My Kids think it’s crazy, Grandkids think it’s cool

[pdavitt]

Hi, my name is Pat Davitt, I’m a retired Systems Architect and now live in the Davis Mountains of West Texas. After much research on this forum and others I am exploring doing a “retromod” of a tandem axle, vintage airstream. The exterior will be close to stock, but the interior and systems will be completely re-designed. The title of this post is the reaction, by my family, to this idea. I’m going with the Grandkids reaction. Don’t have a wife anymore, so it’s just me and Zorro, my Australian Shepherd. Thought doing a little traveling would be a good idea.

The standard electrical system in Airstreams and other brands is what triggered the idea of a retromod. I am looking forward to participating in Air Forums and hope to get to a Rally soon, even though it will be without trailer.

To start things off, attached below is my first attempt at a Power Wiring Design for my project. Since I plan on building a new frame with new axles, weight should not be an issue.

Also, I am not thin skinned, and welcome constructive criticism. I look forward to your comments.

Pat

[uncle_bob]

Hi

Welcome !!!!

A few crazy ideas and points:

1) Separate generator input with some sort of auto start capability.

2) Charge (or not) off of the 7 pin (or something else) from the tow vehicle

3) High efficiency (DC to DC) conversion to 5V (the world lives on USB ...).

4) DC/DC conversion to the 12V rail from 48V. (same issue, much higher efficiency)

5) Isolation / switching to pull the 48V straight from the bulk AC (get the battery out of the act so the battery charge can be properly managed)

6) A 12V "chassis" battery. You will have stuff like power jacks, power stabilizers, propane detectors, smoke detectors, emergency brakes, and the like that pretty much expect 12V. Running the 48V to 12V converter for some or all of this likely isn't what you want to do.

7) Do a carefull analysis of what you need / want / wish to run on the system. Is AC a requirement? If so how much AC? Same thing for your other loads.

8) Unless you are doing something "unusual", it's rare to have a 240V load in an AS. Pretty much everything will run off of 120V. The standard 240V 50A feed does not actually get used as 240V, it's just split into two 120's.

9) What ever you do for cells on the 48V stack, you *do* want balancing, per cell monitoring, and temperature sensing as part of the setup.

10) If your cell stack design involves parallel cells, consider the possibility of two independent stacks. It's a higher cost / higher reliability decision.

Yes, this could go on and on .... enough for now !!!

Bob

[pdavitt]

Bob,

Thanks for your input. Look forward to participating in the forums.

I have listed the Power Center components below.

COMPLETE POWER CENTER - Outback FLEXpower Radian FPR-8048A
Which includes:
Load Center for Radian 8048A Inverter Outback GSLC175PV1-120/240
INVERTER/CHARGER Outback GS-8048A
Charge Controller Outback FM-80
Communications Hub Outback HUB 10.3
System Programming and Management Outback MATE 3


Responses to your comments are below:

1) Separate generator input with some sort of auto start capability.
--> The Outback system has this capability. Am going back and forth on whether to use it or not.

2) Charge (or not) off of the 7 pin (or something else) from the tow vehicle
Would need another charge controller. One that would take a 12v input and convert to 48V output.
--> I may do that. Or, use the TV 12V to charge the 12V Generator start battery? Got to study it.

3) High efficiency (DC to DC) conversion to 5V (the world lives on USB ...).
--> Good point.

4) DC/DC conversion to the 12V rail from 48V. (same issue, much higher efficiency)
--> Originally planned to do that. My thinking now is that, even though it is less efficient, there is more system redundancy using a 240VAC to 12VDC Power Supply.
If for some reason I lose the batteries, I can power the DC buss with any AC source.

5) Isolation / switching to pull the 48V straight from the bulk AC (get the battery out of the act so it can be properly managed)
--> The Outback system has that, complete battery management, including temperature adjustment.

