Mitmat

Thanks Mauritius, yes you're quite correct, - should be V/I to get the 5 ohms. The replies from Sunsynk in Johannesburg were mostly nonsense and seemed to lack depth of knowledge (unlike my own attention to detail regarding the highly complex Ohm's law 🤣). Would you not agree with the following: An MPPT by design will limit current to its load to keep the solar array as close to Vmp/Imp as possible? "Over panelling" Is a common practice that allows for better solar performance early in the day, late in the day and during overcast weather (as long as you don't get close to or exceed the inverter maximum input voltage)? Saying that you cannot use solar panels that are able to deliver more than 13 Amps is a bit like saying that you can't use a 500kVa generator to power a clock radio?

Thanks Scorp007, - that's what the Sunsynk support guys in Randburg JHB are saying but no one can say why. Would you not agree that you cannot try to "force" current into a MPPT (or any other appliance for that matter) without increasing the voltage of the current source?

I was recently informed by a supplier that I couldn't use 605 watt solar panels with the Sunsynk 5kVa. (I'm familiar with max. solar input voltage, series solar panel connection, Voc and the increase in Voc that cold weather and no load can cause). So I sent a few messages to Sunsynk support . Below are some of the responses that I received: "As stated in the technical specification you cannot exceed 13A on the mppts" "You cannot use panels that exceed 13A voc as this will damage the Inverter and void the warranty" "you cannot use panels that exceed 13A voc" "This is because if a fault was to occur that caused the panels to reach the Isc, if the Isc is higher than the MPPT rating over current damage can be caused to the inverter" I was then told that the issue had been resolved and the "ticket" had been closed. So I had a little rant and sent them the following: Quote " The whole point of a MPPT is to keep the solar array performing at its most efficient. This sweet spot of maximum efficiency is as close to the solar panel Imp and Vmp as possible The MPPT does this by controlling the amount of power available to its load (the MPPT's load). The MPPT does not "know" what solar panels are connected to it and it doesn't "care", as long as the voltage is above the start-up voltage and below the maximum input voltage. NB. The MPPT in an inverter system is NOT connected directly to any external load, - the loads that your MPPT is connected to are your battery charge system and the actual inverter DC input. The reason a sophisticated maximum power point tracking system is needed for solar applications, is that the amount of energy that a solar panel receives from our sun is constantly changing (time of year, time of day, temperature and changing atmospheric conditions ie.clouds & pollution). and Ever changing load requirements of the inverter system (effectively R in the equation V=IR). So for example, if the output of the MPPT was connected directly to a pure resistive load (let's ignore inductive or capacitive loads for simplicity). This would be your R, or pure electrical resistance. Let's say that the solar panel Imp is 10 amps and the Vmp is 50 volts. The MPPT will adjust its own resistance "seen" by the solar array to about 500 ohms(V=IR=10x50). The MPPT adjusts its own effective input impedance to keep the solar array voltage and current as close to Vmp and Imp as possible. (impedance because your MPPT is using high frequency switching to keep the panels at Vmp & Imp as well as to control and limit current to load). But now if for some reason the load increases as a result of the load resistance decreasing. The MPPT is going to try to keep the solar array as close to its Maximum Power Point. The MPPT does this by limiting the amount of current to the pure resistive load, if it is unable to do this then it's not a MPPT or it's broken If the Sunsynk MPPT can't limit its output current then there are some serious hardware design flaws or firmware stupidity. I find the possibility of either of those very unlikely. " - end quote I would be very grateful for some "perspective" from other forum members. If I'm misunderstanding things or I'm just plain wrong then please feel free to tell me.

Over the years I've read through many posts on Powerforum while trying to problem solve my own installation "bugs". I hope I can give a fraction of that useful info back. I've seen a lot of posts relating to inverter/ battery comms. frustration. I recently installed a Growatt SPF3000TL-48V with a Pylontech US3000C battery and had what seems to be the expected battery/ inverter comms cable issues. Using the RJ45 type comms cable supplied with the cable kit, I got warnings "04" (low battery) and "20" (BMS communication error) on the inverter. But the first problem was actually the the baud rate DIP switch on the Pylontech US3000C, - which in this case was installed upside down. Below is a picture of the correct settings (binary 1000) for 9600 baud, which I think is the standard RS485 baud rate for the Growatt BMS port. Communication cable solution: In the Growatt user manual on page 8 are the pin allocations for the inverter side of the cable. In the Pylontech US3000C manual also on page 8 are the pin allocations for the battery side of the cable. As this inverter doesn't have a CAN port we are only interested in the righthand column, - below the heading B/RS485. According to the info in the manuals, we need to connect the following together: Pin #1 on the inverter side to pin #8 on the battery side. Pin #2 on the inverter side to pin #7 on the battery side. Pin #3 on the inverter side to pin #6 on the battery side (GND). I didn't have a RJ45 crimping tool and plugs, so I used the short battery link cable that came with the battery. I cut it in half and stripped the outer insulation off. This is just to get you up and running until you have the proper cable made. Cables to be soldered together as follows: Inverter side Orange/white (pin #1) to battery side Brown (pin #8) Inverter side Orange (pin #2) to battery side Brown/white (pin #7) Inverter side Green/white (pin #3) to battery side Green (pin #6) My battery was right under the inverter so I didn't need to extend the 3 cables, but in most cases you will need to. Insulate the solder joins with heatshrink or tape. Plug the cable into the inverter BMS port on the inverter and the RS485 port on the battery, make sure it is the correct way around. ie. Inverter side to inverter and battery side to battery. Inverter settings: Don't turn on the mains utility suppy or connect the solar panels to the inverter yet. You don't want there to be any chance that the inverter will attempt to charge the battery until the settings are correct. Go to menu #5 and select Li for battery type and push enter. The inverter will automatically take you to menu #36 for communication protocol, select L02 and press enter. This is tried and tested, - you should have no more problems.