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Old 10-28-2020, 12:05 PM   #1
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Battery SOC, battery options, strategies, etc.

Hello battery and power experts,

I've been reading through the battery threads, the solar threads, and the generator threads as I think about power management and my long term goals. I've found that my wife and I tend to boondock more often than not, and it's causing me to think about how to manage power more effectively. I'm not especially interested portable generators, and some of the campgrounds where we've camped don't allow them. I would consider one, but it's not my first choice.

We have a 2020 International 23 FB with an aftermarket Zamp solar package that consists of two 90 W panels on the forward portion of the roof, and a Zamp solar controller. It appears to be working relatively well for us so far, although we have encountered shady campgrounds on more than one occasion that limit our recharging ability. We have two AGM batteries at this point in time.

On our inaugural run with our new Airstream, I knew relatively little about AGM batteries, state of charge for these batteries, etc. We own an electric vehicle, and I'm relatively knowledgable about charging, SOC, etc. in that application. I'm finding it to be very different for Airstream batteries. On our shakedown cruise, we camped for 5 days/4 nights in a relatively shady location, and our batteries were discharged to approximately 11.4 V, which I now understand was probably in the SOC range of 10 - 15%. My understanding is that this deep cycle was probably detrimental to the overall health of my batteries, but I had no idea at the time. If you're not familiar with 12 V battery systems, then the natural assumption is that 0 V = 0% SOC, and that 11.4V is probably 75% SOC or more. I now know that it's isn't the case. I've seen information online that indicates that it's not a good idea to let SOC drop below 50% if possible. I've located a few tables or charts online that try to show SOC relative to voltage, but the charts on the web vary considerably. Below you'll an example of one that I've stumbled across online. I'd love to hear thoughts or comments on this information.

As I've thought about upgrading my system, there are a few options that I'm considering.
  • Upgrading my existing AGM batteries to LiFePO4 batteries
  • Adding 2 - 4 additional 90 W Zamp solar panels to my roof
  • Adding a portable solar panel to enhance my ability to recharge my batteries, like the Zamp 230 W unit
  • Adding a generator converted to run on LP gas, perhaps combined with a soft start unit for my A/C
  • Adding additional LiFePO4 batteries, and moving them inside the trailer in the storage space under the bed

My questions for this esteemed group are: Which of these strategies make the most sense? Can I simply swap my two AGM batteries for LiFePO4 and install them in the stock battery box, or will I need to move them inside due to challenges when camping in colder weather? Will this offer a significant benefit over my AGM batteries? Is there an option that would allow me limited use of the A/C on batteries - perhaps a bank of LiFePO4 batteries and an upgraded inverter? What's the ideal combination of these things to allow me to camp the way that I want?

I'm leaning towards adding more panels to the roof and upgrading to LiFePO4 batteries, perhaps inside under the bed. I know that's not a cheap option, and so there will likely be a set of steps to get there.

Thanks for any advice, and thanks for reading this long post. I appreciate any thoughts or comments.
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Old 10-28-2020, 12:47 PM   #2
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That is not the voltage table I would use. Find one that has about 12.6 resting for a full charge.
As for your question, great question with a thousand answers possible. You really should sit down and figure out your anticipated amp-hour usage in a day or a the time you would be out, then you can decide what will meet your needs. If money is no object then clearly Lithium, a nice inverter/charger, more solar, a new solar controller is the premier solution. I did that and have never regretted the decision.
I will say this about solar. We camp in mostly tree-shaded locations and roof-top solar is over rated. I bought a large portable panel that I plug in and it makes a big difference. Though, even with that, if the weather is cold and I run the furnace, mostly in the AM, I need a small generator to recharge after about 5 days.
There are some who have installed 6 solar panels, a huge amount of Lithium battery capacity, and spent way more. They never have to worry about capacity issues. Oh, and you cannot charge your Lithiums if they are below freezing, although you can discharge them. So mine are inside.
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Old 10-28-2020, 01:00 PM   #3
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Thanks for the response. I appreciate it. We camp in the mountains frequently, and even in the summer it can drop below freezing at night. It typically warms up during the day and we have lots of sunny days in Colorado, so I'm thinking the portable solar panel might be a good start.
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Old 10-28-2020, 01:25 PM   #4
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Perhaps this SOC table is more reflective of reality. Thoughts?
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Old 10-28-2020, 03:27 PM   #5
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Yeah! Although I always used 12.2 as 50%, but I now have Lithium and don't care.
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Old 10-28-2020, 03:47 PM   #6
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Don't worry too much about your AGM batteries. Part of their advantage over run of the mill lead acid batts is their robustness and deeper discharge capability. Yes, it's always true for almost every chemistry that depth of discharge has an impact on battery life, but the key is degree, and your AGMs are probably still capable of a very full life.

