Planning and Building a Whole House Battery Backup System

Discussion in 'The Projects Forum' started by LymanBay, Aug 31, 2015.

  1. LymanBay

    Thread Starter New Member

    Aug 29, 2015
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    Hello,

    I've always had a curious interest in batteries and portable power. I've always felt empowered ( pun = happy accident ) not having to rely on the utility companies.

    A short while ago, I assembled a battery backup for an equipment rack in my living room. The parts list is as follows:

    1. 110v AC auto transfer switch. It's a cool device from a solar panel system.

    2. 2500/5000 Watt power inverter.

    3. Duralast Deep Cycle Marine Battery.

    4. Battery Tender Plus High Efficiency model.

    Wiring the Battery Tender to the Duralast battery to maintain a full charge, I connected the inverter. Plugged in to the auto transfer switch, I now have a battery backup system which supports the entire equipment rack. The battery always maintains a full charge and I'm able to monitor for the loss of power from the utility company and switch over to battery backup automatically when power is lost.

    Based on the power demands of the equipment rack, I calculated about 6 hours of power. When I performed a test, the battery supported the rack for over 7 (I wonder why the discrepancy?). Obviously, this is a short term solution in the event of a power failure (I have a generator).

    I want to expand my battery backup so that I can support more of my home for a longer period of time.

    I've been looking at plans to build led acid batteries. What I have found is that within a led acid battery are 6 smaller cells, each of about 2.3v connected in series. When you take into consideration the cost of materials to build a battery and then multiply by the number batteries required, it is not much more expensive to purchase the number of led acid batteries you need.

    Would I have to connect these batteries in parallel? I would be connecting this battery array to a dc to ac inverter of at least 10000 watts. Also, while a battery tender may be able to charge an array of 6 batteries, wouldn't it be a really SLOW charge?

    I'm in the research stage and welcome lots of input. I can't possibly think of everything on my own and embrace a collaborative effort.

    Thanks

    Lyman
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Your power requirements dictate the choice of battery and the chosen battery dictates the maximum charging rate.

    So, maybe you should start by working out how much power you need and for how long.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Since you have a generator, then I would use the battery backup for only those devices you don't want to lose power during the changeover time from the mains to the generator.
    I would think that would be a short list.
     
  4. RodneyB

    Active Member

    Apr 28, 2012
    633
    13
    Make sure your Battery bank is rated at a discharge of 60%. Most inverters draw down to 60% DOD.

    We have 12 Hour daily power cuts so have tried and tested many systems. If you don't have regular power cuts then fit an equalizer to the batteries they help. Also agitate the batteries frequently and rotate them.

    Torque the connections on the battery and inverter, Happy to help where I can
     
  5. LymanBay

    Thread Starter New Member

    Aug 29, 2015
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    0

    It isn't how much power I need in as much as it is power I want.

    Based on the usage report by my utility company, I've never drawn more than 59 amps on a 100 amp service. Lets call it 60 amps.

    I'd like to be able to sustain 30 amps over 12 hours.
     
  6. LymanBay

    Thread Starter New Member

    Aug 29, 2015
    7
    0
    Right. That was the initial idea behind the battery backup; to sustain power temporarily until I can get things on the generator. I get enough power now for several hours on the equipment rack. Additionally, I get several hours on the backup for the aquarium.

    I'd like to build one battery backup to support both and add some other things (refrigerator). The ultimate backup will still be the generator, but, I'd like to get more time out of battery and broaden the scope of what is supported.
     
  7. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    30A x 110V = 3.3kW

    If you have a 48V battery, for instance; it will need to deliver 69A which over 12 hours equates to an available battery capacity of 825Ah but the nominal battery capacity would need to be greater than this, perhaps 2000Ah or more. You must also factor in inverter losses.

    If you want that kind of capacity you should speak to battery/ups specialists and get their advice. It won't be cheap.
     
    Last edited: Aug 31, 2015
  8. crutschow

    Expert

    Mar 14, 2008
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    3.3kW is a very large draw. I seriously doubt that your average draw is anywhere near that high.
    What is the average usage on you power bill?
     
  9. LymanBay

    Thread Starter New Member

    Aug 29, 2015
    7
    0
    Yes, I could BUY the battery backup I need. But what fun would that be?
     
  10. LymanBay

    Thread Starter New Member

    Aug 29, 2015
    7
    0
    Average draw? Good question. I should base this on typical usage.

    I'd speculate that 59 amp max usage was during the summer with AC running. Of course, during a power crisis, I would do without AC. So basing this project on average usage history as opposed to max usage history is wise. I'll contact the utility company to find out.
     
  11. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    How would you acquire a 2kAh 48V battery without buying it?
     
  12. crutschow

    Expert

    Mar 14, 2008
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    It should be on your power bill.
     
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