24 volt with only 4S 12v batteries?

PaintBrush

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Is there any benefit to running a 24 volt system if I only have 4S 12-volt batteries in series (1C 100 AH)? I know 8 batteries are recommended for 24 volt but I want to future-proof my battery bank by going 24 volt instead of 12 volt; I just don't have 8 batteries yet. In other words would 4S be enough to run a 24 volt system with a light load via a 12 volt buck converter?
 

12VoltInstalls

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Maybe cuz it’s late but I don’t understand you. 4S 12V batteries is 48V
So I can’t make heads nor tails of this question about 24V?
 

PaintBrush

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Maybe cuz it’s late but I don’t understand you. 4S 12V batteries is 48V
So I can’t make heads nor tails of this question about 24V?
Sorry, I'm a noob, so I sometimes leave out information or say the wrong thing.
I'm getting 4x 3.2v 100ah Lifepo4 batteries. They will all be optimized for 12 volts, but I was wondering if I hook them up in series they will generate 24 volts.
From the website that I ordered them from (I don't want to advertise the URL and get banned):

NOMINAL VOLTAGE: 3.2V
CAPACITY: 100ah (105ah+ is being reported by customers)
WATT HOURS: 320
FULLY CHARGED VOLTAGE: 3.65V
FULLY DISCHARGED VOLTAGE: 2.5V
MAX CONTINUOUS CHARGE: 100A (1C)
MAX CONTINUOUS DISCHARGE: 100A (1C)
MAX PULSE DISCHARGE (10 SECONDS): 200A (2C)
MODULE WEIGHT: 6.5 lbs
MODULE DIMENSION: 7" X 5.5" X 3"
 

12VoltInstalls

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Well 4 of a 3.2VDC thing in series is 4x3.2=12.8V so no, not 24V - 12.8 is exactly the nominal voltage of a 12V battery.
 

PaintBrush

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Light load: reading lights, maybe a usb fan, and maybe usb charging a phone and a tablet. Not any power-tools, at least not until I get more batteries. My intent is to add electric capacity in a DIY van conversion in stages, but I was wondering if it can be done like that or would I need to wait until I have all the batteries I need.
 

PaintBrush

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Why would you need 24V for that?
I would not need 24v initially but I want to build the capacity over time, without starting out with a 12 volt system, when what I want to end up with is a robust 24 volt system with several PV panels, a big inverter, heaters, fridge, air conditioning, etc.
 

rmaddy

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a big inverter,
Yeah, if you plan on a 3kW inverter (or a bit more) then you do want 24V.

I would not need 24v initially but I want to build the capacity over time
Capacity has little to do with system voltage. You can have a lot of capacity with 12V or little capacity with 48V. So that's not too relevant.
 

Don B. Cilly

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All your loads are USB (5V)-powered? Just get a 12/24V USB charger. Or more than one. They're really cheap.
They'll work on 12, and when you "upgrade", they'll work on 24.
If the lights are not (you could have USB lights)... they're probably 12V bulbs anyway, right? When you go 24, you just double them up, in series.
 

PaintBrush

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OK, I think I'll stick with 12 volts for now and increase to 24 if, and when, I need to.
I may never need 24 volts so I don't need to go that route if I don't need it.
Thanks everyone!
 

Colonel.lp

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If you think you want 24v in the future then there is nothing wrong with using a converter until you get the rest of the batteries, as long as you can source a converter that is rated for your needs and doesn't have too much of a parasitic draw or inefficiency that will drain your system too much.

Also, you will need to get the same 4 extra batteries in the future, and try to get them as close as matched as possible. Not sure how much time between the two events you are thinking, just don't leave it too long or you may risk problems with capacity differences.
 

Jordi

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If you think you want 24v in the future then there is nothing wrong with using a converter until you get the rest of the batteries, as long as you can source a converter that is rated for your needs and doesn't have too much of a parasitic draw or inefficiency that will drain your system too much.

Also, you will need to get the same 4 extra batteries in the future, and try to get them as close as matched as possible. Not sure how much time between the two events you are thinking, just don't leave it too long or you may risk problems with capacity differences.
Agree.

Actually, If you just need USB loads, you can simply connect a chip from aliexpress that transforms 12V DC into 5V DC.
See example: https://es.aliexpress.com/item/32435133117.html?spm=a2g0o.productlist.0.0.6d7e7715u3Lbse&algo_pvid=d17abb59-7559-48b9-bdd6-cd29140cac36&algo_exp_id=d17abb59-7559-48b9-bdd6-cd29140cac36-7&pdp_ext_f={"sku_id":"57570311038"}

Some can work with DC voltages from 5 to 30V (so also usbale with your later 24V battery). Their limitation is the output at just 1,5A or lower and max. 3,1A for the fast charging version. Good for reading lights, charging gadgets, etc. below 10-15W.

Better to start small and grow. Just check however the items you buy can take the 24V and as mentioned, the batteries compatibility. (Batch, old/new, supplier,...)

Success!!
 

Rednecktek

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Yeah, with only 4 cells you're only going to get 12v, so no 24v now...

Unless you rigged in a DC-DC charger to kick it up to 24v...
Then wired in a buck transformer to kick it back to 12v...
But that would be silly. :)

Stick with the 12v system until you need to go larger than about 2500Kw, THEN look into stepping up your whole system to a 24v or 48v based on your needs. I.E. don't panic now, there's always time for panic later. :)
 

PaintBrush

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Hello, again;
OK; I now have 8 of the 12-volt battery modules (mentioned above), and I want to make a 24 volt system out of those 8.
I'm using a Victron 100/50 SCC and a 2000 watt 24-volt PS-2000KAR Giandel inverter (4000watt surge).
I'm thinking about going with this configuration using 2: 120 amp 12-volt BMS's from 'Battery Overkill', which I have.
Questions:
1). what is the black bar after the BMS's on the left? is it a busbar, fusebox, or a shunt?
2). where would a Victron SmartShunt go?; would I need 2 of them - one for each BMS (4s)?
3). should I charge this system as 12-volt separately before combining to make a 24 volt system, or charge it as 24-volt after combining?
4). I have not found anybody else who mentions this configuration, is it dangerous (creates too many amps for this configuration, I know the BMS's could "handle" 240 amps)?
5). would it be advisable to put a 'battery protect' on each bank?, and if yes, where should it go?

Thanks in advance
 

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HRTKD

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The configuration in the diagram you attached to your post is for a 12v system. It will not work for a 24v system.

The easiest/best method is to put the eight cells in series and use a 24v 8s BMS. There are diagrams on the Overkill Solar website for how to wire a 24v 8s battery. My preference is to build a 24v battery instead of putting two 12v batteries in series.
 

PaintBrush

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The configuration in the diagram you attached to your post is for a 12v system. It will not work for a 24v system.

The easiest/best method is to put the eight cells in series and use a 24v 8s BMS. There are diagrams on the Overkill Solar website for how to wire a 24v 8s battery. My preference is to build a 24v battery instead of putting two 12v batteries in series.
I was afraid that I bought the wrong BMS. Hopefully Battery Overkill will refund my two BMSs.
Thanks.
 
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