6) A 12V "chassis" battery. You will have stuff like power jacks, power stabilizers, propane detectors, smoke detectors, emergency brakes, and the like that pretty much expect 12V. Running the 48V to 12V converter for some or all of this likely isn't what you want to do.
--> I was planning on running all of that through the DC Circuit Breaker Panel in the diagram. Is that a bad idea? I do have a question, what is the total 12VDC power requirement for an average 27-30' Airstream?

7) Do a careful analysis of what you need / want / wish to run on the system. Is AC a requirement? If so how much AC? Same thing for your other loads.
--> Am compiling a load analysis for all AC and DC loads. Will use it to tweak the system. Yes, will have AC. However, in order to fit the solar panels on the roof, I planned to use a 18-20 KBTU Mini-Split AC system with the compressor unit on the tongue and a wall mounted air handler.

8) Unless you are doing something "unusual", it's rare to have a 240V load in an AS. Pretty much everything will run off of 120V. The standard 240V 50A feed does not actually get used as 240V, it's just split into two 120's.
--> All of the mini-split AC systems I like require 240VAC. I am also using a 240VAC to 12VDC Power Supply to help keep the split phase legs balanced.

9) What ever you do for cells on the 48V stack, you *do* want balancing, per cell monitoring, and temperature sensing as part of the setup.
10) If your cell stack design involves parallel cells, consider the possibility of two independent stacks. It's a higher cost / higher reliability decision.
--> For #9 and #10, Good points. Am still working on the battery setup. May be AGMs or Lithium. Unfortunately Lithiums may be beyond economic reality.
Conceptually I have 8 12V 200AH AGMs in series banks of 4 each, then paralleled.

Just beginning the detailed design and I want to thank you for your input. You have already helped a lot and don't know it. I read many of your posts and responses, they were invaluable in getting the design to this point.

Thanks,
Pat

[uncle_bob]

Hi

If you are going with lead acid, look at running T-105 6V batteries. They are generally the "best bet" for this sort of thing. Do add up the weight of all this. Even with a custom chassis, weight does matter. Your tow vehicle choice will narrow down quite a bit as you go from 10K to 15K to 20K pounds.

When looking at the Lithium vs Lead Acid decision, consider that you only get about 1/2 of the rated AH from the lead acid stack. You can discharge lead acid's to about 50% of capacity if you want them to last a while. Properly done lithium based stacks can be run to near zero. Lead acid's also are not quite as happy at high discharge rates as lithiums which also drives you in the same direction (2X larger stack).

Next up on the "nasty list", no matter how well you care for them, all batteries you would consider have a finite life. How long that is gets very much into "that depends". It's a reasonable bet that the lithiums will last longer. How much longer is only a guess. Some say 2X.

Yes, this sounds like a lithium battery commercial. Far from it. Lead acids are a very well proven technology. You have a century of practical experience built into your battery with them. High volume production makes them cheap. Properly vented to the outside, there aren't a lot of weird / unknown risks with them. They *are* a good choice.

12V demand on the chassis depends a *lot* on what you have on there. A "typical" unit may have a 12V blower on the furnace as a major 12V load. Some have radiant heat and no blower. The big unknown (to me) is the power required for the emergency brake setup. The trick there is a switch that activates when the hitch fails. The trailer brakes then all come on full. That sounds like <10A as a guess. It would be better to have a number than a random guess ....

One nice thing about a 48V system - courtesy of that being the telephone companies favorite voltage forever and ever there are a *ton* of parts out there for dirt cheap. Things like 48V to 5V or 48V to 12V switchers are very easy to find.

Lots to dig into !

Bob

[pdavitt]

Bob,

Yep, about digging into it. So far I figure I'm about 1 shovel full into it!

A little more of my background. For the last 6 years I've lived in an off-grid regular house. It has 6.5KW of solar panels, 14.4KW of inverters, and two 44KWH 48VDC fork lift batteries. All equipment,except the batteries, is from Outback Power and has performed flawlessly. (I have no affiliation with Outback, they just make good stuff.) Wish I could put a fork lift battery in the trailer, but they weigh about 3,300lbs apiece.

