13.4kwh RV Build Planning Advice

[CarlCruzin]

I placed an order in the group buy for 16x 280ah cells. So far this is my only purchase, but they are going to take a month or two to arrive and I'm trying to have everything else in order or installed so they will be the last step once they arrive.

Once I have the hardware components selected, I plan to make a wiring diagram so I can have those more knowledgeable than me review it for safety and effectiveness.

I will post pictures as the project progresses so hopefully it can be a helpful resource for others.

My original plan was to go 48v, but I'm pretty sure I will do 24v with 8s2p for the following reasons:
1. Hydraulic levelers are on a 100A breaker. I can't find a 48v to 12v 100A converter, but a 24v to 12v 100A is available and reasonably priced
2. I like the option of using a 12v/24v dc to dc converter to charge the battery bank while driving
3. Shock hazard of 48v vs 24v
4. It doesn't seem like there is a compelling reason to do 48v except for a single BMS

Current Build Plan:
- 24v 560ah 8s2p LifePo4 battery bank (Ordered)

- 2x 8s BMS (Still sourcing, recommendations?)

- 24v 3kw All-in-One Inverter/Charger/MPPT/Transfer Switch: Growatt spf-3000tl-lvm-24p (proposed)

- 24v to 12v 100A converter for coach accessories: (on Amazon for $100) (proposed)

- 12v to 24v dc to dc converter for alternator charging: Victron Orion IP20 12/24 (proposed)

- Solar Panels 4x 320w in 2s2p: SolarTechDirect

- While I'm at it I plan to hardwire a 50a Surge Guard


Aside from the above items that my research has led me to believe are good choices, there are other things I need to figure out:

- How to properly mount 4x of the 66.3"x39.2" panels
- Wire, fuse, breaker locations and sizing

 

[snoobler]

The one thing I don't see in there is consumption. Have you done an energy audit (link #1 in my signature if you haven't)? Ultimately, this determines the life of your battery and the size of your array. Without it, you're just guessing and may find this huge battery doesn't do what you hoped.

Overall, your plan seems sound, but your usage could mean the sound plan doesn't meet requirements.

Other things to consider:

1. I see no mention of the need for A/C. I hope this is intended. A/C use will hammer you.
2. Powering your absorption fridge (propane/12V/120VAC) on AC or 12V will use a massive amount of energy - about 5kWh/day alone.
3. Related to #2, if you have the choice of running propane or AC power, propane is your absolute best bet.
4. If you can stow them and plan to stay boondocked for awhile, consider a smaller deployable array you can setup/tear down in 15-20 minutes. If shade is available, you could park in the shade and deploy the panels in the sun, or you could have extra power if needed.
5. Don't touch the existing 12V system. Insert your inverter between the umbilical/ATS and the AC panel. Thus your inverter provides 120VAC to the coach including the existing 12V converters and batteries. Shore power/generator could supply power to the inverter for charging the batteries 48V. The biggest downside to this option is 12V power will only be bout 75% efficient vs. 85% efficient for 120VAC.
6. The 3kW Growatt is a high frequency inverter, so if you ever think you MIGHT want to run your A/C, it won't do it. It MIGHT do it if you add a $300 softstarter to the A/C.

Concerning your final two questions:

• Do your research. If your roof has a polymer or rubberized coating, check with the manufacturer. If you want the best of both worlds, VHB tape + screws into the roof plywood and sealant. Inspect your panel mounting before every trip.
• Wires should be sized based on the current. The "awg chart" link in my signature provides a decent reference. Fuses should be sized for the wire * 1.25. Fuses/breakers protect the wire, not the components.

 

[CarlCruzin]

The one thing I don't see in there is consumption. Have you done an energy audit (link #1 in my signature if you haven't)? Ultimately, this determines the life of your battery and the size of your array. Without it, you're just guessing and may find this huge battery doesn't do what you hoped.

Overall, your plan seems sound, but your usage could mean the sound plan doesn't meet requirements.

Other things to consider:

1. I see no mention of the need for A/C. I hope this is intended. A/C use will hammer you.
2. Powering your absorption fridge (propane/12V/120VAC) on AC or 12V will use a massive amount of energy - about 5kWh/day alone.
3. Related to #2, if you have the choice of running propane or AC power, propane is your absolute best bet.
4. If you can stow them and plan to stay boondocked for awhile, consider a smaller deployable array you can setup/tear down in 15-20 minutes. If shade is available, you could park in the shade and deploy the panels in the sun, or you could have extra power if needed.
5. Don't touch the existing 12V system. Insert your inverter between the umbilical/ATS and the AC panel. Thus your inverter provides 120VAC to the coach including the existing 12V converters and batteries. Shore power/generator could supply power to the inverter for charging the batteries 48V. The biggest downside to this option is 12V power will only be bout 75% efficient vs. 85% efficient for 120VAC.
6. The 3kW Growatt is a high frequency inverter, so if you ever think you MIGHT want to run your A/C, it won't do it. It MIGHT do it if you add a $300 softstarter to the A/C.

