How long will my batteries last...

[ROBERT CROSS]

Originally Posted by Ella

Appreciate the tip, but that is more thought than I am willing to give it. One of the reasons for switching to heated lithium is that we will have more power than we need and won’t have to worry about the temperature / weather as much. Our Airstream is most definitely a means to and end. It is the hiking, seeing new places, and eating good food that we are after and the Airstream is tool we use to get there.

What, if anything, is the advantage of a heated lithium battery?

How does a 100a heated have more power than an un-heated when off SP?

Does it heat itself?

If you don't camp below 24*f what are the advantages?

We don't often 'camp' with full hook-up's in freezing temps...like never.

Bob
🇺🇸

[uncle_bob]

Originally Posted by SuperTrouper

Hi Ella,

If your 27 is like my 27, the black and grey tanks are about the same size. We can extend our stay several days by washing dishes in a collapsible tub and pouring the the dishwater down the toilet saving the grey tank for showers and hand washing. Just gotta be careful not to leave silverware in the soapy tub water when pouring. I have data on this. I also have a flexible "grabber" with a magnet for these types of "fishing" expeditions. - Brad

Hi

Lithiums do have issues with temperature, even the ones with heaters.

Get a shunt based monitor for the batteries. The Victron BMV 712 and Smart Shunt are good options. They take out a lot of the guessing on any battery (lead acid or lithium). If you get the optional temperature probe, they will let you know what the battery temperature is .... very handy ...

Bob

[uncle_bob]

Originally Posted by ROBERT CROSS

What, if anything, is the advantage of a heated lithium battery?

How does a 100a heated have more power than an un-heated when off SP?

Does it heat itself?

If you don't camp below 24*f what are the advantages?

We don't often 'camp' with full hook-up's in freezing temps...like never.

Bob
🇺🇸

Hi

Heated lithiums get the charge temperatures "in line" with what AS states is the temperature range of the RV when occupied and the furnace is running. If you want everything to line up, it lets you check that check box.

There may be a planet somewhere that hits minimum temps at high noon. (so never say "everywhere" ... ). Where I camp and where I've camped for the last 60+ years, it gets colder at night and warmer during the day. Seems there's something about cloud cover and humidity involved as well.

If you are getting up at 4AM to run the generator to charge your lithiums *please* don't camp near me. I'm really grumpy that early in the morning Somehow, I don't think I'm the only one in this category. The rest of your crew likely also agrees with me ...

If you are on shore power, the BMS will cut off charging to a cold battery. There is no problem staying hooked up overnight. If by some chance solar fired up in the middle of the night, the BMS would protect against it as well. Yes, you could leave the heaters on all the time. Sounds like a great way to run your batteries flat in no time ....

Is there a use for the heaters? Sure, but it's not a big one.

Bob

[ROBERT CROSS]

Originally Posted by Jason P M

Hi - I have a 2021 GT 25 FBT with 2 AGM batteries and 180 watts of factory solar. Frig is the standard 2-way 12v/110v 6.8 cu. ft. electric. It's been in the low 50s at night in the Northeast the last few weeks. Assuming I am boondocking and running primarily just the frig, propane furnace and lights, how long would you estimate that my batteries would last? Thanks!

A semi intelligent proclamation, half of the evening, overnight, and an hour the morning, and you're done.
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re....Bob 1 Thank's I reached the same conclusion, with much less brain pocket capacity.
The way we use the AS, heating the batt's just didn't add up, the heat doesn't just magically appear it has to be produced somehow.

Bob
🇺🇸

[jimdelane]

Here is a link to a graph showing capacity vs temp. The drop in capacity is not near as significant as in LA/AGM - about 15% from 68F (20C) to -4F (-20C) at a 1C discharge rate (100A on 100ah battery).
If you are concerned about the cold - build a well insulated battery box to store the batteries in.

Purchase a battery with low temp charge protection.

You can add a 12V heat pad and thermostat or buy a heated battery.

Keep in mind that when temps drop enough, the battery thermostat will kick on and start draining the battery.

With solar, gen or shore power, odds are that drain will not be much of an issue. Lithiums can be run down 80-90% without issue. Do an energy audit and know what you useage is and build the bank accordingy.

https://gwl-power.tumblr.com/post/13...-agm-the-graph

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Digital LED Temperature Controller Module, XH-W3001 Thermostat Switch with Waterproof Probe, Programmable Heating Cooling Thermostat (12V 10A 120W)
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Design Engineering 010480 Cell Saver Battery Insulation Kit
https://www.amazon.com/Design-Engine...99216174&psc=1

[uncle_bob]

Hi

Most "built in" battery heaters only get the battery up to the high 40's (F) before they let it cool back down to the low 30's. How much current they pull very much depends on how cold it is. A coupe of amps (per battery) is not uncommon for a built in.

If you are trying to heat from outside the batteries, you will use a lot more power.

