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kampinguru's avatar
kampinguru
Explorer
Jan 11, 2016

To all you 12V specialists out there.

Good afternoon
Although this is not strictly RV related, I thought that there was a large amount of 12V battery knowledge here so I am going to give it a shot. I have two dissimilar 12V batteries. Picture something like a motorcycle battery and a car battery connected in parallel. I want to dry camp and have a lot of 12V accessories and lights that run off the smaller battery that I need to leave running for 12 hours at a time. How can I provide more power to the smaller battery to run the accessories for a long period. Currently I have a larger capacity battery and a 2A charger running all day and I still kill the smaller battery. Can I use larger wires and run the charger at 12A or will that be dangerous. I cannot charge the batteries overnight as the 120V power is shut down. I would need this to run for 3 days in a row. Similar to an RV show where the RV's are powered all weekend. Thank you very much for your expertise.

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  • time2roll's avatar
    time2roll
    Nomad
    Jan 11, 2016
    Yes connect the large battery in parallel to the small battery (++ & --) and run at 12 amps charging.

    If you are still worried... you need to post the exact equipment. Batteries and charger.
  • kampinguru's avatar
    kampinguru
    Explorer
    Jan 11, 2016
    I can but the 2A is not enough as I have about 8A of draw. I am not sure if running 12A charging on a bike battery will be good for it. It is an automatic charger from Canadian Tire and it does both deep cycle and normal batteries as well as 6V and 12V. The 12V normal battery has a 70Amp start, 12Amp Charge and a 2A charge setting.
  • opnspaces's avatar
    opnspaces
    Navigator II
    Jan 11, 2016
    kampinguru wrote:
    Good afternoon
    Currently I have a larger capacity battery and a 2A charger running all day and I still kill the smaller battery. Can I use larger wires and run the charger at 12A or will that be dangerous.


    Your loads are pulling more than 2 amp out of the batteries. So your 2amp charger is not keeping up. Not knowing your charger I'm going to say that unless it's a Harbor Freight model then if it has a 12amp setting I would charge at 12 amp. Said another way go ahead and try the 12amp setting unless it's a cheap Harbor Freight charger.

    Does your charger say anything on it about being automatic? What is the brand make and model so we can look it up?
  • coolmom42's avatar
    coolmom42
    Explorer II
    Jan 11, 2016
    kampinguru wrote:
    I am not sure how to insert pictures. I have a motorcycle battery in the bike and I have made a jumper to go positive to positive and negative to negative to the car battery with a 15amp fuse inline on the positive wire. I have a 2A automatic charger connected to the car battery.


    Why not charge the bike battery directly? Why do you need to connect it to the car battery?

    Your car battery is going to charge when you drive, at a rate much faster than 2 amps.

    You should be able to look up the specs for the motorcycle battery somewhere, including the optimal charge rates. That should be your first step.
  • westend's avatar
    westend
    Explorer
    Jan 11, 2016
    Use the 12A function. If you have a meter, measure voltage at the battery terminals with charger operating. As long as you have less than 14V, you should be fine.

    If you've run both batteries down to non-operating voltage a number of times, I'd suggest to get a new battery. A flooded wet cell battery will only endure so much beating and then they die. Motor cycle batteries die quicker.

    Without a stated total of the draw of all the devices powered and the capacity of the batteries, there is no accurate answer to what will work.
  • kampinguru's avatar
    kampinguru
    Explorer
    Jan 11, 2016
    I am not sure how to insert pictures. I have a motorcycle battery in the bike and I have made a jumper to go positive to positive and negative to negative to the car battery with a 15amp fuse inline on the positive wire. I have a 2A automatic charger connected to the car battery.
  • GordonThree's avatar
    GordonThree
    Explorer
    Jan 11, 2016
    can you draw us a diagram of what you're doing?

    sounds like your two batteries are not connected correctly, or the large battery is damaged / faulty.

    if the batteries are truly parallel, the small battery should not "die" before the large battery... unless the large battery is already dead.

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