Hi,
before someone suggests doing more research and reading the forum more I would like to say that after dozens of hours spent doing exactly that I'm writing this. I've also watched some videos from Andy's off-grid garage but his style of videos really isn't my cup of tea and quickly it became just the notion of forcing myself to watch something, read something. I want someone to check my thought process, give me some pointers, and move on to another thing.
About my system
My system will be based on the Victron products. At the moment I have one Multiplus II 48/5000 and multiple BlueSolar MPPTs sitting around. As stated above my system will work with a voltage of 48 V. At the moment I have 3,6 kWp solar panels which are currently used only for heating water. Later I'm planning to expand to 10-15 kWp. Part AC coupled but most DC coupled. Yes, I know about the 1.0 rule. And now about the battery pack. I'm going to order 16 pcs of EVE 304 Ah grade A cells from NKON. For now.
BMS
I don't want to cheap out on the materials but the cost of building vs buying a finished battery is a factor for me. So paying for the BMS almost as much as the batteries isn't really a path I would like to choose. Especially if you take a look at what really the BMS is in the way of HW and the SW of the premium BMS doesn't seem to have the capabilities of Chinese BMSs. But I'm getting off the topic.
I have taken a look at the following BMS manufacturers: Orion, REC, JK, JBD, Seplos and Dali. The Dali, Orion, and the REC were eliminated. I think I don't need to explain why I eliminated Dali. The Orino and REC were eliminated mostly due to their price and from my research it doesn't seem they have the capabilities of the other inverter BMSs but I may be wrong. So we are down to the Seplos, JK and JBD. But I'm open to the suggestions.
Let's talk parameters.
Type of BMS (Separate, Common, Hybrid, External)
I don't really care as the only time the BMS starts meddling in normal operation is if something fails and I don't really mind if all does "black". If it protects the batteries I'm happy and maybe happier if it doesn't allow any discharge or charge in that state.
Communication
Yes! Being able to communicate with the Victron system is something I really want. For the sake of SoC, tampering charging (I'm not really sure how this exactly works because now I mainly focus on the BMS. I have Multiplus and MPPT's sitting in the basement but getting to the setting is my priority after solving BMS). I know that people have different opinions on the inverter-bms communication but I really like it so I would really like this feature.
Temperature sensors (Heating function)
The battery pack will be at a place where the temperature won't go outside the range of 15-25°C so heating isn't really needed. About the heating from discharge. Just a quick math. Victron Multiplus 48/5000 has a rating of 4 kW but just for the worst scenario let's count with 5 kW add 10 % power loss and the load is 5,5 kW. I'm not really looking at surge rating because it isn't that much of a problem as long and steady load on the batteries. So 5,5 kW at 48 V is 115A and that is 0,38 C. At that load the cells shouldn't heat much. But I'm open to the experience of others because I wasn't able to find much about how much LiFePo4 heats up. Only that it doesn't heat "much" under 1C. So yes. The temperature measuring capability is nice but I don't really think I need it as much. If someone has experience with how much battery heats up under let's say 0,5C I would really like to hear about it.
Balancing function
Yes. I plan to balance the cells and because they will be grade A EVE cells I think they won't need much of a balancing but it will always be handy to have some. Preferably active balancer because I will always be happier to transfer the energy than "waste it" as heat and raise the temperature inside the battery enclosure. The option of an external cell balancer isn't an option for me because I don't believe that BMS and cell balancer will work optimally if there is a chance of corrupting voltage readings to each other.
User definable parameters
Yes! Probably the main option. The more there is to set up and not just use static preprogrammed values the better. Being able to set up min/max pack voltage by your preference, max current, balancing voltage, SoC reset, etc. Seems like the main feature so I really want it.
Display capability
If it has one it is nice but I will probably use it for the first few months and then forget about it because I'm planning to have data online via something. I'm not sure exactly what I will choose. Maybe just Victron VRM, maybe something else.
Updatable software
A biggie. If there is any bug I want the capability to fix it with software update.
Paralleling capability
I'm planning to expand my battery bank so I really need some BMS that can communicate with other BMS modules. At least with BMSs from the same company and then port data from both to the Victron.
Pre-charge & current limiting
If I got it correctly the current limiting is mainly used in cases when you connect another battery with widely different SoC so the one wouldn't get discharged with massive current and the other on charged with said current. I get that you can use it for pre-charging the inverter, at least theoretically, but you would need to set this function every time when you connect the inverter to the battery. Which shouldn't be much, but. The pre-charging capability seems good until you read about some warnings that the pre-charge timer set to maximum value still isn't enough and it can lead to cycling between turning on and off the inverter and possibly even damaging it. So this functionality isn't really that much of a concern to me. Especially with low-frequency Victron, there could be a problem. But I would probably at least try it if it was built in. When shove comes to push I don't have a problem using a resistor-based pre-charge circuit.
Basically with the priorities set, the only option seems like JK. I'm right? The JBD isn't fully programmable (If I remember the datasheet correctly the SoC reset was the same as OV protection, some parameters seemed like static values), Seplos doesn't have a balancer, only an external one that isn't a part of it and it still looks like like it does have some relays? So possible mechanical failure. JK seems like the most popular on the forum and it also does have the most posts with some problems, but 80% of it looks like a user error.
What I don't like is that apparently, the JK can be in some cases prone to bricking and the last major problem Andy in off-grid garage found wasn't good news either. On the other hand, the speed and just the existence of the new software patch update gives JK bonus points. On the other hand, such a major bug shouldn't happen on a released product with its main purpose thrown out of the window.
