RV system, 12v vs 24v Newby Questions

[Jim SoG]

Ok so basics, I want to run normal LED lights, (No tv or stereo), air con 24/7 (wont need but maybe), Microwave, instapot, Fridge and keep batteries charged up. All of this is theory and I am mainly looking to wrap my head around the differences and costs for this. I cam across this:

The Classic 400 Watt Solar Package Ideal for RV's/ Vans/ Buses​

This setup works well if you:

• Spend a lot of time inside your vehicle, moving or stationary
• Plan to use a large van or RV
• Plan to run most appliances, such as a computer, microwave, fridge and more

Recommended components:

• 400 watts of solar panels and a 40 amp MPPT charge controller
• 300 amp hour lead acid deep cycle battery bank (or 200 amp hour lithium battery)
• 1100-2000 watt inverter

So using these parameters what would a 24v system look like ? Again not trying to get a perfected answer, trying to learn diff 12 vs 24.

Ok I most likely have confused you all by now....LOL

Appreciate your tolerance and help!

Jim

 

[corn18]

I stopped reading @ aircon 24/7. You will need 10+ of those classic 400W solar systems to even try to do aircon 24/7.

 

[Ranger Rick]

12v and 24v "systems" usually refer to the voltage of ones battery bank. In that context, a 24v system can use lower gauge and less expensive wiring. One would need to add a 24v to 12v converter inline from your 24v battery bank to your 12v panel of 12v devices.
The best starting point is to determine your daily power usage = "Energy Audit." Air Conditioner, microwave & coffeemaker are high watt-demand devices. Once you get your daily Energy Audit determined, and you are boon docking, you can determine your inverter size. For AC+ daily use, most folks need a 3000 watt inverter. A 24v battery bank is better for 2000+watt inverters because of less amperage and cheaper wiring. You then determine your battery bank AmpHours, Panels needed, solar charge controller, fuses, etc.
If you thought the "24v" label referred to the solar panels, that label does not mean for a 24volt battery. But rather it refers to voltage output of the solar panels (check the specs for VOC voltage). The total VOC x Coldest temperature coefficient is the number needed to have the proper solar charge controller. The total sum VOCxT voltage of the panels in Series cannot exceed the solar charge controller's voltage rating e.g. for a 100/40 SCC, one must stay below 100 volts.
The Blueprint shows 110v Alternating Current Appliances coming from the inverter. What those appliances are and their amp demand is not given. That number is critical to your properly sizing your RV solar system.
Do some more Internet research for solar shops that will put together a system for your needs.

 

[Supervstech]

Best would be 48v for aircon 24/7 but it can be done with 24V the advantage of higher voltage is lower amps, thus more solar will fit with the same charge controller.

Aircon needs a LOT of battery though. Also a lot of solar.
Do the math, it is disheartening how large the system needs to be to handle aircon.

 

[rmaddy]

Before you start looking to at any schematics or buying any equipment, you need a proper energy audit so you know what your power needs are.

Fill this out:

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

 

[Rednecktek]

Ok, so just for some napkin math references...

Let's say you want to start out with a 100Ah LFP battery because it's the Bee's Knees. What does that battery buy you?

A standard plug-in heater will kill the battery dead in about 45 minutes
An 8000BTU (smaller) AirCon system will last you 1.5 hours
The InstaPot will work for about 2 hours
A microwave will get you about 45 minutes of cooking

Think of Watts like Grams, they're really small and it takes a LOT to do much.

The whole 12v thing VS 24v thing really comes into play when you get up above about 2Kw of inverter to feed all the stuff. As a rule of thumb you want to keep your wires and fuses below 200a of draw, but the larger the amperage, the larger the wires and fuses need to be and that becomes $RealMoney real quick. If you power a 2Kw inverter on a 12v battery you need a 200a fuse and wire (basically, napkin mathing here for the concepts) but if you do a 24v bank, that 200a becomes 100a (because watts are Volts * Amps) which is much thinner wire and smaller fuses. Conversely, if you had a 24v battery system and was willing to pay for the 200a wire you could swing a 4Kw or 4.5Kw system which gives you Moar Powah! to do The Things.

The other factors involved are capacity (how long you can USE all The Things) and generation (how fast you can refill the batteries) which becomes a balancing act for multiple reasons like...

Space for batteries. 24 LFP batteries sounds great until you're sleeping in the drivers seat because there's no bed space left.
Space for panels. If you can only physically fit so much panel on the roof, how much can you generate?
Location. If you're boondocking in Arizona you're going to get a lot more sun than boondocking in Vermont.
Budget. Those $800 BattleBorns look cool, but don't buy you much else on a $1000 budget.
Auxiliary systems. If you need to feed 12v appliances how are you going to do that with a 24v bank?

