Request: Review of Proposed 28KWh / 3KW Solar / 24V/5KW inverter RV system

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,157
I am still in the design phase for my remodel. have four questions for you, please:

1) Double-checking my design, I have two Quattro's together supplying 240VAC. The LG minisplit outdoor unit spec sheet says input voltage should be 208-230VAC.

I noticed on your VRM it says "120.0" and "120.2" volts. Adding that together should mean 240.2V is being supplied to the LG unit? That is over 230VAC. Is this an issue with the LG?

2) Do you have any 240VAC appliances that require 4-wire connections? That is, two hots, a neutral, and a ground?

3) Does your generator supply 120VAC or 240VAC? If only 120, does it supply both Quattro's?

4) If I have the correct schematic for your system, you are NOT using AC OUT-2 on either Quattro. Is that still correct?

I appreciate you sharing your knowledge. Thanks!!!

Sure thing!

1) Not a problem at all. US split phase is 240+ volts
2) Nope; though by testing with a meter, all the appropriate voltages are available and would work for such a device
3) 120. One quattro connects to it and uses it to pass power through on that leg and/or charge the battery. The other Quattro remains inverting. Pure magic! 240 split phase inside no matter what you're connected to for shore power
4) Correct, I don't need an output that's only on when I'm connected to shore. I'm also not currently using AC IN-2 ... though that will change if I get a permanent on-board generator

Given my loads, I really never need more than 13.4 amps (minimum amp draw for the 5k quattro) at 120v. The only time I set it to draw more is if I'm trying to recharge the battery more quickly (e.g. to shut down the generator by sunset).
 

CharlesK

New Member
Joined
Jan 31, 2021
Messages
25
Location
NE Florida
Sure thing!

1) Not a problem at all. US split phase is 240+ volts
Obviously I knew it was working; yours has been working fine. I asked because I could not find anything in the sales literature from LG. However, someone pointed me to "Submittal" documents that have much more technical information. And, presumably these documents are written by engineers. (y)

Looking at a "Submittal" document for an LG outdoor unit, it states "Power Supply (V/Hz/Ø)¹ 208-230,60,1."

That is a range of 208 to 230 Volts at 60 Hz, single phase.

Moreover, Note #1 states "1. Acceptable operating voltage: 187V-253V."

Yup, 240 is within range; therefore perfectly acceptable. :)
Thanks, again.
 

CharlesK

New Member
Joined
Jan 31, 2021
Messages
25
Location
NE Florida
@cinergi
As you might have guessed, I have been following your project and using it as one of the inputs for my own motorhome. Currently it is a block-diagram only, as seen in previous posts in this thread. Feedback from you and others have helped me improve the design. Thank you. :)

Since the basic diagram has been established, I have been working on individual wire sizes, components with specific part numbers, fuses, etc. I have been using a schematic you posted named "NH Electrical V3.drawio" and am wondering if this is the latest and current diagram for your system.

My intent is not to plagiarize your work, but your system is the closest that I have found to meet my particular needs. Also, I am not trying to simply "copy" your system, but I am studying it and other sources, so I understand exactly why each item is selected. Ultimately I will be doing the installation and am responsible for a safe and robust system. I want to know why everything is there and how it works.
 

SolarPrep

Solar Enthusiast
Joined
Jul 15, 2021
Messages
121
CharlesK: Interesting project you have there. I'm considering something similar myself, since I have the opportunity to get an older RV from a good friend. I do want to make a comment or two on inverter mini splits. I'm not that familiar with LG, but am very familiar with Daikin, Fujitsu and Mitsubishi. Most of the units I've worked with have a significant efficiency advantage for the 1 to one units. In other words, not a multi-head compressor. The last project I did the 1 to one units were all above 33 seer, and the multi-head were around 21-26 seer. I don't know if this is the route you are taking, but I've also read other posts where people were considering more than 1 unit. Two compressors takes up more space, but many of the multi-head compressors are much larger. Don't know about fitting one in your space.

It does make a difference if you oversize them too. Efficiency drops rapidly. I'd personally go with 2 smaller units, and run both of them. I've stayed away from ceiling cassettes, because of servicing. Some of them are horrid. There are also wall mounted cassettes, but have never used one.

I see you plan to insulate your coach. Good idea...do as much as you can, you won't regret it. I also second your process to get rid of all the propane stuff.

I missed why you decided to go with 48v. If so, do you need (2) 5k units? Could you use (2) 3k?

Just asking, because your decision process interests me.

Good luck with your project!
 

