12V RV Current Requirements - Bighorn

[Bohemian]

How much current capacity is needed for all the 12V devices exclusive of inverting to 120V and battery charging?

The supplied converter is an 80A model. That puts a top end on the requirement. It should be much lower.

I am asking because I am looking at designing a solar system and considering a 12V battery system vs a 24V battery system. A 24V battery system would need a 24V to 12V converter to run the house 12V dc side.

Also wondering what the advantages/disadvantages of a 24V battery system would be.

 

[wdk450]

Well, there are constant use current draws like the refrigerator logic board and the propane detector. The both have current draws under 1 amp. Next is a large number of "discretionary" small 12 volt loads that you turn on as you see fit, like lights, roof fans; these mostly run under 5 amps. Then there are the intermittent use big loads like the slideout motors, and the landing gear motors. These have fuse ratings up to 50 amps. You may have to hook up a DC current meter with the AC to the converter/charger turned off, and try various living scenarios to see what you draw.

The converter/chargers have the big current ratings to "assist" the battery with the big loads (when plugged in to shore power), not have to draw down the battery during normal living with shore power, and to recharge the battery system as quickly as possible.

 

[Jim.Allison]

The heart of any system is the Bogart Tri-metric. I recomend this device or a similar prior to the installation of solar support equipment. This device will tell you what is going on with all your DC electrical, no matter the charging source. Then you will know what parameters you need to build to.

 

[Jim.Allison]

24v can travel longer distance through a smaller diameter cable than 12v can. It cuts down on cable cost, and makes the system more efficient. I have a 48v input on my solar charge controller and use the 10 gauge solar panel wire.

 

[Bohemian]

I had not thought about the battery for the 12v side. Seeing those large draws it's an essential component.

 

[avvidclif]

24v can travel longer distance through a smaller diameter cable than 12v can. It cuts down on cable cost, and makes the system more efficient. I have a 48v input on my solar charge controller and use the 10 gauge solar panel wire.

Distance has nothing to do with it unless you factor in the current handling capability. 24v @ 10A = 240w. 12v @ 20A = 240 but takes a larger wire.

 

[TedS]

Distance does have something to do with it. That is why higher current requires larger wire to keep voltage drop over distance to a minimum.

 

[Jim.Allison]

Distance has nothing to do with it unless you factor in the current handling capability. 24v @ 10A = 240w. 12v @ 20A = 240 but takes a larger wire.

So what are the specifics of your system?

 

[Jim.Allison]

Distance has nothing to do with it unless you factor in the current handling capability. 24v @ 10A = 240w. 12v @ 20A = 240 but takes a larger wire.

Except 24V and 10A for 20 feet w/ 3% loss is a 13 ga wire. The same 24V and 10A for 30 feet requires a larger 11 ga wire. Distance and ga are critical to the calculation.

http://www.freesunpower.com/wire_calc.php

 

[Bohemian]

Except 24V and 10A for 20 feet w/ 3% loss is a 13 ga wire. The same 24V and 10A for 30 feet requires a larger 11 ga wire. Distance and ga are critical to the calculation.

http://www.freesunpower.com/wire_calc.php

In all electrical circuits required wire size is a function of current requirement and length of wire. Same for any flow and distance. Water through hoses, etc.

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[Jim.Allison]

In all electrical circuits required wire size is a function of current requirement and length of wire. Same for any flow and distance. Water through hoses, etc.

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Exacta'-men'te senior.......

 

[sjandbj]

How much current capacity is needed for all the 12V devices exclusive of inverting to 120V and battery charging?

The supplied converter is an 80A model. That puts a top end on the requirement. It should be much lower.

I am asking because I am looking at designing a solar system and considering a 12V battery system vs a 24V battery system. A 24V battery system would need a 24V to 12V converter to run the house 12V dc side.

Also wondering what the advantages/disadvantages of a 24V battery system would be.

When I designed my system I thought about the 24V system but decided to stick with a 12V set-up. The only advantage for me was if I want to run a larger inverter the higher voltage was going to be a requirement. I have 6 panels on the roof of my Big Country that will produce a max of 960 watts. I choose to wire them in a series-parallel set up to cut the voltage drop to my controller. This allow me to run smaller gauge wire from the roof to the front storage compartment. I have less than 1% drop in my voltage from the roof to the controller which was my goal. I keep both my fantastic fans running to help cool the rig during the summer and I have yet to have the batteries read less than 98% charge. I only have 4 100 amp lithium battery banks but that has so far served me well. When it comes to batteries it is a balance between weight, size vs voltage and capacity. Oh also dollars.
Steve

 

[Bohemian]

The advantages of the 24vdc battery system is lower currents in wires and in charging the batteries. Also, the equivalents inverter charger can handle about 40% more power.

