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Mr. Cucumber

Offgrid battery backup.

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Posted · Original PosterOP

I have 2000 18650 Samsung 20S 18650 cells. I want to arrange them in 100 parallel units making 20 units and 10 units in parallel and 2 of those 10 units in series... Can I do it?.. If I can...then how should I do it to ensure safety and good performance of the batteries and longevity of the cells.

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I'm a little confused on your pack configuration. Figure out how many cells you want in series (voltage. Full charged voltage = number of cells *4.2, nominal voltage = number of cells*3.8) and then divide your 2000 cells by that series number to find how many in parallel.


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Posted · Original PosterOP

My arrangement is shown in the photo...and I thinking of using circuit breakers at the main output lines for example a 500A breaker at thr 14.8v potential line but will a 500A DC circuit breakers work in 14.8V? I know circuit breakers aren't usually tripped by voltage (open circuit) but for 14.8V volts? Will it work? Because I really want to use breakers for their convenience and safety.

IMG_20190207_112251.jpg

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16 hours ago, Mr. Cucumber said:

My arrangement is shown in the photo...and I thinking of using circuit breakers at the main output lines for example a 500A breaker at thr 14.8v potential line but will a 500A DC circuit breakers work in 14.8V? I know circuit breakers aren't usually tripped by voltage (open circuit) but for 14.8V volts? Will it work? Because I really want to use breakers for their convenience and safety.

IMG_20190207_112251.jpg

Okay from what I understand, you want 4 different kinds of modules, A-D. A is a 1s300p configuration. B is two A modules in parallel, giving you a 1s600p configuration. C is 2 B modules in series, giving you 2s600p and so on. This sounds way too complicated to me. The first question I have is why have you chosen a 4s configuration? 16.8V (full charge) is not a lot for such a high power system, which will require massive cables to carry your quoted 500A of current. 

 

If this was my system, I would go for like 25s160p system, giving you a much higher voltage, will reduce your maximum current to around 500A. 105v (full charge) at 500A is 52.5Kw. If you're pulling that much power, I bet your battery pack is the last of your issues. 

 

Also look into the homebrew powerwall forum. They have great info on cells, inverters, and everything else you'll need for a system of this scale. 

 

Also for the love of god invest in a good bms. 


I used to have guides here

CPU: 4670k 4.4ghz GPU: GTX 970 G.1 1534mhz

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Posted · Original PosterOP

After much thought... I've decided to go with 40 A modules in series and get 148 v and which will lower my current draw to 35 amps 

But...what inverter should I use which will give me 5kW of power at 110vac? 

And I'll use a custom bms circuit which will be integrated into all A modules ... (Each cell voltage is 3.7v ...so the inverter should not charge them over 4.1v and drain them below 3.2v just to be safe ...now can you give me an inverter which will work from 128 to 164v on the input) 

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14 hours ago, Mr. Cucumber said:

After much thought... I've decided to go with 40 A modules in series and get 148 v and which will lower my current draw to 35 amps 

But...what inverter should I use which will give me 5kW of power at 110vac? 

And I'll use a custom bms circuit which will be integrated into all A modules ... (Each cell voltage is 3.7v ...so the inverter should not charge them over 4.1v and drain them below 3.2v just to be safe ...now can you give me an inverter which will work from 128 to 164v on the input) 

Look into grid tied inverters, maybe from SMA.


I used to have guides here

CPU: 4670k 4.4ghz GPU: GTX 970 G.1 1534mhz

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On 2/11/2019 at 12:51 PM, Mr. Cucumber said:

After much thought... I've decided to go with 40 A modules in series and get 148 v and which will lower my current draw to 35 amps 

But...what inverter should I use which will give me 5kW of power at 110vac? 

And I'll use a custom bms circuit which will be integrated into all A modules ... (Each cell voltage is 3.7v ...so the inverter should not charge them over 4.1v and drain them below 3.2v just to be safe ...now can you give me an inverter which will work from 128 to 164v on the input) 

the inverter is not going to charge anything, you gonna need a battery management system and a good charger.

 

Also you should first look for an inverter that fits your needs and then build a battery that fit into the right voltage range.

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Posted · Original PosterOP
On 2/15/2019 at 3:09 AM, Pixel5 said:

the inverter is not going to charge anything, you gonna need a battery management system and a good charger.

 

Also you should first look for an inverter that fits your needs and then build a battery that fit into the right voltage range.

Cab you suggest a good high power lithium ion chargers?...

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On 2/16/2019 at 2:53 PM, Mr. Cucumber said:

Cab you suggest a good high power lithium ion chargers?...

there are many options for this but the question is always what exactly do you want to charge with it and from which source.

 

first you need to know your final battery voltage and how much power you will get from the source that is charging the batteries only then you can select a suitable charger.

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