My 2019 Factory Solar experience

[Acheron2010]

2019 Flying Cloud 26 with factory 80 watt solar and two AGM batteries. 50 amp, 2 AC units.
California state park, 30 amp service, 70 degree days, 40 degree nights. Parked South/North orientation, panels on rear, northern side of trailer. No shade.

At 9PM, I went through the trailer and turned off all electrical loads possible, and switched water heater and refrigerator to propane. I disconnected shore power.

Battery shows 100% charged.
Battery voltage 13.6V at meter.
Solar amp hours 364.

Set furnace at 65 degrees. Turned on the inverter, and turned on my 4 amp Resmed CPAP machine.

Up at 3AM for a bathroom call.
Battery voltage 12.5V

6AM (dark outside) Turned off inverter. Furnace came on twice in the morning. Turned furnace up to 68 degrees
Battery life 50%
Battery voltage 12.3V
Solar voltage 1.2

7AM
Battery life 45%
Battery voltage 12.2V
Solar voltage 12.3 ?
Solar charge 0.3, red light is on.

8:30AM
Battery life 65%
Battery voltage 12.5V
Solar voltage 12.5V
Solar charge 0.3

Had to leave, came back at 12PM.
Battery life 100%
Battery voltage 13.1V
Solar voltage 13.1
Solar charge 5.0 amp
Solar amp hours 376

Turned inverter back on, been sitting here for an hour on the computer.
Battery life 90%
Battery voltage 12.7V
Solar voltage 12.7V
Solar charge 4.5 amp
Solar amp hours 381

Once I turn off the computer and inverter I expect to fully charge to 100%.

So, with good discipline, I should be able to survive more than one overnight, with good weather get a 100% charge each day. If temps drop to the 30's I either have to lower the thermostat or get a catalytic heater or...

[lewster]

80 watts of solar is basically nothing. The smallest system that I install is 200 watts (2 panels) but typically go with 400 watts for far better energy transfer. With your 80 watts of solar and your 2 smaller AGM batteries, you might be able to make it thru a night, but what happens if you run into a couple of days of clouds with no sun?

Just a thought............

[uncle_bob]

Hi

The magic stock solar display panel is trying to look at voltage and guess at battery charge state. Unless you get to 13.6V and stay there for a couple hours of charging, you likely are closer to 80% than you are to 100%. It's not that the panel is defective or that it's lying to you. It simply is doing the best it can based on a voltage reading. It has no way do tell just where in the final part of the charge cycle the battery is.

Further complicating things, the panel and charger are indoors. They have no way to tell what the battery temperature actually is. Around freezing a battery that is at the "stop using / 50% charge" point can be up around 12.6V. You do not want to go past this point. The wear and tear on the batteries goes up quickly if you do.

Bob

[AirMiles]

Thanks for sharing your solar/battery usage experience. The data seems about right based on my solar usage experience.

You got about 17 Amp Hours (Ah) of battery charge from an 80 Watt panel through 2 PM. My experience is that three times solar panel wattage is a good day and four times is a great day. Three times 80W is 240W, then divide by 13.0 average battery voltage equals 18.5 Ah on a good day. Four times 80W is 320W, divided by 13.0 average battery voltage equals 24.6 Ah on a great day. You may be able to maintain fully recharged batteries while boondocking if you can keep your usage to around 20 Ah per day. Like Lewster said, 20 Ah per day is not much. My typical daily usage is around 60 Ah and my highest days can be around 100 Ah.

Here is a table that shows "resting" battery state of charge voltages at various temperatures that Uncle_Bob was discussing: http://all-about-lead-acid-batteries...re-correction/ The problem with tables like this is that a boondocking battery is never "resting".

[uncle_bob]

Hi

The other problem with coming up with a table of voltage vs temperature is that they are very dependent on exactly what went into the plates and electrolyte in the battery. Even with a single brand of battery, there apparently are variations by region of the country....

