Check my 48V RV Solar System Design

young7.3

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Jun 28, 2022
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Hey all. Firstly, I did a lot of searching for threads covering this topic but would like personal feedback on this setup. Looking to convert an existing camper outfitted with 190 watts of solar and 1, 12v deep cycle battery to 48v off grid mobile workstation. Our energy demands are below, and wiring diagram is attached. The one thing I am unsure of is how to charge the 48v server rack with the truck alternator. I may just leave it off since we will have 2000 watts of solar. Also toying with the idea of two separate 12v(existing system) and 48v systems. I am practical and will have a generator for emergency/air conditioner use, if needed. Thanks for your input and help.
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Bobert

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Hey all. Firstly, I did a lot of searching for threads covering this topic but would like personal feedback on this setup. Looking to convert an existing camper outfitted with 190 watts of solar and 1, 12v deep cycle battery to 48v off grid mobile workstation. Our energy demands are below, and wiring diagram is attached. The one thing I am unsure of is how to charge the 48v server rack with the truck alternator. I may just leave it off since we will have 2000 watts of solar. Also toying with the idea of two separate 12v(existing system) and 48v systems. I am practical and will have a generator for emergency/air conditioner use, if needed. Thanks for your input and help.
View attachment 100437
I have a 48v system on my 38’ travel trailer. I opted to leave the existing 12v house system in place with the exceptions of upgrading the converter charger and battery to lifepo4. I charge the house battery with it’s own solar panel to lessen the losses associated with inverting to 110 and then converting to 12v. I have similar specs 2100 watts of solar and 100ah of lifepo4 batteries. I use an all in one solar inverter that outputs 3500 watts continuously.
 

young7.3

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I have a 48v system on my 38’ travel trailer. I opted to leave the existing 12v house system in place with the exceptions of upgrading the converter charger and battery to lifepo4. I charge the house battery with it’s own solar panel to lessen the losses associated with inverting to 110 and then converting to 12v. I have similar specs 2100 watts of solar and 100ah of lifepo4 batteries. I use an all in one solar inverter that outputs 3500 watts continuously.
I assume you are happy with your choices? What would you change, if anything, if you had to do it again? What inverter do you use? What 12 volt power draws do you have?
 

rickst29

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Your configuration works, although the all-in one is stated to require mounting on a fire-resistant and nonconducting surface (concrete). Few if any RV "campers" have such mounting locations. Your equipment totals $1500 for battery, $750 for the combination charger/inverter unit, and another $220 for the "48V" -> 12V buck converter. And you have not yet addressed your "need" to charge a "48V" battery (with roughly 54.0 volts) from your alternator. DC->DC battery chargers are readily available for "12V" lithium battery banks, and a few models do "24v" battery banks - but devices which can output up to 54V for charging a "48V lithium battery pack from a 12v source are relatively less common and more expensive.

The actual size of your proposed battery is 100Ah * 51.2 nominal volts = 5120 watt-hours. If properly used (between about 97% maximum charge minimum state-of-charge not less than 15%) you will have a bit more than 80% available for use, about 4100 watt-hours. Your projected usage of 3800 watt-hours seems very close, for use of the battery by itself on a cloudy day.
- - -
I would (and did) stay entirely with "12v" battery packs running in parallel. If you build or buy two "12V" 280Ah battery packs (they each have nominal capacity of 3584 watt-hours), you'll have 40% more battery capacity and no need for the 48V ->12V buck Inverter. You can simply spend the $220 from the unneeded buck Inverter to buy the 2nd BMS, wiring, and a 2nd fuse (and possibly a case) in support of the 2nd battery pack. 12V->12V battery charge units are readily available and cost less. Pretty good Sine-Wave Inverters with the same continuous/peak power specifications can be had at moderate prices, I paid barely $230 to have a good one delivered to my door (Ebay Auction) - and I tested it to full capacity for multiple minutes. You just need bigger wires between the batteries and the Inverter. (I have dual AWG 2/0 cables, and the cable lengths are short.)

The separate MPPT charger could be bought with smaller PV Voltage capacity but more current capability, with the 8 panels wired "2S4P" for an MPPT charger cable of more than 200 PV volts, or wired 4S 2P for the case of an MPPT with a lower PV Voltage limit.
 
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Bobert

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Your configuration works, although the all-in one is stated to require mounting on a fire-resistant and nonconducting surface (concrete). Few if any RV "campers" have such mounting locations. Your equipment totals $1500 for battery, $750 for the combination charger/inverter unit, and another $220 for the "48V" -> 12V buck converter. And you have not yet addressed your "need" to charge a "48V" battery (with roughly 54.0 volts) from your alternator. DC->DC battery chargers are readily available for "12V" lithium battery banks, and a few models do "24v" battery banks - but devices which can output up to 54V for charging a "48V lithium battery pack from a 12v source are relatively less common and more expensive.