I would really like to hear other people's opinions, suggestions, etc. Thank you all for your replies in advance.
before someone suggests doing more research and reading the forum more I would like to say that after dozens of hours spent doing exactly that I'm writing this. I've also watched some videos from Andy's off-grid garage but his style of videos really isn't my cup of tea and quickly it became just the notion of forcing myself to watch something, read something. I want someone to check my thought process, give me some pointers, and move on to another thing.
About my system
My system will be based on the Victron products. At the moment I have one Multiplus II 48/5000 and multiple BlueSolar MPPTs sitting around. As stated above my system will work with a voltage of 48 V. At the moment I have 3,6 kWp solar panels which are currently used only for heating water. Later I'm planning to expand to 10-15 kWp. Part AC coupled but most DC coupled. Yes, I know about the 1.0 rule. And now about the battery pack. I'm going to order 16 pcs of EVE 304 Ah grade A cells from NKON. For now.
BMS
I don't want to cheap out on the materials but the cost of building vs buying a finished battery is a factor for me. So paying for the BMS almost as much as the batteries isn't really a path I would like to choose. Especially if you take a look at what really the BMS is in the way of HW and the SW of the premium BMS doesn't seem to have the capabilities of Chinese BMSs. But I'm getting off the topic.
I have taken a look at the following BMS manufacturers: Orion, REC, JK, JBD, Seplos and Dali. The Dali, Orion, and the REC were eliminated. I think I don't need to explain why I eliminated Dali. The Orino and REC were eliminated mostly due to their price and from my research it doesn't seem they have the capabilities of the other inverter BMSs but I may be wrong. So we are down to the Seplos, JK and JBD. But I'm open to the suggestions.
Let's talk parameters.
Type of BMS (Separate, Common, Hybrid, External)
I don't really care as the only time the BMS starts meddling in normal operation is if something fails and I don't really mind if all does "black". If it protects the batteries I'm happy and maybe happier if it doesn't allow any discharge or charge in that state.
Communication
Yes! Being able to communicate with the Victron system is something I really want. For the sake of SoC, tampering charging (I'm not really sure how this exactly works because now I mainly focus on the BMS. I have Multiplus and MPPT's sitting in the basement but getting to the setting is my priority after solving BMS). I know that people have different opinions on the inverter-bms communication but I really like it so I would really like this feature.
Temperature sensors (Heating function)
The battery pack will be at a place where the temperature won't go outside the range of 15-25°C so heating isn't really needed. About the heating from discharge. Just a quick math. Victron Multiplus 48/5000 has a rating of 4 kW but just for the worst scenario let's count with 5 kW add 10 % power loss and the load is 5,5 kW. I'm not really looking at surge rating because it isn't that much of a problem as long and steady load on the batteries. So 5,5 kW at 48 V is 115A and that is 0,38 C. At that load the cells shouldn't heat much. But I'm open to the experience of others because I wasn't able to find much about how much LiFePo4 heats up. Only that it doesn't heat "much" under 1C. So yes. The temperature measuring capability is nice but I don't really think I need it as much. If someone has experience with how much battery heats up under let's say 0,5C I would really like to hear about it.
Balancing function
Yes. I plan to balance the cells and because they will be grade A EVE cells I think they won't need much of a balancing but it will always be handy to have some. Preferably active balancer because I will always be happier to transfer the energy than "waste it" as heat and raise the temperature inside the battery enclosure. The option of an external cell balancer isn't an option for me because I don't believe that BMS and cell balancer will work optimally if there is a chance of corrupting voltage readings to each other.
User definable parameters
Yes! Probably the main option. The more there is to set up and not just use static preprogrammed values the better. Being able to set up min/max pack voltage by your preference, max current, balancing voltage, SoC reset, etc. Seems like the main feature so I really want it.
Display capability
If it has one it is nice but I will probably use it for the first few months and then forget about it because I'm planning to have data online via something. I'm not sure exactly what I will choose. Maybe just Victron VRM, maybe something else.
Updatable software
A biggie. If there is any bug I want the capability to fix it with software update.
Paralleling capability
I'm planning to expand my battery bank so I really need some BMS that can communicate with other BMS modules. At least with BMSs from the same company and then port data from both to the Victron.
Pre-charge & current limiting
If I got it correctly the current limiting is mainly used in cases when you connect another battery with widely different SoC so the one wouldn't get discharged with massive current and the other on charged with said current. I get that you can use it for pre-charging the inverter, at least theoretically, but you would need to set this function every time when you connect the inverter to the battery. Which shouldn't be much, but. The pre-charging capability seems good until you read about some warnings that the pre-charge timer set to maximum value still isn't enough and it can lead to cycling between turning on and off the inverter and possibly even damaging it. So this functionality isn't really that much of a concern to me. Especially with low-frequency Victron, there could be a problem. But I would probably at least try it if it was built in. When shove comes to push I don't have a problem using a resistor-based pre-charge circuit.
Basically with the priorities set, the only option seems like JK. I'm right? The JBD isn't fully programmable (If I remember the datasheet correctly the SoC reset was the same as OV protection, some parameters seemed like static values), Seplos doesn't have a balancer, only an external one that isn't a part of it and it still looks like like it does have some relays? So possible mechanical failure. JK seems like the most popular on the forum and it also does have the most posts with some problems, but 80% of it looks like a user error.
What I don't like is that apparently, the JK can be in some cases prone to bricking and the last major problem Andy in off-grid garage found wasn't good news either. On the other hand, the speed and just the existence of the new software patch update gives JK bonus points. On the other hand, such a major bug shouldn't happen on a released product with its main purpose thrown out of the window.
I would really like to hear other people's opinions, suggestions, etc. Thank you all for your replies in advance.
