Thank you very much for your quick response I will look into that discharge rate. What size BMS should I purchase for that two hundred amp hour battery? I understand I need a low temp shut off since I live in the high desert of Arizona. Watching your videos I see a little red square BMS that has low temp charge shut off built in. But I don't believe that a 60 amp it's enough for my two hundred amp batteries4 cells in series will yield a 12V 200AH battery. Two of those in parallel will give you 400AH of capacity.
If you are asking about amps instead of amp hours you will have to check your cell's discharge ratings. You can discharge at quite high currents but it does have consequences. You should see a recommended maximum discharge rate.
1. Correct, 4 x 200Ah cells in series is 200Ah @ 12vI have purchased 4) 3.2 volt 200 ah lithium Pro 4
Once I put them together I will have a 200 amp 12 volt battery is that correct?
If I buy two of these and connect them together does that mean I have 400 amps 12 volt?
You have two bottlenecks here, (1) battery bank size (2) the ability to fill up that battery bank (solar, and other charge sources). You have 350W of solar which is roughly enough to fill up maybe a 100Ah (1200Wh) battery on a sunny day.Thanks DZL,
Yes I am talking amp hours I run my fifth wheel trailer lighting refrigerator water heater igniters only. 2)10 inch 12 volt fans running 24 hours a day. Charging telephones and tablets. I have 4) solar panels. 2) 100 watt rhinology and 2)75 watt Siemens. What I would like to achieve is to run my coffee pot for 15 minutes each morning. My thought was two 12 volt 200 amps in parallel to achieve 12 volt 400 amps then I should have plenty amp hours.
A BMS is sized for max current and number of cells in series (4 for a 12v battery). If most or all of your loads are AC, you can get a ballpark by taking the max power of the inverter, dividing by 12v, and dividing by efficiency of the inverter, then add maybe 25%-50% to that for safety margin (this is an oversimplification, but it gives you a ballpark)Another question I have asked in the Forum is how I should control these batteries with BMS.
GXMNOW,Have you totaled up how many watts you will need at peak? And the total watt hours you need for a whole day?
12 volts at 400 amp hours is a total of about 4.8 kilowatt hours of energy. To get a long life, don't plan to use more than about 3,800 watts, which is an 80% discharge. Your 4 solar panels only add up to 350 watts. That is not a lot of power. Are they angled towards the sun, or flat on the roof? Even well aimed, you can't expect to get more than 5 sun hours on a regular basis. 5 sun hours x 350 watts is just 1,750 watt hours of solar a day. If you did use 80% of your batteries overnight, it would take over 2 days with no loads to charge them back up again.
If you do only use 1,700 watt hours (1.7 KWH) in a day, this will work, and if you have bad sun, or are in the shade, you can get and extra day on battery alone. But to do the math, you need to start with knowing how much load you have.
Your peak load will be when the lights and fans are all on, your phones etc. are all charging, the refrigerator compressor cycles on, and you decide to fire up the coffee pot. I don't want to guess how much power that is. You need to either read the labels or actually measure to see what the peak power might be. Whatever that worst case load works out to, that will determine what size inverter you will need, and then how much current your battery bank needs to be able to supply. If you need 1,200 watts, then get at least a 1,500 watt inverter, even double to 2,400 is not a bad idea to handle surges and motor starting. 1,200 watts on a 12 volt system is 100 amps at the battery. Your 400 amp hour battery bank could theoretically run 1,200 watts for about 3 to 4 hours. But then your solar panels need 3 days to put the power back in the batteries. In a perfect world, you should have a BMS that can handle all of the power your battery could put out, but if it turns out you don't need that much power, you can save money if 100 amps is enough, rather than having a system that can handle 400 amps.
So before going through all of the real math, get a decent idea of how much power and energy are actually needed. And expect the system to under perform and add a little overhead. Each device also has some power loss, so as much as 20% of your power may just go away as heat.
I added a storage battery with a hybrid inverter/charger to my grid tie system for backup power, but I am also using it to cycle some power each day to try and reduce electricity cost in the evening. After a few weeks of cycles, I have decided to cycle a bit less power as I am losing about 14% when it takes AC power to charge the battery, and then uses the battery power back through the inverter to feed the house again. My initial calculations were just under 10% loss (90% efficient) but in the real world, it is looking more like a 14% loss, (86% efficient). 7 days ago, I pushed out 7 KWH from the battery, but it took almost 8.2 KWH to charge it back up the next morning. Never forget to figure out and add in the efficiency losses. In my case, I am losing a solid 1.2 KWH to cycle the batteries. My solar production is about 20 KWH/day with the current conditions. So I am wasting 6% of my solar production. Not too horrible. Your 4 solar panels are just making 1.7 KWH, my loss of 1.2 KWH with your small solar panel setup would be losing 70%, that is a completely different story. When working with less production, every loss really starts to matter.
