Boondocking --- Average AH consumption/day?

[SJ-Chris]

I'm going to be adding solar to my 2015 Class C Majestic 28a. I currently have 2 lead acid batteries that state they have 122AH capacity each (from Walmart). I'm trying to figure out if I should add 100w or 200w. My assumption is that 100w of solar will on average add about 30AH/day back into the batteries.

If you have a battery monitor and happen to know on average how many AH/day you use when boondocking I'd love to hear. Let's assume you are NOT using your furnace at night (summer camping) and that you aren't plugged in or solar charging. Yes, I know that everyone's use will be different and that's what I'm curious to see. If you could, please share what your rig is, what your battery bank capacity is, and approximately how many AH/day you go through. Perhaps tell us what sort of things you are running in your RV, and whether you try to be energy frugal or if you consume with reckless abandon (lol!).

Will be interesting to see various people's input! In the end, I'll probably just add 200w as a likely overkill for most typical usage.

Enjoy!
Chris

[MEXICOWANDERER]

The millions of "What if's" are called "permutations" and it is illogical to try to predict them all.

Install, then learn your systems quirks, always relaying on a weak sister battery cell and a hydrometer. Doing so will infuse a self education called "Trends and Tendencies" of your battery and electrical system. For instance with a flooded battery system, too rapid a voltage sag versus amp hours consumed may be it's time to desulphate or "equalize the batteries".

I walk up to the battery shed, spend 10 seconds with a meter then wander off in search of tropical fruit for my breakfast. Once a week I dip the weak sister cell near the door.

[2oldman]

..

[StirCrazy]

I have 480 watts of solar on my 40 foot 5th a 2000 watt inverter and 470 AH of ^v deep cycle batteries. if we dont go nuts we are pretty much self suficent ie make a couple cups of coffee with the keurieg in the morning, let the kids watch a movie at night. even running the furnace in the spring and fall is ok. Idealy I would like to replace my 160 watt pannels with 325 watt pannels and I think it would be even better.

Steve

[MEXICOWANDERER]

Multiple charging sources only affect battery amperage acceptance as voltage rises. Saturation charging means adding more chargers set at the same voltage as the saturation voltage won't yield one more amp. The monster ferroresonant charger is reconnected to provide 29.10 volts. The Trace is set to 30 volts maximum and the voltage regulator on the Lambordini Delco is maxed at 30.

When I put the big charger online it may put out 480 amps and bring voltage to 26.7. The Trace inverter has a charging capacity of 120 amps but not if it is trying to dump into 26.7 volts which is the same as 13.. volts on a six cell system. The Lombardini is air cooled so sometimes I share principal load with the Kubota. This knocks amperage down to less than 300x2 amps (shared). Voltage remains saturated because I hand adjust each charger. Finals are 28.8 volts. Tweaking back from 30. When you reach regulated voltage even at low gravity start points that I deemed as "Saturated Charging" Not recommended for thin plate batteries.

My own rule is the use solar when the highest potential generating power proves to be lower than maximum saturated charging acceptance. For me it means generator charging in the early morning then solar at mid morning to sundown.

[BFL13]

If from 50-70% SOC at 14.4v(say) the batts will accept at least 30 amps, AND both solar and charger (powered by the gen) are at the same voltage set at 14.4, then yes, they will add their amps so you get 30.

If the solar is at say 14.2 and the charger is at 14.6, then as the battery voltage rises closer to 14.2, the solar amps will taper, but the charger's will stay at 20, so you get less than 30 total, tapering till the battery reaches 14.2 and no more amps from solar. Now the 20 from the charger keeps raising the battery voltage until it gets close to 14.6 and amps start to taper from 20.

Once battery acceptance is down to what one charger can do, you can yank the other charger. Say you have two equal voltage chargers doing 20 amps each for 40 amps and they get down to 10 each. You can keep them going as each does 9,8,7 etc, or yank one and it will jump back to 20 and taper doing 18, 16, 14, etc by itself.

