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Running on Empty: Power Anxiety and e-Bikes

by Ted Johnson

Funny thing about e-bikes: I want more, more, more, tech on them.

On my regular bike, the battery died on the cyclometer literally years ago, and I hardly care. I could fix the problem for less than $10, but I haven’t.

But on this Hebb e-bike I’ve been testing, I’m finding the “dashboard” to be lacking.

Hebb Dashboard

Three lights: Green, Amber, and Red. When I’m not using the throttle, those lights indicate how much of a charge the battery has. When I’m using the throttle, the lights indicate how much the batter voltage has dropped based on what I’m demanding of the motor.

It’s like a gas gauge and a tachometer rolled into one–keeping me in a constant state of anxiety. Am just using a lot of power, or am I about to be stranded going up this hill with a dead battery and a 60 pound bike?

This is what I really want:

Distance to Empty

I want the bike to tell me how far I can go at my current level of electric-powered laziness. If I don’t have enough juice to get me to my destination, I’ll put a little more of my own effort. Then I want the bike to recalculate the distance to empty and say, Good boy! when my pedaling has extended my range.

As far as I’ve been able to determine, this data is not available on any e-bike dashboard. I only know that if I wasn’t on an e-bike, I wouldn’t be thinking of this stuff.

By the time the Hebb was giving me amber light, I’d gone 14.3 miles on a combination of flat, hills, and headwinds. The electric power was there, but barely noticeable. I’m not sure at that point whether I was breaking even between the assistance I was getting, and the extra weight of the battery and the motor.

I plan on riding the Hebb until the battery gives up entirely, just to see what the range really is, but I already think I’m well past the point of diminishing return

What’s with that? Are there electrical engineers out there that can explain to me why I can’t get consistent power output, and then have the power fizzle all at once–y’know, like a car?

With the right kind of instrumentation, I could probably handle knowing that I was on empty, and plan accordingly.

 
Burley nomad 229

9 Responses to “Running on Empty: Power Anxiety and e-Bikes”

  1. Roach says:

    Part of the problem is that batteries don’t drain as smoothly as a gasoline fuel tank. The age of the battery, the temperature, the load it’s being put under, and other factors all change how it’s going to drain.

    I assume they’ve figured out ways to level some of these off and provide accurate readings of distance available for pure-electric cars like the Nissan Leaf, but I don’t know what’s being done there or how much of it could be translated to electric bikes.

  2. GDorn says:

    Another significant factor in discharge curves in the battery chemistry itself. LiFePO4, for example, has a much flatter discharge curve than Li-Ion, meaning that it maintains a higher voltage for the duration of the drain cycle. This also means that State of Charge estimators (like your three-LED dashboard indicator) need to be calibrated for the right battery chemistry.

    You might find the Cycle Analyst to be more useful at estimating remaining charge: http://www.ebikes.ca/drainbrain.shtml

    Many e-bike controllers are compatible with this gadget, which can also log battery states over time and let you output the data to a computer for further analysis.

  3. peteathome says:

    The Bionx controller has a function you can turn on that gives the distance and time remaining on the battery. But it is based on the power utilization of the last ?30 seconds or so. If they would use a longer time period, say the last 20 minutes, that would give a reasonable estimate, assuming you aren’t about to climb a mountain.

    • Ted Johnson says:

      We have a Bionx bike here, but I haven’t investigated all the functions of the controller. Instead today I called someone who ought to know, and was told that that Bionx did not have this feature. Must investigate further.

  4. peteathome says:

    code 3779 if you have revision #12 or above:
    http://endless-sphere.com/forums/viewtopic.php?f=16&t=9044&start=0

  5. Bill Hebb says:

    Ted, I agree that the battery meter function is a little lacking, but with experience on how you ride, your load, and the terrain – you pretty quickly figure out the meter and the range remaining. There are meters, such as the Cycle Analyst, that provide more detail, but of course that means more money and raises the retail price. Here is a simple explanation of our meter:
    Basically, the battery meter is similar to the voltage meter on a car. The battery meter sometimes goes into yellow or even red when going up a hill, just as the voltage meter in a car dips as the car is started or accelerated. On flat ground, the lights work as follows:
    Green – First 40% of the charge
    Yellow – Next 40% of the charge
    Red – Last 20% of the charge
    In other words you have a little less than half the range on the green light, and when the light’s red constantly – it is time to conserve the battery or charge the battery soon. Battery range is affected by terrain, wind, weight of the user, speed, and how much effort the rider is using.
    I hope this helps and thanks for the comments on our bike.

  6. BluesCat says:

    I tell ya, I hit my little hill on my way in this morning and two things happened: (1) my left knee complained that I hadn’t downshifted quickly enough, and (2) I had a brief, brisk, unusual headwind. I topped the hill and said to myself “Ted! Where’s my e-bike!”

  7. pam says:

    Yes to that feature.

    Learning the variables is weird. I ride an iZip which has a range of about 16 miles. That’s less than I’d hoped when I bought it given that I live on top of a bigass hill.

    But it’s died on less miles when I have a heavy headwind. It’s got more on days when the streets are dry and there’s no wind. It’s… unreliable.

    I’m kinda holding out for the V2 or V3 version. I love this thing conceptually, but in practice, it could have a) more range and b) what you said, better read outs.

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