Have you totaled up how many watts you will need at peak? And the total watt hours you need for a whole day?
12 volts at 400 amp hours is a total of about 4.8 kilowatt hours of energy. To get a long life, don't plan to use more than about 3,800 watts, which is an 80% discharge. Your 4 solar panels only add up to 350 watts. That is not a lot of power. Are they angled towards the sun, or flat on the roof? Even well aimed, you can't expect to get more than 5 sun hours on a regular basis. 5 sun hours x 350 watts is just 1,750 watt hours of solar a day. If you did use 80% of your batteries overnight, it would take over 2 days with no loads to charge them back up again.
If you do only use 1,700 watt hours (1.7 KWH) in a day, this will work, and if you have bad sun, or are in the shade, you can get and extra day on battery alone. But to do the math, you need to start with knowing how much load you have.
Your peak load will be when the lights and fans are all on, your phones etc. are all charging, the refrigerator compressor cycles on, and you decide to fire up the coffee pot. I don't want to guess how much power that is. You need to either read the labels or actually measure to see what the peak power might be. Whatever that worst case load works out to, that will determine what size inverter you will need, and then how much current your battery bank needs to be able to supply. If you need 1,200 watts, then get at least a 1,500 watt inverter, even double to 2,400 is not a bad idea to handle surges and motor starting. 1,200 watts on a 12 volt system is 100 amps at the battery. Your 400 amp hour battery bank could theoretically run 1,200 watts for about 3 to 4 hours. But then your solar panels need 3 days to put the power back in the batteries. In a perfect world, you should have a BMS that can handle all of the power your battery could put out, but if it turns out you don't need that much power, you can save money if 100 amps is enough, rather than having a system that can handle 400 amps.
So before going through all of the real math, get a decent idea of how much power and energy are actually needed. And expect the system to under perform and add a little overhead. Each device also has some power loss, so as much as 20% of your power may just go away as heat.
I added a storage battery with a hybrid inverter/charger to my grid tie system for backup power, but I am also using it to cycle some power each day to try and reduce electricity cost in the evening. After a few weeks of cycles, I have decided to cycle a bit less power as I am losing about 14% when it takes AC power to charge the battery, and then uses the battery power back through the inverter to feed the house again. My initial calculations were just under 10% loss (90% efficient) but in the real world, it is looking more like a 14% loss, (86% efficient). 7 days ago, I pushed out 7 KWH from the battery, but it took almost 8.2 KWH to charge it back up the next morning. Never forget to figure out and add in the efficiency losses. In my case, I am losing a solid 1.2 KWH to cycle the batteries. My solar production is about 20 KWH/day with the current conditions. So I am wasting 6% of my solar production. Not too horrible. Your 4 solar panels are just making 1.7 KWH, my loss of 1.2 KWH with your small solar panel setup would be losing 70%, that is a completely different story. When working with less production, every loss really starts to matter.
You have two bottlenecks here, (1) battery bank size (2) the ability to fill up that battery bank (solar, and other charge sources). You have 350W of solar which is roughly enough to fill up maybe a 100Ah (1200Wh) battery on a sunny day.
If you increase your battery bank size, you will be able to store and use more power between charging, but you will still need to replenish what you use, and its not possible to recharge a 5kWh (400Ah @ 12v) battery bank with only 350W of solar unless you have other charge sources.
A BMS is sized for max current and number of cells in series (4 for a 12v battery). If most or all of your loads are AC, you can get a ballpark by taking the max power of the inverter, dividing by 12v, and dividing by efficiency of the inverter, then add maybe 25%-50% to that for safety margin (this is an oversimplification, but it gives you a ballpark)
For instance:
2000W / 12v / 0.8 = 208A x 1.5 = ~300A
As to what BMS to choose, this is a more complicated and contextual question.
Wow good info, many thanksYou have two bottlenecks here, (1) battery bank size (2) the ability to fill up that battery bank (solar, and other charge sources). You have 350W of solar which is roughly enough to fill up maybe a 100Ah (1200Wh) battery on a sunny day.
If you increase your battery bank size, you will be able to store and use more power between charging, but you will still need to replenish what you use, and its not possible to recharge a 5kWh (400Ah @ 12v) battery bank with only 350W of solar unless you have other charge sources.
A BMS is sized for max current and number of cells in series (4 for a 12v battery). If most or all of your loads are AC, you can get a ballpark by taking the max power of the inverter, dividing by 12v, and dividing by efficiency of the inverter, then add maybe 25%-50% to that for safety margin (this is an oversimplification, but it gives you a ballpark)
For instance:
2000W / 12v / 0.8 = 208A x 1.5 = ~300A
As to what BMS to choose, this is a more complicated and contextual question.