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12V Vs 24V Battery Bank

Barridge

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Joined
Nov 7, 2020
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Hi Guys! I have a question as to which way is best way to hook up my battery bank. 12v or 24v?
I'm am looking for maximum dailey longevity and battery life.
I am confused with the fact. That with 2 - 12v AGM 200 amp hr batteries hooked in parallel I get 400 amp hrs.
If i hook them in series for 24v, I am only getting 200 amp hrs.
Which is the best way to go?

Thank you guys for being here!
 
Longevity from a specific bank of batteries is best achieved by efficient conversion, and low parasitic loss.

A 1000W load will last JUST as long on a 400Ah 12 v battery, as it will on a 200Ah 24V battery, or a 100Ah48V battery.

The higher the battery voltage, the smaller the wires need to be. That’s all.
 
A 24v system also lets you have larger inverters without the wire thickness and fuse sizes becoming unwieldy. Remember that with any of the lead acid flavors (AGM, FLA, GEL) you can only use 50% of the capacity, so that 200Ah becomes 100Ah before you damage the batteries.
 
I'm working with 1/0 wire on a 24v bank now, and I'm REALLY glad I'm not working with 2/0 on a 12v bank. That 1/0 is a bear to crimp and route.
 
Keep in mind also that all things being equal an Inverter run at 24V will be more efficient than one run at 12V and 48V will be even more efficient. There is more energy being lost to convert 12V to 120Vac versus 24V to 120Vac. Add that into wire losses and it starts to become very significant as you go up into higher Wattage's.
 
Keep in mind also that all things being equal an Inverter run at 24V will be more efficient than one run at 12V and 48V will be even more efficient. T
That is not entirely true for the SMALEX inverters I use. While being used, the 24 volt model is as high as 88% efficient whereas the 12 volt is only 85%, but the idle draw on the 24 volt model is 1 amp or 24 watts, and the 12 volt is 1.6 amps or 19 watts. Others inverters have idle draws that is twice as much in watts in the 12 versus 24 volt versions.

I spend most of my time not using the inverter, so there is a lot of idle draw, at least for a system that has a small battery capacity where it adds up over time. Before I upgraded from lead acid to a larger lithium battery I bank, I was concerned about idle draw on the inverter.
 
It's not just 1/0ga to the inverter, I find I can run 18ga wire to various lights and USB chargers I'm installing. It's much easier routing those really small wires. I went back and forth for a while on voltage trying to decide between 12 and 24. I'm really happy I went with 24.
 
Another advantage of going up to 24 from 12V is that the quality level of the available equipment takes a big jump. You are not likely to find a 12V inverter that offers split-phase 120/240V AC, or built-in generator charging circuits, the ability to hard-wire into the main electrical panel, or the ability to parallel inverters. All of those features pretty much start at 24V.
 
Don't forget that a given solar charge controller can handle twice the solar panels on a 24V system compared to a 12V system. For example, a 40A charge controller can handle 960W at 24V but only 480W with a 12V system. If you wanted to have 960W of panels you would have to buy two 40A charge controllers on a 12V system instead of just one on a 24V system.
 
@Barridge, where will these batteries be deployed? There are good reasons to stick with 12 volt if you have a 12 volt system already.
The batteries are inside our heated cabin about 70 ft. from the panels. (using 002 aluminum wire).
I currently have my panels hooked up as 24v system going to my 12v battery bank.
My batteries are showing their age so I am considering going 24v with a new inverter.
 
The batteries are inside our heated cabin about 70 ft. from the panels. (using 002 aluminum wire).
I currently have my panels hooked up as 24v system going to my 12v battery bank.
My batteries are showing their age so I am considering going 24v with a new inverter.

In your situation, if you have no 12 volt loads, other than an inverter, I would absolutely go to 24 volt unless you didn't want to incur the cost of replacing the existing 12 volt components.
 
The only 12v component I'm using is a 12v water pump.

You can either put in a 24v-12v converter or buy a 24v water pump. Some pumps will work on 12 to 24 volts, so check yours first before you buy replacements.

In my opinion, the system voltage you end up with comes down to how much you want to spend. It's going to cost you more money to go 24 volt. Staying 12 volt costs you nothing.
 
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