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Best way to parallel
#1
Hello all 

I am a beginner and am trying to put a home backup rig together for a conference room and LED lights. 

I have a Tripplite 2000W APS X series 12VDC inverter/charger and am thinking to purchase eight 3.2v 100ah batteries for it. I cannot series connect them all and am trying to think of the best way to parallel connect the batteries. I guess I do not need a BMS as the charger has several safety features in it already and ideally I would like to connect one balancer to it.

I can think of two parallel arrangements:

1) Create four 3.2v 200ah batteries by parallel connecting two batteries at a time. Then series connect the four 200ah enhanced batteries to get 12v. I then connect a 4S active balancer to the 4 enhanced 200ah cells.

2) Create two 12v 100ah batteries by series connecting 4 batteries at a time. Then parallel connect the two 12v batteries. Do I need two 4S active balancers in this case. 

I am probably making many mistakes and any advice on the best parallel configuration, considerations, and what to watch out for would be much appreciated. 

Thank you in advance. 
Jacques
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#2
(01-28-2020, 09:33 PM)JacquesClaass Wrote: I guess I do not need a BMS as the charger has several safety features in it already and ideally I would like to connect one balancer to it.
Incorrect. You should always have a bms. The charger only handles "overall" string voltage/amperage. It does "not" protect from packs becoming different voltages over time

(01-28-2020, 09:33 PM)JacquesClaass Wrote: I can think of two parallel arrangements:

1) Create four 3.2v 200ah batteries by parallel connecting two batteries at a time. Then series connect the four 200ah enhanced batteries to get 12v. I then connect a 4S active balancer to the 4 enhanced 200ah cells.

2) Create two 12v 100ah batteries by series connecting 4 batteries at a time. Then parallel connect the two 12v batteries. Do I need two 4S active balancers in this case. 

It's best to connect your cells in parallel then connect them in series. This minimizes wiring. Please read the FAQ located on the main page for more details on that.

The advantage of having multiple strings is that you could take one of them offline and the system still function, as long as the remaining string(s) can handle the amp load.
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#3
(01-28-2020, 10:12 PM)Korishan Wrote:
(01-28-2020, 09:33 PM)JacquesClaass Wrote: I guess I do not need a BMS as the charger has several safety features in it already and ideally I would like to connect one balancer to it.
Incorrect. You should always have a bms. The charger only handles "overall" string voltage/amperage. It does "not" protect from packs becoming different voltages over time

(01-28-2020, 09:33 PM)JacquesClaass Wrote: I can think of two parallel arrangements:

1) Create four 3.2v 200ah batteries by parallel connecting two batteries at a time. Then series connect the four 200ah enhanced batteries to get 12v. I then connect a 4S active balancer to the 4 enhanced 200ah cells.

2) Create two 12v 100ah batteries by series connecting 4 batteries at a time. Then parallel connect the two 12v batteries. Do I need two 4S active balancers in this case. 

It's best to connect your cells in parallel then connect them in series. This minimizes wiring. Please read the FAQ located on the main page for more details on that.

The advantage of having multiple strings is that you could take one of them offline and the system still function, as long as the remaining string(s) can handle the amp load.

Thank you Korishan. Just to confirm for clarity, are you saying Option 1 is the better configuration - using bus bars to make all the inter-battery connections? That way I will only need one BMS? Would you have any advice on choosing the right BMS Amperage - I was thinking of getting a 200A BMS or is that an overkill? Sorry if I make your brain melt with basic questions.
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#4
I personally would go with Option 1 to start off with, yes. Later on when you have enough cells to make another string then you basically create Option 2 automatically. But instead of 1p configuration, it's Xp for each string. IE 14s80p

The BMS amps are chosen based on what "your" needs require. You don't want to skimp out and go with a too low of an amp rating as you'll burn out the components and spend twice as much money.

The upper limit is really based on the breaker/fuse, not the BMS. To figure out the right sized breaker/fuse, take all of your loads and calculate the amps required turn them. Anything that is a motor, double the amps for surge. If you know for certain that two or motors will "not" start at the same time (like in a workshop where you manually turn on loads), then you can go with the highest amp rating and double that for surge.
Then take those numbers and add an additional 25% for inefficiency slice variances in the ratings of the components in the bms, or other equipment.

If this is for an ebike or other similar 1 device load, then just double the amps of that to get the surge and get a bms for that range. Then just slap a fuse inline for extra safety of the right value.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#5
(01-29-2020, 01:49 PM)Korishan Wrote: I personally would go with Option 1 to start off with, yes. Later on when you have enough cells to make another string then you basically create Option 2 automatically. But instead of 1p configuration, it's Xp for each string. IE 14s80p

The BMS amps are chosen based on what "your" needs require. You don't want to skimp out and go with a too low of an amp rating as you'll burn out the components and spend twice as much money.

The upper limit is really based on the breaker/fuse, not the BMS. To figure out the right sized breaker/fuse, take all of your loads and calculate the amps required turn them. Anything that is a motor, double the amps for surge. If you know for certain that two or motors will "not" start at the same time (like in a workshop where you manually turn on loads), then you can go with the highest amp rating and double that for surge.
Then take those numbers and add an additional 25% for inefficiency slice variances in the ratings of the components in the bms, or other equipment.

If this is for an ebike or other similar 1 device load, then just double the amps of that to get the surge and get a bms for that range. Then just slap a fuse inline for extra safety of the right value.

Korishan, thank you for being an absolute legend! That is very clear and helps a lot.
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