The batteries I'm looking at are Outback 12V 200NC. The URL is below:
http://www.outbackpower.com/outback-...ategory_id=537

Eight of those weigh a little over 1.000lbs.

Pat

[uncle_bob]

Hi

Your full weight budget will (of course) include some structure for supporting the batteries and the "stuff" to vent them. I'd certainly do a few sketch up's to see how they fit in a nominal floor plan. The ideal location for pretty much everything that has any real weight is in the middle of the trailer. Water tanks, axles, and big batteries all compete for the same space. Even worse, they all want to be low to the ground as well.

With a 48V system, you don't have the nutty "thick as your arm" cable requirements for long runs. That at least will let you move some of the "other stuff" a bit off center.

Again, it's not anything that *can't* be done. It's mainly a matter of pushing this here or that there. What it may do is nudge you a bit to one or the other size / design of AS to do the work on. If you are not already playing with some sort of CAD program, it's probably a good idea to pick one. AutoDesk's Fusion 360 is free and it works pretty well. You can even shoot out a mode filel and 3D print it

Bob

[pdavitt]

Bob,

You have hit upon one area about which I am woefully ignorant. The constraints for installing batteries, etc. below the floor deck level. Since I am having a custom frame built, I have a lot of flexibility, including raising the ground clearance, building in extra support, and building steel containers mounted below the floor deck with hatches in the deck for access.

My assumption is that if I am within the longitudinal middle third of the trailer, and as long as I keep the bottoms of the containers slightly above axle height, I should be ok. The belly pan would fit around the containers.

I also assume that if I want to have external door access through the skin of the trailer I need to stay above floor deck level.

Am I correct?

I am using Visio as my design program, been using it a long time for logic diagrams, systems and application design. I looked at AutoCad Lite but the learning curve was too great.

Thanks for all your help,
Pat

[uncle_bob]

Hi

Stuffing a bunch of batteries under the floor is likely to raise the floor level. How much is why you poke around with CAD Anything like this is dangerous to guess at. I'll guess you are adding 18" or so. You also need ventilation and structure as well as the battery height. It could be a bit more, it could be a bit less. A 12" battery + 2" of structure + 1" deck + 1" wire + 2" air is my rough add up.

If you have 16" wheels, the wheel wells come about 8" up into the floor. There's frame above the axle and air above the wheels so that's only a start to all this. Assuming that's not to convoluted, The takeaway is that there isn't a lot of "spare height".

Does your 18" "extra space" raise the whole trailer 18"? Probably not. It will raise it some. Whatever that raise is, your center of gravity and height overall will go up. You will also have to figure out some sort of "skirt" to cover the region. On a 9'6" starting trailer, an 18" raise would get you to 11'. That is still OK for most of the places you are likely to go (you are still shorter than a semi). If you chug around in the north east, you will need to watch the signs on railroad underpasses.

So that's plan A ...

Plan B:

Extend the "wheel well" cutouts in the trailer. You will loose internal volume. Your batteries will be off center a bit. Neither of these are good things. The advantage would be keeping the trailer fundamentally at the same height. My fear is that you simply run out of space for needed items. Back to CAD and making decisions ....

Plan C:

Face up to the fact that both plan A and B have some pretty significant costs associated with them. (very much so for A). Re-evaluate the cost based choice of Lead Acid batteries ....Going from a $20,000 custom frame / structure / skirt to a $40,000 one is cash out of pocket just like money spent on batteries. (No those numbers are not facts, they are pulled out of the air guesses.) A typical full rebuild of an AS generally clocks in above $50K plus trailer, so they aren't all that nutty though.

Bob

[pdavitt]

Bob,

Your last post caused me to re-think my battery plan. Since, as you pointed out, a complex, custom frame plus re-working the skin will be very expensive. So I'm thinking about Lithium batteries again. Would rather spend the money on batteries instead of steel and aluminum.