Solar - that is the key. With the right setup with additional margin to generate above and beyond nominal use, may in itself solve 80% of your desires. Ultimately power has to come from somewhere. Batteries are a reserve. With excess solar, majority of use can be directly from live production. Leaving less dependency on battery reserves for night time use, or extended shade/weather days. I would focus your investment there.

With enough solar, you may very well be able to support some A/C use with an inverter.

For higher power devices, i.e. greater than 800 watts, that may be the domain of a high performance lithium battery.

The predominant strategy today has been to replace the main batteries, or what I call house battery. I have a different opinion in that using high performance lithium for household loads is a expensive and imprudent proposition. AGMs and Lead Acid serve house loads fine. To replace that battery with actual expanded capacity, is even more expensive.

I would consider a higher performance secondary battery bank based on lithium to support high draw devices. This expands capability while also increasing overall capacity. Without money and effort spent replacing capability and capacity that exists and works well. I have performance equivalent to some systems costing 5 figures, for less than $2k. Or about $1k to batts, and $1k to solar. Reference the lithium upgrade link in my sig.
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Old 10-28-2020, 03:59 PM   #7
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With a brand new trailer I would, get to know the trailer, go camping and replace the AGM's down the road if necessary, then contemplate #3 & #4. By then all these today "options" will obsolete.

POI...our Lifeline AGM's lasted 11 Seasons with a few below 11.5v 'mistakes'.

Bob
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Old 10-28-2020, 05:02 PM   #8
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Thanks everyone for your comments and advice.
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Old 10-28-2020, 10:35 PM   #9
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Wow pteck... I’ve read your thread on the Goal Zero product. That’s very interesting stuff!

As an interim step, perhaps I could purchase some portable solar panels, purchase a Goal Zero battery system, and use it in place of a generator. Interesting possibilities there...
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Old 10-29-2020, 12:48 AM   #10
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hello Dennis, welcome to the great world of solar! i still ues my AGMs, although they are 10 yrs old and getting tired. i use a portable solar array that i made my self. all types of panels, controllers. now is the time for solar- new tech in batteries, panels ect. and i always have my generator for back-up. good luck, and keep us posted. kurt
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Old 10-29-2020, 06:44 AM   #11
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Quote:
Originally Posted by Dennis C View Post
Wow pteck... Iíve read your thread on the Goal Zero product. Thatís very interesting stuff!

As an interim step, perhaps I could purchase some portable solar panels, purchase a Goal Zero battery system, and use it in place of a generator. Interesting possibilities there...
The Goal Zero 1000 did not come close to 'replacing' our generator.
Even with 360w of solar the genset was needed to charge on cloudy days. (Was able to return it to Amazon)
POI...plus, it is only plug & play with GZ panels, it did not work with our Zamp Portable Suitcase panels without modifications. (luckily I didn't make them permanent).

IMHO... the GZ is an overpriced battery taking up valuable space.
In addition the Customer Service at GZ sux, it took 3mos to get the hazardous cargo return label causing an unacceptable delay in the refund from Amazon. 😖

Bob
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Old 10-29-2020, 08:34 AM   #12
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I'm wondering if a bigger Goal Zero unit might work better in that regard...

After thinking about this thread and talking with my wife, I'm leaning at this point towards buying the Zamp 230 W briefcase portable solar panel and trying that out next year. It's rare that we need anything like the microwave or the television when we camp, and our use of the air conditioning is fairly rare also. If I can keep my AGMs topped up with a portable solar panel, that might be enough for now.
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Old 10-29-2020, 08:44 AM   #13
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If you want to dry camp with a basic trailer, high demand appliances like A/C or even a toaster are out. The upside is that a solar panel should easily recharge for basic use like lights, TV, and so on. The more you use in a day, the more you need to think about something to recharge the batteries or adding more battery capacity. Good plan to start with portable solar and see how it works out.
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Old 10-29-2020, 08:58 AM   #14
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We haven't seen a need to use the microwave, the television, or air conditioning when boon docking. In fact, I've never used the inverter in the trailer. My needs are more along the lines of running the lights, charging our phones/tablets, running the water pump, and occasionally running the furnace.

