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Old 10-27-2020, 08:53 AM   #71
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Do you have the ability to measure current in and current out? I use several 12 > 6 and then 6 > 12 converters to feed my electronics (router, BR burner, drives, anything with 12v wallwart). This allows me to switch to 6vdc LIFE for extended outrages. I also use 12 > 24 for my winega rd WC3000 booster. I am seeing about an 80%, rated draw, to 90%, light load. I don't have anything that could pad a converter with a 55/60w continuous draw.
Not sure I fully understand the question.

The headlights are a known wattage, and I sized the converts to be nearly twice the needed size to allow them to run cool. Doesn't really consume any extra power having the extra capacity as the headlights only draw what they draw.

The OEM wiring was actually done well, with a totally separate circuit for each of the four lamps. One circuit can go totally out without affecting the others.

Regarding DC appliances in the coach - if there are any capable of running on 12vdc, then I've already got them wired to do so directly. I have eliminated all of the wall warts possible, as they do nothing to add to efficiency.
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Old 01-24-2021, 05:10 PM   #72
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Very helpful read.

My heat & AC struggle so swapping out for Mini Splits is appealing.

Would not mind removing the propane as well
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Old 01-25-2021, 12:39 AM   #73
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QUESTION: How much difference will a higher SEER rating mean to me?

The goal is to be able to run the mini-splits as much as possible on SOLAR and LifeP04 batteries.

One vendor has a 9K BTU unit at 17 SEER, another at 22.8 SEER, another at 23 SEER, another at 25 SEER, and even one at 30.5 SEER.

I even found a 6K BTU unit at 33 SEER. (How many BTU's does a coach bedroom need anyway? (No slides, bedroom accessed by a side-hallway instead of an open bathroom plan)

And, while I am asking, how many BTU's does the front end of the coach need? No slides, 38' DP, adding 1/2" foam insulation to the walls, single-pane windows.

Thanks to everyone who has commented. Our remodeling plan is now much better for it.
Better late than never ...... didn't see this question until these many months later.

SEER is a seasonal energy efficiency rating meaning it tells you relatively how well the unit compares with others if it sits in one place and runs hard when hot and slows down when it's not so hot. So it runs slower before and after the hot summer afternoon and runs slower in the spring months and in the fall months. A full timer might use the system over many months making SEER the important number.

However, part timers or hikers might mostly use the mini split to cool down the RV after returning from a days outing. In that case it will run hard for a few hours (summer) or an hour or two (fall and spring) to cool down the RV. I.e., it won't spend much time loafing at low compressor and fan speed. In this case EER is a more relevant indicator of efficiency. EER is the efficiency under heavy load.

Comparing EER and SEER one finds that some mini splits get higher SEER from a modest EER and some get lower SEER from a higher EER. Best is high SEER and high EER, but that can get expensive.

One of the determinants of SEER is how low the compressor speed can go. Some mini splits can take the compressor throughput down to 30 or 40% of max throughput. I.e., a 9K unit that has a turndown ratio of 3 can only modulate down to 3K. If the cooling demand is less than 3K, the unit must cycle off. That reduces efficiency. Some units can get down to 25% throughput, so will go into cycling less often when cooling demand is low and thus will have a higher SEER relative to EER. The best unit I know of is the Gree 9K Saphire that has a SEER of 38 and has a six to one turndown ratio. It can still modulate at cooling loads down to 1.5K. It has a modest EER but a great SEER because of this. If one is going to have the mini split running lots of hours even if only a bit of cooling is necessary, it's a good unit. The compressor is a bit large and heavy though. The price is good.

For many of us, EER is probably the number to look at. Full timers that will use the mini split throughout the day and night should be looking at SEER.

As to how much cooling is needed, it seems there are a lot of happy mini split users with 9K units covering intermediate sized RVs. A bedroom surely won't need near 6K but mini splits don't come smaller so that one is going to cycle a lot especially since it will be used mostly at night when not so much cooling is needed.