Concerning your final two questions:

• Do your research. If your roof has a polymer or rubberized coating, check with the manufacturer. If you want the best of both worlds, VHB tape + screws into the roof plywood and sealant. Inspect your panel mounting before every trip.
• Wires should be sized based on the current. The "awg chart" link in my signature provides a decent reference. Fuses should be sized for the wire * 1.25. Fuses/breakers protect the wire, not the components.

Hi Snoobler,

Thank you for the detailed response, and analytical questions. I am still learning and have the fear of overlooking some basics that may be obvious to the knowledgeable.

One of the main reasons for installing this system is so I can run the A/C for several hours per day when it is warm. I also don't want to turn on the generator anytime we want to use a 120v appliances such as coffee maker, countertop ice maker, blender, etc. We do not want to camp in RV parks with hookups often, because most seem to be crowded which is the opposite of what we are looking for when venturing outdoors.

According to the test sheets that were provided with my air conditioners, Atwood air command 15032 (13.5k btu) and 15033 (15k btu), they draw 1015w and 897w respectively while cooling. I would like to be able to run one or both for 4-6 hours when the weather is warm. I figured that during the cool/cold months when I would not need the A/C, I would power the fridge with AC power to save my propane for space heating and cooking. The fridge manual states 800w consumption, but I'm not sure how often it will cycle.

I am not fully versed in the different types of AC power, but I assumed that the "Pure Sine" 3000w continuous inverter was the best power you could get. I only found one note about air conditioning unit warnings, is this the base of your concern? (attached screenshot from manual). Overload protection is rated for 5s @ 150+% load, and 10s @ 110-150% load.

The inverter also has an auto-generator start function that can be engaged when the battery bank reaches "x" voltage and shutoff once it reaches "y" voltage. This seemed like an attractive option in addition to what I believe to be an already oversized battery/solar system.

Some other appliances that we will use are:
Microwave/Convection 1600w (occasional brief usage)
2x 3-speed ceiling fans 12v 60w/ea
Keurig coffee 1400w (daily brief usage)
Countertop Ice maker 160-240w
1 or 2 Furion LED TV's 2hr/day avg at most (unsure of power consumption)
Xbox 120w (occasional use by the kids, maybe 1hr/day avg)


I also attached the document that forest river provided for the roof. I see that they use some wood, but not sure otherwise what the roof composition is. Last time I was up there, it looked like fiberglass.

 

[snoobler]

First, consider that your inverter has an inefficiency. To cover your butt, you need to divide any power need by 0.85 because you wlll use more than rated.

My 15000 unit says 1250W, but it burns almost 1500, so I would plan for the worst.

Assuming you have to run both units continuously, that's at least 2250W. That's only 6.5 hours of run time on your 16 3.2V 280Ah cells in however you plan to arrange them, and you'll need at least 3500W of solar (likely more) to be able to support that, or you're done in a day. That's a LOT of solar for an RV. You should PLAN on generator use when running A/C.

Generator auto-start function requires a generator capable of it. Here's Victron's discussion about auto-start requirements and methods. Likely similar for any unit you choose.

Additionally, typical A/C have SURGE meaning for several seconds they have a much higher load at startup than their run Watts. Easily 4X, so it may take you 4000W to spin the compressor in your A/C units. There are $300 soft start units that can be added to any A/C to reduce the surge, but it's still notably higher than the run current, maybe 2-3X. Most of the all-in-one units are "high frequency" meaning they're cheap, light, and they can't handle surge for squat. With high frequency inverters, you should pretend they don't have surge, and you should size them via your surge loads, not run loads. Don't believe those surge ratings in the manual.

I am floored by your 800W fridge. I have a ~7.5cu-ft unit that uses 300W. A 30# bottle of propane will run my fridge for about a month, so I wouldn't consider running it on AC when boondocking (that said, I actually do, but it's the only load, and we have 3kW of solar right now with 12kW of battery of which we only use about 3kW overnight). Absorption fridges are VERY inefficient. My small unit would use 1/3 of your battery a day. Your fridge would almost flatten your battery in 24 hours. If you need heat, use fire. Period.