The actual size of your proposed battery is 100Ah * 51.2 nominal volts = 5120 watt-hours. If properly used (between about 97% maximum charge minimum state-of-charge not less than 15%) you will have a bit more than 80% available for use, about 4100 watt-hours. Your projected usage of 3800 watt-hours seems very close, for use of the battery by itself on a cloudy day.
- - -
I would (and did) stay entirely with "12v" battery packs running in parallel. If you build or buy two "12V" 280Ah battery packs (they each have nominal capacity of 3584 watt-hours), you'll have 40% more battery capacity and no need for the 48V ->12V buck Inverter. You can simply spend the $220 from the unneeded buck Inverter to buy the 2nd BMS, wiring, and a 2nd fuse (and possibly a case) in support of the 2nd battery pack. 12V->12V battery charge units are readily available and cost less. Pretty good Sine-Wave Inverters with the same continuous/peak power specifications can be had at moderate prices, I paid barely $230 to have a good one delivered to my door (Ebay Auction) - and I tested it to full capacity for multiple minutes. You just need bigger wires between the batteries and the Inverter. (I have dual AWG 2/0 cables, and the cable lengths are short.)

The separate MPPT charger could be bought with smaller PV Voltage capacity but more current capability, with the 8 panels wired "2S4P" for an MPPT charger cable of more than 200 PV volts, or wired 4S 2P for the case of an MPPT with a lower PV Voltage limit.
My AIO recommends that it be mounted on a non combustible surface. Nothing is mentioned about it being non conductive. Maybe that recommendation is for an AIO with a higher voltage PV input.
 

littleharbor2

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Sep 15, 2021
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The separate MPPT charger could be bought with smaller PV Voltage capacity but more current capability, with the 8 panels wired "2S4P" for an MPPT charger cable of more than 200 PV volts, or wired 4S 2P for the case of an MPPT with a lower PV Voltage limit.
Other way around for PV wiring. 4s2p for higher voltage and 2s4p for lower voltage. Not trying to be the math police but we don't need incorrect info being posted for all newbies to read.
 

young7.3

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Jun 28, 2022
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Your configuration works, although the all-in one is stated to require mounting on a fire-resistant and nonconducting surface (concrete). Few if any RV "campers" have such mounting locations. Your equipment totals $1500 for battery, $750 for the combination charger/inverter unit, and another $220 for the "48V" -> 12V buck converter. And you have not yet addressed your "need" to charge a "48V" battery (with roughly 54.0 volts) from your alternator. DC->DC battery chargers are readily available for "12V" lithium battery banks, and a few models do "24v" battery banks - but devices which can output up to 54V for charging a "48V lithium battery pack from a 12v source are relatively less common and more expensive.

The actual size of your proposed battery is 100Ah * 51.2 nominal volts = 5120 watt-hours. If properly used (between about 97% maximum charge minimum state-of-charge not less than 15%) you will have a bit more than 80% available for use, about 4100 watt-hours. Your projected usage of 3800 watt-hours seems very close, for use of the battery by itself on a cloudy day.
- - -
I would (and did) stay entirely with "12v" battery packs running in parallel. If you build or buy two "12V" 280Ah battery packs (they each have nominal capacity of 3584 watt-hours), you'll have 40% more battery capacity and no need for the 48V ->12V buck Inverter. You can simply spend the $220 from the unneeded buck Inverter to buy the 2nd BMS, wiring, and a 2nd fuse (and possibly a case) in support of the 2nd battery pack. 12V->12V battery charge units are readily available and cost less. Pretty good Sine-Wave Inverters with the same continuous/peak power specifications can be had at moderate prices, I paid barely $230 to have a good one delivered to my door (Ebay Auction) - and I tested it to full capacity for multiple minutes. You just need bigger wires between the batteries and the Inverter. (I have dual AWG 2/0 cables, and the cable lengths are short.)

The separate MPPT charger could be bought with smaller PV Voltage capacity but more current capability, with the 8 panels wired "2S4P" for an MPPT charger cable of more than 200 PV volts, or wired 4S 2P for the case of an MPPT with a lower PV Voltage limit.
Did you build your own 12v batteries or buy one(or multiple)? Any suggestions for resources on building my own? The one thing I am lacking is storage space for the batteries. If they are lithium i would prefer they be stored in the heated area of the travel trailer so they don't drop below the minimum temp for charging. That was a big draw to the server rack battery to have a smaller profile battery.
 

