# 12 volt vs 24 volt system



## sisterpine

Was just wondering as I drove home from work today. What is the real benefit to 24 volt system over a 12 volt system. Only thing I can think of is I would not need that giant scary fuse thing and I could use smaller wire over a longer distance when hooking to the batteries inverter charge controller etc. Is there stuff that I am missing? thanks, sis


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## Gary in ohio

By doubling the voltage your cut the current in 1/2, wire size goes down.


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## Jim-mi

'Smaller battery to inverter cables' . . . . . . 
Not really.


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## sisterpine

so if i double the voltage and there by cut the wire size down...is that alone enough of a reason to switch to 24 volt? it seems i can get a bigger 36-40/24 inverter by switching so would that be a good thing?


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## WisJim

We still use 4/0 copper from the batteries to our 24 volt inverter (Xantrex/Trace Sw4024), as it draws a lot of amps under full load. We use an Outback MX60 charge controller which allows us to have our panels arranged to produce 48 volts which is reduced to 24volts by the charge controller, so we were able to reduce the cable size from the PV panels to the inverter by a lot. We saved almost enough money in the smaller cable (250 feet distance) to pay for the $600 charge controller, and we get more power due to the MPPT feature of the controller, too.

With 24 volts you could have twice as many batteries, but each one half the size, to store the same amount of energy as with a 12 volt system.


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## wy_white_wolf

Do you need more power and/or battery storage?

Something else to think about

http://www.backwoodshome.com/articles2/yago88.html



> Since most battery interconnect wiring uses fairly large size cables, a cell failure can result in very large currents discharging from one parallel string into another, causing melted battery cables or a boiled dry cell giving off lots of smoke and explosive gasses. It is a good idea to limit your battery bank to no more than four battery strings wired in parallel, with two parallel strings that much safer. You can also reduce the risk associated with batteries wired in parallel by installing a âcatastrophicâ fuse in each individual series string of a parallel-wired battery bank.
> 
> The easiest way to increase battery bank capacity is to switch to a higher voltage system. Since most of todayâs 12-volt DC appliances, DC lighting, and DC to AC inverters are now available in 24-volt and 48-volt versions, a 24-volt system will need four 6-volt batteries in series and a 48-volt system will need eight 6-volt batteries in series to achieve the higher voltage. For example, a 48-volt battery bank having sixteen 6-volt batteries would only require two parallel strings of eight batteries each (8 batteries x 6-volts).


If I was to change from 12v I would propably go all the way to 48v and by pass 24v. All the same equipment will need replaced so it wouldn't be any extra expense except maybe getting batteries and panels to the number for 48v


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## seedspreader

I thought it had to do with efficiencies for items that pull higher volts and amps???


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## greg273

WisJim said:


> We still use 4/0 copper from the batteries to our 24 volt inverter (Xantrex/Trace Sw4024), as it draws a lot of amps under full load. We use an Outback MX60 charge controller which allows us to have our panels arranged to produce 48 volts which is reduced to 24volts by the charge controller, so we were able to reduce the cable size from the PV panels to the inverter by a lot. We saved almost enough money in the smaller cable (250 feet distance) to pay for the $600 charge controller, and we get more power due to the MPPT feature of the controller, too.
> 
> With 24 volts you could have twice as many batteries, but each one half the size, to store the same amount of energy as with a 12 volt system.


 I have a large 250amp Square D QO breaker that I will be using between the batteries and inverter, and I beleive the main lugs will only accept up to 2/0... the inverter itself has post terminals, so getting a 4/0 on there wont be a problem, but how would I get around the 2/0 limitations of the breaker box? Massive split-bolt connectors?


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## Allan Mistler

Another advantage to 24 or 48 volts versus 12 volts became painfully apparent to me as I added onto my system. For every additional 600-700 watts of panels added, I have to add another charge controller since the battery charging current for every 700 watts at 12.7 vdc exceeds the 60 Amp maximum of the Outback MX60.
So now, I'd have to sell my 12 volt Magnum Inverter and buy a 24 volt unit if I wanted to take advantage of the higher system voltage resulting in reduced parts count/cost. Eventually I'll have to anyway as I'll be adding a higher output power inverter. and the 2800 watts of the MS2812 is the highest they go at 12 volts.


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## sisterpine

Allen- when you do change to a 24 or 48 volt inverter what type/brand are you considering. Obviously this is not a project that we will do often so being pleased with our decisions is a big deal. sis


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## Allan Mistler

sisterpine said:


> Allen- when you do change to a 24 or 48 volt inverter what type/brand are you considering. Obviously this is not a project that we will do often so being pleased with our decisions is a big deal. sis


Sis,
I'll definitely be using another Magnum... very, Very impressed with its performance and features (not to mention cost)! I'm currently adding an Allen-Bradley PLC system to control multiple battery charging options (Generator, Water-wheel, Utility power) as well as monitor and log performance of the entire system. This also allows me to communicate remotely from my PC... a fun feature! By adding the PLC, I can eliminate some hardware such as the chicken coop light timer. No doubt that will be made up for by new controls for greenhouse ventilation etc. 
I guess that's the curse of being a newly retired computer programmer/homesteader!!


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