If your fridge has some sort of compressor refrigeration mode (like a residential fridge) rather than propane, then it likely uses much less.

I really think the next step in your process is to use link #1 in my signature and populate all your loads in the spreadsheet. It will tell you what will and won't work.

 

[CarlCruzin]

First, consider that your inverter has an inefficiency. To cover your butt, you need to divide any power need by 0.85 because you wlll use more than rated.

My 15000 unit says 1250W, but it burns almost 1500, so I would plan for the worst.

Assuming you have to run both units continuously, that's at least 2250W. That's only 6.5 hours of run time on your 16 3.2V 280Ah cells in however you plan to arrange them, and you'll need at least 3500W of solar (likely more) to be able to support that, or you're done in a day. That's a LOT of solar for an RV. You should PLAN on generator use when running A/C.

Generator auto-start function requires a generator capable of it. Here's Victron's discussion about auto-start requirements and methods. Likely similar for any unit you choose.

Additionally, typical A/C have SURGE meaning for several seconds they have a much higher load at startup than their run Watts. Easily 4X, so it may take you 4000W to spin the compressor in your A/C units. There are $300 soft start units that can be added to any A/C to reduce the surge, but it's still notably higher than the run current, maybe 2-3X. Most of the all-in-one units are "high frequency" meaning they're cheap, light, and they can't handle surge for squat. With high frequency inverters, you should pretend they don't have surge, and you should size them via your surge loads, not run loads. Don't believe those surge ratings in the manual.

I am floored by your 800W fridge. I have a ~7.5cu-ft unit that uses 300W. A 30# bottle of propane will run my fridge for about a month, so I wouldn't consider running it on AC when boondocking (that said, I actually do, but it's the only load, and we have 3kW of solar right now with 12kW of battery of which we only use about 3kW overnight). Absorption fridges are VERY inefficient. My small unit would use 1/3 of your battery a day. Your fridge would almost flatten your battery in 24 hours. If you need heat, use fire. Period.

If your fridge has some sort of compressor refrigeration mode (like a residential fridge) rather than propane, then it likely uses much less.

I really think the next step in your process is to use link #1 in my signature and populate all your loads in the spreadsheet. It will tell you what will and won't work.

Our fridge is a norcold 18cu ft, so that should explain the increased power usage (but we love the space!). I have not been able to figure propane consumption for the large fridge, but it makes sense that when hookups are not available that propane would make the most sense to heat the absorption refrigeration process, compared to high power consumption electric heating.

Realistically we will just run one A/C if we need cooling relief, I can close off the bedroom and just cool the living area or vice/versa. I figure if we can run both a/c's it will only be on warmer days when in full sun so hopefully we would be getting some good power from the 1280w of solar.

I know a properly sized solar array and battery bank will handle all power needs of full time living, but I am not sure that will be a requirement for the RV. Honestly if 13.4kwh is not enough, then we will adjust our usage. We will mostly try to avoid hot areas where extensive A/C will be needed, and I have looked at smaller room sized portable evaporative coolers for the right climate cooling.

I sent a message to the A/C unit manufacturer to see what their recommendations are for my proposed system. Hopefully they will give me some specs to size the inverter properly.

I will definitely look further into the compatibility of the inverter with the A/C units. I'm not set on this system, but I do like the idea of an all-in-one. If it doesn't suit my needs, then I will gladly spend more for a more appropriate and/or complex product. Do you have a recommendation?

 

[snoobler]

Well, your fridge is almost 3X as large, so yep. 800W makes sense. They will run 16 hours per day or 12.8kWh/day or 15.0kWh/day after inverter inefficiencies.

A 30# bottle will probably only run it a couple weeks. If you get the BTU rating, we can figure it.

1280W of solar means you're eating into your battery even in full sun. You'll never get 1280W on a flat roof unless the sun is truly perpendicular to the panels. So you're likely losing at least 1000W/hour running both. When do you charge your batteries? Not while running A/C. Plan for genny to run the AC or at least double your solar. A single A/C might be manageable for the worst part of the day.

Portable room evap coolers that can provide meaningful cooling are large and use a lot of water. They can use "gallons" per hour when they're truly working, and they need fresh dry air to cool, and you need an outlet, so there's no sealing the doors/windows to keep the cold in. When boondocking, water may be more precious than electrons.

