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second 12 volt battery - 2020 edition

Discussion in 'Gen 3 Prius Main Forum' started by geedub, Apr 27, 2020.

  1. geedub

    geedub Member

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    Hi all. I've read threads here and elsewhere about this mod but I'm more confused than ever. I've been camping in my 2012 Pruis since April 6th, when I closed on my house. I'm not working due to the virus and I'm not ready to commit to buying or leasing a place yet, not until things settle down a bit with the economy and housing market. Glad that my car is a generator!

    For the most part I've had my car in READY for the whole time. I'm running a thermo-electric cooler so I need power all the time. I'll modify the car as needed to minimize the stress on the engine/battery. I've gotten 150K miles with zero repairs so far. Best. Car. Ever.

    A local auto stereo shop quoted me $900 to install a 12 volt in parallel with a manual disconnect. Seems high...

    I may graduate to a Dometic cooler/fridge, and I'm open to solar if that's recommended. I'm in central Florida so A/C will be needed at night, but maybe I can turn the car off in the daytime?

    Anyway, any guidance would be appreciated!

    Jerry

    camp prius.jpg
     

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  2. Johnny Cakes

    Johnny Cakes Senior Member

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    Hi Jerry,

    First, welcome to the world of Prius Camping! It's awesome. I've run the car all night for A/C in Florida for weeks at a time -- it uses less than a gallon per night. I like the "Miles to Empty" display -- a good sleep A/C is about 30 miles. I wouldn't worry too much about "stressing" the engine. Cab fleets the world over use Prius, and they're driving on a 24/7 basis, whereas you only need the ICE to start for a couple minutes each hour.

    Second, not only is that battery cost crazy high, but if you are looking to run your refrigerator when you are not there or want the car OFF, what you are really looking for is a house battery setup that is charged by the Prius. You also want a LiFePo4 battery, not a standard car batterry. Check out Brent's site for an excellent design:
    Brent's Travels: Prius House Battery Migration From Gel Cells to LiFePo4
    I think he mostly uses an Inverter to charge the house battery, but personally I use a 12v charger thereby bypassing the DC/AC/DC current conversion (although you must get one that is LiFePo4 specific if you go that route). Brent's site also has some excellent "how to" posts for Prius camping, but there's a bunch of sites on the Internet with Prius camping tips. From the photo, looks like you don't have to worry about "stealth camping" (which is actually half the fun).

    Third, before going with a Dometic, I would definitely look at Engel fridges as they are the gold standard for Prius camping. The most important thing for Prius camping and running a fridge on a house battery is efficiency and that's where the Engel models excel. Although for my purposes, I just use ice in a cooler. I shop a couple of times per week anyway, so ice is simple and obviously requires no electricity. Now, "northerners" will not know what I'm talking about, but depending where you are in Central Florida, you probably have a "Twice the Ice" (or something similar) nearby for dirt cheap ice (and complete social distancing -- lol).

    Good luck!

    --JC
     
    #2 Johnny Cakes, Apr 27, 2020
    Last edited: Apr 27, 2020
  3. tvpierce

    tvpierce Senior Member

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    I don't know how much you move around, but if you're in one location, and security while you're away isn't a problem, you may want to look at solar. I've been considering a small system for off grid camping with my pop-up camper. The prices have really come down -- like under $200 for 100 watts with a quality controller. Another $100 for a battery and you have a self contained, indefinite source of power.
    Prices for 12 volt compressor coolers/fridges have also come way down.
     
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  4. geedub

    geedub Member

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    Thanks Mr. Cakes. I'll check out the links. I didn't come across them before.

    I've heard the Engel Fridges are more efficient but it appears the newer Dometic CFX3 series has some notable improvements over older models. They claim about 1 Ah to maintain 38F in a 90F environment. Using a regular cooler isn't practical as I'm staying 4 miles from pavement. The dirt road isn't great and when it rains it's a mess. Since I may be "camping" for several months I'm looking for convenience.

    Yeah, definitely not stealth camping. I'm not sure you can even call it camping after many months. The site is in a wetland area so there are all kinds of interesting creatures including yellow flies and mosquitoes (Florida state bird). The yellow flies slice your skin and drink your blood causing severe itching. Given the bugs, strong sun and frequent heavy rains, the screen canopy makes this arrangement far more pleasant. Behind the screen room you can see the shower tent, complete with propane camp shower. Not roughing it.:)

    Thanks tvp. Being in Florida definitely makes solar worth considering.
     
    #4 geedub, Apr 28, 2020
    Last edited by a moderator: Apr 28, 2020
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  5. ChapmanF

    ChapmanF Senior Member

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    I've never owned either one, but had heard of Dometic. Where can I learn more about Engel being the gold standard for Prius camping?

    I did find this comparison that looked useful (though I winced where the guy wrote "amps per hour").

    Waeco CFX vs Engel - a campfire debate | Snowys Outdoors

    and this one (where they also say "amps per hour"! over and over and over. Who taught these guys unit factors, anyway? Does everybody in that market niche just recycle the same mistakes?)

