Working Backwards A good idea? (from Charging to SCC to Batt to Load)...?

[Davetv1423]

Anyone ever work Backwards from The Charging Tools to the Solar to the MPPT to buying a Battery >?

In an RV Setup here -
I have a brand new AC charging system that will trickle to max out at 50amps
I have an MPPT Solar Charge Controler/MPPT that maxes out at 40 amp EPEVER Tracer (100v max).
I have two fixed 100watter solar pannes and 2 more flexible i can bring out when needed (also 100w each)
I currently have two 6volt 235ah batteries looking to replace them with Lipo4 = what is the max batter size you'd recommend??
(i'm guessing 200ah 12v)
Also having a problem sizing a BMS against this -Alieexpress has great deals on 435ah set of 4 but i don't think i need a 400+ah BMS right?
(was looking at Dalie's sp? non-wifi setup).
Thx

 

[kenryan]

Some people forget that batteries must be recharged. In a vehicle, charging is frequently limited and so recharging becomes the limiting factor with regards to battery size. In a scenario like that, it could make sense to size the batteries based upon this limited charging capability. If you use your RV in such a way that you have access to grid power, I would say that you do not really have limited charging capacity. In an RV, a grid connection should provide more charging than you need.

 

[MisterSandals]

Also having a problem sizing a BMS against this -Alieexpress has great deals on 435ah set of 4 but i don't think i need a 400+ah BMS right?

You size your BMS to be larger than your highest charging current or highest load. If using an economy BMS, you may have to oversize your BMS by 50-100%.

You made no mention of what loads you expect to use. Most commonly it is the size of the inverter that determines the size of your BMS.

If you order from China, make sure your spell your battery chemistry correctly because when it comes out of the english to chinese translator it could be LiPo (Lithium Polymer) or who nows what.

 

[Davetv1423]

You size your BMS to be larger than your highest charging current or highest load. If using an economy BMS, you may have to oversize your BMS by 50-100%.

You made no mention of what loads you expect to use. Most commonly it is the size of the inverter that determines the size of your BMS.

If you order from China, make sure your spell your battery chemistry correctly because when it comes out of the english to chinese translator it could be LiPo (Lithium Polymer) or who nows what.

good points - thx.
The load is just a 12vot fridge/freezer (50watts) and a 1500 watt inverter to run a dorm fridge, wifi router, 1 22" tv, 1 computer and some fans.

 

[MisterSandals]

12vot fridge/freezer (50watts) and a 1500 watt inverter

1500W / 12.8V = 117A
50W / 12.8V = 3.9A

With a quality BMS you might squeak by on a 125A BMS but a 150A would be better sized (and less likely to cut out if there are any surge currents.
If you get an economy BMS, you'd probably need at least 200A BMS.

 

[mikefitz]

new AC charging system that will trickle to max out at 50amps

will this charge lithium OK?

two 6volt 235ah batteries looking to replace them with Lipo4

if your systen works fine with around 150 Ah usable typical at 12v, then anything from 200Ah lithium should be equivalent.

sizing a BMS against this

select for expected load. The often used Overkill, JBD, 120 amp BMS is good value and good support on the forum,

4s BMS 120a LifePo4 with M6 Threaded Terminals – Overkill Solar

overkillsolar.com

4S or 3S 12V Li ion or Lifepo4 Battery smart BMS with Bluetooth function UART and RS485 communication with 60A to 120A constant current - LLT POWER ELECTRONIC

1) Application:this smart BMS can work for 3 to 4S Lithium ion or Lifepo4 Battery ,client can choose based on your battery chemistry features 2) Current : constant current of this version BMS can be made with 40A to 120A in accoridng to the different demand 3) Dimension: :Max 138*102*15mm for...

www.lithiumbatterypcb.com

Alieexpress has great deals on 435ah

Sounds iffy, typically large alloy cased cells top out at 300Ah. Search the forum for advice on proven suppliers.

The 1500 inverter at full load is more than the Overkill BMS can tolerate continuously, however if its only the fridge and other modest loads, the continuous current will be well within the 120 amp BMS capability.

Mike

 

[Davetv1423]

will this charge lithium OK?

if your systen works fine with around 150 Ah usable typical at 12v, then anything from 200Ah lithium should be equivalent.

select for expected load. The often used Overkill, JBD, 120 amp BMS is good value and good support on the forum,

4s BMS 120a LifePo4 with M6 Threaded Terminals – Overkill Solar

overkillsolar.com

4S or 3S 12V Li ion or Lifepo4 Battery smart BMS with Bluetooth function UART and RS485 communication with 60A to 120A constant current - LLT POWER ELECTRONIC

1) Application:this smart BMS can work for 3 to 4S Lithium ion or Lifepo4 Battery ,client can choose based on your battery chemistry features 2) Current : constant current of this version BMS can be made with 40A to 120A in accoridng to the different demand 3) Dimension: :Max 138*102*15mm for...

www.lithiumbatterypcb.com

Sounds iffy, typically large alloy cased cells top out at 300Ah. Search the forum for advice on proven suppliers.

The 1500 inverter at full load is more than the Overkill BMS can tolerate continuously, however if its only the fridge and other modest loads, the continuous current will be well within the 120 amp BMS capability.

Mike

is this considered "an eco" BMS? - its $140

39.14US $ 24% OFF|Daly Smart Lifepo4 Bms 4s 12v 24v 36v 48v 30a 60a 80a 100a 120a 150a 200a 250a 300a 400a Li-ion Lto 3s 7s 8s 10s 12s 13s 16s 24s - Battery Accessories & Charger Accessories - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com