How many amps do I have?
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gnubie
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4 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.
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.
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 batteries
gnubie
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They're not my videos 
, Will's. When it comes to a BMS I'm not into that side of things so I'll leave that for someone else to answer. You might want to post in the BMS section of the forum. There's lots of discussion about BMSes there.
, Will's. When it comes to a BMS I'm not into that side of things so I'll leave that for someone else to answer. You might want to post in the BMS section of the forum. There's lots of discussion about BMSes there.Gnubie, I have another question for you. What would be better 4 cells to make 12 volts then connect to 12 volts series. Or would it be better to use eight cells make a 24 volt only downfall I would have to buy a new inverter. my mppt Rover is 12 volt or 24 volt
gnubie
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When it comes to configuring the battery IMO it's preferable to keep all your cells under the management of a single BMS if you can.
If you build two separate 12V batteries and use them in series (for 24v) they will slowly drift out of sync in terms of state of charge. It's not a big problem with lithium but you should bring each battery up to fully charged separately every 6 or 12 months to overcome this problem. I read that Battleborn recommends this sort of treatment. If everything is under the control of a single BMS it will be able to keep all the cells in step with each other so there is no need to do, or even capability of doing, a separate periodic full charge. If things are allowed to get far enough out of step you will have trouble charging and discharging as one BMS will trip and prevent further charging / discharging of the system as a whole, and all your loads turn off.
When using batteries in series you need to ensure that the BMS is rated to work at that voltage, 24V in this case. It's still a BMS for a 12V battery but it can handle 24V across it's terminals.
If you build two separate 12V batteries but use them in parallel (for 12v) you won't get state of charge problems so there is no great need to have them under the control of one BMS. You could do it though by arranging your cells as 2p4s, 2 in parallel and then 4 packs of those in series (12v).
When paralleling lithium batteries you have to consider what happens should one battery's BMS disconnect for some reason. Under charging that would mean one battery would get access to the full charging current, and that may not be good for it. Under discharge one battery would have to support your full load, or its BMS will trip too and then your loads turn off.
12 or 24 comes down to your expected peak load. At nominal 12V, a 2000W inverter running full power might draw 185A while a 24V inverter will draw around half that. Using 24V means lighter wiring, lower rated fuses, lower rated switches. Copper cable isn't cheap but over the distances you have between the battery and inverter (I'm assuming there is an inverter involved here) that may not be much of a factor.
Other factors are at play too. If you are adding to an existing 12V system it might be an advantage to keep everything 12V. What's the rating of your current inverter?
Once you get to > 3000W 24V or higher is IMO the way to go. Over 5000W it's time to start looking at 48V. My opinions only, other people may have different points.
If you build two separate 12V batteries and use them in series (for 24v) they will slowly drift out of sync in terms of state of charge. It's not a big problem with lithium but you should bring each battery up to fully charged separately every 6 or 12 months to overcome this problem. I read that Battleborn recommends this sort of treatment. If everything is under the control of a single BMS it will be able to keep all the cells in step with each other so there is no need to do, or even capability of doing, a separate periodic full charge. If things are allowed to get far enough out of step you will have trouble charging and discharging as one BMS will trip and prevent further charging / discharging of the system as a whole, and all your loads turn off.
When using batteries in series you need to ensure that the BMS is rated to work at that voltage, 24V in this case. It's still a BMS for a 12V battery but it can handle 24V across it's terminals.
If you build two separate 12V batteries but use them in parallel (for 12v) you won't get state of charge problems so there is no great need to have them under the control of one BMS. You could do it though by arranging your cells as 2p4s, 2 in parallel and then 4 packs of those in series (12v).
When paralleling lithium batteries you have to consider what happens should one battery's BMS disconnect for some reason. Under charging that would mean one battery would get access to the full charging current, and that may not be good for it. Under discharge one battery would have to support your full load, or its BMS will trip too and then your loads turn off.
12 or 24 comes down to your expected peak load. At nominal 12V, a 2000W inverter running full power might draw 185A while a 24V inverter will draw around half that. Using 24V means lighter wiring, lower rated fuses, lower rated switches. Copper cable isn't cheap but over the distances you have between the battery and inverter (I'm assuming there is an inverter involved here) that may not be much of a factor.
Other factors are at play too. If you are adding to an existing 12V system it might be an advantage to keep everything 12V. What's the rating of your current inverter?
Once you get to > 3000W 24V or higher is IMO the way to go. Over 5000W it's time to start looking at 48V. My opinions only, other people may have different points.
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1. Correct, 4 x 200Ah cells in series is 200Ah @ 12v
2. If you buy two and connect them all together you will have either 200Ah @ 24v or 400Ah @ 12v depending on how you wire them.
Two things to wrap your head around now that benefit you many times over now and in the future:
1. combine in series voltage increases, combine in parallel amp hours (or amps) increase
2. Amps =/= Amp Hours. Amps are a unit of current (like a flow rate), Amp-hours are a unit of electrical charge, in the context of batteries/energy storage they refer to capacity. So in this context (your question) you are talking about amp hours not amps.
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. Another question I have asked in the Forum is how I should control these batteries with BMS.
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. Another question I have asked in the Forum is how I should control these batteries with BMS.
GXMnow
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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.
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.
GXMNOW,
thank you . And it's obvious I don't have enough solar array. So I plan on getting two more 100 watt rennologys. which would be a total of four 100w rhinology and 2)75 Watt seamens.
I have not a clue on how to figure this if I put it out there maybe you might help?
900w coffee pot 20 minutes
3) 12 v lights small bulb 4 hours
2) 10" 12 v fan 4.8 watts 24 hours
2) cell phones
2) tablets
1) 20" fan .8 amps 6 hours
1) water pump 12 v 1 hour
1)tv 57 wats ac. 3 hours
Microwave 13 amp ac 5 minutes
These loads are all broken up throughout the day.
I live in the high desert of Arizona so the amount of sun I get in a day is really good haven't seen clouds in over a month.
Wow good info, many thanks
I am going to increase my solar array buy 200 Watts rennologys
I have found all my loads but not sure how to calculate.
900w coffee pot 20 minutes
3) 12 v lights small bulb 4 hours
2) 10" 12 v fan 4.8 watts 24 hours
2) cell phones
2) tablets
1) 20" fan .8 amps 6 hours
1) water pump 12 v 5.7 amps 1 hour
1)tv 57 wats ac. 3 hours maybe once a week
Microwave 13 amp ac 5 minutes
These loads are broken up throughout the day not much runs together besides the fans.
Thank you again for your info and if you were able to help calculate I would be appreciative.
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