Parallel 2 miss matched batts while on charge

Discussion in 'Electronics & Electrics' started by xc351, Sep 30, 2019.

  1. xc351

    xc351 Member

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    Well I have a few motorcycles and Instead of buying multiable chargers or swaping them can I simply parallel them during charging.

    It will be on a smart charger (prolly ctek or similar)

    If charger fails/turns off then I'm aware there is a good chance I'd have 2 dead batts in a matter of days.

    Unless there was a way to automaticly cycle between batts every 12hrs or so let's say.

    May look at running multiable cteks but adds up fast.
     
  2. _zak

    _zak Member

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    I might be wrong, but I think the main problem you'll likely to face with the parallel solution is when connecting the batteries. If the two batteries aren't at the same state of charge, current will flow from the one with higher voltage. With nothing to regulate the current, this has the potential to kill both batteries from being charged/discharged too quickly. There's also (an admittedly small) fire risk if the connecting cables heat up enough.

    Blocking diodes in the cables would solve this problem, but the voltage drop they cause will likely throw off the smart charger.
     
  3. slavewone

    slavewone Member

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    This works in the hobby world with matched batteries and similar discharge (lipo has reached min voltage cutout in the same device).

    I don’t think you should be parallel charging them.
     
  4. merlin13

    merlin13 Member

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    With mismatched battery types/capacities, this is what you call an example of No. Do Not Do.

    The "thirstier"/deeper discharged battery will not only try to eat more power from the charger but it can also drag power out of the other battery until the charge states balance. Maybe fine if you want to ghetto charge/cycle NiCads mebbe...

    You'd also need a charger grunty enough to handle both max charge current draws - seen dumb people miss that little gem more than once and wonder why things didn't work out as planned.

    Then there's the confusion you'll be giving to any intelligent charger - the first battery that charges up could trigger the charger to think "Yup, My Job Is Done" then shut down into trickle/standby mode, leaving the second battery t ogo "Hey, Where's the rest of my charge?" Seen this occur more than once at a dumb customer site, who kept complaining some batteries would never fully charge.

    Put mismatched batteries on a dumb charger? Go for it if you're desperate once or twice. Don't when you're not.

    Yeah, if you have a requirement to charge multiple batteries and want to complain about having to buy multiple chargers then buy/build a simple timer-based (555 mebbe...) high-current relay switcher.

    Something that leaves one battery connected at a time to the charger for a suitably guesstimated charge time cycle, then drops that one out to connect the second battery to the charger. The timer then counts down on its fingers until Zero, switches back over to the first one, resets its fingers and of it goes again ad infinitum.

    Stupid Question though.

    You say you have multiple motorcycles, yes? You going to run charging leads to each parked bike (with associated IR drops on any differing lengths of wire to confuse the intelligent charger more perhaps...), or pull the batteries out to sit them side-by-side on the bench?

    Also curious that your bike batteries would need constant trickle/standby charge, considering that they should last months between top-ups if you're not using them on a regular basis.

    So save yourself some hassles and simply swap the one charger over once a week or so, fer God's sake. Surely that can't be THAT difficult to work out a regular schedule?
     
  5. OP
    OP
    xc351

    xc351 Member

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    Both bikes are parked next to each other so will use those quick connectors. I often work away for 2 weeks at a time add a weekend of call or bad weather and you never know. My ute has dual battery's so I'm not concerned about that.

    It's also not just to trickle them but to give them those fancy cycles to keep them in tip top condition.

    May just buy 2 chargers then there not as badly priced as expected.

    I'll prolly grab 2 ctek .8 units as battery's are tiny 8ah-12ah
     
  6. Hater

    Hater Member

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    just swap the charger between each bike every fortnight?
     
  7. cvidler

    cvidler Member

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    that's the only option that'll prevent more expense (at best) or bad things happening (at worst).
     
  8. aXis

    aXis Member

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    If the batteries are the same condition but different capacity, parallel is not problem. That said, batteries are rarely in the same condition.

    Alternatively, you may not need a completely smart charger on each of them. A cheaper float charger with temperature compensation will do an OK job for the bulk of the time, then switch them on to a smart charge / regeneration cycle once in a while.
     
  9. OP
    OP
    xc351

    xc351 Member

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    Just an update bought a ctek cx .8 charger worked great. Was kept on the grom which has been modified with a different cam without decompression ect ect.
    In other words can be a nightmare to start sometimes (batt is new and slightly higher cca then oem)

    Its been a month since I've ridden it started perfect.

    So I've bought 2 more. As I also want to keep a spare 4x4 12v in good nick (which is pushing the limits of the baby ctek) but it's just my old battery (lost cca) from ute that's now kept in shed for my clay target thrower used very rarely. I'll take it in again in a month and see if it increases cca as the ctek does has a desulfar mode.

    It was $25 for a extra cable or $68 for a complete new charger.

    I've also got a 3.8a ctek from a mate that's used to use it in his caravan on a long term loan that will be to big for the motorcycles but may be perfect for 4x4 batts but again will need a $25 cable or hopefully I can use the spare battery camp's from new chargers on it.
     
  10. OP
    OP
    xc351

    xc351 Member

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    Just incase anyone cares. Repco has a 1000min sale on for a 5a ctek as we speak. $88

    I've bought one and just picked it up. May use it on the 4x4 batt for the clay target thrower or use it for my secondary batt on my ute as its a bit adverage.
     

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