The Victron Multiplus 3kW/24 can handle a true 6kW of surge for 30 seconds - enough to run both A/Cs, but just barely. As they cycle on and off they could hit surge at the same time and trip the overload. The next step up for 120V is the Quattro 5K, but it's notably more than the Multiplus (I have one).

The Magnesine MS4024PAE is in the middle, and a good strong unit.

 

[childcarepro]

RV A/Cs are terrible, loud and inefficient. A 15,000 BTU RV A/C consumes 3300-3500W while starting (you'll need a soft start) and 1300-1800W while running. You may have 7.5 hrs of A/C on a full charge with no other loads, but you'll have a hard time fully charging your battery while your A/C is drawing more than you're generating with solar.

A few thoughts:
1. Consider oversizing your solar so you can use more A/C while the sun is out so you start your evening with a full battery
2. Consider switching to SEER 25-28 mini split A/C for 1/3 the energy use
3. Consider upgrading from your absorption to a compressor cooling mechanism for about 1/2 or less energy use PLUS it cools faster (a couple of hours instead of 24 hrs)

If you're not married to the Growatt, I love the Victron ecosystem for their feature rich, connected devices and apps. And while their solar charge controllers are pretty expensive, their smart features are worth it, IMO. And their MultiPlus inverter/chargers are surprisingly affordable compared to inferior options using older technology.

 

[CarlCruzin]

RV A/Cs are terrible, loud and inefficient. A 15,000 BTU RV A/C consumes 3300-3500W while starting (you'll need a soft start) and 1300-1800W while running. You may have 7.5 hrs of A/C on a full charge with no other loads, but you'll have a hard time fully charging your battery while your A/C is drawing more than you're generating with solar.

A few thoughts:
1. Consider oversizing your solar so you can use more A/C while the sun is out so you start your evening with a full battery
2. Consider switching to SEER 25-28 mini split A/C for 1/3 the energy use
3. Consider upgrading from your absorption to a compressor cooling mechanism for about 1/2 or less energy use PLUS it cools faster (a couple of hours instead of 24 hrs)

If you're not married to the Growatt, I love the Victron ecosystem for their feature rich, connected devices and apps. And while their solar charge controllers are pretty expensive, their smart features are worth it, IMO. And their MultiPlus inverter/chargers are surprisingly affordable compared to inferior options using older technology.

I will take a look at those options, thanks! I originally liked the idea of keeping with the propane powered fridge option, but since I am investing in solar and battery bank, that may be a more serious consideration.

I found this inverter/charger by AIMS which claims 4kw continuous, and 12kw surge for 20 seconds. I will look into the victron.

 

[snoobler]

800W is huge and claims of "efficient" are not founded. As you can see, your fridge would deplete your massive battery in a single day. Absorption fridge work off heat, and the only efficient way to deliver heat is with fire.

AIMS is made by Sigineer where you can find cheaper re-branded units in the states. Here's a 5kW unit:

Affordable Electric Vehicle Batteries & Components from Electric Car Parts Company

Electric Car Parts Company is your one-stop-shop for affordable electric vehicle parts and components including batteries. Shop our selection and order now!

www.electriccarpartscompany.com

My neighbor purchased the 6kW version for the sole purpose of driving his 3hp deep well pump, which surges to 15hp at startup. It hasn't been deployed yet, but the kitchen test of running his 1800W microwave went great. The inverter didn't seem to notice with stable frequency and voltage values. A test run of the pump is planned within the next few weeks with temporary hook-up.

The downside to these inverters is they tend to have lower efficiency. This one maxes out a 88%.

 

[CarlCruzin]

800W is huge and claims of "efficient" are not founded. As you can see, your fridge would deplete your massive battery in a single day. Absorption fridge work off heat, and the only efficient way to deliver heat is with fire.

AIMS is made by Sigineer where you can find cheaper re-branded units in the states. Here's a 5kW unit:

Affordable Electric Vehicle Batteries & Components from Electric Car Parts Company

Electric Car Parts Company is your one-stop-shop for affordable electric vehicle parts and components including batteries. Shop our selection and order now!

www.electriccarpartscompany.com

My neighbor purchased the 6kW version for the sole purpose of driving his 3hp deep well pump, which surges to 15hp at startup. It hasn't been deployed yet, but the kitchen test of running his 1800W microwave went great. The inverter didn't seem to notice with stable frequency and voltage values. A test run of the pump is planned within the next few weeks with temporary hook-up.

The downside to these inverters is they tend to have lower efficiency. This one maxes out a 88%.

Thanks for that link, that looks like a great price!