Batteries really depleted overnight or is it a BMS problem?

[Mcstiggens]

Greetings all,

I have just begun my new boon dock life in my travel trailer. I am in the process of upgrading the solar system on the trailer since it comes from the factory with only one tender battery and one 165w panel to charge it. In the interest of time and the need to power everything sufficiently (and having no time to dive into the complete install yet) I simply purchased two 200AH LifePO4 batteries, wired in parallel to power everything I need. Only lights, 12V fridge and furnace at night.

The first couple of nights were a breeze and the batteries emerged the next morning with barely any depletion of charge whatsoever, as it should be with that much battery.

In the day I would run a charger that was connected to a separate portable solar generator that I built. A simple top-up and I was doing just fine.

Just before bedtime last night, I ran the genny to blast the heat and top up the batts for good measure. They were at 12.8V at this point and 13.1V after I shut off the genny)

Cut to this morning; I woke up to flashing lights on my furnace thermostat alerting me to "low battery" state. So I go look on my mission control interface and sure enough, it shows batteries as "low".

So I go out and test the batteries with a multimeter and they test at around 10V.

Panicked, I fired up the genny and started charging them. About an hour in, I test the batts and they are back up to 13V

I ran the genny for 3 hours this morning and after I shut it down, the batts were 13V+.

The temps were around 29-30F last night. Not too cold for these batts as far as I know.

Something seems up. They should have no issue whatsoever running my rig overnight and should emerge with power to spare. Also, if the truly were depleted like that, it should take 6 to 8 hours to reach a full state of charge I think.

Could it be a BMS issue? The batteries are Li Time brand BTW. They have good customer support but I am waiting to hear what they have to say about it.

Thanks for any ideas you might have on this.

Mcstiggs

 

[Q-Dog]

The batteries sound dead. 14volt would be closer to charged up.

 

[JeromeS13]

+1 Sounds like you're not fully charging your batteries...

 

[WindWizard]

LFP batteries require a different charger than Lead Acid Batteries. Make sure that your charger is setup for LFP batteries. Once a LFP Cell starts to reach full charge is approaches 3.4 volts. To fully charge the batteries then once the voltage of the charger reaches 13.8 volts then it needs to charge the LFP batteries at a constant voltage and not a constant current. Just charging to 13 volts will never fully charge you battery.

LFP batteries do not like to be below freezing temperatures.

 

[Mcstiggens]

My smart charge device never show anything over 13.9V fully charged. I've never seen 14V.

Also, when "fully charged" @ 13.1V they powered everything for two day without even showing any depletion. So this idea that they are not charging fully does not make sense.

All indications show that they are/were fully charged. After doing their initial charge when I purchased them, using a 10amp smart charger for around 8 hrs, the charger read as "full charge" at 13.8V or so.

Just now I tuned on the furnace, every light and the fridge was running. When I tested them they were at 13.2V even with the load.

If they were really run down to 10V in a matter of 7 hours (roughly) and magically charged to over 13V in an hour or less, something doesn't add up.

 

[sunshine_eggo]

LFP batteries MAY require a different charger than Lead Acid Batteries.

Fixed, but often true in an RV due to shitty wiring and poor AC-DC converter behavior/models.

LFP batteries do not like to be below freezing temperatures.

13.0V may be as low as 30% SoC.
13.1V may be as low as 40% SoC.

If the batteries don't have low-temp charging protection, charging at 29-30°F may damage them.

LFP takes on more charge at lower voltage than lead acid, plus it seems to move much more slowly than lead acid voltage... staying mostly constant until the battery is nearly full.

As stated above, until you see voltage AT THE BATTERY terminals of 13.8V+, you're not fully charged. If the battery is resting at 13.4V after 5 minutes of sitting or under a very light load, you are likely at a high state of charge.

