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  • #16
    Are you saying that if I run at 25 amps at 24 volts, and my controller is limited to 30 amps, that at 12volts I would be over the 30 amp rating of the controller? That is how I understand it, and I think that is what you are saying.

    This controller may have a wattage rating, but I havent seen it. I know it is 30 amps, and at 24 volts (which I think is its max output voltage), that's 720 watts. I assumed that the current was limited on both input and output current, but I guess it's not really possible to have more amps going in than are going out.

    I guess what I'm saying/asking is that if I have a 24v battery bank and I charge it with 30 amps, and I have say 4 of these 340 watt panels, the controller will limit the output current to that 30 amps, even if I have more than that "available", but I would be able to maintain that full 30 amps for a longer period of the day, and have higher production on days with low light because I have an over sized array?

    Is this reasonable thinking? At this point I am just trying to understand some theory.

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    • #17
      The higher end controllers will limit the output although running at full throttle may not be the best way to operate your equipment. the cheaper MPPT controllers may not be so forgiving. Also there are some "so called" MPPT controllers being sold that aren't even MPPT. If there are fans incorporated into your controller the noise may be bothersome. What controller are you using?

      Anyway my point was to mention the benefit of going higher voltage which allows you a larger solar array due to lower amperage for the same wattage.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #18
        Got it. Sensij, above, recommended the tracer unit, so that's what I bought. Tracer charge controller. Would this one be OK to run at full throttle? At the moment we are maybe using 3 hundred watt hours a day. Maybe. I am thinking of in a year or two adding the fridge ( I started another thread for that) and really I'm just looking to understand how this works to make sure I get the right equipment.

        Is there anything wrong with running an oversized array in an effort to charge in unfavorable conditions?
        Last edited by Basketcase; 04-19-2017, 03:40 PM.

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        • #19
          The Tracer is a true Mppt controller, and has no fans so that's all good. What you can do is split your array for a "virtual tracking" setup. Half facing Southeast and the other half facing Southwest. This will give you more power at the beginning and end of the day as well as less clipping and loss of potential power. Most battery banks need more time in absorb phase than the solar day allows. Splitting your array will give you earlier full bulk charging, allowing you to go into absorb sooner and for a longer time although that parameter isn't adjustable in the tracer controllers as far as I know.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #20
            So do you think that 2 panels "split" would have a longer "solar day" than say 3 panels all facing south? We happen to have a very large roof facing directly due south, and the pitch happens to be the correct angle for our location in summer.

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            • #21
              Longer, yes, higher harvest, no.

              What are your unfavorable conditions?
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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              • #22
                Originally posted by Basketcase View Post
                So do you think that 2 panels "split" would have a longer "solar day" than say 3 panels all facing south? We happen to have a very large roof facing directly due south, and the pitch happens to be the correct angle for our location in summer.
                The manual for the tracer tells you that as long as you are within the Voc and Isc limits for your controller, you can oversize the array up to 3X that actual max charging power (24 V * 30 A = 720 W). I wouldn't recommend oversizing that much, but 3x 340 W panels (1020 W) is reasonable on a 30 A controller. You *might* see some clipping (controller limiting to 30 A output when more would have been available) if your batteries run down too low, but chances are good that with normal discharge, by the time in the day you'd get into clipping, your battery would already be in absorb and at constant voltage, self-limiting the current. The extra array power improves your chances of holding the absorb voltage for the programmed length of time, and actually getting into float.

                What you don't want to do regularly is back into the float voltage because you lose the sun before absorb is complete. One way to protect against this is either to set float to equal the absorb voltage (safe if you are cycling daily, but not if the battery is mostly sitting), or increase the amount of time it holds absorb to effectively keep it in that mode all day.

                For that same amount of charging power, you would probably be better off with 4x260 W panels. You should be able to put two 60 cell panels in series safely on that controller, and by raising the array voltage you reduce the current for the same power. Reduced current means less line loss if the wiring is fixed, or lower wiring expenses if you target a particular loss. Also, with two strings in parallel instead of three panels in parallel, you dodge the requirement for overcurrent protection on each string.

