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  1. #1
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    Fuel gauge for E bikes?

    I just finished my first build on a Jamis Commuter with an 8 spd rear hub. I used mostly BMS Battery components (36v bottle battery and a Q100 328 rpm front hub motor driving 700c wheels. The BMS controller (KU65) turned out to be a dud and I replaced it with an inexpensive Greentime controller. The bike runs great producing an unassisted 22mph on level ground. When I discarded the KU65, the battery meter went with it. Now I need a way to determine how much charge is left in the battery when I'm out riding. I'm not looking for a fancy analyzer just something to keep track of my remaining "fuel". Ideas, sources?

  2. #2
    Senior Member rscamp's Avatar
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    The Cycle Analyst V3.0 of course.

    A Watts Up meter is a lower tech approach that requires wiring in series with the power source. It does measure capacity and energy consumed... http://www.hobbyking.com/hobbyking/s...up_Ver_2_.html
    Rob

  3. #3
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    Cycle Analist is simply micro computer which simply reads electrical values and does simple math calculationa, like Amps times Hours=AH.
    IT is rather specialized product for people who knows something about electricity.
    how many doctors, lawyers or other ebike owners know what Watthour is?
    What he needs like many ordinary owners is a meter which display bars which disappapear as battery gets depleted.
    Very simple and intuitive but not so easly done.
    there are specialized chips which count the discharge and display on LCD display. That what high quality ebikes use, not CA.

  4. #4
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    Powell is right on track. I'm looking for something small and unobtrusive that tells me how much juice I have left. Anybody market such a device?

  5. #5
    Senior Member rscamp's Avatar
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    Quote Originally Posted by powell View Post
    Cycle Analist is simply micro computer which simply reads electrical values and does simple math calculationa, like Amps times Hours=AH.
    IT is rather specialized product for people who knows something about electricity.
    how many doctors, lawyers or other ebike owners know what Watthour is?
    What he needs like many ordinary owners is a meter which display bars which disappapear as battery gets depleted.
    Very simple and intuitive but not so easly done.
    there are specialized chips which count the discharge and display on LCD display. That what high quality ebikes use, not CA.
    I understand what the OP wants. If either of us knew of such a thing we would have answered his question already. Right?

    More complicated than the OP wants is the V3 CA. This does have exactly the guage the OP wants but wrapped up in a more complex and harder to use package.

    Very simple to install but requiring an easy mental calculation (subtract consumed from the fully charged value) is a capacity meter. I think this is the way to go as once learned this tool is useful for many other things.
    Rob

  6. #6
    Senior Member CigTech's Avatar
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    May your feet keep move'n with the wind to your back.

    CigTech

  7. #7
    Transportation Cyclist turbo1889's Avatar
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    A good digital volt-meter displaying and accurate to at least the 0.1V would work as well once you got used to figuring how much you had left by the voltage of your battery both under load and at rest. That is what I use but I don't have it wired into my bike, just got a multi-meter in my bike bag that I can check the battery in a jiffy with if needed (also good for tracking electric problems if necessary).

  8. #8
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    Again,
    CA is a specialized product for EV ,ebike DIY people not for average Joe. He need just bars displayed no subtracting, no multitude of electrical units which he does ot understand .
    just get into skin of non tech person.
    With good old Lead Acid it was relative easy simply because along with discharge voltage dropped so simply voltmeter was enough.
    No so with Lithium where voltage drops little with discharge.
    With lithium you need chip which can perform Columb count, which counts charge coming out of battery and charge put into battery.
    sorry that is so specialized and electric tech stuff but it must be performed by chip if you want any meanenful results displayed.
    here is Texsas Instrument chips who perform Columb count.http://www.ti.com/analog/docs/litabs...=1&familyId=64
    those voltage based 3-light Chinese FULL-HALF-LOW indicators so popular on China brands are next to useless.
    Last edited by powell; 05-21-13 at 05:37 AM.

  9. #9
    Senior Member rscamp's Avatar
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    Here's a new product I just developed. I take a V3.0 Cycle Analyst and put black tape over all of the screen except for the fuel gauge graphic.
    Fuel Gauge Icon.jpg

    Rob

  10. #10
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    I'm looking for simple and unobtrusive (cheap would be a bonus). I think I'll just carefully determine my range using my odometer. Mostly I just glide and enjoy the ride so I don't think my occasional pedaling is going to skew the numbers very much.
    Last edited by ammodave; 05-27-13 at 09:39 AM.

  11. #11
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    Sorry, double post.
    Last edited by ammodave; 05-24-13 at 10:31 PM.

  12. #12
    Senior Member CigTech's Avatar
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    May your feet keep move'n with the wind to your back.

    CigTech

  13. #13
    Senior Member rscamp's Avatar
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    Quote Originally Posted by CigTech View Post
    This is meant for a lead-acid battery. As previously pointed out, measuring voltage alone with many battery chemistries does not provide any meaningful indication of state of charge. This will also likely have the wrong voltage range anyways...
    Rob

  14. #14
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    Yes...voltage <alone> based indication is pretty useless, as the voltage ranges differ per battery chemistry, and the voltage drop curves are non-linear, in different ways per battery chemistry and type.

    Something that can calculate watt-hours consumed from reset is the best. Either a CA or a watts-up or similar, which has an internal shunt and can monitor the combination of voltage and current and time to get watt-hours. Knowing the energy content of your battery in total watt-hours will then give you "percent consumed". I like the CA standalone model, as it is flexible per any controller and can be moved from bike to bike as required. Similarly I also hook up a watts-up meter now and then - don't need a CA or Watts-Up for short range city rides under 20 miles, in general.

  15. #15
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    The CA has other features which include total miles traveled so even if you travel under 20 miles it's a good idea to use the CA. This will allow you to keep track of how many total miles you've gone using that particular motor or you can move the CA with the battery and keep track of the mileage for that particular battery/batteries.

    EDIT: That's total miles of the life of the motor/battery and not just the individual trips. It's like the odometer of a car.
    Last edited by EBikeFL; 05-24-13 at 06:21 PM. Reason: clarification


    If we don't make changes to our use and abuse of energy, Mother Nature will make it for us.
    Be a part of the solution to Global Warming instead of a contributor.

  16. #16
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    Yes...I like the odometer. Its nice to know I've now got 8000 miles on my trike since I put the CA on it...

  17. #17
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    chvid,
    can you refresh what edrive/kit?/ you use?

  18. #18
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    For this purpose you can simply use ZTS Multi-Battery Tester it tells about the battery life of an electric bike. It is very easy to use and provide better results. Electric bikes are rapidly being popular in the world because these bikes use electricity instead of petrol. In future Honda bikes will be available with electric motor instead of petrol engine.

  19. #19
    Senior Member DrkAngel's Avatar
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    Lightbulb

    Li-ion types can work fairly well with a simple volt meter.
    For better accuracy and for LiFePO4 types you would want an Amp hour, watt meter.
    Digital 60V/100A Balance Voltage Power Analyzer Watt Meter Tool - $19.99
    Looks to be a great little tool! No Balance Function!

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