Thys van Schoor Posted January 15, 2020 Share Posted January 15, 2020 I do have a solar system at my house. I do use Trojan T-125, 3 volt batteries and do have 16 batteries installed. The system was installed nearly 5 years ago and I can see that my batteries are reaching the end of there lifetime. The batteries doesn't keep their voltage as previously and do need refilling of battery water on a regular basis. What I would like to know if it is possible to change to lithium batteries without much change to the system. Can I just replace the deep cycle batteries with lithium batteries Trust to hear from you Regards Thys van Schoor Quote Link to comment Share on other sites More sharing options...
Coulomb Posted January 15, 2020 Share Posted January 15, 2020 2 hours ago, Thys van Schoor said: I do have a solar system at my house. I do use Trojan T-125, 3 volt batteries I believe these would be 3 cell, nominally 6 V modules. Quote and do have 16 batteries installed. These would be wired as two strings of 8 modules in series. Quote The system was installed nearly 5 years ago and I can see that my batteries are reaching the end of there lifetime. I thought you might get a few more than 5 years from Trojans. Are they being equalised? They really need a brutal nearly 8 V per nominally 6 V module to charge the cells that have gone lower than the rest. Many inverter-chargers can't handle that sort of voltage properly. You might be able to wake them up with a separate charger, and get another year or two out of them. The equalisation charges will cause vigorous gassing, so you'll need lots of water. Quote What I would like to know if it is possible to change to lithium batteries without much change to the system. Can I just replace the deep cycle batteries with lithium batteries Yes and no. You can just replace the Trojans with a bank of lithiums with their own BMS, e.g. PylonTechs, but for best operation and longest life, you'd really want to add a Victron BMV and a small computer running ICC (assuming an Axpert inverter). You need to make a few settings changes to your inverter, but after that they are essentially zero maintenance. Quote Link to comment Share on other sites More sharing options...
Thys van Schoor Posted January 15, 2020 Author Share Posted January 15, 2020 Thanks for your response. If you talk about "equalised" what do you mean by that. If you say wake them up with a separate charger. How do I do that? I check the batteries again because it is a 3 cell battery but I thought it is 3 volt Quote Link to comment Share on other sites More sharing options...
Coulomb Posted January 15, 2020 Share Posted January 15, 2020 2 hours ago, Thys van Schoor said: If you talk about "equalised" what do you mean by that. An "equalising" charge is a controlled over-charge of a (usually) flooded lead acid battery. These charges are ideally applied once every several months, with other charges going to the usual bulk charge voltage, which for Trojans might be about 7.2 V per nominally 6 volt module. The idea is that the cells with the lowest state of charge get charged to full, while those that are already full use the energy to split water into hydrogen and oxygen. There may be a little recombination of 2H₂ and O₂ to 2H₂O (hydrogen and oxygen back to water), but since the cells are flooded, you can just replace the lost water next time you water them. That way, you don't need direct connection to the inter-cell straps; you can just wire the battery in series, yet you can still charge each cell "individually", up to a point. Over time, the cells will age slightly differently, so they will end up with different capacities. Without this equalisation, the capacity of the battery is limited by the capacity of the cell with the lowest state of charge. When the cells are equalised, each cell has about the same state of charge, so you get more capacity. Quote If you say wake them up with a separate charger. How do I do that? You'd take one or two 3-cell modules out of circuit, and attach ideally a 6-volt charger to each one, this charger being able to pump in enough current to get the module to nearly 8.0 volts (the exact voltage depends on the manufacturer and the ambient temperature). If you can't get a 6 volt charger, charge pairs of modules with a nominally 12 V charger, to nearly 16.0 V. Charge to the voltage and for the time recommended by the manufacturer. Then put them back in circuit. Alternatively, your battery charger may be able to be set up for automatic periodic equalisation. This is ideal, because you don't need to disconnect the modules, don't need the extra charger, and you don't have to even be there. Some models of Axpert inverter-chargers have equalisation features, for example. You still haven't told us what model of inverter-charger you have. Quote I check the batteries again because it is a 3 cell battery but I thought it is 3 volt The electrochemistry of lead and sulphuric acid are such that the cells are nominally 2 V cells. Hence each three cell module is nominally 6 volts. A common "12 volt" car battery is 6 cells in series; it will have 6 filler caps (assuming it's a flooded type of course). Quote Link to comment Share on other sites More sharing options...
Thys van Schoor Posted January 16, 2020 Author Share Posted January 16, 2020 I will get back to you regarding the model of my inverter Quote Link to comment Share on other sites More sharing options...
Thys van Schoor Posted February 5, 2020 Author Share Posted February 5, 2020 I do have a magnum inverter, model MS4348PE Inverter/charger Quote Link to comment Share on other sites More sharing options...
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