Bob

[tschambo]

We just spent a night in Ely NV. Woke up to 14F. The furnace ran all night set at 58 degrees and my husbands CPAP. Don’t have solar. Battery read 11.8 in the am. Don’t need solar for one night. We also had lights and tv on before going to bed. 30’ Flying Cloud.

[AirMiles]

Originally Posted by tschambo

We just spent a night in Ely NV. Woke up to 14F. The furnace ran all night set at 58 degrees and my husbands CPAP. Don’t have solar. Battery read 11.8 in the am. Don’t need solar for one night. We also had lights and tv on before going to bed. 30’ Flying Cloud.

Check the battery voltage/temperature table for 11.8V at 14F. http://all-about-lead-acid-batteries...re-correction/ Your battery was at a "zero" state of charge. Basically at a level where permanent damage will occur. Of course, having solar would not have helped in this situation since much of the drawdown was after sunset.

What you will need if you continue to encounter these conditions is a battery bank with more Amp Hours or a generator to run in the evening to boost charge the battery while powering the TV.

My first set of Airstream batteries only lived for ten months from using the furnace in cold temperatures and drawing down the battery too deeply. I'm all for using a battery like a propane exchange tank - replace it when it runs out of juice. But if you continue drawing down the battery to a temperature-compensated "zero" state of charge, you will be replacing your battery very frequently. It may be more cost effective to increase the size of your battery bank rather than frequently buying new batteries.

This comment is intended to help others learn from my past mistakes.

[ROBERT CROSS]

Originally Posted by tschambo

We just spent a night in Ely NV. Woke up to 14F. The furnace ran all night set at 58 degrees and my husbands CPAP. Don’t have solar. Battery read 11.8 in the am. Don’t need solar for one night. We also had lights and tv on before going to bed. 30’ Flying Cloud.

You may very well need new batteries.
Consider running your generator until you go to bed. Get a book to read. You should be fine. 👍

Bob
🇺🇸

[Doc Foster]

Depending upon which Resmed CPAP you have, a 12 volt adaptor can be purchased, that way you would not have to run your inverter. Dang it, Airstream stopped putting in 12 volt sockets.

Something like this - https://www.resmed.com/epn/en/consum...w-output-.html

[68 Overlander]

Originally Posted by Acheron2010

So, with good discipline, I should be able to survive more than one overnight, with good weather get a 100% charge each day. If temps drop to the 30's I either have to lower the thermostat or get a catalytic heater or...

Maybe. I agree what others are saying about dynamic voltage readings. You never really know the Battery SOC until they have rested for "some" time but by that time, you have further confused the equation with more DC change, whether charge or discharge.
If you are want to get a better picture of how many amp hours you are using/replacing with solar alone (80 isn't much) you need a meter with a shunt that can total amp hours. There are several and they are all in the $200 range. Trimetric, Victron, Expion 360 will all give you the info you need.
Getting the CPAP over to the straight DC side will help too. Inverters are great but they all use up DC power to make, well dc power in this case. Your CPAP runs on DC anyway so I'd cut that middleman while you sleep. There are small Lithium battery packs that will last 3 nights before needing charged. Every AH counts.
Airstream's solar option, while better than nothing is really just teasing the consumer and not a boondocking package by any means. Good to build on but hey, you might be frugal enough to make it work for you and applaud you for trying. Good luck and thanks for the info.

[SilverWind]

I have an A&M Solar installed 500 watt panel system with two Lifeline 235 aH AGM 6 Volt Batteries on our 2017 25FB.

I was told by A&M to try not to let the batteries go below 70 percent and never to 50 percent or lower. The battery life will be appreciably reduced with that much draw down, and quality AGM batteries are very expensive.

You may be a candidate for a lithium battery system which lets you draw down pretty low without doing damage. They are very expensive and are temperature sensitive and may not charge properly in very cold weather.

Side note. The Airstream factory "solar ready" wiring system is adequate for the small wattage systems that they seem to install. A larger, more capable system will require heavier wiring and the appropriate heavier duty control systems.

