24v - 1000 Ah - ?

[TommyD]

We are upgrading our off grid System. Re Batteries, currently have 12 - 2v, 850 Ah old lead acid and want to go to 24v - 1000Ah LiFePO4. I am intrigued by building my own Battery Bank but using and getting 40 of the 3.2 - 200 Ah in a 8s5p configuration versus 5 - 24v - 200 Ah fully assembled doesn’t seem to make much sense. Difference in price isn’t really that great when amortized over say 20 years. Also seems to be a tighten, neater operation. So, just personal preferences, joy of building issue or are there some good reasons for the “40 route” , including BMS, etc.?Thanks

 

[John Frum]

Ok so price isn't a concern for you, cool.
With indiviual cells you could make 5x 24 volt batteries each with its own bms and then parallel them.
That way you have a dedicated management for each cell.

 

[John Frum]

You would also gain some flexibility in the physical layout.

 

[John Frum]

It would also be kind of fun if you are so inclined.
I know I would be.

 

[TommyD]

So, just wanted to confirm costs; see attached . $1720 more for the ”5Pack“, guess less cost of 5 BMS’s, bus bars, cost to build Battery case, say $400, so $1320 more expensive, divided by 20 years equals $66 per year. Guess, all in, convenience is worth it to me. Must say very pleased to have found this site and met M. Dare; totally changed me from continuing with lead acid to LiFePO4!!

 

[John Frum]

I assume the 24volt batteries come with bms and the raw cells don't.

 

[TommyD]

Yes, that’s right.

 

[Jejochen]

I should make my own. Then you know what bms you are etc... premade packs can have good bms...or crap bms... check a few video's from will where he opens stuf up.
5 bms's are not really necessary, i you go with batrium you have a quality bms, you'll need 1 supervisor, and for each cell a blockmon, wich are dailychained together.

 

[Steve_S]

Hmmm, you could build 4x 280AH for 1120 Ahrs. $4349 USD delivered (air - cheaper by sea)



REF: https://www.alibaba.com/product-det...a2700.icbuShop.0.0.764520d22qNJc8&bypass=true

Amy Wan is our contact there at Xuba. Mention you are coming from DIYSolarForum and get the bus bars &bolt kits tossed in (just make sure Amy knows how many you need) A long thread on these is in my signature.

Considering the 40X 200AH costs $4700 USD for 5 packs / 1000AH
There is an economy to be found.

PS, Orion makes GOOD BMS' but when you start adding up the dollars it can get steep quickly. I generally advise folks to make the packs in dependent for fault tolerance and switch over capability, if one pack shuts down the rest keep going.

ALSO - VERY Important, setting up a proper parallel system to maintain optimal balance in charge & discharge. Please read his excellent tech doc by Victron: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

 

[TommyD]

Thanks for this Steve! I had just reviewed the Victron document; see attached. So many pieces of the puzzle to get right! So, assuming I wired these correctly, do both the leads from the MPPT CC and the leads from the Inverter/Charger attach at same place on the Battery Bank?

 

[Steve_S]

Without getting into fuses, breakers etc, the Bus Bar scenario works best overall. The "main" cables from the (+) & (-) Bus Bars go to the SCC & Inverter, I recommend a Heavy Switch to disconnect the battery bank at this stage, as there will be times for maintenance etc where that will be needed. And of course a Fuse per battery pack, best on the terminal of the pack. In the diagram below, everything past the switch is open to whatever setup you have.

Depending on BMS used, if it has relays or not, shunts etc then they would be added between the bus & pack for monitoring the individual pack. If you want to monitor ALL incoming / outgoing power then that shunt / hall sensor would be placed after the bus bars.

I've switched to using MRBF Fuses which work a treat especially for this application and they don't break the brank either.

Bay Marine – Marine Rated Battery Fuse and MRBF Single Fuse Holder Kit – 30-300A | eBay

Choice of Fuse Sizes Available: 30A, 40A, 50A, 60A, 75A, 80A, 90A, 100A, 125A, 150A, 175A, 200A, 225A, 250A, 300A. Fuse Size List Ignition Protected – Safe for installation aboard gasoline powered boats.

www.ebay.com

I used 4 Post 3/8's Bus Bars in my system with covers. Bluesea has several versions but there are others, beware of cheapos.

BusBars - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

The switch shown above is the 9001e

e-Series - Blue Sea Systems

350 Amps continuous rating for inboard gasoline or diesel engines.

www.bluesea.com