Bobert

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I assume you are happy with your choices? What would you change, if anything, if you had to do it again? What inverter do you use? What 12 volt power draws do you have?
My choice was primarily financial in addition to very limited space inside the camper. I discovered that for a fraction of the cost of a small system I could make a system using used solar panels and an AIO for a few thousand dollars not including the batteries that would supply the same amperage as a campground shore power 30 amp connection. So I went for it. I got really lucky, the AIO I purchased fit exactly in the space I had available for it and later when I purchased 4 12v lifepo4 batteries they also fit exactly in the space I had for them. Space was so tight that it took months for me to figure out where I could put the PV disconnect so that it wouldn’t interfere with the Ventilation of the AIO. If money and space were no object I would have probably used victron equipment primarily for the power sharing capability but as it turns out we rarely use shore power and when we do it’s no big deal to manually throttle the charging back so that it works satisfactorily. All things considered I can’t say I would do anything different if I had it to do over again but if I had more money I would get larger output panels and 10k more battery. I have a typical travel trailer manufactured in 2000 and I added a few things when I rebuilt it. It has a fairly heavy draw hydraulic slide out motor, lp furnace 2 diesel heaters, 4 vent fans. water pump, lights, the control circuits for the fridge, ac and lp heating all connected to the original rv fuse box. I have 6 different tank heaters and an outside outlet that are fused directly to the house battery. Our usage of these items varies but the general rule is that if the 100ah lifepo4 battery is nearly full at sundown it will still have power in the morning. None of the 12v loads have a significant affect on power consumption except for the heaters and the vent fans and these never run at the same time. My max continuous draw is around 10 amps at 12 volts. Generally I will turn off the inverter at night as we presently don’t have any essential 120v items that we use but if I need to I can charge the house battery from the AIO.
Did you build your own 12v batteries or buy one(or multiple)? Any suggestions for resources on building my own? The one thing I am lacking is storage space for the batteries. If they are lithium i would prefer they be stored in the heated area of the travel trailer so they don't drop below the minimum temp for charging. That was a big draw to the server rack battery to have a smaller profile battery.
I used 4 100 ah Lifepo4 batteries and connected them in series to create my battery bank the space I had available. I did not have the correct shape for a rack battery and plumbing is close by my battery box so I opted for a more moisture resistant approach.
 

young7.3

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Just when I thought I had my system figured out, I am having second thought. I am not oppsoed to a 12volt system as most of my demand is 12 volt (fridge, lights, water pump, heater fan, awning/slide motor). Looking at a 12 volt system again, I am trying to size a charge controller. In series, my system would have 8, 250 watt panels (37.5v/6.7a). Total= 242 volts and 6.7 amps. There arent any affordable controllers to handle that amount of voltage and watts. Other configurations, like rickst and littleharbor said...4s2p= 150 volts/13.4 amps. 2s4p= 75 volts/26.8 amps. What setup would you all suggest? Right now I am leaning toward a 40 amp MPPT rich solar controller. Can I use inline fuses on the parallel arrays to avoid a combiner box?
 

littleharbor2

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40 amps @12 volts is 480 watts. You're going to need a much larger controller or a lot less panels. The controllers rating is for output, not input.
 

rickst29

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If the 8 panels will lie FLAT on the trailer roof, (rather than being angled into angle of incidental sunlight), you're probably looking at around a 25% reduction in actual power (it varies according to the season, and the intensity of sunlight as well.) At peak power on a perfect day in late June, near noon, you might see around 1600 actual watts (peak at exactly solar noon, in late June). Unless you're doing a lot of stuff in late fall, winter, and early spring, you're "2000 nominal watts" of panels may be a lot more than you need - in my own travel trailer, my ratio of Solar nominal watts to "12v" Amp hours is around 1:1, and the batteries are fully charged well before 2PM daylight time on every moderately clear day. They only utilize the later hours of the afternoon charging day when I run the Air Conditioner from the batteries, or when the day was partly/mostly cloudy.

In any case, littleharbor2 has ignored post #1 in "warning about" a small MPPT controller. (The EG4 "off-grid inverter/charger" which you propose to use is capable of very high MPPT output amps, and extremely high Solar input voltage). The 8 panels can possibly even be wired "8S", with the total of V(oc) still not approaching the 500 volt limit.
 

littleharbor2

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In any case, littleharbor2 has ignored post #1 in "warning about" a small MPPT controller. (The EG4 "off-grid inverter/charger" which you propose to use is capable of very high MPPT output amps, and extremely high Solar input voltage). The 8 panels can possibly even be wired "8S", with the total of V(oc) still not approaching the 500 volt limit.
My previous comment is in regards to the OP's comment right before mine. He is talking about staying with a 12 volt system and using a Rich 40 amp MPPT solar controller. My point being the limited output of this controller @12 volts. Go ahead and try to shove a ton of solar into it. You're only getting Max. 40 amps@14.8 = 592 watts.

