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  • Starting with Battery Backup

    I am in the process of building a backup system for two rooms in my home, my computer office and the master bedroom. In the event of a power failure, I hope to operate on battery for up to 12 continuous hours.

    I currently have a battery and a 1K/2K pure sine wave inverter that I can operate my computers for 4.5 hours. I am using a smart charger connected to the grid to recharge the battery.

    I will be moving the batteries into a tool shed with the inverter and running wires into the house for power. I will be adding solar power and, hopefully, wind power this Spring. I am also working on acquiring a gas generator so I can charge the batteries and power the heater system and two refrigerators periodically as needed for long term power outages.

    I will be building power panels in the room so I don't tie directly to the electrical wiring in the house. (I just learned about the electrical code issues of connecting to internal wiring, even if it is separated from the main breakers.)

    ==== Additional Information ====

    Solar power has been an interest of mine for a few years now. I have researched and read a lot about it and understand its costs and limitations, especially for my area.

    What actually triggered my taking action on it was when my computer UPS went out and I started looking into replacing it with one that will last for several hours. I already have a battery charger so I bought a marine battery and a pure sine wave inverter that keeps my computer up for over 4 hours. It cost about the same as a modified sine wave UPS that would only last about 15-30 minutes under the same load.

    Because the price of Solar cells is falling, I have also planned on adding solar to my system. I have designed a cat porch to extend out my office window that is just the right size to mount two 100 watt panels on for rain cover. The panels will get about 4 to 5 hours of sun in the winter and even more in the summer.

    I live in an area where we get lots of wind. I expect that a small vertical style windmill could provide a reasonable amount of electricity to help charge the batteries.

    Eventually, I hope to take both my bedroom and computer office completely off the grid for the majority of the time, and backed up by the grid as necessary.
    Last edited by n4pgw; 11-28-2015, 04:05 AM. Reason: Additional Information

  • #2
    Originally posted by n4pgw View Post
    I am in the process of building a backup system for two rooms in my home, my computer office and the master bedroom. In the event of a power failure, I hope to operate on battery for up to 12 continuous hours.
    Then you have no need for solar whatsoever. Once you learn the true cost will never consider solar as back up or primary power.

    All you need is a charger and battery to do what you want. Regardless how the battery is charged, it will be the same size and type. Difference is a AC commercial charger is a lot cheaper, faster and more reliable than solar. And just for 12 hours, a generator is the real answer as it will be less expensive than a battery option, and can produce a lot more power for a lot longer time.
    MSEE, PE

    Comment


    • #3
      Originally posted by n4pgw View Post
      I am in the process of building a backup system for two rooms in my home, my computer office and the master bedroom. In the event of a power failure, I hope to operate on battery for up to 12 continuous hours.
      Great; such UPS systems are available off the shelf.

      If you want to you can add solar later. They're not really related. You might be able to share one component (the inverter) but you'll see benefits by keeping the two systems separate.

      Comment


      • #4
        I have a 24v operational battery back up system consisting of eight golf cart batteries, and a 1500 watt inverter. It will run the two circuits of my household transfer switch I need for the computer, tv, reefer and lights, the bare essentials. When the batteries get down to 75 or 80% I switch over to the Lister gen set and carry on plus charge batteries with my 25 amp power supply/charger. I can run a day and a half on the batteries. Thanks to the helpful information I received here I have a pretty nice battery system that I was able to add to the generator system. I may get some panels later.

        Comment


        • #5
          Originally posted by n4pgw View Post
          I currently have a battery and a 1K/2K pure sine wave inverter that I can operate my computers for 4.5 hours. I am using a smart charger connected to the grid to recharge the battery.
          Great - although as was pointed out, solar isn't really cost effective in the long run as compared to the poco, but one may want to do it for other reasons.

          Hopefully you aren't powering all your gear until the inverter's low-voltage disconnect trips.

          There is a lot of good info in the forums, but I have found it convenient to divide a solar project into two parts - load vs battery, and THEN how much panel power it takes to keep them healthy in your geographic area in the winter. By treating it as two subjects, you can cut down on the information overload.

          For instance, forgetting solar for the time being, pull out the power formula for some quick napkin-calc figures on how long you can run your stuff until you reach 50% DOD.

          100ah battery / 12v system

          100 * 12 = 1200 watthours total
          1200 / 2 = 600 watthours *usable* <--- typical 50% DOD point, although peukert plays a part, but for now the napkin is good enough.

          So, using something like a P3 International Kill-A-Watt meter, how many watts does your gear pull, and for how many hours? Try not to exceed 600 watthours before recharging.

          To keep things tidy, you may want to look into the Powerwerx Super Powergate PG40S if you like to deal with Anderson connectors for your dc gear for both charging, and an ats switch. Voltages are adjustable inside the unit.

