Forum Discussion

mrskittle's avatar
mrskittle
Explorer
Jul 14, 2020

setting up a battery bank

I'm a long-time camper, first time TT owner.

We do most of our seasonal camping in campgrounds without hookups so I'm looking to get my battery bank all set up for some 3-4 day trips. After thinking about it a lot and doing lots of research, I figure I'll lay out my goals and see if folks can help me along.

GOAL: I want to use the camper without worrying about draining the batteries to unwanted levels each day and then not have to run my generator for more than an hour a day to get back to full charge.

The rig is a modest 20 ft Gulf Stream Visa. It is such a huge step up from the 12 ft, bare-bones pop up that we had. Unlike that camper, we'll be using the battery on the new one for more than just a single ceiling light. In the new one we'll need power for the water pump, lights, and exhaust fan. This also includes the low draw from appliances like the fridge and water heater, which will run off propane. The exhaust fan, which draws around 4 amps, is the most important of these. In addition, I plan on adding a 1000 watt inverter to supply some AC power for small appliances like a coffee maker and electronics. What I'm not looking to do is wire anything into the camper electrical panel to supply power to the entire rig from the batteries. While it may be desired on occasion, I don't expect to run the air conditioner without shore power.

I currently have 2 group 24 deep cycle batteries. My understanding is that group 27 are better fo the application, but for now I'm working with what I've got on hand. I'm looking to wire them in parallel to boost the amp hours. I also want to run the 1000 watt inverter off the same 2 batteries. I would feel comfortable wiring the batteries in parallel to just supply the camper but adding the inverter raises some questions, espically about charging. I'm guessing that I'd have to install a switch on the hot wire to the inverter to shut off while I charged. I should clarify that I'll charge by hooking shore power to the generator and using the built-in charger in the camper. I do have a stand-alone charger if that might be a more efficient/faster way to go.

To summarize, I want a reliable battery bank that will last for the day with modest use of the camper. I want to run a 1000 watt inverter off the same batteries to occasionally run small appliances and electronics. Finally, I don't want to run my 2000w generator more than an hour to charge the system back up after a day's use. I hope this all makes sense.
  • jdc1's avatar
    jdc1
    Explorer II
    Jul 14, 2020
    Forget the coffee maker. It draws a ton of power. Get a "french press". Two ways to go here. Add a solar panel or two (100-200watts) or get an inexpensive generator to charge those two batteries.
  • jdc1's avatar
    jdc1
    Explorer II
    Jul 14, 2020
    Forget the coffee maker. It draws a ton of power. Get a "french press". Two ways to go here. Add solar. You already have a generator. Connect that inverter directly to the battery. You'll have better results with less amperage drop.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jul 14, 2020
    Do an energy audit, best done with a battery monitor to determine your needs. Your batteries are NOT deep cycle regardless of what they say on the label. Marine deep cycle batteries are a compromised starting battery.

    You might want to plan for 2x 6V GCs deep cycle batteries which will give you 230Ah, ie 115Ah to 50% discharge. Your present batteries are about 160Ah. 2 GCs would be wired in series. GCs are also heavier and taller.

    Inverters can draw a lot of power. For 1A AC they draw 11A DC or 11Ah.

    What does this mean? Aren't your current batteries wired in parallel?

    "I currently have 2 group 24 deep cycle batteries. My understanding is that group 27 are better fo the application, but for now I'm working with what I've got on hand. I'm looking to wire them in parallel to boost the amp hours."
  • time2roll's avatar
    time2roll
    Nomad
    Jul 14, 2020
    For fastest charging you may need to replace the converter. I recommend the PD-14.8 for fastest charging. Post your converter model number for best comments.

    http://www.bestconverter.com/9200-148-Modified-Deck-Mount

    The 60 is fine on 2 batteries. Get the 80 if you might go to 4 batteries in the future.

    Solar is great if you have any direct sunlight. 400+ watts could eliminate the generator completely.
  • mrskittle's avatar
    mrskittle
    Explorer
    Jul 14, 2020
    I should have clarified that I'm not interested in going with solar at this point. I plan on wiring the inverter straight to the battery and mounting it in the front of the camper to avoid a long wire run.
    I've used the french press for years and enjoy the "camp coffee" I get from my old press. However, sometimes I just want the simple pleasures of life, hence the upgrade from the pop-up to the TT and the opportunity for some drip coffee.

    I did a sort of energy audit but testing the draw of each possible motor present in the camper. The exhaust fan is about 4.5 amps, the water pump is up at 7 amps, and so on. I'll still need to assess the draw of anything I want to run with the inverter.