CharlesK

New Member
Joined
Jan 31, 2021
Messages
25
Location
NE Florida
CharlesK: Interesting project you have there. I'm considering something similar myself, since I have the opportunity to get an older RV from a good friend. I do want to make a comment or two on inverter mini splits. I'm not that familiar with LG, but am very familiar with Daikin, Fujitsu and Mitsubishi. Most of the units I've worked with have a significant efficiency advantage for the 1 to one units. In other words, not a multi-head compressor. The last project I did the 1 to one units were all above 33 seer, and the multi-head were around 21-26 seer. I don't know if this is the route you are taking, but I've also read other posts where people were considering more than 1 unit. Two compressors takes up more space, but many of the multi-head compressors are much larger. Don't know about fitting one in your space.

It does make a difference if you oversize them too. Efficiency drops rapidly. I'd personally go with 2 smaller units, and run both of them. I've stayed away from ceiling cassettes, because of servicing. Some of them are horrid. There are also wall mounted cassettes, but have never used one.

I see you plan to insulate your coach. Good idea...do as much as you can, you won't regret it. I also second your process to get rid of all the propane stuff.

I missed why you decided to go with 48v. If so, do you need (2) 5k units? Could you use (2) 3k?

Just asking, because your decision process interests me.

Good luck with your project!
The minisplits and new Victron equipment have not yet been purchased. I am currently working on the interior remodel such as upgrading plumbing, wiring, cabinetry, flooring, insulation, etc. I am staying with 12VDC and 110VAC for the coach interior. Therefore, the choice of a 24VDC vs. a 48VDC battery bank is a separate issue. I am pretty well set on 48VDC at this point in time.

Meanwhile, comments and suggestions are welcome. (y)

Given that, thank you for your comments. Let me address your questions.

1) Mini-splits: I have not yet made a final decision on the sizings. I have settled on LG because the outdoor unit will fit in the former propane tank basement compartment. This compartment is already open on the back and bottom, so there will be plenty of air flow. If needed, I can modify the compartment door for additional air flow. Overall in the coach, there is reasonable room for one outdoor unit. Having two outdoor units is problematic for both space and locations.

Why LG? The outdoor unit fits in the basement. Some of the other brands would mean an extremely tight fit, if at all. The basement height is not that great in this particular coach.

Indoor Units: The coach is physically divided into two areas: the back bedroom and the front area (seating, galley, table, cockpit). There is a self-enclosed bathroom in the middle off of a side hallway. The plan is to install one wall unit over the cockpit (above front windshield) facing aft. And, install one wall unit at the very rear of the coach, over the bed, facing forward. The bathroom would be cooled when occupied by running the ceiling exhaust fan. This will pull cool air from the rest of the coach. For cold weather, the plan includes radiant floor heating including the bathroom. This is in addition to the heat capabilities of a mini-split.

My current thoughts are to install a 7K wall unit in the bedroom and a 12K or 15K wall unit up front. The outdoor unit could be either an 18K or a 24K unit. Any of the combinations I mentioned are supported according to the LG specifications of combinations for both heat and cool. From what I understand the 18K outdoor unit would be more efficient than the 24K because it would not be turning completely on and off as much.

The SEER rating for the LG 18K outdoor unit is 22. The SEER rating for the LG 24K outdoor unit is 20.3. Neither is as efficient as 33 SEER, of course. But they do support two (or more) indoor units with a single outdoor unit.

However, if I install a 15K indoor unit up front and it turns out to be inadequate for cooling, I can only upgrade the 15K to 24K if the outdoor unit is 24K according to LG. Hmm...

2) Inverter Sizing: I decided on two 5KVA units because of my Energy Audit. I included that in my first post in this thread. I have made some adjustments along the way that persuaded me to use 5K instead of 3K. The extra margin affords me some peace of mind knowing that I will have the extra power available if needed.

Once the 5KVA decision was made, the Victron Multiplus units were out of the equation. The largest is 3KVA. That led to two Quattro 5KVA units.

I also decided to use two Victron inverter/chargers. Doing so means that everything works identically with a) 50A (120/240VAC) shore power, b) he on-board 8KW(120/240VAC) diesel generator, or c) two 120VAC inverters configured in split-phase providing 120/240VAC at all times.

3) 24V vs. 48V.
My DIY battery will consist of 32 3.2VDC cells. If I configure them as four 24V batteries, I will need four BMS units. If I configure them as two 48V batteries, I will only need two BMS units. That saves a couple of hundred dollars.

Each Quattro 48V5KVA units currently sells for $283.05 less than the Quattro 24VKVA units. For two Quattros, that is a $566.10 savings to use the 48V units.


Additionally, there are some technical reasons that others have mentioned that also indicate 48V is a better choice for this particular project. Some may be listed here. Some from another forum I frequent.

Again, thanks for your comments.
 

