More Newbie questions - OTR Air Solutions, Thinking Roof units

[neoneddy]

My overall goals

Solar 8-10 panels (Maybe I'm in a dream world)
2500Ah+ (12v)  House battery system
Smaller generator that fits in the old AC condenser area use to charge house batteries as needed, not to support the system full time.
Main Alternator also helps charge house system as well, maybe the house system should be 24v then.

I plan on using spray foam insulation on the roof and walls.  Including the front and electrical panel area.  In the year I plan to insulate well.  I found while driving the shell, any air leak from the engine compartment into the cabin will suck hot air in.  So I need to stop the air and radiant heat.


AC system
I was thinking 2, one in each emergency hatch, was thinking the Coleman Mach 3 PS models.  That's 1000 watt AC for each.  I'm hoping to avoid a big diesel generator, can those ACs be run  safely from alternator + a 12 or 24v 3000+watt inverter

In reading responses in my other thread https://www.busconversions.com/bbs/index.php?topic=31761.msg357062#msg357062 . Seems like 3 is the way to go. 

[Jon]

You are going to need a good bank of house batteries, an alternator with high output and if you insist on using inverter power plan on at least 2 to reduce their load.

Typical roof air units are going to draw 13 amps at 120V or 130 amps at 12V. If you run two AC units a 270 amp alternator is going to be run at its capacity with no margin to handle other loads like a refrigerator, water pumps, etc. at which point you are depleting batteries.

I have no clue why folks insist on using inverters when a decent sized diesel generator will handle those loads without even breaking a sweat and it will sip fuel. My 20KW generator uses less than 1/2 GPH when I dry camp and I am an energy hog when I am running the generator because it has so much output.

[Beesme]

Totally agree with Jon , use a diesel generator and use the solar for helping batteries when you wanna be quiet and don't need the ac . I have 12kw diesel and it uses very little fuel and it very quiet in the hush box !jmho though !

[daddysgirl]

WHATEVER YOU DO.... Please remember BALANCE of weight on both sides. The monster engine batteries were opposite the heavy condenser compartment for a reason. This rule goes for the whole bus...all three axles. If you put too much weight on one side...well, let's just say you will wish you didn't. This is important from a practical perspective, but more importantly from a potential safety standpoint. Tire size is one thing that will depend on how heavy you are. But just as with everything else in life BALANCE is important


For 40' you need 3 roof units. Running them to your electric panel is, IMHO, the best way to go.
Depending on your insulation...you'll need a way to keep yourself cool driving into the sun. Some folks configure a duct system for their AC units. Some raise the roof to accommodate it.
I am thinking of adding a small AC unit to the front, maybe through the spare tire compartment. I'm not to that phase yet.

And I totally agree with the above. A diesel generator is money well spent. The bigger the better.

[daddysgirl]

Oh, BTW...
This is a totally personal choice, but...
I would limit spray foam to parts of the ceiling near the front, and the walls forward of the rear bogie. But not over the engine or wheel wells. God forbid you ever have a fire...that foam lets off cyanide gas when it burns, and it is highly combustible.
But like I said, it's a personal choice and I mean no offense to those who love it. The objective is to insulate (ya, we know that) but you want to prevent condensation. That means airtight and/or vented.
Everyone has their own method, this is simply my humble opinion. 

[neoneddy]

The house batteries I'm think at least 10 maybe 12 AGM batteries in a 24V configuration I'd love to do LiFe, but I think that's an upgrade I could make later.

One of the reasons that I wanted to build my own conversion vs buying used is because of the advancements in technology.  I love diesel, don't get me wrong, but I believe isn't a good genset $5-10k?   What about ones like the Robin RGD 5000?  There is one on local craigslist for $1000 or so.

If I'm going to spend money, I'd rather buy into more solar and small generator to supplement, vs the other way around.   I know I'm new and filled with optimism, hit me on the head as needed.

[daddysgirl]

You should do whatever is practical for you. Nothing is really wrong (unless it's not debatable).
I do have a question...
Why a house system with so many batteries...and 24v?

[neoneddy]

I want to make sure we can boondock effectively, we'd like to do some BLM stuff, and the Padre Island trip  most years. 

