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  1. #1
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    Question what size (AH) battery should I get for 2x19km commute???

    Hi,

    I'm about to buy batteries for a 36V 20A brushless geared system (http://www.ebike.biz/bmc.htm) and I'm interested in recommendations for what size / type of batteries to get. The ride I have is 2 x 19km commute (i.e. 38km total in the day). I plan to put reasonably substantial pedal effort in along the way on the flat & use batteries to keep up speed up the hills. I have several hills, but they aren't mountains. The options I'm pondering are:

    (a) Battery Type - Lead Acid or "36V 10Ah LiFePO4 Ebike Battery" (latter from http://evpower.com.au/-Lithium-Ion-L...atteries-.html for AUS$399)?
    (b) Capacity of battery - mainly a question for the sealed Lead Acid option (as the LiFePO4's are 10AH)? Basically I'm interested in going for the 10Ah LiFePO4's for weight, however if the 10AH isn't going to be enough then I'd consider the SLAs.
    (c) Plan to Charge at Work or Not?

    Question 1 - What sort of AmpHours (AH) do you think I'd be looking at for a round trip ride? I guess this will indicate whether the 10Ah LiFePO4 option would require a charge at work or not? What setup would you recommend?

    Question 2 - If I plan to charge at work (not sure how much the 2nd charger would be though), what setup would you recommend?


    Thanks

  2. #2
    Senior Member raevyn's Avatar
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    I personally would go for the 36v10ah one. I work at an electric bike shop in Calgary, and for me, its not just about the weight. lithium batteries are going to have a longer battery life than the SLA batteries, so you shouldn't have to replace them as often.
    However, taking a look at that website, EV power, I am not sure how keen I would be to buy a battery pack that is completely wrapped in duct tape.

    For the distance, The ones that we sell at my work, the lithium polymer 36v10.5ah batteries go an average distance of 35-45 km on one charge.
    If you were looking to charge at work, you could probably get away with a smaller batter pack, such as a 36v8.2ah, or a 36v5.6ah lithium polymer battery. the only downside to charging at work, is just bringing the charger with you. there are a few companies out there who provide you with rather large chargers that are not very convenient to carry around with you. you can get smaller ones though. Mind you it will also depend on how well the batteries are made. before you buy a battery from anyone, I would suggest finding out from anyone that you can, thier experience with those batteries, and if they preform to your standards.

    As for the motor, be careful. I havent had alot of experience with BMC, but my store has not had the greatest luck with them. we currently have a geared BMC motor in the shop because while the customer was riding, all the internal gears became stripped, and seized. a few of the other bmc motors we have received, we had to take apart and rewire them to get them to even work. I have not heard what experience other places have had with these motors, and maybe we just have bad luck with them, who knows. so again, I would advise getting as much feedback as possible.
    Swing Dancin', Load Haullin' Mama!

  3. #3
    put our Heads Together cerewa's Avatar
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    If you don't want to pay extra for a larger lifepo4 battery (20 amp hour) AND you don't want to pay extra for a second charger, you could just go with a 10 amp hour battery and one charger and carry your charger with you every day. With a 36 volt system, a charger plus a 10Ah battery will be much lighter and smaller than a 20Ah battery with no charger.

    If you use your motor only on uphills and pedal without electric assist the rest of the way, 10 amp hours is probably enough for your round trip without charging at work.
    Some awesome folks who are working to give Haitians the ability to manage their safety and their lives:
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  4. #4
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    Before buying anything, go to the endless-sphere forum. They have loads of information on who has the good batteries and who the good and bad sellers are. You will save yourself much grief and potential dollars this way.

    That battery listed seems to have a low discharge rate for its size, so it is probably not a battery you want to abuse or discharge all the way every day. You should opt for a 20 ah if you are interested in maximizing the batteries cycle life or alternatively charge at work.

  5. #5
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    Question

    Quote Originally Posted by snowranger View Post
    That battery listed seems to have a low discharge rate for its size
    How did you see this? i.e. what figure are you looking at? What would be a normal/good discharge rate?