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,157
The minisplits and new Victron equipment have not yet been purchased. I am currently working on the interior remodel such as upgrading plumbing, wiring, cabinetry, flooring, insulation, etc. I am staying with 12VDC and 110VAC for the coach interior. Therefore, the choice of a 24VDC vs. a 48VDC battery bank is a separate issue. I am pretty well set on 48VDC at this point in time.

Meanwhile, comments and suggestions are welcome. (y)

Given that, thank you for your comments. Let me address your questions.

1) Mini-splits: I have not yet made a final decision on the sizings. I have settled on LG because the outdoor unit will fit in the former propane tank basement compartment. This compartment is already open on the back and bottom, so there will be plenty of air flow. If needed, I can modify the compartment door for additional air flow. Overall in the coach, there is reasonable room for one outdoor unit. Having two outdoor units is problematic for both space and locations.

Why LG? The outdoor unit fits in the basement. Some of the other brands would mean an extremely tight fit, if at all. The basement height is not that great in this particular coach.

Indoor Units: The coach is physically divided into two areas: the back bedroom and the front area (seating, galley, table, cockpit). There is a self-enclosed bathroom in the middle off of a side hallway. The plan is to install one wall unit over the cockpit (above front windshield) facing aft. And, install one wall unit at the very rear of the coach, over the bed, facing forward. The bathroom would be cooled when occupied by running the ceiling exhaust fan. This will pull cool air from the rest of the coach. For cold weather, the plan includes radiant floor heating including the bathroom. This is in addition to the heat capabilities of a mini-split.

My current thoughts are to install a 7K wall unit in the bedroom and a 12K or 15K wall unit up front. The outdoor unit could be either an 18K or a 24K unit. Any of the combinations I mentioned are supported according to the LG specifications of combinations for both heat and cool. From what I understand the 18K outdoor unit would be more efficient than the 24K because it would not be turning completely on and off as much.

I recommend 24k because if both the 7k and 12 or 15 are running, the ODU will be underpowered; if you're in the sun in 85+ degree weather, you're going to need it.

The IDU sizing is critical, too - you do not want them cycling because every time an IDU cycles, the entire system takes time to adjust and if one of them is cycling frequently enough, the overall system is degraded and your other room will suffer. Ask me how I know ;)

If you're VERY well insulated (including good windows), 7k and 12k sounds reasonable (I don't know your rig length and other details ... too lazy to go back and look lol). I run with 9k and 12k in my 38' well-insulated 5th wheel (13'5" tall).

The SEER rating for the LG 18K outdoor unit is 22. The SEER rating for the LG 24K outdoor unit is 20.3. Neither is as efficient as 33 SEER, of course. But they do support two (or more) indoor units with a single outdoor unit.

However, if I install a 15K indoor unit up front and it turns out to be inadequate for cooling, I can only upgrade the 15K to 24K if the outdoor unit is 24K according to LG. Hmm...

2) Inverter Sizing: I decided on two 5KVA units because of my Energy Audit. I included that in my first post in this thread. I have made some adjustments along the way that persuaded me to use 5K instead of 3K. The extra margin affords me some peace of mind knowing that I will have the extra power available if needed.

Once the 5KVA decision was made, the Victron Multiplus units were out of the equation. The largest is 3KVA. That led to two Quattro 5KVA units.

If your AC legs are well-balanced, 3k is doable, but it can be tough to know how balanced you are. You're generally talking about how balanced the kitchen is and perhaps the bathroom if a hair dryer is involved. For me, the microwave and fridge are on one leg and the plugs are on another leg (toaster, coffee, blender)... I've turned everything on including AC and my overall usage was 4500 watts (about 2200 per leg). I rarely see more than 2500 watts total. You'd really have to push things or have unbalanced legs to get into a pickle. And the Victrons handle overload condtions (many seconds) quite well. But, consider where they're mounted; the hotter they get, the less power they can provide. So if they're gonna see 100F, then 3k could easily be a problem.

I also decided to use two Victron inverter/chargers. Doing so means that everything works identically with a) 50A (120/240VAC) shore power, b) he on-board 8KW(120/240VAC) diesel generator, or c) two 120VAC inverters configured in split-phase providing 120/240VAC at all times.

Yup I plug into 15, 20, and 30 amp 120v as well as 50 amp 240 and the interior doesn't know the difference. Combined with PowerAssist, this is a very powerful feature. I love it!

3) 24V vs. 48V.
My DIY battery will consist of 32 3.2VDC cells. If I configure them as four 24V batteries, I will need four BMS units. If I configure them as two 48V batteries, I will only need two BMS units. That saves a couple of hundred dollars.

