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12v battery used for 2nd battery charging

Discussion in 'Gen 2 Prius Accessories & Modifications' started by TommytheSalami, Nov 23, 2021.

  1. TommytheSalami

    TommytheSalami New Member

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    Hello!!
    I've been lurking for years, but just bought my first Prius! I recently moved to Texas from Oregon, and unfortunately I had to sell the beloved 2013 Nissan Leaf named "Rocko" because the heat down here would kill him.... and there isn't much charging infrastructure down here. I bought a gen 2 Prius as both my main transportation and as a tinker project. So far I love the Prius and I'm excited to play around with it.

    My question is about how the 12V battery system works.... I would really like to use the Prius as an emergency generator to charge a LiFePO4 battery bank in tandem with a solar array. My Plan is to connect a Renogy 50ah DC-DC battery charger to both the solar array and the 12v battery of the prius via a quick connect to the battery. The inverter would be connected to the battery bank. I am trying to figure out how many feet and what gauge of wire I will need for the connection from the car to the charger and I am stumped. I have seen on the forums that others have said the prius outputs around 40ah at 12V. Can I count on those numbers for a sustained load without harming the 12v battery? And when calculating the voltage drop over the wire run do I need to take anything else in consideration or can I just start the calculation at 40ah 12V? Is this a horrible idea?

    Thanks in advance!!
     
    #1 TommytheSalami, Nov 23, 2021
  2. Another

    Another Senior Member

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    Bigger is better when it comes to wire. It might also be helpful to post a sketch of what you intend to do so we can see exactly what you’re planning to do and how your connecting things.
     
    #2 Another, Nov 23, 2021
  3. Another

    Another Senior Member

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    #3 Another, Nov 23, 2021
  4. ChapmanF

    ChapmanF Senior Member

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    It is about a 40 AH battery, maybe 45.

    The fact that those numbers are in AH (ampere hours) should give you a very good idea how long you could 'sustain' a load with it. Roughly: a 2 amp load—20 hours; 10 amp load—four hours; 40 amp load—one hour.

    Any of those would represent complete discharge. You can scale them down appropriately to stay within a less extreme depth of discharge for the sake of the battery's cycle life.
     
    #4 ChapmanF, Nov 23, 2021
  5. TommytheSalami

    TommytheSalami New Member

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    Sorry I guess I phrased that question incorrectly... I shouldn't have said 40ah I should have said 40amps.... So the question is really can the system output 40 amps over a sustained period, because my guess is that it wasn't designed for a constant load that high.... But im no electrical engineer. I'll mock up a drawing and post it! Also I saw those kits to tap into the hybrid battery and they are really cool! I am hoping to keep this project around the price of a small generator though so it's out of my budget.
     
    #5 TommytheSalami, Nov 24, 2021
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    #6 Another, Nov 24, 2021
  7. sam spade 2

    sam spade 2 Senior Member

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    Yes, probably.

    I think you would be MUCH better off by increasing the capacity of the solar array and not involving the car at all.

    Exactly what advantage are you trying to gain with your idea ?
    It is highly likely that any small gain you make will be MORE than offset by some corresponding loss......like much shorter life from the 12 V in the car.
     
    #7 sam spade 2, Nov 24, 2021
  8. TommytheSalami

    TommytheSalami New Member

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    Welllllll I decided that what I was planning was more overkill "wow wouldn't this be cool" doomsday prepping rather than rational emergency preparedness. I decided to go with a 1kw inverter to hook directly to the car and go with propane storage for emergency heating and food preparation. That will give me the ability to power my internet connection and laptop for communication. That's all I really need. I have a propane heater, I bbq so I always have a decent amount of charcoal, and I have two 60lb dogs with lots of dog food that can keep us warm lol. I will spend my money on the damn AC evaporator core that just went out..... 1500 bucks from an independent shop. I also need to do struts and brakes soon. I really appreciate the responses... kinda bummed I don't get to do my doomsday prepper plan but it's probably all for the best!
    Thanks!
     
    #8 TommytheSalami, Nov 25, 2021
  9. TommytheSalami

    TommytheSalami New Member

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    Also the idea behind involving the car was to provide power overnight.... I have no idea how to quote people so who knows if you will see this sam spade 2
     
    #9 TommytheSalami, Nov 25, 2021
  10. Another

    Another Senior Member

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    If doomsday comes, will you need power for an internet connection? Better to get some amateur radio equipment.
     
    #10 Another, Nov 25, 2021
  11. sam spade 2

    sam spade 2 Senior Member

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    You hit the "reply" button and the quote automatically pops into your reply window.
    Now knowing your motivation, I think you need to either:
    Plan to do without most power overnight.
    OR
    Build up a "real" off-grid solar system with enough of it's own batteries to supply all of your needs.

    I find it rather interesting that you are worried about keeping Internet connectivity in a "doomsday" situation.
     
    #11 sam spade 2, Nov 25, 2021
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