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  1. #1
    Lyen lyen's Avatar
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    Power needs from San Francisco to San Jose in California?

    Hello All Ebike Gurus! How much power do you think it takes for you to go from San Francisco to San Jose in California? The reason I asked is because we have a group of people interested to doing long ride in the Bay Area. Let say if you + the ebike + the battery weight = 300 LBS (136 kg), and the trip is 70 miles (112 kilometers) 1 way and your battery is the 48V LifePO4, and your average speed is 20 MPH (32 kph), on flat + typical wind resistance on a sunny day, throttle ony (no pedaling assume this is for a duration contest), then how much aH (amp hour) of the battery power do you need? I appreciate everyone help & input.

    Here's the link to the bike path from San Francisco to San Jose:
    http://www.bikely.com/maps/bike-path...o-San-Jose-2-0
    Last edited by lyen; 05-08-09 at 07:14 AM.

  2. #2
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    Keep in mind that the bike weight is endogenous - the more juice you need, the heavier the bike, etc.

  3. #3
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    The answer is a hell of a lot. Why no pedaling? If it is flat, you hardly need an electric other than to keep speed up that high against wind resistance.

  4. #4
    Lyen lyen's Avatar
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    I actually live in San Francisco & I do not commute that far usually. If I do, I will be driving my car. However, there is a group people I know who want to challenge each other. However, some of those have got the electric scooters such as small Currie, Schwin, Xtreme and the bigger Vespa style type,without pedals. Therefore, to make it fair we agreed to run with throttle only for those who use electric bikes. Like I said before, considered it as an unofficial contest for range on a single charge. The only rule is the total weight limit (rider + bike + motor + battery) cannot be over 300lbs (136 kg) regardless electric bike or scooter. The gross weight must included the rider because no one want to break the spokes on the wheels and to be fair to each other in terms of the EV classification.

  5. #5
    Certified Non-Voter wernmax's Avatar
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    I know my TidalForce uses 35 watt hours per mile at 36 volts. me and the bike + batteries weigh in at 290 lbs. Battery pack is a usable 10 amp hours NiMiH and 20 lbs, so 10 miles of no-pedal riding on a charge.

    I'd say your going to need a 2.8 Kilowatt, 140 lb, 70 amp hour, 36V NiMiH battery pack. Or about a 70 lb, 55 amp, 48V pack for a 70 mile trip, assuming modest elevation change.

    You might lose half the battery weight using A123 LiFePo4's or equivalent. I paid $1,000 for a 48V 10 amphr pack. I see their down to about $700 with BMS on some sites, so $5,000 for 70 amphr? Ouch.
    Last edited by wernmax; 05-09-09 at 05:05 PM.

  6. #6
    put our Heads Together cerewa's Avatar
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    You might lose half the battery weight using A123 LiFePo4's or equivalent. I paid $1,000 for a 48V 10 amphr pack. I see their down to about $700 with BMS on some sites, so $5,000 for 70 amphr? Ouch
    Nah, A123 batteries have about the same energy density as other LiFePO4 batteries, they cost extra just because of their high "C" rate.

    I'm guessing that given the problem posed in post #1, 70 miles at 20MPH, (assuming brushless motor) you would need maybe 30 watt hours per mile, but I'm not sure how hilly it is. This is 2,100 watt hours which means you'd need a 48v40Ah pack or maybe 48V50Ah.
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  7. #7
    Senior Member Mr. Fly's Avatar
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    Quote Originally Posted by cerewa View Post
    ...but I'm not sure how hilly it is.
    It's quite hilly. Bikely says better than 3500 ft's worth of elevation change. That sounds about right since I occasionally ride a significant portion of that route as my commute home (on a non-powered bike so I can't provide any pointers to the OP).
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  8. #8
    Certified Non-Voter wernmax's Avatar
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    Quote Originally Posted by cerewa View Post
    Nah, A123 batteries have about the same energy density as other LiFePO4 batteries, they cost extra just because of their high "C" rate.
    Right, but I meant about half the weight of the NiMiH's.

  9. #9
    Daily Rider Robert C's Avatar
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    OK, I have a similar route in Northern California. Paradise to Chico (easy) and back (not so easy). here are the numbers
    Distance17.93
    miles Estimated Time0:58:31
    Ascent62
    feet Descent2067
    feet Start Elevation2218
    feet Finish Elevation213
    feet Minimum Elevation194
    feet Maximum Elevation2218
    feet

    Keep in mind, I have to turn around and go the other way at the end of the day. No recharging and it will be sitting outside through the day in temps varied from 40f - 110f. Can it be done affordable. I am comparing it to my motorcycle that costs about 16 cents per mile (all factors, including fixed are in that number).