Did a quick internet search and I can get a 48V 200AH+ lithium for about 10K. Since my AGM plan batteries were about 5K the 15K difference is probably close to what the custom frame work would be. Two of them would be about half the weight of the AGMs and their footprint would be considerably smaller. Each of them weighs 282 lbs and is 26.77"Lx19.68"Wx11.8"H.

Thanks again for sage advice,
Pat

[uncle_bob]

Hi

I certainly would not call it a slam dunk either way. The lithium's come with a bill for electronics as well:

To get a lithium stack to run a good long life, the charge on each cell needs to be kept the same. One would think that's automatic, it's not. It gets done by little circuit cards that do the dirty work of moving charge on or off a cell to keep it "same same".

Next up are those wonderful scare movies on TV. Lithium battery bursts into flames for no reason what so ever and destroys half the planet. Lithium's can and (rarely) do catch fire. When they do it's a tough one to put out (think liquid nitrogen). Monitoring them for temperature and voltage is a good idea.

All of this is available stock from a number of outfits. You don't have to build it yourself. The point is to be sure it comes with your batteries. If it isn't stock, then it's some sort of add on item.

No matter who you get your batteries from, some will do better than others. That's just manufacturing. That makes sorting out the good guys from the not so guys a bit tough. You *do* want to get good batteries no matter what sort you go with. Working out who to buy from is "interesting".

Yes, going around in circles a bit. That's how all design work proceeds.

Bob

[pdavitt]

Bob,

So true! The brand I am looking at is Smart Battery. Also, both the Outback Charge Controller and Inverter/Charger are completely programmable to conform to Lithium battery requirements.

The specs for the 48V 200AH are below.

Nominal Voltage 51.2V
Charge Voltage 58.4V
Peak Discharge (5 Sec) 2000A
Continuous Charge / Discharge Rate 100A
Capacity (amp hours) 200AH
Capacity (watts) 2560W
Usable Capacity (AH) 216AH
Depth of Discharge 100% DOD
Reserve Minutes @ 20A 600 min
Reserve Minutes @ 50A 240 min
Self Discharge <3% per mo
Chemistry Lithium Iron Phosphate (LiFePO4)
Cell Type Cylindrical
Modular Series or Parallel Connection
Built in Automatic Battery Protection System Internal
Automatic Low Voltage Disconnect 32V
Automatic Short Circuit Protection Instant
Automatic Over Voltage Protection 63.2V
Automatic Reverse Polarity Protection Instant
Internal Cell Thermal Safety Fuse Yes
Flame Retardant Electrolyte Yes
Length Way Circuit Boards Yes
Automatic Internal Cell Balancing Yes
Automatic Fault Recovery Yes
Explosion Proof Stainless Steel Cells Yes

[Swillv8]

I'd suggest a classic motorhome they are the way to go. Also would give some airstreamers something to copy lol

[uncle_bob]

Hi

I don't see anything wrong with the numbers on those batteries (other than a typo on the capacity - watts number). Only you can answer the most basic question of: Are they big enough?

I would still stick with a 12V "chassis battery", even in a TT, in addition to the lithium stack. More or less it's KISS for things like the brakes and sensors. A single battery in the 70 to 100AH hour range would be gross overkill. I sort of like overkill when it comes to safety There is a bit of interesting wiring involved, but none of it is to nutty. You already are dealing with multiple interconnected systems.

Bob

[pdavitt]

Bob,

I assume I could use the same 12V battery, if properly specified, for generator start in addition to the items you mentioned. Adding a small 4 stage charger to the system should not be a problem.

Thanks,
Pat

[Foiled Again]

When it comes to electricity and batteries I admit I'm totally willing to defer to anyone who can use a wire stripper with skill.

My question therefore is simply - what are you planning to USE your Airstream for once you've finished it? It sounds like it'll be equipped for a zombie apocalypse bugout survival pod. Having seen the hail and tornados you can get in Texas, I see the appeal...but a semi with an intermodal trailer might be better built for a survival scenario.

