Announcement

Collapse
No announcement yet.

24v vs 12v

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • 24v vs 12v


    I went solar cold turkey after my power got shut off. I have a harbor freight 45w kit. 5 lead acid semi truck batteries. 1500 powerdrive inverter. A 700w 900 peak gas generator and a 6/2 amp AC battery charger.

    Thinking my next move should be to upgrade my solar charging..i saw a 230w poly panel for 76 bucks on ebay but the catch is its 24 volts and im on a 12v system.

    If i chose to get the 24v panel should i

    A:get a sixth battery and wire them all in 24v pattern with a 24-12 dc-dc stepdown to my inverter

    B:wire 4 batteries on 24v pattern and stepdown to the other two batteries on 12v pattern(so i could use my 12v battery charger in a pinch)

    C: something totally different from a and b

    im a solar noob so take it easy on me lol all im really looking to do is power a mini fridge 24/7 off the grid. I can power everything else but thats my obstacle. Its a 1 amp 115v, 75w rated pulls 90-100w on startup and trickles down to 20 w as it cools. My fridge starts and runs great for 3 hours but by that time my inverter has drained to 11volts, alarms and shuts down.

    first problem i know is my cheapy harbor freight plastic film panels. The other problem is cash. I can get a 100w 12v poly panel for $95 bucks or a 230w 24v panel for $76 bucks. I entered my info into this solar calculator online and it says i need 800w of solar to do what im trying to do. If i got worked up to 800 with 230w panels it would be cheaper but ill have to mod to 24v.

    any advice on this would be great, or if you are doing this what does your setup consist of? My batteries are 50 bucks each panels were 120 for the kit.inverter was 40 bucks.

    on a side note what are your guys views on golfcart batteries or agm?

  • #2
    Tap the brakes. Using Truck batteries is a plan for disaster. A 230 watt panel may or may not fit your needs. First thing to do if you are serious is get the Harbor Fright Boxes the panels came in and sell them as they are worth more than the panels.

    Second is give up on truck batteries. They are not made to be cycled and a waste of your time.

    One thing you need to know right up front is ask yourself why you want to take anything off grid? The answer CANNOT BE to save money or mother earth because both are impossible. Battey cost alone is going to cost you 5 to 10 times more than just buying power form the POCO. If your objective is to have power during outages, solar is not for you as there are much less expensive and more reliable ways to achieve that. So why do you want to do this?

    If you are serious you are going to have to start over from scratch and define an objective and that starts with determining how many way hours per day you need. Forget about a budget. It cost what it cost. Like I said this cannot be done to save money. Not possible. Example your fridge will use roughly 1 Kwh per day or about 10 to 15 cents worth of electricity per day. Here is what it will take and cost estimate.

    Batteries. = 4 x 6-Volt 225 AH Trojan Golf Cart T-105 Flooded Lead acid batteries. $600, or Trojan also make a T-105 AGM $1100. you replace every couple of years.
    Minimum Panel wattage = 400 watts. if you use a MPPT Controller or 600 watts with a PWM Controller. $400 to $800
    15-Amp MPPT Charge Controller $200. 15 amp PWM Controller = $40. Go with MPPT it is less expensive because if you go with PWM requires 200 more watts in panels.
    400 watt True Sign Wave Inverter = $220
    Misc materials and hardware = $200

    Total $1400 to $2000 if you want it to work and do what you expect. All that to generate $40 to $60 per year electricity. In 2 or 3 years replace the batteries for more than it cost you this time of $600.
    MSEE, PE

    Comment


    • #3
      im doing it because the power company wants 1100 bucks to get it turned back on, no payment plan..so the 400 bucks or so ive spent over the past 3 months has gave me power until i can work something out with power company. Its just not cutting it for running fridge.the shop i got the lead acid batteries said he had some used agm batteries coming in but no word on price. Money is my issue...im back on rent 1050 and all my bills are in disconnect, power shut off so im kinda forced to do this..unless i win the lottery or something im trying to set up a system with what little money i have.

      Comment


      • #4
        Get a Caframo fan to keep cool. Good airflow for the power used.

        Comment


        • #5
          ok i went against the advice of scrapping my truck batteries and starting over, because thats not an option at the moment, im in survival mode right now so this is what i have to do.

          I found a 15 amp charge controller that comes with a monitoring system with app i can download on my phone.

          ive decided to go with the 230w 24v panels..ill buy one at a time until i have 4 panels.

          The issue ill face after the switch is my whole system is 12v so ill have to step down with a dc-dc converter (15amp i imagine)

          but can i set two of my 12v batteries aside to charge with a 12v charger and still be hooked up to the 4 batteries on the 24v side.

          Will charging the 12v side damage the dc-dc converter?

          will it charge the 24v side?

          Comment


          • #6
            230 watt panels aren't 24 volt panels. You will need to buy an expensive MPPT controller and use a minimum of 2 panels to charge a 24 volt battery. Plus the cost of a 24 to 12 volt converter. While cheaper than simply paying your delinquent utility bill you aren't going to get much useful power from your proposed set up. Are you living in a home without power? What are you trying to power with this setup?
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

            Comment


            • #7
              Originally posted by kdaddy1980 View Post
              I went solar cold turkey after my power got shut off. I have a harbor freight 45w kit. 5 lead acid semi truck batteries. 1500 powerdrive inverter. A 700w 900 peak gas generator and a 6/2 amp AC battery charger.

              Thinking my next move should be to upgrade my solar charging..i saw a 230w poly panel for 76 bucks on ebay but the catch is its 24 volts and im on a 12v system.