Head over to the Resources section (or someone's handy signature link) and grab the Power Audit form. It's going to tell you 3 primary things. 1: How big does your inverter need to be. 2: How much battery bank you need to feed it for $N many days of krappy weather. 3: How much solar panel you're going to need to put up to recharge those batteries in a reasonable amount of time.

The biggest challenge I think for any RV system is physical space. Where do you stick the batteries? How much roof area do I have for panels? Where do I stick the inverter? Where do I stick the AirCon condenser and compressor and evaporator? Where do I stick the cat tree?

The nice thing about the Power Audit form is that you can play around with it all you want and just save copies. Start by just putting in the wish list of things that would be cool to have like 12k BTU AirCon for 24 hours and the 5000w stereo system and the MargaritaMaster-9000 and the 65" TV with satellite internet. It's all just blanks on a form, you can't break anything. Then throw in how much solar panel you think you can mount and how much battery capacity you think you can stuff under the floor boards and the couch and such. Then start whittling away until everything meets in the middle.

There WILL be a point where what you NEED and what you can ACTUALLY DO will overlap and THAT will be YOUR system. It won't be a perfect system for me, or a perfect system for Supervstech, but it'll be perfect for YOU and that's the goal.

If you're really wanting AirCon for any length of time I highly recommend starting out with a 24v system so you can have the larger inverter that is going to power the Aircon. I also highly recommend going with LFP because you just can't beat the storage density. Grab a tape measure and some graph paper and start doodling out what you've got to work with for space.

I know, it sounds like a royal PITA to do all the number crunching, but it's cheaper than spending thousands of dollars on stuff to find out you can't use (Learn from my spare parts bin!) it and just missed your return window. Once you've got a rough plan of what kind of parts you'll need, run it past us to figure out what you missed. Don't worry, we ALL miss Something our first couple of tries.

 

[corn18]

I know, it sounds like a royal PITA to do all the number crunching, but it's cheaper than spending thousands of dollars on stuff to find out you can't use it and just missed your return window.

X1000

I started buying parts and then tried to make the system work. I think the only part I have left from the original setup is the Victron shunt. Sold all the other kit on Ebay @ $.50 on the dollar. Ouch.

Let's do it right the first time and save you a lot of money.

 

[kenryan]

Here are some thoughts on 12 volts versus 24 volts.

For any given amount of power (watts) the amperage will increase as the voltage decreases. For example, 240 watts at 12 volts is 20 amps, but 240 watts at 24 volts is just 10 amps. This is important because electrical wire is rated with regards to how many amps it can carry. You need larger wire to carry more amps. So, in a 12 volt system the wires will need to be of greater diameter than for a 24 volt system. Also, some components, such as the solar charge control, are rated for a maximum number of amps. So a charge control that is connected to a 24 volt system can accept twice as much wattage from solar panels as the 12 volt system. You can still use more solar panels on the 12 volt system, but you will need to use a more expensive charge control that is rated for more amps.

The two primary advantages of the 12 volt system (in a vehicle) are that 1. lots of equipment is available in 12volt and 2. charging off of the vehicle charging system will be less complicated that a 24 volt system.

With regards to your proposed system, you need to decide if you really want air conditioning. Air conditioning requires so much power that you will need a system that is far more robust than a system that does not need to feed an air conditioner. And we are not talking about a system that is just a little bigger (and more expensive). For AC it will need to be much bigger and much more expensive.

As others have noted, you need to do a power audit first.

 

[Rednecktek]

Oh, and I think I should say something else very important:

Don't panic! You're not the first or the last to go through this!

You're going to feel a little overwhelmed, that's OK. We're here to help.

 

[Jim SoG]

I stopped reading @ aircon 24/7. You will need 10+ of those classic 400W solar systems to even try to do aircon 24/7.

Hey great way to encourage a new guy trying to learn...........

