RV Help with concept especially fusing

[-TX-]

That makes two of us!

Honestly though, big or small = same systems pretty much. For that matter, I'm sure Suneagle or King could both give you an example of a small 12v system that is far more dangerous than mine. Finding the room for everything has been my greatest hurdle.

[Mike90250]

Ok, I'm just asking because it is unusual for a camper to be 24V. If you have no need for 24V, then just wire your batteries in the normal configuration as parallel 12V and you won't need a step down device? There are balancing issues to consider with parallel 12V batteries, but it is also the typical way it is done on a camper.

Ha. That's contrary to the usual advice. At a certain power level, increasing the system voltage improves performance and efficiency. Small installs do fine with 12V, but as things get larger, so must the system voltage. Laws of science and math rule electricity.

[Sunking]

There are balancing issues to consider with parallel 12V batteries, but it is also the typical way it is done on a camper.

Only out of ignorance, mostly due to being trapped inside a 12 volt box. Batteries are not 12 volts, they are 2 volts. If you need 400 AH at 12 volt, then use 400 AH batteries. Like a pair of Rolls S550 6 volt batteries or Trojan L16's. Just have to think outside of the 12 volt box.

Lead acid batteries come in sizes of 5 AH up to 6000 AH batteries. If you use 12 volt jars, about the largest you can find is 200 to 300 AH. Good luck lifting one up.

[SunEagle]

This is true. I have 2 x 6v 232Ah batteries in my RV which is not big but is also series wired 12v battery system that has a potential 2780watt hour capacity. If I decide to go bigger I will go with higher Ah batteries that will be wired in series to create the same 12volts.

[ewarnerusa]

I also have 2x6V batteries in series. I don't disagree with the benefits of higher voltage once your power needs go up. But your typical RV devices and appliances, in addition to all of the electric trailer components like lights and brakes, are designed for 12V.

[Wrybread]

Another excellent reason RV setups are 12v (besides "ignorance") is convenience and cost. Once you go down the rabbithole of 24v wiring you need, at a minimum:

- a new inverter
- a step down transformer for your rv appliances and lighting
- a step up transformer to charge your batteries from your alternator

That's not even getting into the added layer of complexity and labor.

As with many things in solar, *especially in RVs*, there's a lot of compromises made. And there's not necessary anything wrong with that.

[Sunking]

Another excellent reason RV setups are 12v (besides "ignorance") is convenience and cost. Once you go down the rabbithole of 24v wiring you need, at a minimum:

- a new inverter
- a step down transformer for your rv appliances and lighting
- a step up transformer to charge your batteries from your alternator

That's not even getting into the added layer of complexity and labor.

As with many things in solar, *especially in RVs*, there's a lot of compromises made. And there's not necessary anything wrong with that.

See you are stuck inside a 12 volt box. I never said a word about 24 volts in a RV. Who has the reading comprehension problem? You think batteries are 12 volts, they are not, they are 2 volts. If you need 400 AH @ 12 volts, buy 400 AH batteries. That would be 2 6-volt 400 AH batteries wired in series. Paralleling batteries cost you a lot more money and significantly shortens battery life. In the long run will cost you twice as much. Just because that is the way you do it does not make it smart or right. It just means you are ignorant and need educated.

[Wrybread]

See you are stuck inside a 12 volt box. I never said a word about 24 volts in a RV. Who has the reading comprehension problem? You think batteries are 12 volts, they are not, they are 2 volts. If you need 400 AH @ 12 volts, buy 400 AH batteries. That would be 2 6-volt 400 AH batteries wired in series. Paralleling batteries cost you a lot more money and significantly shortens battery life. In the long run will cost you twice as much. Just because that is the way you do it does not make it smart or right. It just means you are ignorant and need educated

Can I please get "I need educated" on a tshirt?

This is a forum for Rv solar setups. Saying you're not talking about RVs is a cop out. And saying it's cheaper (and worth the outrageous increase in complexity) for most RVs to go 24 volt demonstrates a lack of real world experience with Rv solar.

The last person you scared into taking your advice is still trying to source parts to make things work. And good luck finding that step up transformer that'll let him charge his 24v bank off his alternator anywhere near as efficiently as before.

But I know, I need more educateding.

[-TX-]

I also have 2x6V batteries in series. I don't disagree with the benefits of higher voltage once your power needs go up. But your typical RV devices and appliances, in addition to all of the electric trailer components like lights and brakes, are designed for 12V.

Getting around that minor issue cost $100 for a step down, that's pretty much it. If I, for one, had stuck with 12v the costs would have been substantially more. So I don't think the RV 12v thing is a major issue to overcome, it's about just the determination of doing what's best.

[Wrybread]

> Getting around that minor issue cost $100 for a step down, that's pretty much it

Out of curiosity, how many amp of 12 volt power does that output?