Specifications

Nominal system voltage: 12V/24V Auto Recognition

Rated Battery Current: 40A

Rated Load Current :20A

Max. PV Input Short Current :50A

Max. Battery Voltage: 32V

Max. Solar Input Voltage: 100 VDC
 

rickst29

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Did you build your own 12v batteries or buy one(or multiple)? Any suggestions for resources on building my own? The one thing I am lacking is storage space for the batteries. If they are lithium i would prefer they be stored in the heated area of the travel trailer so they don't drop below the minimum temp for charging. That was a big draw to the server rack battery to have a smaller profile battery.
I built 'em. There are gazillions of DIY examples on the site, with great pictures of them often included with their descriptions, 280Ah is a very widely used size for these packs, you would maybe be able to get by with only two of them. I like Docan, as a USA seller of battery cells.
 

rickst29

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If the camper roof can accept all 8 panels (without interference from AC units, vents, TV antennas, and other on-the-roof "disruptions" of the otherwise flat surface, I will recommend use of a 48V battery. Please advise of the number and size of AC units which you intend to support via the Inverter.
 

young7.3

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The roof is 29' long and can support all 8 panels without interference. The camper has one, 1600 watt a/c unit, but I didn't plan on sizing the system for using the a/c unit. I understand the charge controller sizing and all that, which is leading me back toward using a 24v or 48v system, mainly because I have a source for used 250w panels and would like to utilize them. This is kind of driving me crazy haha.

I am going to research building my own battery, 48v, and dc to dc converter to see if I can save some money.
Would you all recommend a better/different 48v to 12v converter than the Victron linked below?
 

littleharbor2

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If your 12 volt loads are not to large there's always the option of having a separate 12 volt system. I run my water pumps, VHF radio and stereo in my home with their own panel, controller and battery. An option to think about.
 

rickst29

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The roof is 29' long and can support all 8 panels without interference. The camper has one, 1600 watt a/c unit, but I didn't plan on sizing the system for using the a/c unit. I understand the charge controller sizing and all that, which is leading me back toward using a 24v or 48v system, mainly because I have a source for used 250w panels and would like to utilize them. This is kind of driving me crazy haha.

I am going to research building my own battery, 48v, and dc to dc converter to see if I can save some money.
Would you all recommend a better/different 48v to 12v converter than the Victron linked below?
That's a really good one, although the 30A Victron limit might not be sufficient for all your 12-VDC needs. (I wouldn't want to use it above 25A.) This one (with higher current capability) is avaiable from a 100%-rated Ebay seller for considerably less money, and has other sellers (with worse seller ratings) offering it for a few dollars less. I don't own the unit myself. https://www.ebay.com/itm/354058876961

EDIT: the cheap ones are meant to be the sole source of power for their 12v output "consumers", with no higher voltage charging devices present on the bus. Use of a cheap one would probably require removal of the "12v" SCC output from the smaller 190w solar panels, as well as any engine-based charging capability or interconnect.
 
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young7.3

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Well, I decided to go with a split system. Keep everything that is on 12v as is, and do the EG4 48v battery and 3000EHV-48 for my 120v needs. And the 2000 watts of solar on top. I'll upgrade the 12v battery and 12v solar at a later date, or buy a buck converter and power them off the 48v battery.
Keeping the 12v system will simplify the install and allow me to get up and running quickly. I have to have the camper ready by Sept 1 for a trip and didn't have the time to dive into making my own battery or else I would have. Thanks for the help everyone. Tips and suggestions are still welcome. I'll post the setup when I get it installed.
 

rickst29

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Well, I decided to go with a split system. Keep everything that is on 12v as is, and do the EG4 48v battery and 3000EHV-48 for my 120v needs. And the 2000 watts of solar on top. I'll upgrade the 12v battery and 12v solar at a later date, or buy a buck converter and power them off the 48v battery.
Keeping the 12v system will simplify the install and allow me to get up and running quickly. I have to have the camper ready by Sept 1 for a trip and didn't have the time to dive into making my own battery or else I would have. Thanks for the help everyone. Tips and suggestions are still welcome. I'll post the setup when I get it installed.
Sounds good, if the 190w solar (supporting 12v batteries) can remain present while the big array is added. Assuming this to be a traveling RV, there are also engine-based DC->DC options for supporting the "house" 12v battery bank, even if the batteries are of different types (SLA "engine" and "LFP" house being the typical issue to be addressed).

I don't think that any of the 'simple but dumb' buck converters can handle the 12v destination load (or bus) being charged by any other power source (including both the "12v solar" SCC, and any engine-related DC->DC charger or hard-wired interconnect.). They are built to be the sole source of power when used, and will lose the "magic blue smoke" when high "12v" voltage (provided by the battery or another charger) attempts to override their own output-only voltage regulation circuits. (They can't be run backwards at all.) The Victron can definitely handle that situation, at higher cost.
 
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