    Refrigeration on the Road: The Best 12V Portable Fridges for Vanlife
     
  6. geedub

    geedub Member

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    I've been looking at the Dometic CFX3 series and think they might be a game changer...

    I'm wondering if I really need a 2nd 12 volt. I have a 300W inverter that I plug into the 12v outlet to charge laptop, toothbrush, etc., and if I can run the fridge on the one 12v why expand? The Dometic CFX3 35 I'm considering pulls about 1 amp each hour, and has three levels of battery protection. If I could run the fridge for 6 or 8 hours with the car off, that would be enough for my needs. What do I gain from adding another battery?
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    I'd assume you have a tightly sealed hose running the exhaust gas out? I mean, that looks like a suicide tent. Is that a thing, lol?
     
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  8. geedub

    geedub Member

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    Well, it's a screen room, but my main hangout area is just behind the car so the exhaust is not pleasant. Funny you should ask because I'm starting a new topic as we type about that very issue.
     
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    I'll hold you to that: if you don't start that topic soon I'll send out a search party, lol.
     
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  10. Johnny Cakes

    Johnny Cakes Senior Member

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  11. ChapmanF

    ChapmanF Senior Member

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    Oh no, not you too! Stop!!!1! "Amp each hour" isn't a thing.

    An amp is a unit of electric current: it's already a rate (3600 coulombs per hour). If you're talking about the amount of energy consumed, the amount that's equal to a one-amp current steadily flowing for one hour is one amp⋅hour.

    If your fridge draws that much every hour (whether it draws 1 amp all the time, or 2 amps when it's running but only runs half the time, etc.) then it draws one amp⋅hour each hour (Ah/h).

    The Dometic guys do get it right in their own specs:

    ahph.png

    but both of the review writers I linked earlier made the same mistake and said "amps per hour" (one of them over and over and over again). It seems to be a mistake that's well entrenched among some.

    May seem like a pedantic point, but really, paying attention to the units of things can make a lot of stuff easier to think about.

    Your Prius aux battery nominally holds 45 amp⋅hours (if it is new, and fully charged), so you would think you could get away with running the Dometic for several hours no sweat; also, the Dometic is said to contain its own voltage monitor circuit so it will show mercy to the battery if it gets too low, and should still leave you enough to get the car started.

    I might take a chance that way myself. I would, however, make sure my pocket-sized lithium jump pack in the glove box was charged and ready in case needed.
     
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  12. geedub

    geedub Member

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    Thanks. I started the topic exactly because I'm ignorant about electronics, so, yeah. I'm bothered when people say "I could care less" when the correct phrase is clearly "I COULDN'T care less". o_O

    I replaced the 12 volt about 3 months ago. The Dometic I would get has three levels of battery protection programmable. The most conservative setting supposedly leaves plenty of cranking power.
     
  13. 2012 Prius v wagon 3

    2012 Prius v wagon 3 Active Member

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    Nice work on setting things straight regarding units. I agree, very important to track those carefully.

    Slight correction on the "energy" statement - that should be "charge," not energy. I believe when talking about a battery, this rating is called "capacity," and is measured in Ah.

    And it matters, and can be an issue if not tracked carefully, since the energy will be different depending on the voltage drop. So for example, current at the 12V battery, that may then be stepped up or down to 5V for example, will have a corresponding change in current to get the same power (energy / time). But current is simply charge / time, e.g., Coulombs per second.
     
  14. ChapmanF

    ChapmanF Senior Member

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    Good catch. Yes, energy would have been watthours or joules. Charge is right.
     
  15. geedub

    geedub Member

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    So, I'm still trying to understand what the benefit of an extra battery is to my situation. It seems like I can just plug a fridge into a 12v socket and keep the car in READY. If I did want to run a fridge with the car off, the new Dometics can be set to shut down before the battery discharges below starting levels. I'm getting a jump pack either way so I'll have insurance.

    So what do I gain?
     
  16. ASRDogman

    ASRDogman Senior Member

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    Less stress on a battery that wasn't designed for what you are doing.
    More amperage, power. Less chance of the battery(12v) dying if you forget and turn the car off...
     
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  17. geedub

    geedub Member

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    Am I correct in thinking that we're talking about running the second battery in parallel, and the effect is basically that of enlarging the battery (capacity)?
     
  18. Ed Beaty

    Ed Beaty Active Member

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    I recommend checking out this video on second battery installation. OP also employs the Domestic cooler in his Prius. If you go to his YouTube channel there are MANY more interesting/well done vids on his Stealth Prius project. Excellent.
     
  19. geedub

    geedub Member

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    Thanks. I've watched his videos and I agree they're well done.
     
  20. Mendel Leisk

    Mendel Leisk Senior Member

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    That extols a concept, that there's a "surplus" of charge, that can be used without consequence. I don't think that's the case.