For best success you need to have adjustable voltage chargers, so you can make them all the same set voltage to keep adding their amps all the way so one does not drop out part way along. Most converters are not adjustable (PowerMax ones are though) but many solar controllers are, so most likely you will adjust your controller to match the converter's voltage.

I think you might like my old ugly graph everyone must be getting tired of 🙂

[SJ-Chris]

With my Aili battery monitor installed, I'll be able to answer this questions once I install the solar and run a test, but I'm sure some of you will be able to provide an answer already.....

Do multiple charging sources (ie. generator PLUS solar) have a cumulative effect on how quickly your batteries can get charged? I understand that in theory there could be limits, but I don't think we are in that range here...

Let's assume your battery is between 50-70% state of charge.

Let's say your 200w solar is adding 10amps/hr charge to your batteries on it's own.

Let's also say that your generator is adding 20amps/hr charge to your batteries on it's own. (Yes, I know that as you get closer to 100% full the charge rate will slow down, but let's assume we are not close to 100% yet).

In the above example, if you had your solar charging AND your generator on at the same time, would it be providing 10+20=30amps/hr worth of charge to your batteries? Or do the two systems somehow/somewhat interfere with each other?

Just curious...

Thanks!
Chris

[BFL13]

wopachop wrote:
It was 5.51a coming from the panel and 3.3a to the trailer.
Took that back at noon. Only thing running is my ab fridge and this laptop plugged into a small inverter.

You guys are smart. How much of that 2a difference would you expect to be going into the batteries? Is a good percentage just wasted heat? Or were both of those true? Yes going into the batteries....and yes wasted heat?

They are (2) costco 6v.

Not clear as stated. "From the panel" and "to the trailer" does not quite mean "from the controller to the trailer" and "to the battery out of what comes from the controller"

Wasted heat is inside the battery after the amps get to the battery posts. (charging efficiency)

I got a 6 amp DC draw with my 60w laptop on inverter being powered by trailer batteries. If I had 5 amps of solar at the time, it would all be going to the inverter powering the laptop and another amp from the batteries to make 6 total.

[time2roll]

No idea on AH usage. 400AH battery stays charged with 600W solar. Monitor is a simple voltmeter. If I see 14.2+ I know I am good for another two+ days. No worries.

[SJ-Chris]

wopachop wrote:
It was 5.51a coming from the panel and 3.3a to the trailer.
Took that back at noon. Only thing running is my ab fridge and this laptop plugged into a small inverter.

You guys are smart. How much of that 2a difference would you expect to be going into the batteries? Is a good percentage just wasted heat? Or were both of those true? Yes going into the batteries....and yes wasted heat?

They are (2) costco 6v.

I recently solved this mystery, and all battery related guessing, by adding a ~$45 battery monitor. Here is a recent post:
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30168196.cfm
Let's you know exactly what is going into or out of your battery and the current state of charge (% and how many AH you have in your battery bank at any given time). Fun stuff! #nerdout

-Chris

[wopachop]

Is that a joke about making a mistake? Quite possible its been a long fun weekend. Teach me even if you make fun at the same time. Happens all the time. A lot of my friends are mechanics who laugh until they finally understand the question and then they give good advice.

[3_tons]

“Actual Results May Vary By User”......

[wopachop]

It was 5.51a coming from the panel and 3.3a to the trailer.
Took that back at noon. Only thing running is my ab fridge and this laptop plugged into a small inverter.

You guys are smart. How much of that 2a difference would you expect to be going into the batteries? Is a good percentage just wasted heat? Or were both of those true? Yes going into the batteries....and yes wasted heat?

They are (2) costco 6v.

[wopachop]

Good point. Will go outside and do a clamp reading real quick.

[2oldman]

BFL13 wrote:
the other loads get any amps being supplied first, then the battery gets what's left over.

Yeah. A battery monitor is a really nice tool.