Newbie needs help sizing

[Sbalone]

Hi gurus. I’ve been spending money on batteries and inverters that I thought I researched well. Uh, no.

I’m in a Dynamax super C with a large residential fridge, needing to boondock. PO put in 900 watts roof top solar; I’ve purchased 2 12volt 230 AH Lifepo4 batteries and a 4000w Sungold Power inverter charger 12v. Batteries and inverter are unboxed but not installed. Each battery has 200w BMS.

Reading posts here, it seems I should have bought a 24 or even 48v inverter. I might be able to exchange the 12v inverter for a 24v 3000 or 4000w inverter. I need to balance this system, with fixed inputs of: 900 w solar, and probably 460 AH Batteries. I’ve done a back of envelope energy audit, I’m not confident of the numbers.

I can’t fit more batteries in the designated compartment, and returning the batteries would be too pricey.

Can I balance this system with a different inverter?

 

[DIYrich]

Fridge only? What are the power specs (startup, or LRA)? I'm guessing 15 amps 120v max, which is 1,800 watts. If so, you are fine with a 12v system.

 

[Q-Dog]

My biggest concern would be the idle current draw of that inverter, or how much power does the inverter use just to be turned on? When you have limited solar you need to conserve every watt you harvest.

 

[FilterGuy]

Each battery has 200w BMS.

Do you mean a 200A BMS?

Reading posts here, it seems I should have bought a 24 or even 48v inverter. I might be able to exchange the 12v inverter for a 24v 3000 or 4000w inverter.

In a camper, it is always a hard choice. 48V has become the best path forward if the application has no 12V DC loads.... but that is not usually the case with an RV.

Unfortunately, if you can't return the batteries, you may be unable to select a higher voltage. Some of the batteries with the specs you quote don't allow you to put them in series. What brand/model do you have?

 

[Sbalone]

Fridge only? What are the power specs (startup, or LRA)? I'm guessing 15 amps 120v max, which is 1,800 watts. If so, you are fine with a 12v system.

Do you mean a 200A BMS?

In a camper, it is always a hard choice. 48V has become the best path forward if the application has no 12V DC loads.... but that is not usually the case with an RV.

Unfortunately, if you can't return the batteries, you may be unable to select a higher voltage. Some of the batteries with the specs you quote don't allow you to put them in series. What brand/model do you have?

Thanks- yes of course, 200A BMS. The batteries are LiTime (formerly Ampere Time), and I need to check but I believe I can wire them in series

 

[Sbalone]

Fridge only? What are the power specs (startup, or LRA)? I'm guessing 15 amps 120v max, which is 1,800 watts. If so, you are fine with a 12v system.

Thanks Rich. Haven’t found the LRA yet, but tag in fridge works to 980 watts, so I’d guess your 1800 watts is close. I’ll run very occasional microwave at 1100 watts, and miserly use of my Starlink router and lighting. Only other significant draw (?) will be two propane furnaces- I need to look up specs for the draw from the fans.

 

[rdavisinva]

Building an in-vehicle system is always challenging.
We had the same space issues for the batteries, but after the price of LifePO4 dropped, just eventually decided on a battery and started there.
Choose 12V batteries for a number of reasons and like you, already had the inverter and wanted a self heating battery bank to allow solar charging when the vehicle interior is cold.
To cover those times when the vehicle has sat unoccupied overnight and below freezing inside, self heating was a big consideration for us.
The other driving force for 12V was having a 12V DC to DC charge controller with a solar priority that uses any solar provided first and then will add current from the alternator.
We chose RedArc because it has a solar priority feature along with the typical amperage limits that protect the alternator.
All the other DC to DC chargers we looked at years ago when we built our first on-board system had arrangements where the solar input would shut-off when the DC to DC was charging the auxiliary battery bank from the alternator when driving.
We also want to power 12V appliances like a diesel 2 in 1 cooktop that acts as a cabin heater and a 12V mini-split AC system.

If none of the above considerations are present for you, then the higher the voltage, the more efficient the system and the smaller the wire gauge. I never looked into 24 or 48V self heating batteries, but assume if they are available with 12V, they come in higher voltages. I just wish the battery manufactures offered smaller self contained units with a BMS, self heating, high temp protection, and so on. It just seems like we are always having to build a system out of components that were designed for shore based systems and go through a retrofit into a small vehicle space. Our first system used small AGM batteries because they were the best fit 6 years ago, but now at end-of-life.

