stoic Posted December 30, 2018 Share Posted December 30, 2018 I have 3x US2000B pylons. and i will probably add another 3 in June. I see that the inverter i got accepts 38-66V so do i need to connect these three batteries in parallel to stay within that limit? This also means i am gonna run at around 150A for just three batteries and if i am going to connect three more i am going to sit at around 300A. This too me sounds a bit scary. but non the less. What is the best way to connect the batteries in parallel? Looking at my image below the positive from battery three to the buzbar is seems net longer than battery 1 to buzbar. Will this cause an uneven charge? Is there a better way to connect this, or is this standard? Quote Link to comment Share on other sites More sharing options...
Elbow Posted December 30, 2018 Share Posted December 30, 2018 1 hour ago, stoic said: I have 3x US2000B pylons. and i will probably add another 3 in June. I see that the inverter i got accepts 38-66V so do i need to connect these three batteries in parallel to stay within that limit? This also means i am gonna run at around 150A for just three batteries and if i am going to connect three more i am going to sit at around 300A. This too me sounds a bit scary. but non the less. What is the best way to connect the batteries in parallel? Looking at my image below the positive from battery three to the buzbar is seems net longer than battery 1 to buzbar. Will this cause an uneven charge? The setup connects the positive into the one end of the string and the negative to the other end. So the total length positive + negative is the same for all batteries. So each would see the same resistance in total between it and the common energy source (ie the charger), so they should charge same rate. But in any event the batteries are smart and will manage the charge to each contained cell so if one battery is charged before another it will simply stop charging its cells and no harm done. When I watch my pair discharge it is amazing how closely the cells move. Usually there will be a 10 or 20 millivolt difference from the highest to the lowest. 0.02v or 0.1% As for the load: Pylon recommends charging at 25A and recommended discharge C/2 which is also 25A. So three would be 75A and 6 would be 150A "Max" charge/discharge 50A for each battery so you are right that you could have 300A with 6 batteries. But that's 14.4kW, is that realistic? Is your inverter so powerful? The cables from Pylon are rated 125A but they do recommend using two sets (connected opposite ends of the the string - if you could have more than 125A. So you might want to fuse each set of cables from charger to batteries with 125A fuses and you'd be limited to 240A or so but that is still well above the recommended C/2 and would give you well over 10kW. Chris Hobson and stoic 1 1 Quote Link to comment Share on other sites More sharing options...
Coulomb Posted December 30, 2018 Share Posted December 30, 2018 (edited) 2 hours ago, stoic said: I see that the inverter i got accepts 38-66V so do i need to connect these three batteries in parallel to stay within that limit? Definitely. Even two in series is nominally 90 V, way over your inverter limit. Don't stress over the battery current; 300 A will only flow if you have a ~ 15 kW load, assuming your inverter(s) could dish out that sort of power. 2 hours ago, stoic said: Is there a better way to connect this, or is this standard? There is no perfect sharing for three cells / modules / batteries (there are perfect sharing arrangements for two or four modules). I'm calling each US2000B box with cells in it a module; the whole thing is a battery. What you've drawn there is standard. While it's a long way for module 3 to the positive bus bar, it's shortest to the negative bus bar, and it takes two bus bars to make a circuit. Each module sees four "hops" to the bus bars; the problem is that the outer links see more current than the inner links, and so the modules don't share the load perfectly. I believe that module 2 won't see as much load as the other two, because none of its current is through the "lazy links" at the end of the chains, where the current is lowest, so the voltage drop (on the lazy links) will be lowest. I hope I got that right; it's really easy to get twisted with these things. If you really want to get pedantic about it, each module should have its own equal-length cables to the bus bars. But that won't work out with the provided cables, I would guess. My suggestion is to not worry about it. Elbow's pair match very well, because two (connected at the diagonals) do share perfectly. Four will only share perfectly if you do a sort of double diagonal connection (not just add one module to your diagram above). Again, this isn't convenient with the connections and cables provided, and the BMS will hopefully balance the modules as they are charging. I believe that the middle modules will get less charging as well, so things cancel out, but you might want to consider doing a "tyre rotation" every now and then to "even the wear". Edit: The double diagonal is where you diagonally connect two pairs or modules, then diagonally connect the pairs. This requires some modules to have three connections, and you only have two terminals. [ Edit: finished the last sentence re "tyre rotation". Duh. ] Edited December 30, 2018 by Coulomb Elbow and stoic 2 Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted January 5, 2019 Share Posted January 5, 2019 Pylontechs are designed to be run in parallel. The BMS has been designed around this. The inverter you are wanting to use is fortunately approved for use with a Pylontech. With the BMS there is no need for a busbar as the BMS irons out imbalances. Your diagram is standard and reduces imbalances and the rest is managed by the BMS. Quote Link to comment Share on other sites More sharing options...
stoic Posted January 5, 2019 Author Share Posted January 5, 2019 7 hours ago, Chris Hobson said: Pylontechs are designed to be run in parallel. The BMS has been designed around this. The inverter you are wanting to use is fortunately approved for use with a Pylontech. With the BMS there is no need for a busbar as the BMS irons out imbalances. Your diagram is standard and reduces imbalances and the rest is managed by the BMS. Unfortunately i have three inverters. One on each of my phases... so i beleive will still need a busbar to split the power over the three inverters. I am however using one CC for the three batteries in parallel Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted January 11, 2019 Share Posted January 11, 2019 On 2019/01/05 at 4:18 PM, stoic said: Unfortunately i have three inverters. One on each of my phases... so i beleive will still need a busbar to split the power over the three inverters. I am however using one CC for the three batteries in parallel Ok I wasn't aware of that - yes you need busbars. Quote Link to comment Share on other sites More sharing options...
Danyel Posted April 13, 2020 Share Posted April 13, 2020 Hi I am new here, I have a question regarding this. I want to install a system with 5600W from panels so I am choosing a Votronic VMII 5000 W with 4800W in paneles and then a BlueSolar 15/35A with 800W installed in panels. My question is, Do I need a bus bar to charge batteries as these two devices are in parallel? Does the bus bar needs its own protection or it´s enough with the devices protections properly sized? Thanks!! Quote Link to comment Share on other sites More sharing options...
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