    The camper only has one battery at this point. I have a second one that I already had around from using on the pop-up camper. I am looking to mount the second one on the camper and wire them together.
  • campigloo's avatar
    campigloo
    Explorer
    Jul 14, 2020
    Ditch the coffee pot is good advice. We use a 10 cup percolator and use the propane stove to make it work. Makes a great cup of coffee and uses 0 watts. Walmart, about $15.
  • camperdave's avatar
    camperdave
    Explorer
    Jul 14, 2020
    We can easily do 3-4 days on a pair of 6v batteries in our rig. Modest inverter usage (300w inverter) for charging things up, but no real power usage. Just lights and fans when needed. For that length of trip, we don't need a generator or solar.

    But I do highly recommend the aeropress.com it is way better than a french press, it actually makes great coffee and is simple to use. I prefer it to drip even at home.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Jul 14, 2020
    2x 6V golf cart batteries wired in series. These are TRUE deep cycle batteries, not "dual purpose". They store a lot of energy and handle discharging and charging better.

    Get rid of your existing converter and replace it with a combination inverter/charger/automatic transfer switch. Easy to install (hook you DC fuse/distribution panel directly to the battery bank). Even easier to use (it will charge the battery back when shore power is available and automatically switches from shore power to battery when there is a load).

    Buy a GOOD battery monitor like a Victron BMV-700.

    If you don't use the coffee maker I am certain you can get by with less than 1 hour per day on the generator. If you want the automatic coffee maker and a toaster, you will have to fire the generator up shortly after breakfast. Worst case, run it a second time before evening until the battery monitor says the battery bank is full.

    If you are going to be travelling a lot, I strongly suggest a DC-DC battery charger. That way even if you hit the road immediately after breakfast you can be sure the batteries will be fully charged.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jul 14, 2020
    mrskittle wrote:
    To summarize, I want a reliable battery bank that will last for the day with modest use of the camper. I want to run a 1000 watt inverter off the same batteries to occasionally run small appliances and electronics. Finally, I don't want to run my 2000w generator more than an hour to charge the system back up after a day's use. I hope this all makes sense.


    Do an energy audit.

    Unfortunately lead acid wants to be charged to 100% full on as many cycles as possible.

    Running a generator to get to 100% state of charge is an expensive and noisy business.

    The group 24s are overmatched by boondocking for more than a day or so. For longer life, don't take them below 50% state of charge.

    Consider SiO2 chemistry when the group 24's fail. SiO2 do not require being fully recharged and can be used down to 20% state of charge.
  • valhalla360's avatar
    valhalla360
    Navigator
    Jul 14, 2020
    mrskittle wrote:
    I should have clarified that I'm not interested in going with solar at this point. I plan on wiring the inverter straight to the battery and mounting it in the front of the camper to avoid a long wire run.
    I've used the french press for years and enjoy the "camp coffee" I get from my old press. However, sometimes I just want the simple pleasures of life, hence the upgrade from the pop-up to the TT and the opportunity for some drip coffee.

    I did a sort of energy audit but testing the draw of each possible motor present in the camper. The exhaust fan is about 4.5 amps, the water pump is up at 7 amps, and so on. I'll still need to assess the draw of anything I want to run with the inverter.

    The camper only has one battery at this point. I have a second one that I already had around from using on the pop-up camper. I am looking to mount the second one on the camper and wire them together.


    CATraveler covered most of the points I would bring up.

    You can use high draw items, but they are in a different range of power draw.
    - Energy Audit: A battery monitor is better but you can estimate by taking the amp draw of each item and multiplying by the time that it will be operating. This will give you the amp-hrs used. (for 120v items running on the inverter, you multiply by 10 to get a rough estimate of amp-hr in 12v DC).
    - Your batteries are basically starting batteries and mixing two of different age, condition is generally not the best approach. The worst battery will tend to drag the better battery down to it's level. (a pair of 6v golf cart batteries are real deep cycle batteries and will have more amp-hrs and hold up better)
    - One of the problems with charging with a generator is as they hit around 80% charge, they accept gradually less amps...to get to 100% takes a very long time. They also like to live life at 100% charge, so between trips put them on a charger. Below 50% is generally considered bad. A compromise is to charge to 80% and then limit the drawdown to 50%...so you only have 30% of the rated amp-hr for the battery bank as usable. So if your energy audit says you need 50 amp-hr per day, you are probably looking at needing around 170amp-hr battery bank (assuming you charge each morning with the generator).

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