Each Quattro 48V5KVA units currently sells for $283.05 less than the Quattro 24VKVA units. For two Quattros, that is a $566.10 savings to use the 48V units.


Additionally, there are some technical reasons that others have mentioned that also indicate 48V is a better choice for this particular project. Some may be listed here. Some from another forum I frequent.

Again, thanks for your comments.

48v can be an advantage with lots of solar panels because you don't have to buy SCCs that handle such high battery-side amperage.

I'm happy with my 48dc decision and I'd do it again.
 

richard cabesa

Solar Enthusiast
Joined
Mar 16, 2021
Messages
94
I am still working on the solar panel configuration. There are numerous other threads on this forum that are very helpful. For now, my thoughts are to cover the motorhome roof with as much wattage that will fit and still leave space for the necessities (TV antenna, radio antenna, exhaust vents, shower skylight). The roof membrane will be replaced after the roof air-conditioning units are removed. So,solar panel selection is being delayed.
I'm going to suggest going ahead and put the panels right over that bath skylight. You will still get enough light coming through and around to not need to turn on the light in the bath.

I did this and it is amazing how much thermal gain it eliminated. You are not in there to look at the stars. It actually made our bath MORE comfortable and cooler. It used to cook in there
 

CharlesK

New Member
Joined
Jan 31, 2021
Messages
25
Location
NE Florida
Thank you, @cinergi . The coach is 38' long, with no slides. I am adding to the insulation, but it does have single-pane windows. Given your comment, that definitely leads me to an ODU of 24K. The back bedroom (very small space only big enough for a queen bed) will get a 7K IDU. The only decision left is 12K or 15K for the front 2/3rds of the coach. I am leaning toward the 15K because of all the glass, including the windshield.

Thank you, @richard cabesa for the skylight comment. I had already thought that might be a worthwhile idea. You confirmed it. I have already eliminated three skylights, and covered up one more vent with Reflectix when not in use. It has made a HUGE difference.

I am also hoping that after I remove the existing roof A/C units, the shade afforded by covering most of the roof with solar panels will help reduce the thermal gain overall. The panels may even eliminate the sound of a hard rain on the roof.
 

SolarPrep

Solar Enthusiast
Joined
Jul 15, 2021
Messages
121
Charlesk: Do you already have the PV panels? If not, you might consider bifacial panels. I like that idea of going right over the skylight. Was out looking over my buddies 38' coach (1 slide) yesterday considering the idea of cutting out the floor for the shower, and dropping it a couple of inches and completely eliminating the sunroof. There is some plumbing under there, but it looks do-able.

I wish his coach didn't have any slides. I don't like them, we don't need them and don't care about resale value.

The choice for Victron is a good one. Have you looked at the new Multiplus 2 units? 50 amp bypass seems to be aimed at your market.
 

CharlesK

New Member
Joined
Jan 31, 2021
Messages
25
Location
NE Florida
Charlesk: Do you already have the PV panels? If not, you might consider bifacial panels. I like that idea of going right over the skylight. Was out looking over my buddies 38' coach (1 slide) yesterday considering the idea of cutting out the floor for the shower, and dropping it a couple of inches and completely eliminating the sunroof. There is some plumbing under there, but it looks do-able.

I wish his coach didn't have any slides. I don't like them, we don't need them and don't care about resale value.

The choice for Victron is a good one. Have you looked at the new Multiplus 2 units? 50 amp bypass seems to be aimed at your market.
Lowering the bathroom floor would be a major undertaking for my coach. Even if there is room below (which I do not think so on my coach), the bathroom has a full fiberglass tub/shower surround from floor to ceiling. I.e., it is enclosed on 5 sides with a single fiberglass unit. It will be much easier to mount the solar panels on unistrut that is elevated above the roof line. Coach height is not an issue as the planned height for the panels will probably still be lower than the existing roof A/C units (which are going away).

Panels have not been purchased yet. Prices and capabilities seem to be changing almost monthly. I will evaluate bifacial panels when the roof is ready. I do not know how much there is to gain with bifacial panels installed flat about 4-6" above a white rubber roof compared to single-sided panels. But, first, I am removing the two roof A/C units, lots of extraneous skylights, vents, antennas, etc. Then I will be replacing the TPO roof. Panel installation and a new TV antenna are the last items on the roof list.

If I understand correctly, the new Multiplus 2 units are only available in 12VDC and limited in size to 3000VA (2400W). My requirements are different. Two Quattro 48/5000/70 units in a split-phase configuration are appropriate for my needs. The two units together will provide 10,000VA (8,000W) of power with both 120VAC and 240VAC available at all times. I will not be using the pass-through capabilities on the Quattro units (otherwise known as AC-in-2).

@SolarPrep : Thanks for your comments. :)
 
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