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Adding second 12v battery

Discussion in 'Gen 3 Prius Accessories and Modifications' started by Terrell, May 2, 2019.

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  1. Terrell

    Terrell Old-Timer

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    Oops, I fixed that now. I was able to play it here on PriusChat, but maybe that's because I'm the owner? Anyway, it should work now.
     
    #21 Terrell, May 19, 2019
    Mendel Leisk likes this.
  2. Terrell

    Terrell Old-Timer

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    Without the battery tray, that stud sticks up too high, and might eventually poke a hole in the battery. I thought about adding a thin piece of wood there to prop the battery up above the height of the stud, but then I've lost my anchor, unless I could figure out how to still anchor with the stud. I read about someone who just hammered that stud over, but I don't wish to change anything on the car itself. And I think the stud makes a good anchor, and the battery tray holds the battery nicely.
     
    #22 Terrell, May 20, 2019
    Last edited: May 20, 2019
  3. Terrell

    Terrell Old-Timer

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    The refrigerator only draws 6.5A. But how much it draws over time is the issue. On a camping trip (before the second battery), after three consecutive hot days, my 12v battery was drained to the point where the refrigerator shut itself off at 11.4V on the battery (it's a feature to prevent total battery draining).
     
    #23 Terrell, May 20, 2019
  4. Montgomery

    Montgomery Senior Member

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    I really like the idea of two 12v batteries due to the fact that I miss being able to run things without having the system in the "on" position. Also, the way this battery is installed, it constantly gets charged without interfering with the operation of the vehicle. To do this right, from the description of the video, cost could run $200 to $500, depending on availability of the parts listed. In the long run, if one was to keep their Prius for over 10 years, it is worth it.
     
    #24 Montgomery, May 20, 2019
  5. Greenteapri

    Greenteapri Active Member

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    Played fine for me.

    That's amazing! Video demonstration of your system in use...?

    I'm looking forward to your second video tutorial, sir.
     
    #25 Greenteapri, May 20, 2019
  6. Terrell

    Terrell Old-Timer

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    Look in my signature, and you'll see three of my videos. :)
     
    #26 Terrell, Jun 15, 2019
    don K otay and Greenteapri like this.
  7. Terrell

    Terrell Old-Timer

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    Correct. It cost me $194.08, but I already had a few things, like velcro and quick connects. And the battery I used is my "old" Prius 12V battery, which, according to Toyota, had only about half it's capacity anymore. So I bought a new battery (I think it was over $200 from Toyota) and repurposed the old one into my system. I plan to keep this car until it dies.

    The convenience of having the second battery with the automatic relay is worth it to me. While traveling, I used to plug the refrigerator into a 12V outlet hooked to the car, then when stopped, unplug it and plug it into a second battery. But sometimes I forgot. Plus the second battery was not getting charged, just drained every time I stopped. I tried to help it with solar panels, but on a camping trip with cloudy sky and trees, the second battery died on the third day.

    With the relay, both batteries get charged while driving, both get charged with the solar panel, and I don't need to remember to swap the 12V refrigerator plug back and forth all the time. Plus it's fun to show people. :)
     
    #27 Terrell, Jun 15, 2019
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  8. Montgomery

    Montgomery Senior Member

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    Cool stuff man, cool stuff!
     
    #28 Montgomery, Jun 15, 2019
  9. bobzchemist

    bobzchemist Active Member

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    Do you (or does anyone) know if the battery charging system is 100 amps or lower?
     
    #29 bobzchemist, Jun 16, 2019
  10. Haschwalt

    Haschwalt Member

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    Terrell, thanks foe the vid.

    Some questions but are you hooking the fridge to the cigarette lighter outlet but directly to the 12V terminals?

    I live in cloudy climate so I think solar would not be effective but I want to Be able to run a fridge 24/7 in Prius without using ready mode.

    If I hook up a second battery to the first 12V one, are you able to simply keep running the fridge or will it stop to ensure your main 12V doesn’t die?
     
    #30 Haschwalt, Jun 21, 2019
  11. bobzchemist

    bobzchemist Active Member

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    The entire point of putting in a relay/solenoid/battery isolator is specifically to keep your main 12v battery from dying while still allowing some power drain. Otherwise, you could just hook the two batteries together and call it a day. Since it only takes two or three times of running a car starting battery to zero to destroy it completely, I would not suggest this.

    Some of the isolating setups allow you to use a portion of the charge of the main 12v when the car is off, others lock it away completely. It would depend on the efficiency of the fridge, but to be able to run a fridge 24/7 even when the car is off certainly sounds like you'd need a fairly large battery as your second one. I wouldn't use a starting battery for this if you can avoid it.

    Please note that even deep-discharge batteries are significantly harmed by running them down to zero. I strongly suspect that it would be cheaper to replace what's in your fridge than it would be to replace a battery. There are devices that will shut the connection to the second battery down also if the power level gets too low. Looking into how RV's and boats handle this would probably be a good idea.
     
    #31 bobzchemist, Jun 21, 2019
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  12. Haschwalt

    Haschwalt Member

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    I would be dwelling in the car full time so I’d be able to charge it in ready mode over night for 8 hrs or so.

    It’s the 16 hrs or so that ready mode would have to be off (I don’t want to run ready mode while not in the car bc anyone can break in and drive away).

    I read that the 12V Prius battery shouldn’t be discharged below 50% - so how many usable Ah can one get from it?

    This guy macaloney.blogspot.cm/2015/03/powering-fridge.html did two batteries in a similar setup to OP and stated he got 14 Ah but not sure if that’s full
    drain. A dometic cfx-28 12v fridge sips .75 Ah per hour, giving 19 hrs of run time (more than plenty for daily dwelling with using ready mode for 8 hrs of the day).
     
    #32 Haschwalt, Jun 21, 2019
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