Let us know what you decide. Am always looking for ways to learn from others that solve the same problems we have.

 

[Sbalone]

My biggest concern would be the idle current draw of that inverter, or how much power does the inverter use just to be turned on? When you have limited solar you need to conserve every watt you harvest.

Thanks- specs say idle is 45w, with a "power saver" mode of 18w

 

[Sbalone]

Building an in-vehicle system is always challenging.
We had the same space issues for the batteries, but after the price of LifePO4 dropped, just eventually decided on a battery and started there.
Choose 12V batteries for a number of reasons and like you, already had the inverter and wanted a self heating battery bank to allow solar charging when the vehicle interior is cold.
To cover those times when the vehicle has sat unoccupied overnight and below freezing inside, self heating was a big consideration for us.
The other driving force for 12V was having a 12V DC to DC charge controller with a solar priority that uses any solar provided first and then will add current from the alternator.
We chose RedArc because it has a solar priority feature along with the typical amperage limits that protect the alternator.
All the other DC to DC chargers we looked at years ago when we built our first on-board system had arrangements where the solar input would shut-off when the DC to DC was charging the auxiliary battery bank from the alternator when driving.
We also want to power 12V appliances like a diesel 2 in 1 cooktop that acts as a cabin heater and a 12V mini-split AC system.

If none of the above considerations are present for you, then the higher the voltage, the more efficient the system and the smaller the wire gauge. I never looked into 24 or 48V self heating batteries, but assume if they are available with 12V, they come in higher voltages. I just wish the battery manufactures offered smaller self contained units with a BMS, self heating, high temp protection, and so on. It just seems like we are always having to build a system out of components that were designed for shore based systems and go through a retrofit into a small vehicle space. Our first system used small AGM batteries because they were the best fit 6 years ago, but now at end-of-life.

Let us know what you decide. Am always looking for ways to learn from others that solve the same problems we have.

Thanks. I decided against self-heating batteries, but the LiTime 230 AH batteries I bought have low-temp protection (and a favorable review from Will Prowse).

 

[Sbalone]

Do you mean a 200A BMS?

In a camper, it is always a hard choice. 48V has become the best path forward if the application has no 12V DC loads.... but that is not usually the case with an RV.

Unfortunately, if you can't return the batteries, you may be unable to select a higher voltage. Some of the batteries with the specs you quote don't allow you to put them in series. What brand/model do you have?

I confirmed these can be wired in series. They are LiTime 230 AH, 12V- can be connected in series up to 4 batteries.

 

[Q-Dog]

Thanks- specs say idle is 45w, with a "power saver" mode of 18w

Power saver mode may or may not work well with your refrigerator. If not, you will use about 1kWh per day just to keep the inverter running. With 900 watts of solar, you likely need almost 1.5 hours of sun every day just to keep the inverter on.

 

[Dave in AZ]

Thanks- specs say idle is 45w, with a "power saver" mode of 18w

Hi, looked at your inverter charger and options for replace. Yes, I would replace it, 4000w is huge for 12v cables. Literally off the charts, 333A and charts mostly stop at 200A!

You are really pretty well set up to just run a 24v system. Put your 2 batteries in series for a nice easy balanced 5900Wh bank. Then I would swap your $935 12v 4000w inverter charger with their 24v solar inverter charger at $539. It is cheaper than their 24v 4000w inverter charger ($935), and is a nice unit combined with mppt solar, that lets you prioritize solar, autoswitch to generator or shore power and back to battery, etc. It has breaker overcurrent protection built-in.

3000W 24V Solar Inverter Charger

Hightlight: ★ All-in-one solar charge inverter: 3000 Watts Pure Sine Wave Inverter Combined with 60A MPPT solar Charging and 40A AC battery charging ,you can enjoy the stable power from the sun and the utility grid to keep you powered under any circumstances. ★ Four charging modes: AC Priority...

sungoldpower.com

Now it is a 3000w inverter, with 6000w surge, but you don't need 4000w from your power usage. It does use the about same amount of watts just sitting there, 50w with eco mode of 25.

You're maybe locked into Sungold equipment if you want to swap, so the idle consumption of these is all about the same, 45 or 50w, 19w or 25w power saver. I downloaded and read the owner's manual for power saver on these, it would work fine for your fridge. So say 25w idle power for this 3000w solar unit. For $400 saved from that 4000w unit, you can get 600 more watts panels up there and not worry about anything! You should be able to fit a few more panels up there, I can fit 900w on my Tacoma pickup truck camper shell!

