Battery Drain

[DW 24X]

Twice while boondocking, the house batteries have died.

2022 24X with (2) 100ah lithium batteries. 300 watt solar panels.

I have the generator on auto with quiet time for nighttime. I have the inverter on and the load is 45 watts. The battery is around 13V. This has occurred twice, both on the third night without shore power.

Thoughts on how charged the battery should be at night? Do I have a short?

Is there a calculator or other guide?

[malligator]

Self-heated batteries?

[DW 24X]

Yes but not on. low temp was 50 degrees.

[DW 24X]

Standard 24X battery heater. not heated battery

[Wazbro]

Originally Posted by DW 24X

I have the inverter on and the load is 45 watts. The battery is around 13V.

45 watts at 13 volts is about 3.5 amps which will deplete 200 amp hours in about 57 hours, if no incoming charge.

[OrangeCrush]

You have a compressor fridge and that is probably drawing the lions share of your battery. 3 days using the fridge at around 50-60amps per day will chew up most of a 200ah bank. That 45 watt inverter draw is also a problem and you need to figure out where it's from so you can manage it.

[DW 24X]

Thanks for the replies. But if the generator is set on auto and it runs periodically to maintain charge, why is it depleted with minimal load at night. The 45 watts is a CPAP.

[fran&frank]

I don't think your batteries should be that depleted under the scenario you describe. With 300 W of solar your batteries should be fully charged by night if it was sunny and if you have a generator running your battery charger should be fully charging them as well. Voltage is not an accurate way to assess the status of your lithium batteries, do you have a battery monitor that uses a shunt to accurately monitor the state of charge? Are your chargers and monitor set up correctly for lithium batteries?-- Frank

[DW 24X]

Thanks for your reply. Everything is stock so I am assuming it is set up correctly. It has the Victron shunt and I should have reviewed the history after the last dead battery.

With the Onan Auto feature, the generator turns on and off at the Airstream settings.

It is very disconcerting to have the whole house go dead. The only way to get it started again it to start the engine and then the generator.

I need to get this figured out as it is not meeting my expectations.

[Rocinante]

Do you have a Victron BMV monitor? If so, does it confirm the expected amperage draw, and how long does it say your system should last at that rate? If not, you definitely need something like that monitor to help you figure out what else might be pulling down your batteries in a single night.

[Boxite]

Every time I read thru one of these type threads….. I am grateful I still have an ordinary lead-acid deep cycle battery.

[Xman]

I checked the information on the battleborns that came with our 24X and it indicates that at 0A, a single battery is charged at 13.6V resting and 14.4v charging. I looked at the settings on the auto start for the generator and it comes on at 12.4V and turns off at 13.2. This is how it came from Airstream and we have not used the auto start so it may be that yours is set the same way. On the Battleborn flier this indicates that the charge at 12.4V would be between 9% and 14% and at 13.2V it would be at 70%.

It may be worth contacting your dealer to see what Airstream or Battleborn recommends for the autostart settings. We just run the generator manually and look at the SmartShunt readings as discussed below.

You should be able to see the state of the battery using the Victron Smart Shunt that came in the 24X. Download the Victron app and connect using bluetooth and it will estimate time left on the batteries charge. This is a feature that our dealer never told us about and there is no information in the owners packet on it. We just noticed it when we were adding the bluetooth dongle to the MPPT.

Hope this helps.

[Rocinante]

This issue is not unique to lithium batteries, and in fact the BMV monitor and the predictability of lithium batteries makes this a much easier problem to identify and resolve than with basic AGM batteries.

If you have a Victron BMV-712 Smart in your van, this issue will be quite easy to figure out. I predict you're drawing far more amps than you think you are and that you will benefit from finding those additional draws and shutting them down when they aren't needed. https://www.victronenergy.com/batter.../bmv-712-smart

[DW 24X]

These posts are helpful. I wish I would have looked at the shunt app. Next time.
When it is overcast, I use the auto gen. I might look at setting the upper end higher.

Great discussion.

[uncle_bob]

Hi

Just to clarify a few things:

All 24X's come with a BMV712 installed as stock. It *might* not be powered up, but most are. The app will tell you a lot. It also will let you check the BMV 712 settings. They may still be at defaults (which are not correct for lithiums).

They all also come with a switch that lets you turn on the battery heaters. Unless you *need* to charge below freezing. Just leave it in the off position.

