Sizing and brand suggestions.
- Thread starter lj1064
- Start date
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
200AH cells can discharge at 1C or 200A for 1 hour and take 100A (0.5C Rate) charge.
A decent BMS capable of 200A continuous is not hard to get with various options and features. But choosing one depends on the configuration 24V/8S or 48V/16S and the intended use / application.
Generally we advice people to Over Spec the BMS so as to keep it from the Useable Limit edges, generally 20-25% larger is fine. This applies to both FET & Relay/Contactor types of BMS. This is also to cover for any momentary surge potentials. EV's and other heavy use cases generally rely on Relay/Contactor based systems due to the amperage loading & increased fault tolerance & safeties.
General Rule is basically not to exceed 250A draw from a battery bank. This can be exceeded if a battery bak is properly configured as multiple battery packs within a bank will split/share the load & charge capacity.
A quick guide: 250A @ 12V = 3000W, @ 24V = 6000W and 48V = 12,000W excluding surge and not corrected for Inverter inneficiency which can rage from 82-95% efficient depending on grade & brand.
BTW: Passive Balancing is of little use with Bulk Commodity Cells and due to the size of these cells (it's intended for smaller capacity cells). Active Balancing can work with the large capacity cells and helps keep the cells more level and with a lower differential. CAUTION this is an area which is tricky, we know of Known Good and some really bad ones too.... QNBBM & Heltec make good Active Balancers BUT they must be chosen / selected carefully.
Hope it helps, Good Luck
A decent BMS capable of 200A continuous is not hard to get with various options and features. But choosing one depends on the configuration 24V/8S or 48V/16S and the intended use / application.
Generally we advice people to Over Spec the BMS so as to keep it from the Useable Limit edges, generally 20-25% larger is fine. This applies to both FET & Relay/Contactor types of BMS. This is also to cover for any momentary surge potentials. EV's and other heavy use cases generally rely on Relay/Contactor based systems due to the amperage loading & increased fault tolerance & safeties.
General Rule is basically not to exceed 250A draw from a battery bank. This can be exceeded if a battery bak is properly configured as multiple battery packs within a bank will split/share the load & charge capacity.
A quick guide: 250A @ 12V = 3000W, @ 24V = 6000W and 48V = 12,000W excluding surge and not corrected for Inverter inneficiency which can rage from 82-95% efficient depending on grade & brand.
BTW: Passive Balancing is of little use with Bulk Commodity Cells and due to the size of these cells (it's intended for smaller capacity cells). Active Balancing can work with the large capacity cells and helps keep the cells more level and with a lower differential. CAUTION this is an area which is tricky, we know of Known Good and some really bad ones too.... QNBBM & Heltec make good Active Balancers BUT they must be chosen / selected carefully.
Hope it helps, Good Luck
I have a 280ah 24v battery that I run a JBD BMS on. I looked at high amperage BMS's which are pretty expensive and ended up monitoring my amp draw before ordering a new BMS. In my case, the battery only supplied 80a at the highest which allowed me to purchase a much cheaper 100a BMS.
Can you tell us more about the way you intend to configure the cells (12 / 24/ 48 volts) and your installation (sources of charge, main loads and their usage...).
Do you just want a BMS to protect the battery or one that can manage external equipment (like start a generator, cut power hungry equipment while keeping other essential ones running, regulate battery heating and cooling...)?
Do you just want a BMS to protect the battery or one that can manage external equipment (like start a generator, cut power hungry equipment while keeping other essential ones running, regulate battery heating and cooling...)?
Yes, thanks for guidance. Sometimes knowing how to ask helps. 48v in an s, have 6 used 289w panels 3 each in series. The main load is a beer brewing system that is used for about 5 hrs used 5.5 kWh and peaked at 1473w. this will be used when other loads are not in use, power tool battery charging, garage door opener, pellet grill… Of course temp control on charging, Didn’t know they did some of the other things you listed. Have a mppt lv5048.
Deciding if these "other things" are important for you (as well as your budget) will help you decide which kind of BMS you need: a basic "battery protection" BMS (less expensive and suitable for low capacity and less critical applications), or an energy management system.
As @Steve_S said, look at the balancing principle and capabilities of the BMS. I just spoke with someone with 24V / 400Ah Winston cells that are completely out of balance after 2 years (low cell: 3.14V / high cell: 3.27V) - his BMS balances at 150mA (note: I am surprised that expensive Winston cells got that much out of balance! so I can only imagine what is possible with more economical cells?). I also agree with @Steve_S when he says "Passive Balancing is of little use with Bulk Commodity Cells"
Note / disclosure: I designed the TAO BMS for off-grid applications and I believe that every product has its place to suit specific applications, battery types and user requirements. I spend most of my time helping people define their requirements and yes, I point some of them to competitors' products. Problems arise when a BMS is selected based on undefined requirements, misunderstanding of what it does or not, and/or price. I have started a BMS comparison chart (very incomplete at this stage and I welcome any input to correct missing data / add BMS's). I attach it here just for you to have an idea of the criteria used for the comparison and what some BMS can do. My advice would be to first understand those criteria, then define how each of those criteria is important to you. On that basis you can look at the BMS you can afford and check it against your own requirements grid... Feel free to ask any question on the definition of those criteria and why they may be important (or not) in some situations.
As @Steve_S said, look at the balancing principle and capabilities of the BMS. I just spoke with someone with 24V / 400Ah Winston cells that are completely out of balance after 2 years (low cell: 3.14V / high cell: 3.27V) - his BMS balances at 150mA (note: I am surprised that expensive Winston cells got that much out of balance! so I can only imagine what is possible with more economical cells?). I also agree with @Steve_S when he says "Passive Balancing is of little use with Bulk Commodity Cells"
Note / disclosure: I designed the TAO BMS for off-grid applications and I believe that every product has its place to suit specific applications, battery types and user requirements. I spend most of my time helping people define their requirements and yes, I point some of them to competitors' products. Problems arise when a BMS is selected based on undefined requirements, misunderstanding of what it does or not, and/or price. I have started a BMS comparison chart (very incomplete at this stage and I welcome any input to correct missing data / add BMS's). I attach it here just for you to have an idea of the criteria used for the comparison and what some BMS can do. My advice would be to first understand those criteria, then define how each of those criteria is important to you. On that basis you can look at the BMS you can afford and check it against your own requirements grid... Feel free to ask any question on the definition of those criteria and why they may be important (or not) in some situations.
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