25w idle, 24hrs, is 600wh. With 900w panels, that is less than an hour to cover your system needs. 20 min if you add some panels.

Anyhoo, it looks to me like you have almost everything you need, just swap out that inverter, wire your 2 batteries in series to 24v, maybe add a few more panels. Really nice system, pretty much exactly what I would put in small truck camper myself.

Oh, you could also just get the 24v replacement version of your inverter charger, except I would go 3000w instead of 4000w, that is plenty of AC power for you and lower idle consumption, at 39w or 16w power saver mode.

3000W DC 24V Pure Sine Wave Inverter With Charger

Sungoldpower 3000W DC 24V Pure Sine Wave Inverter With Charger. Hightlight: This LFP Series Pure Sine Wave Inverter is a combination of an power inverter 3000w, battery charger and AC auto-transfer switch. GFCI socket, low frequency, low Idle Current, BTS cable, remote control. Adjustable...

sungoldpower.com

But I like the solar version better still, more charging source automated choices, builtin displays showing power in and out and from where, builtin CB and protection, cheaper.

 

[Sbalone]

Hi, looked at your inverter charger and options for replace. Yes, I would replace it, 4000w is huge for 12v cables. Literally off the charts, 333A and charts mostly stop at 200A!

You are really pretty well set up to just run a 24v system. Put your 2 batteries in series for a nice easy balanced 5900Wh bank. Then I would swap your $935 12v 4000w inverter charger with their 24v solar inverter charger at $539. It is cheaper than their 24v 4000w inverter charger ($935), and is a nice unit combined with mppt solar, that lets you prioritize solar, autoswitch to generator or shore power and back to battery, etc. It has breaker overcurrent protection built-in.

3000W 24V Solar Inverter Charger

Hightlight: ★ All-in-one solar charge inverter: 3000 Watts Pure Sine Wave Inverter Combined with 60A MPPT solar Charging and 40A AC battery charging ,you can enjoy the stable power from the sun and the utility grid to keep you powered under any circumstances. ★ Four charging modes: AC Priority...

sungoldpower.com

Now it is a 3000w inverter, with 6000w surge, but you don't need 4000w from your power usage. It does use the about same amount of watts just sitting there, 50w with eco mode of 25.

You're maybe locked into Sungold equipment if you want to swap, so the idle consumption of these is all about the same, 45 or 50w, 19w or 25w power saver. I downloaded and read the owner's manual for power saver on these, it would work fine for your fridge. So say 25w idle power for this 3000w solar unit. For $400 saved from that 4000w unit, you can get 600 more watts panels up there and not worry about anything! You should be able to fit a few more panels up there, I can fit 900w on my Tacoma pickup truck camper shell!

25w idle, 24hrs, is 600wh. With 900w panels, that is less than an hour to cover your system needs. 20 min if you add some panels.

Anyhoo, it looks to me like you have almost everything you need, just swap out that inverter, wire your 2 batteries in series to 24v, maybe add a few more panels. Really nice system, pretty much exactly what I would put in small truck camper myself.

Oh, you could also just get the 24v replacement version of your inverter charger, except I would go 3000w instead of 4000w, that is plenty of AC power for you and lower idle consumption, at 39w or 16w power saver mode.

3000W DC 24V Pure Sine Wave Inverter With Charger

Sungoldpower 3000W DC 24V Pure Sine Wave Inverter With Charger. Hightlight: This LFP Series Pure Sine Wave Inverter is a combination of an power inverter 3000w, battery charger and AC auto-transfer switch. GFCI socket, low frequency, low Idle Current, BTS cable, remote control. Adjustable...

sungoldpower.com

But I like the solar version better still, more charging source automated choices, builtin displays showing power in and out and from where, builtin CB and protection, cheaper.

Dave- thanks much for the detailed reply. Yes, I think I'll talk to Sungold to exchange my inverter. I'l probably go with just the 3000w inverter/charger, since I have what my RV guy called a "cadillac' in solar charge controllers already. I wouldn't know - its a Midnite Classis "Turbo"

I can't fit any more solar panels on my roof. I've got 9 100W panels there now, and I've got two ceiling fans and two A/C units that take up room. I didn't mention, I've also got a 8KV Cummins diesel generator on board.