Nothing wrong with your choices if you've got the money, time, interest and skills - but it's a long complex job and it is easy to get frustrated. Just an observation not a wet blanket, you could just blow the same amount of cash on a new Airstream and be traveling next week.🎵🎶🎵

Wanna spend long periods off grid? Smokeless Joe did a nifty tow vehicle - a Sprinter flatbed carrying a big diesel generator and a Mini car for running around when he just wanted a daily driver. His thread would make good reading for you. Just search "contemporizing". What impressed me most was that he got all his appliances to run on diesel, even the stovetop.
He also was an early convert to split system a/c units.

Whatever you do have fun!

Paula

[uncle_bob]

Originally Posted by pdavitt

Bob,

I assume I could use the same 12V battery, if properly specified, for generator start in addition to the items you mentioned. Adding a small 4 stage charger to the system should not be a problem.

Thanks,
Pat

Hi

You certainly could use it for a variety of intermittent power needs. To me the emergency braking is the biggie. It's very unlikely you will ever need it. If you do need it, you want to be sure it works. You also don't want to get into a massive hassle if that's an "inspection item" on a trailer in your state. There's absolutely zero consistency about even if a trailer gets inspected, let alone what they inspect. It's very much a state by state thing.

Bob

[pdavitt]

Paula,

LOL! Loved your post. No, no Doomsday or Zombie Apocalypse scenario. I retired about two years ago from a high stress, project oriented job and moved five years ago to the Davis Mountains in West Texas. I actually "retired" five years ago, but the company kept me on the payroll for another three years. "Working from home."

I discovered I needed a stressful project to so I could really enjoy life again. The stressful part of this project is I am using my own money instead of the company's. I wanted to get a Airstream travel trailer, to mostly, full-time travel the country. Sooo, I decided to design and have built, my ultimate Airstream. I am systems guy so starting with the electrical made sense.

Thanks for your comments, and wish me luck.

Pat

[pdavitt]

Bob,

Thanks for your thoughts. I have designed in a 12V generator starting, emergency brake actuator battery. Plan to keep all the other DC items you mentioned on the main DC breaker panel.

The Outback system has an AUX RELAY out that activates when the system detects an AC source. Going to use this functionality control a NC relay that sets the Neutral/Ground bond. Below is my latest schematic.

Pat

[slowmover]

Introduced simply as a point of reference, the propane system is the reason we have self-contained trailers. Maximizing that is greatest utility.

As to boondocking, water capacity matters most.

The electrical system is so far down in importance as to be almost negligible. Seriously.

For general camping and extended stays it is the first two that matter.

It's not opinion.

The problems are weight, safety and utility.

Propane can't be touched in this regard.

Start again by reviewing, "what is camping"?

Shirt-sleeve weather. Cooking and bathing. Space heating (minimally, as one is outdoors as much as possible).

Take your time.

I recommend a plan that shows maximum time away from any re-supply to shore up the ends. X-people over Y-nights. No trips to the store.

What this will show is a balanced approach.

The point to one of these trailers is to add some food and clothing to travel. Similar to stock integrated systems.

For someone wanting to recreate "home" as currently configured, a diesel bus is the method.

Solar is a marginal gain at high expense. (Several panels and best batteries is about it fir changes).

Keep reading.

IMO, time spent building may be fun. It'll be years long. And amateur interior design mistakes are the inevitable result (that's a full time staffing position). Practicality will be sacrificed.

Plenty of great trailers ten years old. Modify one instead fir "better" electrical capacity. Go camping, and be years ahead.

Travel is the thing.

Good luck

.

.

[uncle_bob]

Hi

I'm not sure I would do a relay for the ground / neutral thing. One of the great advantages of a fully isolated converter approach is that you can get around these sort of issues. The guys who do this on boats are *very* big on that part of it.

Bob