Also if you don't mind my asking, what are the stats on your battery bank, and how many watts of solar?

[Sunking]

But I know, I need more educateding.

OK we both agree. What got you on my radar and why everyone else is giving you a hard time is you claim to be an expert with 20 years experience. Pure rubbish. You can make an RV system any voltage you want, but if you do anything other than 12 volts, you have several issues to get around.

[-TX-]

> Getting around that minor issue cost $100 for a step down, that's pretty much it

Out of curiosity, how many amp of 12 volt power does that output?

Also if you don't mind my asking, what are the stats on your battery bank, and how many watts of solar?

40 amps, rated and supposedly. DC run amps are pretty low in an RV though. Lights, stereo... biggest hog is the propane heat blower at 4amps.

1900w of solar, 16500wh of battery (which I've learned is meaningless. More like 40~ amps storage)
.

[Sunking]

40 amps, rated and supposedly. DC run amps are pretty low in an RV though. Lights, stereo... biggest hog is the propane heat blower at 4amps.

1900w of solar, 16500wh of battery (which I've learned is meaningless. More like 40~ amps storage)
.

TX you got things mixed up a bit. Everything has to be matched up to work with everything else. Let's start with the battery. A Lead acid battery has a minimum charge current requirement, and a maximum you should not go over. As a general rule of thumb the minimum is C/12, and maximum is C/8. Perfect is C/10. This window of C/8 to C/12 fits nicely with Solar because on average you get 4 hours of charge time with solar, and your battery should be sized for 5 days reserve with 3 days usable.

OK if you have a 200 AH battery, you are looking for at least 200 AH / 12 H = 17 amps minimum and no higher than 200 AH / 8 H = 25 amps. So what panel wattage is required using a MPP_T controller. That depends on the battery voltage. If 12 volts minimum is 13 volts x 17 amps = 220 watts and maximum is 13 volts x 25 amps = 325 watts. If it is 24 volts then 440 watts and 650 watts. 48 volts is 880 watts and 1300 watts.

Now there are some exceptions to the rule. Example a Golf Cart battery is a hybrid battery and not a True Deep cycle battery. GC batteries still have the minimum C/12 charge rate but they can be charged faster than C/8 up to C/4 if required. That does not mean they should be charged faster, but there are some applications that will require faster charging. Example if you live in someplace like doomy gloomy Seattle with a 1.2 Sun Hour day in winter months you need a large wattage panel that generates a C/4 charge current.

There is another side of batteries you need to know. They have a limited amount of current they can deliver without excessive voltage loss. This is due to the battery Internal Resistance. What is that limit. It is the exact same as the maximum Charge rate of C/8. Again there are exceptions like a Golf Cart Battery which is a hybrid battery with lower Internal Resistance. So how is it a problem? Well I hope it may have hit you already. What good is a battery when fully charged up if the voltage sags below the equipment threshold. Example say you have a 12 volt 200 AH battery with a 1000 watt Inverter attached to it. You plug in your 500 watt coffee pot. and two minutes later your Inverter shuts off from under voltage of 10.5 volts. Nothing is wrong with the battery or Inverter. When you do the math you discover 500 watts at 12 volt through an inverter pulls 50 amps form the battery that can only handle 30 amps. The battery voltage sagged to 11 volts and add another .5 volts on the wiring reached the Inverter at 10.5 volts causing the Inverter Low Voltage Disconnect to operate. Did exactly what it was suppose to do. The problem is the design.

So if you have 1900 watts of panels means you have to run a battery at 24 volts with a minimum capacity of 590 AH and no larger than 850 AH. Translated to watt hours is 14,000 to 20,000 wh. So what size Inverter can that battery handle. Make it easy, no larger than panel wattage give or take a few percentage points. 2000 watts.

Everything is made to work with each other. You would not pull a freight train with a truck would you?

[-TX-]

I don't know how long it will take me to understand the deep tech details like you have mastered, but I''m closing in on understanding the general concepts. I think I'm doing alright with 24v/1900w/690ah and *cough* 3000 watt inverter. And the great thing about solar is it's no less a money pit than the boat I once owned so I know as i understand more the setup will change. I'm at a good starting point.

[Sunking]

I don't know how long it will take me to understand the deep tech details like you have mastered, but I''m closing in on understanding the general concepts. I think I'm doing alright with 24v/1900w/690ah and *cough* 3000 watt inverter. And the great thing about solar is it's no less a money pit than the boat I once owned so I know as i understand more the setup will change. I'm at a good starting point.

You are good except the Inverter is to large and I doubt you have any need for one that large. It needs a 150 amp circuit at 24 volts.

You can get away with it, but do not be surprised if one day you turn something large on and the RV fills up with smoke. Being a PE is a lot like a doctor. We are sworn to do no harm to the public and cannot take any other stance.