 

[Isaac-1]

It sounds like you have a plan, I too would likely downsize the inverter in your situations, but would probably drop down to a 2,000 or 2,500 watt high quality model

 

[Scott SD]

If boondocking and space is available, look at using a ground array. I built a 300w array with (3) Newpowa 100w compact panels and it works great. Depends on available storage space also, but 200w is small enough.

 

[Rocketman]

A few points to consider (just make sure you have it covered - your RV is different from mine).

12v stuff - if you move to a 24v battery you will need to convert back to 12v for lights, pumps, etc. slides & hydraulics can sometimes be on this battery- you need to figure out how to power them. Victron makes a good 24v to 12v converter.

Do you have a “Boost” switch? This is a switch to allow your house battery to help start your engine- in case your chassis battery is low. If you have it - with lithium’s you cannot hit the switch and the starter (can fry the FET’s in the BMS). You can slowly charge the engine battery for 15 min or so, then release the switch and try the starter.

Which battery does your generator start with - house or chassis? (They are connected up both ways).

How does your alternator work with house batteries? Many have a “BIRD” To charge both batteries- you need to figure out and adjust its operation. Plus provide charging somehow to both batteries.

If you go 24v - you need to completely disconnect the 12v side.

If you go 12v lithium for house - you need to figure out the alternator aspect. You can ruin an alternator by overheating it if your house battery is low and you startup and drive for hours. A super C has massive alternator cables going to the battery.

You can damage lithium’s by having them full and then driving for many hours while pumping 14.4 to 14.5v into them for hours while driving.

You also need to make sure you have the 120v 30a (or 15a) shore power and the 240v 50a shore issues solved.

I think these were all the issues I had to solve on my MotorHome.

Here is how I solved these.
I have a 12v lithium battery 544ah with a Victron Multiplus 12/3000 inverter. (Everything is Victron except the battery- really good equipment). Victron has since come out with a Multiplus II 12/3000 2x120v which is designed for RV’s and handles both sides (30a or 50a) with no issues. I wish it was out when I bought my stuff - oh well.

Alternator: I completely disconnected the alternator from the house battery. I added a Dc-Dc 30a Victron charger to give me a little charging while driving. I added an extra 100w solar panel and mppt to the engine battery to keep it charged (50w would have been fine).

I still have the Boost switch- just cannot hit it and the starter at the same time.

My rig was easy to install the inverter and have it running all my plugs- the 50a (240v doesn’t cause be issues) - I have an inverter electric sub panel.

I have 1400w of solar for the house. I can tilt it one direction if needed. Tilting helps a LOT!

Make sure you have a shunt based battery monitor- like Victron Smartshunt or BMV712. This lets you know if your batteries are mostly full or almost empty. Helps a lot to know if you should run the generator or if you don’t need to.

I added a Victron smart battery protect (BP65) going to my 12v fuse box. This way if something gets left on and my batteries run low, it will shut off the loads before my BMS goes critical. Batteries can sometimes have issues recovering from sleep mode - better if everything shuts down before the bms does. Then Solar can fix it in the morning. Note: cannot have charging sources or inverters going through battery protects.

The Multiplus 12/3000 works very well for us. It can run all the low draw stuff plus one high draw item (microwave, hairdryer, etc) or two medium draw items - toaster.

Good Luck on your project.

 

[Roadrunner27]

Thanks Rich. Haven’t found the LRA yet, but tag in fridge works to 980 watts, so I’d guess your 1800 watts is close. I’ll run very occasional microwave at 1100

Hi gurus. I’ve been spending money on batteries and inverters that I thought I researched well. Uh, no.

I’m in a Dynamax super C with a large residential fridge, needing to boondock. PO put in 900 watts roof top solar; I’ve purchased 2 12volt 230 AH Lifepo4 batteries and a 4000w Sungold Power inverter charger 12v. Batteries and inverter are unboxed but not installed. Each battery has 200w BMS.

Reading posts here, it seems I should have bought a 24 or even 48v inverter. I might be able to exchange the 12v inverter for a 24v 3000 or 4000w inverter. I need to balance this system, with fixed inputs of: 900 w solar, and probably 460 AH Batteries. I’ve done a back of envelope energy audit, I’m not confident of the numbers.

I can’t fit more batteries in the designated compartment, and returning the batteries would be too pricey.

Can I balance this system with a different inverter?

watts, and miserly use of my Starlink router and lighting. Only other significant draw (?) will be two propane furnaces- I need to look up specs for the draw from the fans.

 

[Roadrunner27]

Have you gotten any further with this project? Have the same exact RV and also installing LifePO4 batteries.