 

[Jim SoG]

12v and 24v "systems" usually refer to the voltage of ones battery bank. In that context, a 24v system can use lower gauge and less expensive wiring. One would need to add a 24v to 12v converter inline from your 24v battery bank to your 12v panel of 12v devices.
The best starting point is to determine your daily power usage = "Energy Audit." Air Conditioner, microwave & coffeemaker are high watt-demand devices. Once you get your daily Energy Audit determined, and you are boon docking, you can determine your inverter size. For AC+ daily use, most folks need a 3000 watt inverter. A 24v battery bank is better for 2000+watt inverters because of less amperage and cheaper wiring. You then determine your battery bank AmpHours, Panels needed, solar charge controller, fuses, etc.
If you thought the "24v" label referred to the solar panels, that label does not mean for a 24volt battery. But rather it refers to voltage output of the solar panels (check the specs for VOC voltage). The total VOC x Coldest temperature coefficient is the number needed to have the proper solar charge controller. The total sum VOCxT voltage of the panels in Series cannot exceed the solar charge controller's voltage rating e.g. for a 100/40 SCC, one must stay below 100 volts.
The Blueprint shows 110v Alternating Current Appliances coming from the inverter. What those appliances are and their amp demand is not given. That number is critical to your properly sizing your RV solar system.
Do some more Internet research for solar shops that will put together a system for your needs.

Thank you, that was clear and makes sense.

 

[Jim SoG]

Before you start looking to at any schematics or buying any equipment, you need a proper energy audit so you know what your power needs are.

Fill this out:

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

Awesome link, thank you.

 

[Jim SoG]

Ok, so just for some napkin math references...

Let's say you want to start out with a 100Ah LFP battery because it's the Bee's Knees. What does that battery buy you?

A standard plug-in heater will kill the battery dead in about 45 minutes
An 8000BTU (smaller) AirCon system will last you 1.5 hours
The InstaPot will work for about 2 hours
A microwave will get you about 45 minutes of cooking

Think of Watts like Grams, they're really small and it takes a LOT to do much.

The whole 12v thing VS 24v thing really comes into play when you get up above about 2Kw of inverter to feed all the stuff. As a rule of thumb you want to keep your wires and fuses below 200a of draw, but the larger the amperage, the larger the wires and fuses need to be and that becomes $RealMoney real quick. If you power a 2Kw inverter on a 12v battery you need a 200a fuse and wire (basically, napkin mathing here for the concepts) but if you do a 24v bank, that 200a becomes 100a (because watts are Volts * Amps) which is much thinner wire and smaller fuses. Conversely, if you had a 24v battery system and was willing to pay for the 200a wire you could swing a 4Kw or 4.5Kw system which gives you Moar Powah! to do The Things.

The other factors involved are capacity (how long you can USE all The Things) and generation (how fast you can refill the batteries) which becomes a balancing act for multiple reasons like...

Space for batteries. 24 LFP batteries sounds great until you're sleeping in the drivers seat because there's no bed space left.
Space for panels. If you can only physically fit so much panel on the roof, how much can you generate?
Location. If you're boondocking in Arizona you're going to get a lot more sun than boondocking in Vermont.
Budget. Those $800 BattleBorns look cool, but don't buy you much else on a $1000 budget.
Auxiliary systems. If you need to feed 12v appliances how are you going to do that with a 24v bank?

Head over to the Resources section (or someone's handy signature link) and grab the Power Audit form. It's going to tell you 3 primary things. 1: How big does your inverter need to be. 2: How much battery bank you need to feed it for $N many days of krappy weather. 3: How much solar panel you're going to need to put up to recharge those batteries in a reasonable amount of time.

The biggest challenge I think for any RV system is physical space. Where do you stick the batteries? How much roof area do I have for panels? Where do I stick the inverter? Where do I stick the AirCon condenser and compressor and evaporator? Where do I stick the cat tree?

The nice thing about the Power Audit form is that you can play around with it all you want and just save copies. Start by just putting in the wish list of things that would be cool to have like 12k BTU AirCon for 24 hours and the 5000w stereo system and the MargaritaMaster-9000 and the 65" TV with satellite internet. It's all just blanks on a form, you can't break anything. Then throw in how much solar panel you think you can mount and how much battery capacity you think you can stuff under the floor boards and the couch and such. Then start whittling away until everything meets in the middle.

There WILL be a point where what you NEED and what you can ACTUALLY DO will overlap and THAT will be YOUR system. It won't be a perfect system for me, or a perfect system for Supervstech, but it'll be perfect for YOU and that's the goal.

If you're really wanting AirCon for any length of time I highly recommend starting out with a 24v system so you can have the larger inverter that is going to power the Aircon. I also highly recommend going with LFP because you just can't beat the storage density. Grab a tape measure and some graph paper and start doodling out what you've got to work with for space.

I know, it sounds like a royal PITA to do all the number crunching, but it's cheaper than spending thousands of dollars on stuff to find out you can't use (Learn from my spare parts bin!) it and just missed your return window. Once you've got a rough plan of what kind of parts you'll need, run it past us to figure out what you missed. Don't worry, we ALL miss Something our first couple of tries.