  10. #10
    Certified Non-Voter wernmax's Avatar
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    740 watts = 1hp.

    1hp is the power required to lift 33,000lbs 1ft in 1 minute. Conversely, 1lb to 33,000ft, or any combination in between.

    Total weight of battery, motor, bike, rider, and other needed gear....330lbs? Perfect.

    Average power needed to cruise 20mph on a flat....35whrs/mile.

    Approximate total elevation gain required on one charge...2,000ft.

    36 mile round trip. Assuming little or no power usage for 18 miles because 1/2 the trip is downhill.

    18 X 35whrs for distance = 630whrs

    2000ft/(330lbs X 100 =1hp) = 20hp for 1min = 246whrs.

    Assuming a 36V NiMiH battery pack and 80% depth of discharge....

    630 + 246 = 876/36V = 24ahr X 1.20 = 28.8ahr

    So if my math is right, you need a 36V30Ahr battery, no pedaling.

    Subtract 1/2 that if you pedal about half. The 36V13Ahr NiMiH pack on the TidalForce 750 (1 hp) gets me about 12 miles down the road with light pedaling, mild hills, 20mph.

    I'm betting 36V20amps would do you. At 10 cents/kilowatt recharge, less than 1c/mile.
    Last edited by wernmax; 05-21-09 at 07:24 PM.

  11. #11
    Certified Non-Voter wernmax's Avatar
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    Of course, the real savings with an electric bike come from not having to pay gas, insurance, license and registration fees on a "motor vehicle".

  12. #12
    Daily Rider Robert C's Avatar
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    Quote Originally Posted by wernmax View Post

    I'm betting 36V20amps would do you. At 10 cents/kilowatt recharge, less than 1c/mile.
    Intesting and somthing to consider...

    I wonder about the paybck on an ebike kit that will still cost about $1,000USD. I also quesion the the 1c/mile when the need or fequent battery replacement is factored in. It is still someting I am considering.

  13. #13
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    Depends on rolling resistance and how aerodynamic are you? Slick tires and not aerodynamic, I'd get 48 volt 40 ah packs and you should be able to maintain 20 mph easily. High pressure skinny slick tires and spandex, shaved legs, tucked the whole time, you might get away with 25-30 ah pack or if you go 40 ah, you might average like 30 mph instead.

  14. #14
    Both Coasts...
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    70AH or 1 mile per AH is my real world guesstimate. Speed/wind kills range - I have a 250W, 15 mph pedelec that can do 100 miles on 30AH but that's fairly flat and pedaling the entire way. 20-30mph will require at least 70AH to travel 70 miles and that may even come up short. Which is a very bad thing for any electric powered vehicle...

    I also have a 20 Mph, 750W standup scooter that needs at least 18AH to travel 4-5 miles. As you can see there's a huge difference in range depending on many factors.

  15. #15
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    You can't go by amp hour so much as watt hours. The voltage really has an effect. Also, it depends on the battery. Lead acid packs will lost quite a bit of capacity due to the peukert effect (SP?) I've read you might only get 8ah from a 12 ah pack with a decent amperage draw.

    Assuming you get actual ah from the pack, I'm gonna say it's more like 1/2 ah/mile. With my 74 volt pack, I can travel ALMOST 4 miles/amp hour at 20 mph. Since you're running 48 volts, you'll get about 2-3 miles/amp hour at around 20 mph.

    I didn't exactly pull these numbers out of my butt - I've been doing experiments with the cycle analyst and different voltages. Only thing I havn't really changed was the motor - I'm using a 5303 and pretty happy with it. I'm not lugging around 60 pounds of lead acid either (60 pounds is roughly 6 12 volt 12 ah SLA). I'm only lugging around 10 pounds of LiPoly which gives me a safe range of 25 miles doing anything from 20-30 mph with an occasional 50+ mph burst.

  16. #16
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    Amp-hours are meaningless. Watt-hours are everything. Effective capacity (watt-hours) is a function of discharge rate - the slower you drain the batteries, the more power you get.

    The amount of power an e-bike uses is pretty closely related to how hard it would be to pedal that bicycle were it set up as a fixie. An aerodynamic recumbent design might use 1/5 the power of an upright mountain bike - whether applied to motor or muscle, drag is drag. Furthermore, much like your legs, electric motors work best with a given "cadence" - if you're running the motor with lots of juice at low RPMs to get up a hill, efficiency plummets.

    Based on what I've read of others' exploits, you'd want at least a 30AH 48v LiFePO4 pack for all but the most aerodynamically optimized of upright bicycles. For a recumbent, 20AH might work, though you'd be cutting it pretty close.

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