a load.

64.89A was the peak this time around, although I did not notice when it happened exactly, it was sometime in the first third of the trip, and was probably climbing the hill out of the canal tunnel. That gives about 2KW peak power usage.

Now I know a lot more about the numbers to watch for during a longer trip, and my range in the "cold".

I am now recharging the pack thru the meter to see what amount of power it takes to restore it to "full". It's about 60F back there right now; the batteries don't feel warm (the charger only outputs 1.8A absolute max, and 1.5A nominal max).

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