After some calculations on what 2000AH would require at 24V I've reduced it  to 1/4 to 580AH @ 24 v or so.   

Why 24v?  I'd like the bus alternator to also charge  the battery bank, We can also run twice the amperage over the same gauge wire.  The solar system will also be 24v, I have seem some that run 48 for the transmission lines to the charge controller, I might do that as well.

Attached is my thoughts right now.  Actually I'll need to do some more figuring.  I don't think I can fit those panels along side the AC units. I don't know, slow and steady is how I like to work.  Do small trials, before going all in.  Thank  you everyone.

[Jon]

The beauty of building your own conversion is you can do whatever you want. The downside is you become the test pilot if you decide you don't like the use of technology that has been used and is extremely reliable.

I can assure you that any solar or battery system set up you choose to design will likely work, but I can also assure you that in terms of cost the current systems with dual inverters, a diesel generator and at least 3 roof airs will keep you comfortable with almost no human intervention or power management issues for less money unless you ignore the cost of all the batteries you are going to need and their replacement cost when they fail prematurely because they are being worked to death..

[Geoff]

24 volts looks good on paper but it is impractical in a 12v RV world.  I took my 24v/300 amp gear driven alternator off my engine and it's been sitting on the floor of my shop for ten years.  No takers.  Instead I run a more practical 160 amp 12v truck alternator and a 40 amp 24v alternator for my starting batteries and the few 24v relays I have left.  To me, solar panels are good for keeping the batteries charged up while the bus is stored outside.  So you can't even park in the shade if you use solar panels.  Kind of self defeating.

--Geoff

[luvrbus]

I thought solar panels just need daylight not direct sunlight  where are the solar guys when you need one 

[sledhead]

I like the 24 volt system . it works better for inverters and for all the 12 volt rv needs they can be done with a 24 - 12 converter  + the idea of a small inverter generator like a honda 7000 watt or 2 x  3000 watt in pairs  will work great and use very little gas and our quiet to run . I did this on the M C I and the system worked great . the system I have now is OLD school ( 12 k diesel genne and all 12  volt inverter ) and works but the future is solar and inverters and a small generator system with more efficient heating and coiling system . but to do this it will cost more money to set it up

dave   

[lostagain]

Solar panels work great if the sun is high and bright. No so much if you are in the shade, or on a cloudy day, or up North where the sun is low. For me, the most practical and cheapest, is minimal batteries and a good size generator. A generator doesn't care what the weather is like outside.

JC

[Geoff]

24v versus 12v.  Its okay to have to spend more money to have 24v because it is more efficient.  I don't think so.

And for AC, I have three 15k Coleman rooftop units with interior ducting.  The front one blows on the driver or wherever you aim it.  One air can run off the alternator/inverter or the 8kw genset can run all three airs while charging the house batteries.  I rarely run 3 roof airs at once.  When traveling, we run two roof airs and the microwave/convection oven when we stop to eat.  This is all routine to us.

We don't need solar panels.  We can camp off our four golf cart batteries and start the generator when we need it.

--Geoff

[bevans6]

What I did, and believe me it works just fine.  24 volt house bank tied to start bank.  On the road, bus alternator (Delco 50DN) feeds both.  That is the main reason for a 24V house bank.  Second main reason is the high power cables can be a lot smaller.  House bank is designed at 250 AH at 24 volt.  Magnum 4024 inverter is run from the house bank and from the bus alternator when the bus is running, or from generator or pole plug when parked.  House AC is a single rooftop 15KBTU, runs just fine from the invertor.  All house 12v loads (which are tiny) are drawn from a center tap on the house bank with a Vanner equalizer.

In use, I start the bus, when the alternator kicks in I start the inverter, then I start the AC unit.  When I park and turn the bus off, I turn off the AC until I either start the generator or plug in.  Switching sources is fully automatic but I don't like to cycle the AC unit while it is running, it's not smart enough to always delay starting while the compressor is loaded.  So this idea works just fine if you accept the limitations, which there are a few.  My main reason for doing it this was was to use what I had (the inverter and the bus alternator) and to avoid having to buy and run a large diesel generator (I had a 3000 watt inverter generator already). 

Brian