Mini splits do have the losses of the copper lines between the indoor and outdoor units, but that's about 1% per four feet. That's far less than the duct losses in a ceiling unit. I'd say this explains why 9K mini splits seem to replace a 13,500 conventional ceiling unit with no problem.

IMHO.
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Old 02-21-2021, 07:23 PM   #74
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And, while I am asking, how many BTU's does the front end of the coach need? No slides, 38' DP, adding 1/2" foam insulation to the walls, single-pane windows.[/B]
This question bothered me since it was posted .... so I had to finally look into it. I generated a simple spreadsheet to calculate BTU/Hr requirements in an RV. I had to make some assumptions and educated guesses, but here's what I came up with for my 30' 5er.

Note that in this example I'm assuming 75F inside and 95F outside or 80F inside and 100F outside .... i.e., a 20 degree difference. See the notes. I believe the results are somewhat pessimistic.

The spreadsheet provides steady state heat flow into the RV from the ambient. I.e., if you come back from a hike and the RV is 90F inside, it's going to take a while to cool down. What you see below is "steady state" after cool-down.

I'd say this calculation pretty much confirms why folks do fine with a 9K mini split.

PM me if you'd like a copy of this spreadsheet so you can insert your own numbers.

Here's what it looks like .......

Click image for larger version

Name:	RV BTU Estimate.JPG
Views:	9
Size:	291.3 KB
ID:	318839
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Old 02-22-2021, 05:38 AM   #75
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This question bothered me since it was posted .... so I had to finally look into it. I generated a simple spreadsheet to calculate BTU/Hr requirements in an RV. I had to make some assumptions and educated guesses, but here's what I came up with for my 30' 5er.



Note that in this example I'm assuming 75F inside and 95F outside or 80F inside and 100F outside .... i.e., a 20 degree difference. See the notes. I believe the results are somewhat pessimistic.



The spreadsheet provides steady state heat flow into the RV from the ambient. I.e., if you come back from a hike and the RV is 90F inside, it's going to take a while to cool down. What you see below is "steady state" after cool-down.



I'd say this calculation pretty much confirms why folks do fine with a 9K mini split.



PM me if you'd like a copy of this spreadsheet so you can insert your own numbers.



Here's what it looks like .......



Attachment 318839
Where are the calculations for the greenhouse effect at the front? In my experience, there is interplay between windows/windshield that goes beyond how much thermal load there would be with the same amount of glass spread out over a long wall.
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Old 02-22-2021, 06:59 PM   #76
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Where are the calculations for the greenhouse effect at the front? In my experience, there is interplay between windows/windshield that goes beyond how much thermal load there would be with the same amount of glass spread out over a long wall.
See the "windshield" entry near the bottom. Increase it if you think it's too low. Not sure about the "interplay between windows/windshield" you mention. Seems both are exposed to the outside temperature and one or the other is hit with radiant heat from the sun (or both at 45 degrees). Note that I did double heat pickup along one wall assuming radiant from the sun on that wall.

Personally, I'd drape something across the windshield to slow heat gain there. Maybe some other windows as well. And foam inserts in ceiling vent fans.
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Old 02-22-2021, 07:08 PM   #77
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See the "windshield" entry near the bottom. Increase it if you think it's too low. Not sure about the "interplay between windows/windshield" you mention. Seems both are exposed to the outside temperature and one or the other is hit with radiant heat from the sun (or both at 45 degrees). Note that I did double heat pickup along one wall assuming radiant from the sun on that wall.

Personally, I'd drape something across the windshield to slow heat gain there. Maybe some other windows as well. And foam inserts in ceiling vent fans.
I guess what I was getting at is no matter how careful we all are about shielding our cab areas, they tend to pick up much more heat than expected.

When on the road this gets even worse as there is no way to block the sun from the windshield and front side windows while driving, so my question also related to this. If you're taking out the generator from a coach, unless you've got OTR a/c which can keep up you'll need to run one (or two) of the house units to keep the interior comfortable.

