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Friday, December 11, 2009

More Power Usage Data

The day after the trip in the last post, I took another trip in that general direction, the 11-mile-one-way trip where I recharge at the destination.

The first leg of the trip was 11.298 miles, about 48 minutes time actually moving (VeloAce does not count total time, only time in motion), with end odometer reading 942.3 miles.

It used up 9.059Ah, 328.8Wh, for around 36.3Wh/mile.

Peak amps was 77.57A, 29V pack sag, 37.59V pack end voltage, and 2437W peak.

Recharge at destination gave back about 9.4Ah.

Return leg was same distance, same trip time, using 9.28Ah, 327Wh, 2402W peak, 36.48V pack end voltage, 27.27V sag. End odometer was 953.6 miles.

I forgot to write down the data from my grocery run the next day, which was about 2 miles.

My trip to and from work the next day, around 5 miles total, with no recharge until returning home was 960.8 miles odometer total for 151Wh, 4.379Ah, (30Wh/mile). 97.5A peak, 2915W peak.

I think this peak is happening because I often end up at some point on the trip to work suddenly being cut off by traffic pulling out of parking lots, etc, onto the street, even though I'm right there (they do it to other cars, too), so I have to slow dramatically down or even outright stop, and then I'm in a high gear since I had no time to shift back down. Accelerating in high gear takes a lot more startup current for longer periods, so I try never to need to do this.

Acceleration once I can implement a more severe current limit on the motor is going to be pretty wimpy. :-(


  1. Since the bearings went bad in my pedal crank and occasionally continue to click even after replacement, I have decided to design and try to build a new ebike. I wonder if I can put a rear coaster wheel on the front. Here is the thing, though. I am considering using a power wheel chair motor affixed to the front fork to drive it.

    The motor would need to be pretty small and have right angle output which would allow it to use a worm gearbox. That could enable a higher gear ratio, which I would need to be about 40 to one. Who knows, there may be an alternate solution for you for the troubles you just mentioned. :I

  2. Do you carry both the wheelchair charger and the Sorenson power supply to charge all three batteries during trips? Just curious

  3. @Don: I carry no charger for most trips, such as grocery runs or work, as I have nowhere to plug in. (used to plug in at work but can no longer put the bike where it is safe to run the cord).

    For longer trips I carry the wheelchair charger, as the Sorenson is about 15-20 pounds itself, since it's a linear supply with a huge transformer and heavy heatsink.

    Then I rotate the charger between pairs of batteries, and use a shorting jumper plug in place of whichever one of the three batteries is not currently being charged. I try to rotate it every half hour, at most every two hours.

  4. @Joe: Were the bearings the self-contained cylinder type, or were they the older individual-bearing/separate-race type? If they were separate races, it's possible one of the races is cracked, or scored, possibly even that a sliver of metal has found it's way into the grease on the bearings, and it clicks every time it is pressed between the bearing and the race.

    If you spread the dropouts, you could put a coaster on the front, but you will need to invent a way to rotate the sprocket on it in reverse to activate the brakes should you want to use them, and ensure that the torque arm is very securely fastened to the fork.

    If all you are using it for is to attach the motor chain to it's sprocket, then there is no need to worry about the brakes, but you should probably still affix the torque arm.

    The powerchair motors are heavy, partly because of the gearbox--around 10 to 20 pounds, depending on model. Mine is close to 20, might as well call it that. It also has enormous torque at 36V, and has broken multiple things on the bike under various conditions.

    All the powerchair motors commonly available secondhand have right angle gearboxes whose output shaft *is* the wheel axle, so they are not light. There are some that don't directly drive the wheels this way, and thus are lighter, but I haven't personally held one in my hand.

    I have considered a few ways of using a powerchair motor on the front fork, including bolting one or two on *with the powerchair wheels* to give me a lowspeed (12mph) trike with no coasting ability, but which could seriously haul several hundred pounds of cargo with little effort.

    The added weight right at the front end is the main reason I have not tried it, but that point may be moot with the next post, anyway.

  5. If Joe doesn't already have the wheelchair motor I suggest a much better choice would be one of the scooter motors with the built in gear box. As much torque as the other motor but much lighter in weight. He can use the normal front brake and ignore the coaster brake. He will need a bigger gear than normally comes on a single speed bike... something more like 24-28t.
    I just did that with a two wheel drive e-scooter.

  6. @M.E. Your new projectt would be able to do some serious hauling.

    The bearings are the older American type using the single piece crank and with each piece separate. I like that type. They can be worked on with regular tools like channel lock pliers. The metal sliver is something I plan to check on since all the bearing parts are new.

    I was considering something like a rear hub from a child's 16 or 20 inch bike and then spoking it onto the 26" rim in the hope that it would be narrow enough not to need spreading the fork, enlarging dropout slots, or shaving down the axle a little.

    I wonder if I made the torque arm moveable would the brake work if the motor output doesn't move.

    @Lee, I see that the power wheel chair motor is too big and heavy. I have what appears to be a Currie Electrodrive motor that I might have to try. It has about a 5 to 1 gear reduction. I was wondering about some kind of car power seat or window motor so that I might not need to try to attach a bigger sprocket on the wheel. I'm not planning to get very fast assist on this one.

  7. Power window and chair motors are too small--I tried them already, if you look back at the very first few posts. I don't recall if the results were posted systematically; just the idea itself, probably.

    Radiator fan motors *are* often powerful enough to use as friction drives. I did a couple of versions of them, one quite successful, using two of them.

  8. Would adding ultracapacitors of the type used in high power car stereos (1F-2F) in parallel with the battery pack provide an *adquate* current boost in those low-speed, high gear conditions?

  9. As far as I am aware, there is not enough energy storage (in joules) in those to supply enough power to make a difference. I don't remember how to calculate it out, but I have seen threads about it on Endless Sphere discussing it, including the calculations, and it did not work out favorably.


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