          Welcome aboard!

          Comment


          • #6
            Originally posted by Sunking View Post
            Then you have no need for solar whatsoever. Once you learn the true cost will never consider solar as back up or primary power.

            All you need is a charger and battery to do what you want. Regardless how the battery is charged, it will be the same size and type. Difference is a AC commercial charger is a lot cheaper, faster and more reliable than solar. And just for 12 hours, a generator is the real answer as it will be less expensive than a battery option, and can produce a lot more power for a lot longer time.
            Thank you for your reply.

            I am aware of the costs of solar, and it sucks, but it is an interest, and soon to be hobby for me. The electric rates are about $0.11/KW. At that rate, it does look like it could take 6 years to pay for itself.

            A generator is in the works for some critical areas and to charge the battery bank, but I have medical equipment and computers that I don't want to lose power to between the time the power fails and the generator is started.

            Comment


            • #7
              Originally posted by jflorey2 View Post
              Great; such UPS systems are available off the shelf.

              If you want to you can add solar later. They're not really related. You might be able to share one component (the inverter) but you'll see benefits by keeping the two systems separate.
              Thank you for your reply.

              I haven't found cost-effective UPSes that will do what I want. I wish I could, it would simplify this project.

              You may be right about separate systems, and there will be some separation, but I don't know how much at this time.

              Right now, I am taking it one day (or one piece) at the time.

              Comment


              • #8
                Originally posted by stevo View Post
                I have a 24v operational battery back up system consisting of eight golf cart batteries, and a 1500 watt inverter. It will run the two circuits of my household transfer switch I need for the computer, tv, reefer and lights, the bare essentials. When the batteries get down to 75 or 80% I switch over to the Lister gen set and carry on plus charge batteries with my 25 amp power supply/charger. I can run a day and a half on the batteries. Thanks to the helpful information I received here I have a pretty nice battery system that I was able to add to the generator system. I may get some panels later.
                Thank you, stevo, that's very encouraging.

                It's that transfer switch that I have problems with. I live in someone else's home so what I can change is limited. I just need to figure out how to get the wires run without having to tie to the internal wiring. I can do that when the time is right.

                Comment


                • #9
                  Originally posted by PNjunction View Post
                  Great - although as was pointed out, solar isn't really cost effective in the long run as compared to the poco, but one may want to do it for other reasons.

                  Hopefully you aren't powering all your gear until the inverter's low-voltage disconnect trips.

                  There is a lot of good info in the forums, but I have found it convenient to divide a solar project into two parts - load vs battery, and THEN how much panel power it takes to keep them healthy in your geographic area in the winter. By treating it as two subjects, you can cut down on the information overload.

                  For instance, forgetting solar for the time being, pull out the power formula for some quick napkin-calc figures on how long you can run your stuff until you reach 50% DOD.

                  100ah battery / 12v system

                  100 * 12 = 1200 watthours total
                  1200 / 2 = 600 watthours *usable* <--- typical 50% DOD point, although peukert plays a part, but for now the napkin is good enough.

                  So, using something like a P3 International Kill-A-Watt meter, how many watts does your gear pull, and for how many hours? Try not to exceed 600 watthours before recharging.

                  To keep things tidy, you may want to look into the Powerwerx Super Powergate PG40S if you like to deal with Anderson connectors for your dc gear for both charging, and an ats switch. Voltages are adjustable inside the unit.

                  Welcome aboard!
                  Thank you, PJ,

                  The PG40S is exactly something I want! Thank you. And, yes, I do use powerpole connectors almost exclusively.

                  My Kill a Watt was received a few days ago. It is currently plugged into my inverter and shows usage of my computer equipment on the battery. I'll be using it to measure the other outlet uses soon.

                  Because it isn't lighted and doesn't have a memory, I'll have to do some rerouting of the wires to get readings. I may be ordering one that has those features.

                  My first test was to take the battery to a full charge, then I ran my computer equipment until the inverter shut down. That was just the test. I now operate with a 35 amp power supply connected so it takes the load off the battery while I have grid power. When I shut down, I connect the battery charger to top off the battery since it charges the battery a little higher than the power supply does.

                  I am thinking that a solar power converter may shut down the power from the batteries if the level drops below a preset level. I am planning on ordering one and connecting a regulated power supply to it to test it. I am looking for a supply where I can set the voltage to 15 or more volts and feed an MPPT converter. That's just the thought for now.

                  I think my next task is going to be to start building the power panels for the different room walls and wiring them together.