  6. #6
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    500 watts / 38 volts /10 ah = 1.3C rate. That's in line with the low end LifePO4, not to say that this is inadequate or anything. 500-700 watts is what your system will use. Just don't take it down all the way all the time.


    Compare this to PSI, Headway or others with 3C or LiPo at 10C. You don't need those.

  7. #7
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    Quote Originally Posted by snowranger View Post
    Compare this to PSI, Headway or others with 3C or LiPo at 10C. You don't need those.
    snowranger, you wouldn't have links to the manufacturer sites for Headway & PSI? (i.e. trying to ramp up on understanding what's good/value for money re LiFePO4s)

  8. #8
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    Just search on headway on ES, and find posts from Victoria. Just PM her. Someone just bought a 36 V 20ah from them for $600 something. Don't know much about PSI.

  9. #9
    Senior Member raevyn's Avatar
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    you can also look at www.itselectric.ca and www.ebikes.ca they are pretty reliable. I personally have the 48v10.5ah battery from its electric, and I personally know both owners of both places.
    Swing Dancin', Load Haullin' Mama!

  10. #10
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    There's a subjective aspect to amp hour ratings that is worth considering...

    My bike is rated for 24V 12 Ahr. when I doubled the battery pack, I ended up with 24V 24Ahr which created a good match to for my morning commute.

    However, when I bought lithium ion batteries, I purchased 2 packs at 40V 6AHr for a total of 40V 12AHr.

    Anyway, the point that I am trying to make is: the 12Ahr of lithium batteries produces a similar range as 24Ahrs of SLA batteries.

    I believe that there are several reasons for this:
    - the increase in volts is pushing my bike to faster speeds, and I find myself coasting with the throttle off.
    - I also find myself using less throttle more often.
    - the lithium batteries weigh 13lbs, and the SLA batteries weigh 40lbs
    - the lithium batteries dont experience the voltage sag like lead acid does

    anyways, best of wishes to you!

    -
    Last edited by SeizeTech; 04-19-09 at 11:34 PM.

  11. #11
    Member 24X18's Avatar
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    Post What about Batteries//??

    There are THREE Types that can be used for Electric Vehicles..meaning Bikes/Scooters..
    The SLA..sealed lead acid..
    The Ni-MH..nickle-metal hydride..
    The Li-Ion..Lithium Ion/there are several types..
    ===
    SLA..gives the most power--torque/and are the cheapest..YET--they weight alot---
    Ni-MH..are very light-weight..they charge very good..they HOLD a Charge Very Good---
    Li-Ion..cost a TON-of-Money...are very light-weight..Last a Long Time---
    ===
    SLA...can cost...$$200.00 minimum for a better than average--amp rating..just over 20-LBS/
    Ni-MH...will cost about../300-400 dollars(USD)..they have less power than the SLA..as a battery pack(they have issues)...
    Li-Ion...is incrediably---a great choice...but cost upwards--near $$600.00(USD)...even $$800.00(USD)...
    ===
    I doubt you could get going on Li-Ion for 400-dollars(USD)...
    ===
    SLA---really makes all the points come together///
    I use 2-12volt...18ah..types..they cost me $$188.00/...
    ===
    I've been shopping Battery's..for over a YEAR..I can have a Li-Ion SET for my Scooter..at about $$800.00(top price)..but if you start crunching the SPEC-sheets..it really all..BOILS--down fairly close to the same thing..
    Except--Li-Ion can create Performance Levels..along the way of ownership..
    ===
    On the money side./..I can't find a better battery than SLA...
    ===
    ...and Ni-MH may be prone to a bad-sector--(a poor operating-CELL)..
    That's been my experiance shopping--alot...
    I would like Li-Ion..but SLA....really fits my experiance in building a Scooter...
    my next project--will use a very light-weight..composite(cheap)material..and 1000-watt motor---
    and 48-volts and haven't gotten a AMP--figured in yet...//
    ===
    I would recommned---SLA.

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