 

[Mcstiggens]

LFP batteries require a different charger than Lead Acid Batteries. Make sure that your charger is setup for LFP batteries. Once a LFP Cell starts to reach full charge is approaches 3.4 volts. To fully charge the batteries then once the voltage of the charger reaches 13.8 volts then it needs to charge the LFP batteries at a constant voltage and not a constant current. Just charging to 13 volts will never fully charge you battery.

LFP batteries do not like to be below freezing temperatures.

Yes, I am using the proper charge device and it has done its job effectively.

 

[sunshine_eggo]

If they were really run down to 10V in a matter of 7 hours (roughly) and magically charged to over 13V in an hour or less, something doesn't add up.

It's your lack of understanding of these batteries.

 

[sunshine_eggo]

Yes, I am using the proper charge device and it has done its job effectively.

Link product.

 

[Mcstiggens]

Fixed, but often true in an RV due to shitty wiring and poor AC-DC converter behavior/models.

Well I was not relying on the rv systems soley. I ran a separate smart charger. Also, my battery monitor/shunt and interior battery indicator are telling me that the battery is "fully charged" when I test it at 13.2-ish v.

 

[Mcstiggens]

It's your lack of understanding of these batteries.

apparently so

 

[JeromeS13]

Well I was not relying on the rv systems soley. I ran a separate smart charger. Also, my battery monitor/shunt and interior battery indicator are telling me that the battery is "fully charged" when I test it at 13.2-ish v.

Sounds like your shunt settings are not correct for LiFePO4.... Interior battery indicator is likely based on voltage and highly inaccurate.

 

[Partimewages]

Smart charger = dumb.
You need to post some links to your equipment to get an accurate assessment.

 

[Mcstiggens]

https://www.amazon.com/dp/B0C68Y373B?psc=1&ref=ppx_yo2ov_dt_b_product_details

Link product.

Well it's not the fanciest of chargers but it does indicate that it is the correct type?

 

[Mcstiggens]

Sounds like your shunt settings are not correct for LiFePO4.... Interior battery indicator is likely based on voltage and highly inaccurate.

THAT sounds like the best analysis so far.

 

[sunshine_eggo]

Well I was not relying on the rv systems soley. I ran a separate smart charger. Also, my battery monitor/shunt and interior battery indicator are telling me that the battery is "fully charged" when I test it at 13.2-ish v.

The interior battery indicator is wrong. The battery monitor/shunt is wrong. They must be configured properly to work with your batteries.

https://www.amazon.com/dp/B0C68Y373B?psc=1&ref=ppx_yo2ov_dt_b_product_details

Well it's not the fanciest of chargers but it does indicate that it is the correct type?

that's a 10A charger. Assuming you have a 100ah battery, it will take a MINIMUM of 10 hours to fully charge the battery.

Charging for an hour only adds 10%.

 

[JeromeS13]

that's a 10A charger. Assuming you have a 100ah battery, it will take a MINIMUM of 10 hours to fully charge the battery.

Charging for an hour only adds 10%.

10%/hour is also assuming zero load from the battery during charging.

 

[Mcstiggens]

Smart charger = dumb.
You need to post some links to your equipment to get an accurate assessment.

Makes sense about accurate assessment but I don't understand smart charger=dumb. If it is an "up-to-date" charger that is designed for charging lithium, what else is there?

 

[sunshine_eggo]

Makes sense about accurate assessment but I don't understand smart charger=dumb. If it is an "up-to-date" charger that is designed for charging lithium, what else is there?

"smart charger" is a marketing term.

Do you still have a converter in your RV?

 

[Mcstiggens]

The interior battery indicator is wrong. The battery monitor/shunt is wrong. They must be configured properly to work with your batteries.



that's a 10A charger. Assuming you have a 100ah battery, it will take a MINIMUM of 10 hours to fully charge the battery.

Charging for an hour only adds 10%.

Which is precisely what I said. How could it show as charged in only an hour? I did charge for 10 hours during initial charge