Energy Storage #5 - working with it

Before the pack was shipped to Italy from Sweden I had it cycled a few times and knew the BMS was doing its job. There are basically two types of BMS implementation strategies. Either the balancing is done right on the cells. Benefit is opportunity to measure celltemperature, a very important parameter. Or, you can run wires from each cell to a central unit. Each has its merits and also challenges. I choose to use the 123BMS by dutch firm 123Electric https://123electric.eu . It uses the former, distirbuted method. It has an intrinsic scalability to it and also a built in Bluetooth com´s to an app. Very easy and it has worked well. The picture below shows the cell balancing app page. As you can see the balancing is within 30mV (millivolts) which is really good. The individual cell temps are also shown. In my case one or two cells show one or two degrees mismatch in temp always and I dont think it is likely to be the cells, but rather measurement issue. It has no practical meaning. 

 

The main app page shows a graphic of a solar installation. It does not correctly depict a boat installation that is a little more complex when you dont have your charge and load circuits necessarily separated. But, you do get some useful information. There is some opportunity to move the current probes around to monitor things in a better way. I would have preferred to have the battery in focus, only showing what goes in and out of it. 

For the first page to have some useful data presented the app needs to know the capacities of charger and battery pack as well as inverter. These are easily set on this page.

On the battery app page you set your limits where the BMS will act on low voltage and on high voltage as well as when to begin to balance. You can also set when you want to allow charge and discharge to restart after the BMS has gone into protecting the battery pack. You want to think about all of these situations and how these may affect the longevity of your pack. 

As the LFP system came on line, it all worked fine. With shorepower connected the existing 60A charger did its job although it is a lead-acid charger and does some tricks. Howeverm it cant produce a voltage above the the maximum level premitted for the LFP bank so there is never an overvoltage cut off situation. This also means that the LFP bank is never charged to 100% as the voltage tops out at around 28,0volt. This is just fine. But, with engine running the generator puts out higher voltage and charges the LFP very close to the V-max limit of 3,60 volts per cell (28,8 volt). There will be a situation when the BMS says it is full and shuts off. 

As for capacity it turned out that I got it tested by chance. Upon returning back in port, shorepower was reconnected and the 230volt circuit came alive. After three days I noticed that the 24volt charger was actually turned off, I had forgotten to turn it on after reconnecting shore power. All utilities on board had been running on the LFP bank for three days and it showed 80% capacity. Pretty good.