I also carry a Honda 2000 generator for very cold weather heating.

[tschambo]

Guess this really shows my ignorance. I thought half the battery charge meant have the numbers o the display. Duh. We actually have a Honda 2000 generator we ran the first night with freezing temps in Jackpot but then thought with as little as the number dropped we could get away without it the 2nd night. Ha. Guess not. Thanks for educating me.

[uncle_bob]

Hi

One further hint if you are charging batteries from a generator - it takes a lot longer than you might think. Four hours of run time per day is a pretty good guess at the minimum time to keep things up to "full". Two hours in the morning and two hours in the evening is about as close as you want to cut it.

Bob

[nryn]

I’m wondering—is it possible to charge the batteries from solar and the generator at the same time or is it one or the other?

[68 Overlander]

Originally Posted by uncle_bob

Hi

One further hint if you are charging batteries from a generator - it takes a lot longer than you might think. Four hours of run time per day is a pretty good guess at the minimum time to keep things up to "full". Two hours in the morning and two hours in the evening is about as close as you want to cut it.

Bob

I’ve always used the 50-90% concept when boondocking for a few days. It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high. I usually sacrifice that 10% and save it for when I get back to shore power and can charge over night. That keeps my gen run time to ~ 2 hours per day.
Solar certainly does help.

[uncle_bob]

Originally Posted by nryn

I’m wondering—is it possible to charge the batteries from solar and the generator at the same time or is it one or the other?

Hi

Simple answer - it will be one or the other. In most cases, that will mean it all comes from the converter / charger. That's not all bad. Your converter / charger should put out 30 to 50A into the batteries. The 5A or so that an 80W panel will deliver is pretty much nothing by comparison.

Charging lead acid's is not all about peak current. It takes a *long* time to get from 80% charged to >=100% (yes batteries can go past 100% rated charge level). Since you stop using at 50%, the difference between 80% and 100% is almost twice the usable battery.

Bob

[nryn]

Ok that’s what I figured. Thanks, uncle bob.

[68 Overlander]

Nryn,
When we test this in the shop, it is usually the converter however not always. When the battery bank is large enough to accept the full rated output of the converter, say 60 amps, and an additional charge source is added, the current will increase to the point where the battery internal resistance will not accept any more. Might only be a few more amps or maybe more but it will begin to taper rather quick as the resistance builds.
A lot of toy haulers and motor homes delivered over the years with huge battery banks have 2 converters wired in parallel to handle the duty of a large bank plus the normal loads of the accessories.
As I’m sure you know it’s a shared load. If you have a 55 amp converter like Airstream uses and are consuming 10 amps for lighting etc, you have derated your charger to 45 amps.
That said in your typical configuration in an Airstream with a pair of interstate group 24s I would be surprised if you ever saw more than 40-45 amps delivered to those batteries say 50% discharged but maybe. It would be brief if you did and would begin to taper.

[Paprika]

"It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high."

This is one way in which lithium batteries have a big advantage: they can bulk-charge at full speed right up until they're full. That long absorb period that all lead-acid batteries suffer through, during which juice is being fed to the battery more and more slowly, is all but eliminated.

I'm not saying everybody needs lithium. They're expensive as heck, and they have some drawbacks of their own. But when it comes to charging, they're a lot faster, because the time-consuming absorb phase is not necessary.

[68 Overlander]

Originally Posted by Paprika

"It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high."

This is one way in which lithium batteries have a big advantage: they can bulk-charge at full speed right up until they're full. That long absorb period that all lead-acid batteries suffer through, during which juice is being fed to the battery more and more slowly, is all but eliminated.

I'm not saying everybody needs lithium. They're expensive as heck, and they have some drawbacks of their own. But when it comes to charging, they're a lot faster, because the time-consuming absorb phase is not necessary.

I totally agree with that Paprika. We are all students of the benefits of each now as we were when AGM came out. Getting easier for those that spend a lot of time boondocking to justify upfront cost.