When all that glass up front gets sun shining through and bouncing between the two other windows up there it tends to magnify the heating effect, just like in a greenhouse. A straigthforward calculation based on the sq footage alone won't account for this.
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Old 02-22-2021, 11:29 PM   #78
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I guess what I was getting at is no matter how careful we all are about shielding our cab areas, they tend to pick up much more heat than expected.

When on the road this gets even worse as there is no way to block the sun from the windshield and front side windows while driving, so my question also related to this. If you're taking out the generator from a coach, unless you've got OTR a/c which can keep up you'll need to run one (or two) of the house units to keep the interior comfortable.

When all that glass up front gets sun shining through and bouncing between the two other windows up there it tends to magnify the heating effect, just like in a greenhouse. A straigthforward calculation based on the sq footage alone won't account for this.
Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
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Old 02-23-2021, 04:44 AM   #79
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Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
Some motor homes do have an engine powered compressor for dash air. Our coach has OTR (over the road) a/c designed to keep the entire coach comfortable, so we're fortunate in this regard. Even with this though, the front few feet of the coach are the warmest while on the road in the summer due to the glass.

The curtain behind the cab area does make a huge difference if using dash a/c - there is no way it will keep up if trying to cool the whole coach but just the cab area is usually manageable. Won't work for everyone though.
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Old 02-28-2021, 01:16 PM   #80
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Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
Oops. I said "convection cooled" in the above. Since we are talking about cooling, I should have said "convection heated." I.e., driving at 60 through 90F air will keep the outer skin of the RV very close to 90F even though it's cooler inside. And warmer yet on any wall that is getting direct sun. And maybe warmer still from friction of the moving air.

Even when sitting still there is some convection heating of the outer skin from a breeze or just air flowing downward along the skin because the skin is cooled somewhat from the cooling going on inside. But, for the most part, when sitting still, the outer skin will be a bit cooler than the outside temperature as heat is pulled in through the wall and dispensed by the A/C unit. Only direct sun on a wall can take it above outside ambient. Thankfully that only occurs on one wall (or to a lesser extent on two walls depending on sun angle).
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Old 03-26-2021, 03:39 PM   #81
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OP here.

I am still in the design phase of the electrical system.

The propane tank has been removed.

That basement bay will be the location of the mini-split outdoor unit. The plan is for a 2-zone outdoor unit (18K BUT), one indoor unit over the cockpit of the diesel pusher (12K BTU) and one indoor unit in the bedroom (7K BTU). There is not a clear path from the front to rear of the coach for airflow (side hallway), so two units makes sense.

The existing MSW inverter and separate charger will be removed and replaced, probably with a Victron Multiplus 24/3000. Lifepo batteries (DIY 24V, 280AH) are in the design. I am thinking 3 DIY batteries for a total of 20KWh.

The one issue that has me somewhat stumped is the need for 240VAC for the mini-split. It will be the only 240VAC item in the coach.

To get split-phase 240VAC with a Multiplus (or Quattro) requires two units connected together. The onboard diesel generator is 120VAC. I believe the Multiplus has its own transfer switch (from shore power and/or genny). (Please correct me if I have this wrong!) The wiring seems to be much more complex.

There is also a lack of basement space in this 1991 coach. The Lifepo batteries will not fit where the current house batteries reside. Also, that space is not well protected from the elements either. I understand that Lifepo batteries like to be comfortable (not too cold, not too hot).

And, I want to locate the batteries, inverter/charger, solar controls, etc., etc. in the same space.


So, here are my thoughts:

I have read where some folks will use a small inverter to power a single device, such as a refrigerator or TV. This saves some energy by not having a whole-RV inverter running all the time.

So, why not a single-use inverter just for the mini-split? And, select a 240VAC split phase inverter?

Include a complete 120VAC system with solar, 24V batteries, one inverter/charger, proper fuses, shunt, panel boxes, etc.

Then, connect a 240VAC split phase inverter directly to the batteries to supply power ONLY to the mini-split. One that comes to mind is:
AIMS Power PICOGLF60W24V240VS, 6000 Watt Low Freq Inverter Charger

I know it says it has charging capabilities, but the only input listed on the spec sheet is 24V.