The "300W" of solar is 100W going to a charger that takes care of the chassis battery. The other 200W goes to the house battery. With all the junk on the roof, they get a lot of shade. Counting on anything more than 100W into the house battery is a bad idea.

It's amazingly easy to bump the various light switches as you go in and out of the van. Bump this or that and you have a light running all night long. I have empirical data on this.

The fridge has two compressors on it. If both are fired up, you get a 10A drain. Yes it's nice that the freezer is on its own compressor. Does that average out to 3A or something higher? It depends a lot on temperatures a your use profile. It *could* be well above 3A if you just loaded the freezer with fresh caught fish.

You also have various motion activated lights that might or might not come on at times. There's a couple amps of load when they do.

Running with the inverter on all the time is not a great idea. Depending on settings, it might pull an amp just sitting there. Shut it off unless you have a need for it.

Next up, you may or may not have some sort of hotspot installed. For now, let's assume not.

So:

Play with the lights in the evening, run the microwave for a while. Run the water pump for various reasons. Turn on the vent fans for a while. How much was that? Maybe 20 to 40AH depending on exactly what you did. If you started off "full" you might be at 160 to 180AH after an evening of play.

Run for 24 hours at 5A drain. Next evening you have used up 120 more AH. Do the same "stuff" in the evening and that's another 20 to 40AH ....

120 + 20 + 20 = 160
120 + 40 + 40 = 200
0 to 20AH in from solar

You have something in the 0 60AH capacity remaining.

12 hours until morning is 60AH at 5A

Yup, at some point that night it goes dead.

Bob

[vanderwielen]

Originally Posted by OrangeCrush

You have a compressor fridge and that is probably drawing the lions share of your battery. 3 days using the fridge at around 50-60amps per day will chew up most of a 200ah bank. That 45 watt inverter draw is also a problem and you need to figure out where it's from so you can manage it.

Nope, the fridge/freezer will draw 75w when the compressor is on with a duty cycle of 33% when the ambient is 70. I suspect you don't have an AI and are simply parroting others via previous posts.

[Rosie_2020]

Yep 2 Lithium batteries �� I can buy 10 gel cell batteries and at 74 maybe that close to a life time supply ��

[uncle_bob]

Hi

Fridge math:

You have a peak current drain with everything running. In the case of the specific fridge used in the X that number is just slightly over 10A for the two compressors together.

10A at 12V is 120W

Typically when looking at batteries, you look at amp hours rather than watts. The question is almost always "is it empty yet.

If you ran at 10A for an hour that's 10 AH. 120W for an hour would be 120WH.
If you ran at 10A for 24 hours, that's 240AH. In watt hours, it would be 2.88 KWH

Fridges don't run "full bore" all the time. How much they run depends on temperature. The number you are after is at the *back* of the fridge. In an RV, that's going to be a bit warmer than the rest of the area.

If you think that the fridge runs 33% of the time, take the 240AH and divide by three, that gets you 80AH per day. If you think it's closer to 20% then you get 48AH per day.

You now have a number you can compare to the 200AH of *usable* battery capacity you have on the X. If you have a different rig and it has lead acid batteries, the usable capacity will be roughly half of what the battery label says.

There are a lot of compressor fridges out there. It is rare to see one that has dual compressors in it. Size and install details also matter. Coming up with a single conversion factor for max amps to battery drain just isn't possible.

This is why you really do need to get that BMV-712 working

Bob

[Johncapp]

Almost all CPAP machines will run on 12 v. You just need a different “brick” transformer. Call the folks at Second Wind CPAP. They were most helpful in finding mine. Then hook up directly to 12v and you don’t need to run the inverter at night. I don’t think that is your entire problem but this would help.

[richard5933]

Since this happens after your third night of camping without shore power, I'm going to agree with the others that said there is a problem with the settings on your generator's auto-on feature. My guess is that you're not fully charging the batteries - just barely getting enough in them to make it through the first & second night. By the third night you hit the breaking point and use the reserve capacity.

It's also worth checking to find out if your solar is actually charging the batteries at all during these events. You should be able to monitor the amount of charge going into your batteries during the day when the generator is not running. I'm guessing that either the charge parameters are set wrong or the solar system is not charging for some other reason. If it were, then you'd have enough charge to make it through the night easily with only a 45-watt load.

Or, your actual load is much higher than 45w. Perhaps not everything on the house side of the system is actually going through your shunt? How many ground wires do you have on your house battery negative connection?