                  Comment


                  • #10
                    Originally posted by n4pgw View Post
                    I am thinking that a solar power converter may shut down the power from the batteries if the level drops below a preset level.
                    Solar charge controllers go between panels and batteries. They will not "shut down the power from the batteries" to the load (i.e. inverter) if the voltage gets too low. Most inverters have a LVD (low voltage disconnect) to keep you from pulling the batteries down too low. However, this is a last ditch safety feature and CANNOT be used to protect your batteries. If you rely on the LVD, you will destroy your pack very rapidly.
                    I am planning on ordering one and connecting a regulated power supply to it to test it. I am looking for a supply where I can set the voltage to 15 or more volts and feed an MPPT converter. That's just the thought for now.
                    MPPT controllers will often do odd things when you connect a fixed output supply to them, since a power supply's output has a very different V/I characteristic than a solar panel.

                    If you have an adjustable power supply you can use it for battery charging without any additional controller.


                    Comment


                    • #11
                      Originally posted by n4pgw View Post
                      I am aware of the costs of solar, and it sucks, but it is an interest, and soon to be hobby for me. The electric rates are about $0.11/KW. At that rate, it does look like it could take 6 years to pay for itself..
                      Sorry but not even realistic. In 6 years you will be at th eend of life on your second set of batteries, or third new set. Even if you actually used the batteries every day utilizing every possible Watt hour., battery cost alone will be many multiples higher than what you pay the electric company. Battery cost alone fully utilized will be 40 to 60-cents per Keh. Used as Back up as you intend, $100 per Kwh. So please don't go fooling yourself. You simple have no need for solar
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by n4pgw View Post
                        I haven't found cost-effective UPSes that will do what I want. I wish I could, it would simplify this project..
                        That is because you are looking at it wrong. Buy Charger>Batteries>Inverter and you have now made a Dual Conversion UPS. Jeff is speaking of a manufactured UPS, I am speaking of a DIY UPS with more capacity and capability.

                        73's
                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by n4pgw View Post
                          I haven't found cost-effective UPSes that will do what I want. I wish I could, it would simplify this project.
                          Just remember that most UPS's don't have the right batteries in case you start to cycle it often. Inside most are "high rate", or "general purpose" agm's, with multiple batteries in series/parallel which we try to avoid to prevent issues with balance etc. For a handful of temporary emergency uses, this may not matter, but I'd hate to see you spend bucks on a system that is inappropriate for cyclic use if your emergency becomes more than temporary.

                          Just be aware that if you get the bug, the first thing that happens is cyclic operations, and the loads grow!

                          RFI and mppt - if you do any HF work, then be sure you can test / return a unit quickly. Some are better than others, and as you know, each installation is different. Simpler PWM controllers may be in order unless you do something dumb like tie-wrapping the transmission line and the controller leads together. All my Morningstar pwm controllers are quiet, unless you force the issue. Some old timers still use the 1970's ping-pong controllers which are VERY inefficient, because they assume that *any* form of switching or pulsing is an automatic fail. Too bad they don't even test out a simple *quality* pwm controller, and fall victim to el-cheapo stuff or live in the past when bell-bottoms were the thing.


                          Comment


                          • #14
                            consider an inverter with the AC charger already built in. Xantrex makes inverters for backup systems, Connect your batteries and Plug and Play.
                            4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf

                            Comment


                            • #15
                              Originally posted by Logan005 View Post
                              consider an inverter with the AC charger already built in. Xantrex makes inverters for backup systems, Connect your batteries and Plug and Play.
                              Good suggestion with some minor limitations and a bit pricey. But me thinks this guy is a ham radio operator and listens too much to the kooks on QRZ who only know enough to be dangerous. Example most hams on QRZ recommend gel batteries and way too small of a battery to be usable.

                              N4PGW we are really trying to help you. So far you have not gave us any justification for solar other than hobby. A hobby is fine but is a 100 to 200 watt panel, and a small 12 volt battery up to 250 AH. You want back up and solar is a very poor choice for that, especially if any real power is involved like two rooms with one having a computer and ham radio gear. .

                              All you are asking for is 12 hours which can be reasonable expectation, especially in your location of Lenoir NC. You are far enough away from the coast as hurricanes are not much a threat, and far enough south winter storms are not an issue. Biggest threat to you is Hillbillies and Moonshiners.

                              Being a ham you most likely already have what you need, your Astron DC Power Supply or like model. That is the best 12 volt battery charger money can buy. All you neeed is the correct size battery and an Inverter. There is no need for solar, save your rmoney for a quality battery.

                              It is impossible for an Off-Grid Solar Battery system to ever break even. At a minimum 5 times more expensive than what the POCO will charge you if you utilize the power everyday. So do not fool yourself into the notion off-grid will pay off.

                              Solar is a really poor choice for radio, RFI generated wikll reender your radio equipment useless during daylight hours. Especially if you violate NEC requirements for grounding like most hams do because they do not know chit about grounding. .
                              73's
                              MSEE, PE

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