                With 4 panels, two pointing SW and two pointing SE might be better than all 4 south, but I'm not sure the difference is enough to deal with the custom mounting you'd need on the south facing roof you've described.
                Last edited by sensij; 04-19-2017, 04:40 PM.
                CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                • #23
                  Maybe this is flawed thinking, but my thoughts are that by creating an over sized, split, or whatever, array, that on cloudy days I can still have decent charging, and I can start charging earlier and later in the day. I am planning to cut it somewhat close with the AH of the batteries vs proposed load and if I put on a larger array (cheap) and less batteries (expensive and consumable) I am hoping that I can accomplish my goals. The goal is a fridge (1400 watt hours) and about 300 watt hours of lights/cell phone chargers. I'd like to do this with the controller I have, 4 batteries total of 230AH@24v and enough panels to minimize the risk of deeply discharging the batteries. Keep in mind this is only in operation from may to september. In my other thread, we sort of went into this. Seems like both topics are starting to merge together but good info in both.

                  In the above scenario, on a good day, I should have no problem maintaining that load with 2, 600 watt panels. But given a day or 2 of clouds, etc, it may be risky. This is why I was thinking overize the array. On a good day, I'll be producing more than I need, but possibly increasing the odds of keeping up with the load on a bad day.
                  Last edited by Basketcase; 04-19-2017, 04:42 PM.

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                  • #24
                    Sensij, I think we were typing at the same time yesterday. That's a great explanation. Thank you! It certainly give me a lot to think about. Since you know this controller, I'm sure you can tell me if I can build my own cable for the communicatons port going between the contoller and the mt50? I assume I can but I just want to make sure. I'd figure cat5 with T568A or B connections. I am also wondering about the "LOAD" portion of the controller. Is this simply a pass through of the batteries voltage, or is it going to be a regulated 12v output regardless of battery voltage? I looked through the manual and it is not clear. If I do this, the inverter would be just for the refrigerator and I'd keep everything else 12v.

                    Thanks again to everyone for helping a newb!

                    Comment


                    • #25
                      Originally posted by Basketcase View Post
                      Sensij, I think we were typing at the same time yesterday. That's a great explanation. Thank you! It certainly give me a lot to think about. Since you know this controller, I'm sure you can tell me if I can build my own cable for the communicatons port going between the contoller and the mt50? I assume I can but I just want to make sure. I'd figure cat5 with T568A or B connections. I am also wondering about the "LOAD" portion of the controller. Is this simply a pass through of the batteries voltage, or is it going to be a regulated 12v output regardless of battery voltage? I looked through the manual and it is not clear. If I do this, the inverter would be just for the refrigerator and I'd keep everything else 12v.

                      Thanks again to everyone for helping a newb!
                      The LOAD output is simply a pass through of the battery voltage which is switched based on the sensed battery voltage. If the voltage is below the LV setpoint the LOAD output will be turned off to protect the battery (which is already pretty well toast at the typical LVCO voltage).
                      The output cannot carry full battery current, and so is best used for lighting loads or to drive a relay. It is not voltage regulated, so attached equipment should be able to withstand 14-15V during charging or equalization.
                      SunnyBoy 3000 US, 18 BP Solar 175B panels.

                      Comment


                      • #26
                        Originally posted by Basketcase View Post
                        Since you know this controller, I'm sure you can tell me if I can build my own cable for the communicatons port going between the contoller and the mt50? I assume I can but I just want to make sure. I'd figure cat5 with T568A or B connections.
                        You can build your own cable, a standard ethernet cable should work. It is RS-485 though, so don't try to plug it into an ethernet port on your computer. An RS-485 to USB is needed if you want to do your own data collection.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                        Comment


                        • #27
                          Originally posted by inetdog View Post

                          The LOAD output is simply a pass through of the battery voltage which is switched based on the sensed battery voltage. If the voltage is below the LV setpoint the LOAD output will be turned off to protect the battery (which is already pretty well toast at the typical LVCO voltage).
                          The output cannot carry full battery current, and so is best used for lighting loads or to drive a relay. It is not voltage regulated, so attached equipment should be able to withstand 14-15V during charging or equalization.
                          That is what I expected but I was hopeful that maybe once I go to 24v that I wouldn't need extra parts to run my 12v accessories.

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                          • #28
                            Originally posted by sensij View Post

                            You can build your own cable, a standard ethernet cable should work. It is RS-485 though, so don't try to plug it into an ethernet port on your computer. An RS-485 to USB is needed if you want to do your own data collection.
                            Thanks. Good to know. The cable it comes with is pretty short and it should really be more accessible than the controller is going to be.

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