You wrote "....48 v bank with 200 amp..." but "200 amp" is not a size but rather a load. Could you clarify what you mean?Hello Dear Sirs !
I would like to know for a 48 v bank with 200 amp how many 18650 batteries are needed and the BMS how many amps are needed.
Thanks in advance !
Jose
Typically you buy a BMS with a little more capacity than expected use. Also the tend to come in round numbers. For example, a 100a BMS would make sense as it's 30a more than 70a - e.g. 30% headroom.I feel very happy with just one day in this forum, the professional and educated way to answer people like me who are not experts or professionals in the energy sector.
To be more exact, my need is 70amp x 12 hours of continuous work at 48 volts.
Yes, at 100% and 2500mah cells, it would be 4,704 - e.g. 40kwh. However, you can't actually discharge a lithium-ion battery 100% and have it last very long. So you need to think in terms of a 50kwh battery that you discharge about 80% to get 40kwh of useable power. So now we're up to about 5,900 cells @ 2500mah each.Using the formula that you sent me, it would be 4,704 cells, my second question at the beginning, what capacity would the BMS be for these cells.
I am a bit confused, a BMS does the charger function or a battery charger is required to be added to the BMSTypically you buy a BMS with a little more capacity than expected use. Also the tend to come in round numbers. For example, a 100a BMS would make sense as it's 30a more than 70a - e.g. 30% headroom.
Yes, at 100% and 2500mah cells, it would be 4,704 - e.g. 40kwh. However, you can't actually discharge a lithium-ion battery 100% and have it last very long. So you need to think in terms of a 50kwh battery that you discharge about 80% to get 40kwh of useable power. So now we're up to about 5,900 cells @ 2500mah each.
My own DIY powerwall is 81kwh - so I can say (from experience) that a 50kwh DIY battery bank of 18650 cells is a significant undertaking! You might consider EV batteries or LifePo4 bricks - just a lot less manual hookup / cell processing.
Thank You so MuchCharging is handled by a charge contoller, often a mppt solar controller/ inverter charger combo, it can be a battery charger but it needs to be made fore Lithium , then you have different chemisties of lithium cells needs to be for the right chemistry
later floyd
Thank You so Much !!Hi there Emmanijoa, oh you have a lot of questions I see That's good!
I can surely suggest you to start from this: become a guru of capacity and voltage calculations, and talking about batteries... lets take any random type of battery, the 18650. Please do read the whole FAQ section here, you can find a good starting kit.
So, to start with: terminology, abbreviations, measurement units. I'd say, it's no good to talk about BMS without knowing what's underneath it.
So, getting back to what OGITC was correctly saying... these are the first things to know:
A = Ampere, we love amperes. We measure current with amperes. So we could measure how many amps (current) are passing though a wire, a nickel strip, a copper bar by using, for e.g., a DMM (multimeter). That measurement will only give us an instantaneous measurement. "Now the TV is using 0.9A"... "Aww good to know"... "0.9A at 230 volts!"... "wow" (obviously the answers are from our other significant person LOL). My whole house in this moment is using:
View attachment 25491
1.62A of current at 220V. It's an instantaneous measurement.
Ah = Ampere per hour. Oh, this is good, we can measure a capacity with this. We measure our battery capacity with this. Now I'm checking cells capacity, actually it's been my main activity since May. My wife, sun, family, friends and random people met in the street really don't understand why I'm charging cells to discover their effective capacity (LA = Lithium Addiction, search it please). The last cells I checked gave me a capacity of 2047mAh measured today June 25th with an IR of 31, checked in charger n.2 (I have only 3, that's why I'm so slow! But I'm a bit of a noob still). So this cell, a 3.7V cell connected to a load (a load which runs at 3.7V) could give 2.047A for one hour. Obviously if the load only requires 1/10th of 2.047A (0.2047A) to run, then this cell should last 10 hours!
OGITC is OffGridInTheCity
These were some of the first things I learnt! (What about V volts, oh you must know everything of volts and Ohm law; power; resistance, and watts, oh I love watts, it says a lot of things, for e.g. with one number you can rapresent two other numbers, and watts/hour, Wh) ... (Ah, and "battery jargon", SD, SOH, SOC, ...).
And, yes, do ask a load of questions, post diagrams, schemas and photos!
Enjoy,
jes
It would be best if you could describe what exactly you want to power with the battery.To be more exact, my need is 70amp x 12 hours of continuous work at 48 volts.
Thanks a million for tour assistanceThat size of a battery as you are describing by your demand, and as explained from other commenters what actually that would mean if you build it with 18650 cells (used??), how much time do you have to finish this massive undertaking?
If you are planning to use this system sometime within the next 2 years, I would suggest to go on the Alibaba.com website, search for LiFePo4 280Ah cells, and just order 4x16=64 of those, which would give you about your required capacity. I am sure they can be delivered to any place in the world to your door within a few months. You just might have to pay a bit extra for customs fees.
But in general, you will end up with probably less of expense as well, as you need a lot of equipment to process thousands of cells quickly.
And the LiFePo4 system will be much safer as well, as there is almost no parts to fail, when comparing to the thousands of cells where each single one is a point of failure.
But its your choice
The BMS doesn't determine capacity. It only limits voltage and current.
I don't know exactly what you are asking (not very good translation I'm afraid) But I think you are asking about the condition of each parallel batch of cells in a battery.but i think it dose not limit every battery, only every group in this case, am i right
if i am, how can we check if there is any battery goes down if it is not functioning well??