A 24v battery would need to have 2x the AH as a 12v battery...

[Johannlog]

A 24v battery would need to have 2x the amp hour as a 12v battery in order to have the same amp hours as a 12v battery, in that case would it not be better to make a 12v battery?
I am aware of the difference in wire prices etc,
I already have a 12v Giandel 2,200W inverter and the cost of buying a 24v inverter doesn't seem worth it for my needs, however I have read that it is better to connect the lithium cells in a battery such that you get higher voltage.

 

[Lt.Dan]

False. A 12v 100ah battery is the same as 24v 50ah battery

12.8v X 100ah = 1280 watt/hours
25.6v X 50ah = 1280 watt/hours.

Same capacity. Going off of AH is very misleading. One must always refer to watt/hours.

 

[Johannlog]

I see, thanks so much for clarifying that!

 

[MichaelK]

Always remember the adage: in series, voltage adds, but amperage stays the same. In parallel, amperage adds, while voltage stays the same. The second formula to remember is volts X amps = watts.

So, wiring a single 100Ah 12V battery you would get 100Ah X 12V = 1200Watts of power.
By wiring two 100Ah batteries in series you would get 100Ah X 24V =2400Watts of power
By wiring two 100Ah batteries in parallel you would get 100Ah + 100Ah X 12V = 2400Watts of power.

 

[Supervstech]

Always remember the adage: in series, voltage adds, but amperage stays the same. In parallel, amperage adds, while voltage stays the same. The second formula to remember is volts X amps = watts.

So, wiring a single 100Ah 12V battery you would get 100Ah X 12V = 1200Watts of power.
By wiring two 100Ah batteries in series you would get 100Ah X 24V =2400Watts of power
By wiring two 100Ah batteries in parallel you would get 100Ah + 100Ah X 12V = 2400Watts of power.

Oops... ya want me to edit your mistake?

 

[apcorob]

Mr. Superstech,
I sure do since I can't see anything wrong and am trying to figure this out!!!!
thanks!

 

[Steve_S]

12V LFP battery has 4 cells, 24V has 8 cells and 48V has 16 cells.

12V: 4 cells X 3.2V nominal X 280AH cell = 3.584kWh
24V: 8 cells X 3.2V nominal X 280AH cell = 7.168kWh

You can add battery Packs in Parallel to increase the Storage Capacity but NOT the Voltage.
Packs in Parallel will split the Charge/Discharge. If a Single battery puts out 50A, two in parallel will output 25A.
A 12V/280AH Battery Pack can output a Max of 280A for One Hour. This is the 1C Rate Limit.
A 12V/280AH Battery Pack can take a Max of 140A for charging. This is the 0.5C Rate Limit. It would take two hours to fully charge from 0% SOC.
* SOC is not like the DOD term used for Lead Acid Batteries. There are differences in the language because of the chemistries.

When connecting Battery Pack in Parallel to create a Bank there are a few considerations.
1) Each battery pack should be capable of "Stand-Alone" operation. Meaning that it can take the Full Charge & Discharge potential of your system.
2) Each battery pack MUST be Fused. for a 280AH battery, either a 250A or 300A fuse or breaker is suitable. ONLY QUALITY PARTS ! NEVER cheap out on Safety Stuff.
3) Each battery Pack should use exactly the same length & gauge of cable from Batt Terminals to DC Busbar to maintain balance, impedance & resistance can cause all sorts of issues. Balance is essential.
• Keep the DC side wires between the battery and the inverter as short as possible.
• Do NOT keep the battery wires far apart. Keep them taped together to reduce their inductance and induced voltages. This reduces ripple in the battery wires and improves performance and efficiency
4) The BMS' should be matched up so that each Pack is configured identically.
5) You CAN have different capacity Battery Packs within a Bank. However, a large difference in AH Capacities can present several issues, It is best to try and stay as close to similar as possible. Under 100AH difference is not bad and can be dealt with easily, greater than 100AH becomes more complex.
6) You CAN ADD BATTERIES to an LFP bank without suffering issues over time. Provided that the existing battery packs have not deteriorated due to misuse or abuse.

Your GIANDELL 2200W Inverter will pull 184A +/- to output 2200W @ 120V. You can safely fuse/breaker your batteries with 200A or 250A. If you do go into the Surge Side then more likely 250A would be best.

Hope it helps, Good Luck

 

[Supervstech]

Mr. Superstech,
I sure do since I can't see anything wrong and am trying to figure this out!!!!
thanks!

I meant editing MichaelK’s it looks right by daylight... I must have been tired when I posted.

 

[Lt.Dan]

I meant editing MichaelK’s it looks right by daylight... I must have been tired when I posted.

I thought the same thing, the only thing I could think of was using 12.8v instead of 12v (3.2v x 4 = 12.8v) which gives you 1280wh, not 1200wh.

But the concept and math were all correct.

 

[Forbisher]

Oops... ya want me to edit your mistake?

He said watts instead of watt hours?

 

[Supervstech]

He said watts instead of watt hours?

There it is.

 

[MichaelK]

oh

 

[Diysolar123]

just to make it clear from now on all energy discussions are to be in therms and power talk in BTU/hr only!!!

how much clearer can this be!!!!
One Therm (US) = 100,000 BTU59°F = 105,480,400 joules = 29.3001111 kWh.

its that simple people... you are welcome ;-)

 

[OnTheRoadAgain]

Can this all be summarized to say that basically.......

Taking the same two batteries yields the same total watt hours regardless of whether they are in parallel or in series ?

And further that the advantage of 24v over 12v is "mostly" in the cost of the inverter, cables and convenience for 12v appliances?

 

[rmaddy]

Taking the same two batteries yields the same total watt hours regardless of whether they are in parallel or in series ?

Correct. An X volt battery with Y Ah capacity yields XY Wh. Connect Z of those batteries in any configuration and you get XYZ Wh total in every case.

And further that the advantage of 24v over 12v is "mostly" in the cost of the inverter, cables and convenience for 12v appliances?

24V (or higher) means less amps. That means smaller wire (cheaper lighter), smaller fuses/breakers, lower voltage drop. It's actually slightly less convenient for 12V loads because you need a DC-DC converter.

 

[OnTheRoadAgain]

yep, meant to say "in-convenience"

 

[fblevins1]

LOL, you guys are killing me. But through all that wonderful banter I am still learning. But as stated above the math would be the same whether or not you stated it as Amps time Voltage or Amp Hours times Voltage. Ok...shutting up now.

 

[rmaddy]

But as stated above the math would be the same whether or not you stated it as Amps time Voltage or Amp Hours times Voltage.

A x V = W and Ah x V = Wh. Those are not at all the same thing. If by "the math" you simply mean the numbers then yes. 12V x 100A = 1200W and 12V x 100Ah = 1200Wh. Both are "1200" but one is watts and one is watt-hours. They have different and specific meanings even if the unit-less numbers happen to be the same.

 

[MichaelK]

You've got all the numbers wrong. Go back and correct them. The Voc is ALWAYS greater than the Vmp, and the Isc is always greater then the Imp.

 

[rmaddy]

You've got all the numbers wrong...

Wrong thread?