The LG mini-split unit that I am considering specifies a 20A breaker. The best info I have found is that the unit actually will pull 15A at most. So, that would be 3600W. The 6000W AIMS unit should be able to do that without issue.

There probably are others out there that will work as well.

By the way, I have read about autotransformers. One could be used to supply the 240VAC. But, that would be taking output from the main inverter that is supplying 120VAC for everything else in the coach. A separate 240VAC inverter would be connected directly to the batteries and would not affect anything else in the coach. (Yes, the battery bank has to be large enough. But that is in the plan.)

Am I headed in the right direction?
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Old 03-26-2021, 05:08 PM   #82
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OP here.

I have made some preliminary decisions, and am still researching and reading your comments. Thank you.

Please let me share what I have so far. And, this is subject to change.

Battery Bank: 12VDC LiFeP04 batteries in a 24VDC configuration. Number of batteries will depend on results of electrical usage survey.

HVAC: Taking a very serious look at a two-zone 18-24K BTU minisplit with a small Indoor unit in the bedroom and a larger Indoor unit in the center of the coach facing forward. That still leaves the bathroom (the floor plan is a side hallway with a completely closed bathroom; not a walk-through bath). The Outdoor unit would go in one of the basement bays; possibly the one where the current gas furnaces live. There are 120VAC mini-splits, but they have smaller BTU's and that would require two complete installations for the coach. The larger Outdoor units require 240VAC.

Finding locations for the Indoor Units is a bit of a challenge. Since I am removing/redesigning/replacing most of the cabinetry, etc. anyway, I can redesign as needed. The installation manuals for some of the Indoor Units are helpful. Online youtube installation videos seem to be helpful as well. (What did we ever do before the Internet? )

Remove the new Coleman heatpump from the roof up front.

Remove the original Coleman A/C from the roof over the bedroom. (It still runs, including the heat strip.)


Floor Heat: Looking at a 120VAC mat system to be installed over the existing 3/4" marine plywood floor. Then, probably engineered wood, or some type of vinyl flooring (no carpet). DW is still in the interior design phase. I priced a 24V mat system from one supplier. The price was about 5K, just for the parts. I would be providing the labor, but I still thought this was high. 120VAC pricing appears to be much more reasonable.


240VAC: This is needed for the above mini-split. Victron apparently makes an inverter/charger model so that two of them can be connected to supply 240VAC.

The existing generator will provide 120VAC to the two inverter/chargers.

Shore Power will provide 120VAC to the two inverter/chargers.

Victron apparently makes a unit that will convert 24VDC to 12VDC so I can power all of the 12VDC house items: water pump, lighting, etc.

A couple of you suggested using the 12VDC output from the system to supply 12VDC to the House lighting, etc. AND keep a 12VDC battery charged. I am not quite sure why this is that beneficial. I guess if the Inverters go offline I could still have lights and a water pump? Powered by the 12V battery?

I am considering NOT connecting the main engine alternator output to the House system. In fact, I think I want to completely separate the Chassis and House systems at all times. The only time I may need to connect them is if the Chassis batteries die and I need to start the main engine. Others have said a temporary connection with Jumper Cables will do the trick until Emergency Repairs can be completed.


Solar will provide some high voltage power to one or more MPPT controllers to charge the batteries. Not sure where they are connected yet, but will learn that once I start the electrical schematics.


This is a work in progress. No physical work on the new electrical system has started. I have removed the propane range, propane fridge, incandescent lighting, fluorescent lighting, and a few other things. I have temporarily installed new LED ceiling lights. I have removed a lot of the cabinetry, jack-knife sofa, carpeting, etc. Next, I will be working on removing the gas lines, propane tank, some skylights, etc. as I continue to plan the new electrical system.

The comments so far have been extremely helpful. Both what to do, and what not to do. Thank you!!!
I put our 240v mini split on a step up transformer. Plugged into a 15 amp circuit and it works great. No need for 240v coming in. I did this so I can run them on a smaller generator. You might want to look at Schneider inverters. They have a 6800 watt single unit. That is what I am going with.
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