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Charge voltage needed for 24 V system

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  • #31
    Thanks for the reply.
    If the open circuit voltage is max 92v but the charge is limited to 40A @ 24v one can wire the panel to 48v max 20amp or not?
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    • #32
      Originally posted by GeorgeF View Post
      Thanks for the reply.
      If the open circuit voltage is max 92v but the charge is limited to 40A @ 24v one can wire the panel to 48v max 20amp or not?
      What's the Voc on your panels? That MPPT charger can handle over-wattage but not over-voltage. Are you in a cold climate?
      Last edited by sdold; 08-16-2019, 01:20 PM. Reason: Clarified that MPPT charger can handle oversize (wattage) panels


      • #33
        Hello, I am hoping to find some help! I am building my first system and have been researching like crazy and just can't find the answers I am looking for. I have 8 195w 12v mono panels and 4 12v 100ah lead acid batteries along with a 24v 3500w pure sine inverter. I'm looking into the Victron SmartSolar mppt charge controller and am so confused as to which controller will suit me best. I will eventually add 2 to 4 more panels and switch over to Battle Born lithium batteries for my 24v system. Can anyone shed some light on which controller would suit me best? My panels are 195w 21.6 open circuit voltage short circuit current 10.83a working current 9.02a output tolerance +3% temperature range -40c to +80c. Also how should I wire my panels to get the most efficiency? I would like to put my panels 220' away if possible?


        • #34
          You can expect a max of about 44 amps to charge the batteries for 24 volt batteries. Each of those panels, at max production, will send 5.5 charging amps at 24 volts, and with 8 of those panels they need to be set up at least 2 in series and 4 of these sets in parallel (2S4P).

          So now, looks as if the Victron 100/50 will handle this.

          There's a bit more work to be done. For example can your batteries handle this possible 44 amps? If these were my Trojan FLA batteries, they take 13% or 26 amps max, so all 8 panels would overcharge the battery. The Victron can limit production to something less than its max, so by setting it to 26, you'd be safe there.

          How likely are you to see this max production? On panels that tilt, and I move into the sun, I get really close, but on my flat roof panels, perhaps I've seen 2/3 max output, but as winter turns into summer, I expect higher production from the flat panels.

          For wiring the panels 2S4P will work with the 100/50, but the only other way to set the panels up at 4S2P, at first is less than the 100 volt rating, but you need to plan for the record low temperature in the month you operate off. Renogy lists a tempertaure cooefficient for panels and they push more volts as it gets cold, so at the starting the four panels in series pushes 86.4, but as it gets colder more math needs to be done to see how much it goes up.

          You mention upgrading. I'm not sure you will need to add more panels when you swap to Battleborn Batteries. You will probably have enough panels, but if you do put more panels for battleborns, if you want to take advantage of the extra output, than you may need another charger controller. I have three Victron Charge controllers working together to charge my three different arrays I use. Once you have the first set installed, you will see.

          Probably the most important thing is to take a look at your power requirements and do an audit so you can see if 400 ah of battery is enough for your needs. 200 AH usable with FLA. If you use that big inverter, you will burn through that very quickly. Wiring from the inverter to the battery becomes a lot on those large draws.


          • #35
            chrisski!! Thanks for responding so quickly! I wish I could join in on the intelligent conversation with you. I have to tell you that I'm a complete novice! I'm in the process of building a cabin and was decided on solar. I ordered a 1570w kit from eco-worthy thinking that it would be turn key lol. Now I realize that was a mistake! I was going to build a system but with everything I have going on I thought I'll just get a kit and save myself some research. Now I'm in 3k with eco-worthy and am also a proud owner of a $2500 solar refrigerator from ecosolarcool that you have to have a separate charge controller to run properly and validate the warranty. I'm not turning back now!! After pondering on your response it seems that I will have to increase my battery bank to do what I am trying to do? From what I understand I really don't want lead acid. I'm not sure if I can do 16 Battleborn right now. I recently seen a video on building lithium batteries. Maybe I should go that route if I need 1600ah I think. So basically I have the 8 panels that are good out of the kit. From there I will have to get a real charge controller, and some good batteries I suppose. I will take any advice and or suggestions!


            • #36
              If you take some time, look at the stickies, you’ll learn quite a bit on how to build a system. Then, start a post about your own design and ask for critiques. I’m about a year into this since I first started my design.

              An energy audit is key to determining your needs.

              I have a rather small system with 1350 watts of panels and 12 volts 440 ah batteries on my RV. I still use propane for cooking and heating, and don’t even think of using Air Conditioning. On a sunny day, I can be charged in 2 hours on moderate usage, and four hours on some heavier usage.

              I opted for lead acid acid batteries for my first build with the intent to upgrade to lithium in about a year with a 24 VDC upgrade. With the times I’ve used my RV, I am happy with my energy production and charge times, I see no reason to drop the money for Lithium’s.

              Assembling lithium cells into a battery is still foreign, but from what I’ve seen. If you decide to build your own battery pack, something slightly larger than my 12 volt 440 ah system people say cost them the same I paid for my Trojan FLA batteries, and about the same price as a single Battleborn.