              If i chose to get the 24v panel should i

              A:get a sixth battery and wire them all in 24v pattern with a 24-12 dc-dc stepdown to my inverter

              B:wire 4 batteries on 24v pattern and stepdown to the other two batteries on 12v pattern(so i could use my 12v battery charger in a pinch)

              C: something totally different from a and b

              im a solar noob so take it easy on me lol all im really looking to do is power a mini fridge 24/7 off the grid. I can power everything else but thats my obstacle. Its a 1 amp 115v, 75w rated pulls 90-100w on startup and trickles down to 20 w as it cools. My fridge starts and runs great for 3 hours but by that time my inverter has drained to 11volts, alarms and shuts down.

              first problem i know is my cheapy harbor freight plastic film panels. The other problem is cash. I can get a 100w 12v poly panel for $95 bucks or a 230w 24v panel for $76 bucks. I entered my info into this solar calculator online and it says i need 800w of solar to do what im trying to do. If i got worked up to 800 with 230w panels it would be cheaper but ill have to mod to 24v.

              any advice on this would be great, or if you are doing this what does your setup consist of? My batteries are 50 bucks each panels were 120 for the kit.inverter was 40 bucks.

              on a side note what are your guys views on golfcart batteries or agm?
              If you run a 24v battery system you will need a 24v inverter, not a 12v inverter running from a 24v to 12v stepdown. IMHO, you are better off paying for restoration of POCO service. With your limited knowledge of battery electrical systems, any power you generate will cost many times more than power from the POCO

              Comment


              • #8
                Originally posted by littleharbor View Post
                230 watt panels aren't 24 volt panels. You will need to buy an expensive MPPT controller and use a minimum of 2 panels to charge a 24 volt battery. Plus the cost of a 24 to 12 volt converter. While cheaper than simply paying your delinquent utility bill you aren't going to get much useful power from your proposed set up. Are you living in a home without power? What are you trying to power with this setup?
                they are advertised as 24v 230w ebay $76..and the mppt controller with monitoring app is $160..my power has been off for 3 months now. Im powering all the lights in my house tvs fans laptops etc..i can run a fridge for a while on batteries but mostly rely on a small generator for the mini fridge and charging the battery bank at night.i backfeed the power through a double ended cord plugged into an outlet in the back room of my house.and that works for me for now..but id like to be able to charge the batteries more when im gone at work all day, right now i cant get them up past 12.4 on solar alone.yeah i know its a ****ty harbor freight panel but its better than nothing at this point.. thats why i want the 230w panels but like i said its advertised as 24v so whats up with that? Im really only trying to manage to run this mini fridge without the generator, if i have to put it on a timer and only run it for short periods i can do that. But the cheap panels cant keep up with even 20w for more than a few hours before the inverter hits 11.0 and starts its shutdown.
                Last edited by kdaddy1980; 07-17-2017, 08:04 PM.

                Comment


                • #9
                  Originally posted by Logan5 View Post

                  If you run a 24v battery system you will need a 24v inverter, not a 12v inverter running from a 24v to 12v stepdown. IMHO, you are better off paying for restoration of POCO service. With your limited knowledge of battery electrical systems, any power you generate will cost many times more than power from the POCO
                  ok, i see, because im going to be pulling almost 3000 peak watts when the fridge starts that converter will be fried right? Well i found a 24v converter 2000w 4000 peak for $125..might be affordable in another week or two.
                  Last edited by kdaddy1980; 07-17-2017, 07:28 PM.

                  Comment


                  • #10
                    Originally posted by kdaddy1980 View Post

                    they are advertised as 24v 230w ebay $76..and the mppt controller with monitoring app is $160..my power has been off for 3 months now. Im powering all the lights in my house tvs fans laptops etc..i can run a fridge for a while on batteries but mostly rely on a small generator for the mini fridge and charging the battery bank at night.i backfeed the power through a double ended cord plugged into an outlet in the back room of my house.and that works for me for now..but id like to be able to charge the batteries more when im gone at work all day, right now i cant get them up past 12.4 on solar alone.yeah i know its a ****ty harbor freight panel but its better than nothing at this point.. thats why i want the 230w panels but like i said its advertised as 24v so whats up with that?
                    Well with a REAL MPPT controller which it sounds like you have, you should be fine with TWO panels 60 cell panels are NOT 24 volt panels and anybody telling you they are doesn't know what they're talking about. You need a Vmp. of around 36 volts to charge a 24 volt battery fully. When solar panels get hot the voltage drops. A 60 cell panel, especially a 230 watt version put out less than 30 volts Vmp. @ STC rating. In real world conditions that will drop to below 28 volts and you need more than that to properly charge a 24 volt battery.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      so this is false??
                      Attached Files

                      Comment


                      • #12
                        No it is not false. It is just a 60-cell 30 volt panel. It takes 72 cells or 36 volts minimum for a 24 volt battery panel. They are looking for folks who do not know what they are doing.

                        It is a very old panel designed for PWM controllers, or can be used in Grid Tied. You want to use a voltage of 36 to 120 volts to charge a 24 volt battery with MPPT controller. So you can use two of those panels in series with a MPPT controller and be fine.
                        Last edited by Sunking; 07-17-2017, 08:35 PM.
                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by Sunking View Post
                          So you can use two of those panels in series with a MPPT controller and be fine.
                          Im really strapped for cash and trying to spend little as possible at one time.what if i wired my 3 HF panels in series until i can get a second 230w. That would give me 36 volts right? And the 230w panel is 30 volts so together would be 66v?

                          Comment


                          • #14
                            upon further reasearch it says never to hook up a battery or any other power source to the 12v side of a 24-12 dc-dc converter.load only. So that answered that question.

                            Comment

                            Working...
                            X