Quick question - If I add a Zamp 230 W portable panel, does that add to the aftermarket 180 W Zamp panels on the roof, giving me 410 W to charge my batteries? Or does the portable panel bypass the 180 W panels on the roof, giving me 230 W to charge my batteries?
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Old 10-29-2020, 09:19 AM   #15
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I cannot say exactly how your trailer is wired, but the usual method is it adds to it. The portable panel probably has its own controller and the wiring may go directly to the battery bus. Some will tell you that the portable panel controller and the stock installed solar controller will fight each other. I can tell you from my personal experience, that is not the case. You will get the full available amps from all of the panels.
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Old 10-29-2020, 09:25 AM   #16
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Quote:
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We haven't seen a need to use the microwave, the television, or air conditioning when boon docking. In fact, I've never used the inverter in the trailer. My needs are more along the lines of running the lights, charging our phones/tablets, running the water pump, and occasionally running the furnace.

Quick question - If I add a Zamp 230 W portable panel, does that add to the aftermarket 180 W Zamp panels on the roof, giving me 410 W to charge my batteries? Or does the portable panel bypass the 180 W panels on the roof, giving me 230 W to charge my batteries?
Once again...I would use the panels you have, get a baseline of use and add another suitcase if needed.
We have two Zamp 180w panels, charging thru the 7-pin umbilical.
You shouldn't have a problem adding another suitcase.
No "fighting" in our use either.

Bob
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Screenshot of our two panels charging together...
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Old 10-29-2020, 09:52 AM   #17
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I looked into the exact same thing and spoke at length to a technician at AM Solar about the possibility. What I learned is that mismatched solar panels fight each other tending to produce power at the level of the weakest panel when run through the same charge controller. The fix is to run the portable panels through its own charge controller directly into the battery. However this bypasses the house system so that it won't capture the measurement of amp hours inputted by the portable panels unless the portable system is also wired through the ground shunt.

The other issue is voltage drop over distance. Most portable panels have relativly short and lightweight extension cords. One way around this somewhat is to replace the cord with a very heavy duty cable or rewire the two portable panels in series to make a higher voltage then mount the charge controller in the trailer. Probably have to buy a new charge controller because the one on the portable panel wont be capable of handling the higher input voltage.
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Old 10-29-2020, 10:33 AM   #18
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We ditch the 6v golf cart batteries put two SOK lithium under the front lounge, add the lithium charge controller to our IOTA converter/charger, kill switch, 80ANL fuse, used #2 wire. We had existing solar 200w on the roof + 160w suitcase (see Robert Cross above on how to wire the suitcase) and a AiLi Voltmeter Ampmeter 80V 350A meter (complete with shunt). The upgrade was about $2000 Canadian - or about $1600US -

I should mention all we do is Boondock - usually 14 day trips 5-6 times May - Sept OHYES we do carry a Champion 3400 LP genny for those sunless skies
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Old 10-29-2020, 10:43 AM   #19
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Hi

For solar, your best bet by far is to put more panels on the roof. Pack as many up there as you can practically get. Running them that way, into a single controller eliminates the two controller spiral of death. It also eliminates the need to deploy and re-pack portable panels.

We run lithiums in the battery box *and* inside the trailer. I do have the ability to disconnect the battery box if needed. With the BMS in the batteries working as it does, that has never been needed.

Going from AGM to lithium will roughly double your "battery run time". Dropping another pair under the bed will double that number. Is the value of this worth the cost? Only you can make that decision.

A small Honda 1KW generator is an easy item to pack (small and light weight). They also are amazingly quiet (even for a Honda ...). 1KW is plenty to run any normal converter / charger to top up your batteries. With lithiums, charging is fast and a couple hours run in the middle of the day would take care of things quite well ....

Fun !!

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Old 10-29-2020, 10:50 AM   #20
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Typically if you plug in external panels to a factory connection on the outside of the trailer, then you must have a charge controller on the panels in order for them to be able to charge your batteries. Alternatively, you could have a charge controller inside the trailer wired to the outside connector and then you would not need an integrated charge controller with the panel. Notice that when you by a portable panel you have the option to buy it with or without charge controller depending on your setup.

You are at an inflection point of deciding how far you want to go. At the low end, you could add to the AGM array and add some solar panels. That is the least expensive and least useful route. AGM's are a huge upgrade from traditional lead acid batteries but they are still pigs in terms of weight.

If you go the lithium route, you will likely have to upgrade a number of components and wiring. It will be very expensive. Just a 100 A/hr battery is about $1000, a hybrid inverter maybe $1300, etc. If you have the components professionally installed, anticipate that the installation cost will be equal to the sum of the parts cost. So if you buy $5000 of components add $5000 for installation. Not for the faint of heart! I have not heard of anyone who took the lithium plunge who regrets it.
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