Taking the 15% above to be the magic number, you would need to heat up to 70F to get back all that "lost" capacity. You are now into the several amps per battery range. How that translates to amp hours ... that depends.

If you have two batteries and each heater pulls 5A to get to 70F from 20F, and it runs 25% of the time to do that ... yikes ... You are running 2.5AH to get back 30AH. Run like that for a day and you are way over on the negative side of the ledger ..... not wise ....

Bob

[Jason P M]

Originally Posted by DKB_SATX

Re: the voltage guesstimator inside your trailer: While it's useful to have this voltage meter to get a rough idea of what's going on with the system, it requires some calibration of the user to refine its accuracy.

Voltage is an imprecise indicator of state-of-charge in the first place (it's affected by temperature and by how recently a charge or load has been placed on the battery.) The accuracy of the meter inside the Airstream is further hampered by where it's taking the measurement (resistance of wiring and connections), the calibration of the meter itself or both.

With very little 12v load, my meter inside tends indicate around 0.1v low compared to a good multimeter at the battery posts. Before you dismiss that, remember that the "useful range" of float voltage on the batteries is from 12.6v (fully charged) to around 12.0v (50% SoC) so now that 0.1v error represents around 15% of usable capacity. With both roof fans running the difference is closer to 0.2v.

Further complicating things is the "float voltage" I mentioned above. While the fridge compressor is running (or a vent fan or some other fairly large load) the battery voltage will be significantly below its "float" (or resting) voltage which gives you a rough guess as to state of charge. The good thing about this is that your estimate of run time will be very conservative if you're not careful... the bad thing is that it can contribute to "range anxiety" and have you thinking everything's going to go dark well before it actually might.

If you're going to rely heavily on the 12v system, a shunt-based battery monitor like the Victron BMV-712 or the old faithful TriMetric will tell you what's really in there.

What is the difference between the Victron BMV-712 and the Victron MPPT that comes with the factory solar package? The MPPT seems to give a bunch of various input and output readings.

[DKB_SATX]

Originally Posted by Jason P M

What is the difference between the Victron BMV-712 and the Victron MPPT that comes with the factory solar package? The MPPT seems to give a bunch of various input and output readings.

I don't know exactly what features the Victron solar controllers include... if they have a shunt-based battery systems monitor, they'd probably give you all the functionality of the BMV-712. Hopefully someone with experience with the product will chime in.

[nryn]

The MPPT is a solar charge controller. I have mine wired to my BMV-712, but I think even without that wire they will either communicate wirelessly or the controller will be able to give you battery voltage (battery voltage appears in the app—I don't know if this is from the 712 or read by the MPPT itself).

What the MPPT will not give you is SOC based on electrical device usage. That's what the 712 is for.

I check the 712 to see what my SOC is based on percentage or for an estimate on amount of time left on the batteries. I don't really care much about how much solar I'm generating or what the voltage of the batteries is. These may be interesting pieces of information and useful when diagnosing issues but for me, anyway, the state of charge is the only number I care about, and I generally only care about it when I wake up (if the furnace was running) or when I go to bed (and will turn the furnace on).

I think a lot of people like monitoring a bunch of things all the time. I do enough of that in my day to day life. Anyway, state of charge is useful, usable information and the 712 will provide that (the MPPT won't).

[uncle_bob]

Originally Posted by Jason P M

What is the difference between the Victron BMV-712 and the Victron MPPT that comes with the factory solar package? The MPPT seems to give a bunch of various input and output readings.

Hi

MPPT = converts solar panels to 12V to charge the batteries

BMV-712 = battery "fuel gauge"

Without the 712 (or something similar) there is no good way to know how many amp hours are left in your batteries.

Bob

[Jason P M]

Originally Posted by uncle_bob

Hi

MPPT = converts solar panels to 12V to charge the batteries

BMV-712 = battery "fuel gauge"

Without the 712 (or something similar) there is no good way to know how many amp hours are left in your batteries.

Bob

Thank you. Would you recommend adding the BMV-712 or the SmartShunt? Would either work on its own or would I need additional Victron equipment?

[uncle_bob]

Originally Posted by Jason P M

Thank you. Would you recommend adding the BMV-712 or the SmartShunt? Would either work on its own or would I need additional Victron equipment?

Hi

The BMV-712 has more functionality due to the display. To me that makes it more useful.

Either one works pretty much on its own. The SmartShunt needs a cell phone to talk to if you want to know anything. The BMV-712 only really *needs* the cell phone at setup. Both display data much better on a phone than the little 712 display.

If you decide to do something with multiple solar controllers, then indeed keeping things all one brand is a really good idea. That's getting a bit past just putting on a "fuel gauge".

Bob

[jimdelane]

The SmartShunt requires a smartphone with the free Victron Connect app to program and monitor the batteries.
The Victron 712 has a physical gauge which you can program and monitor with but also can use the Victron Connect app.
The Victron 712 seems to have more bluetooth transmitting range than the SmartShunt. Usually that is not too much of an issue.