 

[Silverado23]

When I designed my system I thought about the 24V system but decided to stick with a 12V set-up. The only advantage for me was if I want to run a larger inverter the higher voltage was going to be a requirement. I have 6 panels on the roof of my Big Country that will produce a max of 960 watts. I choose to wire them in a series-parallel set up to cut the voltage drop to my controller. This allow me to run smaller gauge wire from the roof to the front storage compartment. I have less than 1% drop in my voltage from the roof to the controller which was my goal. I keep both my fantastic fans running to help cool the rig during the summer and I have yet to have the batteries read less than 98% charge. I only have 4 100 amp lithium battery banks but that has so far served me well. When it comes to batteries it is a balance between weight, size vs voltage and capacity. Oh also dollars.
Steve

I did nearly the same. I considered a 36v battery system but I kept my system otherwise 12 v as I did not have the room for a 36v to 12 v converter anyway I have 9 panels producing 765 watts and run a series parallel system from the panels to the charge controller. I did have to run heavy wires from the charge controller to the 3 batteries (deep-cycle not lithium). I use the battery power for all 12v power and even turned off the converter so I only use the solar system to charge the batteries. Have not had any issues and the battery are somewhat hard to run down without turning on an inverter.

 

[Jim.Allison]

the lithium batts are a great choice. if you got the bucks. designing for lithium in the future is not a bad idea if your limited on cash.

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Depending on how much demand you put on your inverter, the cables between your batts and your inverter can get pretty large too, depending on how far you are going to run them.

 

[sjandbj]

the lithium batts are a great choice. if you got the bucks. designing for lithium in the future is not a bad idea if your limited on cash.

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Depending on how much demand you put on your inverter, the cables between your batts and your inverter can get pretty large too, depending on how far you are going to run them.

Jim is correct on both counts.
I did a lot of research and got so much help from several people on this forum who had already done this project, and I might add did it well. Without their input I would have made several poor choices that would have cost me big dollars.
The lithium batteries are very pricey upfront. I am hoping that over the long term the batteries will be a good choice. As far as the wire from the batteries to the inverter goes each invert should come with wire size requirements. It is important to keep the run form the batteries to the inverter as close as possible. If lead acid batteries are used then they must be separated from the the inverter. With the lithium or AGM batteries that is not a problem. I have runs from the batteries to the inverter i have 4/0 wire and solid copper buss bars. All this might be a little overkill but in the end I would rather wire that is just a little larger than too small.

 

[danemayer]

Is there anything special that needs to be done to reduce the fire hazard associated with Lithium Ion batteries? Over the past 6 or 7 years there seem to have been quite a series of recalls on laptop batteries, and more recently on hoverboards, all involving Lithium Ion batteries causing fires. Boeing aircraft have been grounded and a couple of Tesla autos have had problems. And I think there are now special handling requirements when shipping them.

So - anything special that needs to be done?

 

[sjandbj]

Is there anything special that needs to be done to reduce the fire hazard associated with Lithium Ion batteries? Over the past 6 or 7 years there seem to have been quite a series of recalls on laptop batteries, and more recently on hoverboards, all involving Lithium Ion batteries causing fires. Boeing aircraft have been grounded and a couple of Tesla autos have had problems. And I think there are now special handling requirements when shipping them.

So - anything special that needs to be done?

Dan,
I did not do anything special. the batteries I chose were Lithium Iron Manganese Phosphate (LiFeMnPO4). From what I have read these are much more stable and do not have the same properties that the others have. I think that any battery bank if not properly protected could cause a fire if they are directly shorted out. i have two 400 amp fast acting fuses on the system. One being directly on the buss bar before it feeds the system.

 

[Jim.Allison]

the inverter input DC cables do get expensive, the ability to place the batts next to the inverter is a big plus. Routing is one of the biggest factors contributing to diameter because the more length you have the more diameter you need. This kind of ends up in an endless cycle because the larger diameter requires larger bend radius, resulting in more length. Ideally the + and - cable should be the same length, by the time you make the several connections such as fuses, switches, and everything else between the positive terminal, and the input on the inverter, unbalanced wire lengths contribute to the already imbalanced system. Keeping the cables short, compact, and direct to the inverter is a big plus both in efficiency and money.