Great advice and for sure a voice of experience, thank you, and I rather do the PITA on paper than from my wallet. I am nowhere near buying a system, just starting out in my brain, and for sure the wants/needs will be clear I am sure as I keep auditing. Thank you sir!

 

[Jim SoG]

Here are some thoughts on 12 volts versus 24 volts.

For any given amount of power (watts) the amperage will increase as the voltage decreases. For example, 240 watts at 12 volts is 20 amps, but 240 watts at 24 volts is just 10 amps. This is important because electrical wire is rated with regards to how many amps it can carry. You need larger wire to carry more amps. So, in a 12 volt system the wires will need to be of greater diameter than for a 24 volt system. Also, some components, such as the solar charge control, are rated for a maximum number of amps. So a charge control that is connected to a 24 volt system can accept twice as much wattage from solar panels as the 12 volt system. You can still use more solar panels on the 12 volt system, but you will need to use a more expensive charge control that is rated for more amps.

The two primary advantages of the 12 volt system (in a vehicle) are that 1. lots of equipment is available in 12volt and 2. charging off of the vehicle charging system will be less complicated that a 24 volt system.

With regards to your proposed system, you need to decide if you really want air conditioning. Air conditioning requires so much power that you will need a system that is far more robust than a system that does not need to feed an air conditioner. And we are not talking about a system that is just a little bigger (and more expensive). For AC it will need to be much bigger and much more expensive.

As others have noted, you need to do a power audit first.

Thank you for explaining the 12 vs 24 thingy, it makes sense and math dont lie, might be fudged, but dont lie...LOL Thanks!

 

[corn18]

Hey great way to encourage a new guy trying to learn...........

My apologies. You're right.

 

[John Frum]

@Jim SoG does your travel trailer have any batteries currently?
Also please post a picture of the ac/dc distribution panel with the cover open so we can see the fuse and breaker maps.
Also is your generator 120/240VAC split phase or just 120VAC?
Finally what is the watt rating for the generator?
All of these questions will help us get a sense scale and proportion.

 

[12VoltInstalls]

two primary advantages of the 12 volt system (in a vehicle) are that 1. lots of equipment is available in 12volt and 2. charging off of the vehicle charging system will be less complicated that a 24 volt system.

I’m not against 24V systems

I’m totally for 12V in a camper over the road or boondocks living. If you don’t have backup equipment you can probably find a 12V inverter at an auto parts store, walmartha, or rv profit center. 24V not so much.

Plus there is so much 12V LED lighting that conveniently swaps out or can be added.

My opinion: rooftop RV aircons are not good matches for 12V RV systems but minisplits can work on 12V. The instapot and induction cooktops don’t compute for me.
People do and have done all above successfully and unsuccessfully however.

Just my thoughts. I’d figure out if you can use 12V and the costs, inconvenience of being 24V and decide from there. Or build a nice 24V system but have a 100- or 200W 12V system separately for 12V lighting which is what I’d probably do

 

[Rednecktek]

As @12VoltInstalls mentions, sticking with a 12v system has LOTS of advantages over going to 24v in mobile applications. The plethora of 12v stuff available vs 24v stuff is a HUGE advantage. Really the only downside to 12v systems are the inverter and amperage limits and the difficulty getting enough solar to feed it as your SCC's are going to be based on amperage they can put out, not the voltage you're using. I.E. even if you could stick 1200w of panels on your roof, if your using a 12v system you'd need 100a worth of charge controller rather than 50a at 24v.

Did that make sense?

It really comes down to that Venn Diagram of Want vs Need vs Budget that the Power Audit is going to help you find.

The induction cooktops do make sense, they're the most efficient way to boil water on a BTU-Watt scale, you just have to be willing to house the system to provide for it. InstaPot's are a really long drawn out draw and while it can be done, it really hurts. Same goes for AirCon. Can it be done? Absolutely. Is it worth it? Maybe. Is it gonna cost you? You better believe it!

 

[djnorth]

Regarding InstaPots, I measured with a Kill-A-Watt meter tonight the energy consumed to cook a Taiwanese beef stew with 100 minute cooking time under high pressure in a 6 quart cooker: 560Wh. For reference, this is an unusually long cooking time in the Instapot; a chicken stew typically runs 15-25 min cooking time, depending on recipe.

 

[jberger]

There is another upside to Induction cooking, because the heat is going into the pot and not the air, it's doesn't heat up the kitchen and you don't need to ventilate unless it's absolutely required. My wife liked the induction in the RV enough that we replaced our stove at home with one.

If I didn't have a TON of 12v loads already in place, I would have gone 48V and used a converter for 12V. But we stuck with 12v and just paid the price in terms of wiring, terminal blocks, fuses, etc.