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  1. #1
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    Charging SLA batteries in series didn't work - why?

    I had planned to charge each of my 3 SLA batteries individually, then when I got home last night (my inaugural commute!) I realized that there was a flaw in my plan...unless I wanted to get up at 3 am to switch the charger to a new battery, I wasn't going to get them all charged by morning. My only option was to wire them back up in series and charge them as a pack. I didn't know if it would work. Apparently it didn't. I don't have a working volt meter right now, so all I have to go on is the battery meter that came with my ampedbike kit, but it definitely wasn't at full charge. The pack probably got charged some, but I was hoping that after 8 hours at 1 amp they would have all been fully charged...especially since I had about a half charge in them when I got home.

    So, did I do something wrong in my setup, or can you really not charge all three connected in series like that? Should I buy 2 more chargers so I can charge all 3 independently all night?

  2. #2
    Senior Member karma's Avatar
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    no you can charge all 3 what voltage is you charger? if you charge them in series the charger should be a 36volt charger.



    ..charger..

    3x series-36volts

    3x parallel-12volts
    Last edited by karma; 08-22-08 at 10:55 AM.
    karmaelectronics.info
    youtube karmabike1

  3. #3
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    Ahhh. So, it's not that I can't connect them to charge all at one time, I just need to connect them in parallel, not series?

  4. #4
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    If you are using them in series you should be able to charge them in series. Could one of the wires in your series pack have come loose?

  5. #5
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    karma is right. If you only have one 12V charger connect them in parallel to charge them at 12V. When using them you can then connect them in series to use them as one 36V battery. If you want to charge all three batteries while connected in series you'll have to get a 36V charger.

  6. #6
    Senior Member ken cummings's Avatar
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    And a 36 volt charger is not the best idea. The pack with the highest resistance will have a higher voltage drop and charge faster leaving the others with less charge. Could even leave that one burned out.
    This space open

  7. #7
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    I agree that charging in parallel is better as it balances the 3 batteries.
    8hours at 1 Amp will not be enough to charge 3 parallel batteries. Assuming they are 8AH each you need 3 times that amount at 100% efficiency. You need a higher amp charger. Some bats are 12AH. You would need 36hrs to charge them at 1 Amp. Assuming 100% efficiency. Real life you need 50% more charge or 54hours at 1 Amp. This will go down to 18hours at 3 Amp or 9 hours at 6 Amps. So to charge overnight you need a min of 6Amp charger.
    Since they are 12V batteries any automotive charger can do 6Amps. So go to an autostore and take look at what they have. Buy an automatic one that shuts off if the batteries are charged.

  8. #8
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    Any reason I can't take a standard 1.5 amp 36 volt charger (times two) hook them together and charge my 10ah 36 volt pack at 3amps? On both sides of the charger it would seem I could splice the wires together making it a one plug charger to the wall, and one plug to the bike.

  9. #9
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    That would work. For 10AH and 36V charger at 1.5A should get you charged in 8-10 hours. So overnight is feasable without doubling up.
    Remmember SLA don't like deep discharges which means you should not exceed 5AH worth of drain. That will half your range but also your chargetime.

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