New to LiFePO4

[Bluie]

Our Cougar has the 400i solar package and Dragonfly LiFePO4 batteries. Our first time out dry camping the batteries were fully charged. They lasted two nights in a very shaded campsite. After the two nights I ran the generator for two hours to recharge the batteries since I knew the solar wouldn’t keep up in the shade. They were at 13.2 volts after the two hours on the generator and didn’t last 24 hours.

Should I have run the generator longer? Should I have run the generator after the first night to keep the batteries topped off? We’re new to this LiFePO4 thing, Solar and 12 volt refrigerator.

[firestation12]

Originally Posted by Bluie

Our Cougar has the 400i solar package and Dragonfly LiFePO4 batteries. Our first time out dry camping the batteries were fully charged. They lasted two nights in a very shaded campsite. After the two nights I ran the generator for two hours to recharge the batteries since I knew the solar wouldn’t keep up in the shade. They were at 13.2 volts after the two hours on the generator and didn’t last 24 hours.

Should I have run the generator longer? Should I have run the generator after the first night to keep the batteries topped off? We’re new to this LiFePO4 thing, Solar and 12 volt refrigerator.

To better provide some fact based answers for you, it would be helpful to know: what were the items running on 12 volts during the first 48 hours versus the third 24 hours? What device determined the batteries were fully charge before the camp out? Wouldn’t that same device let you know if the batteries were fully charged after 2 hours on the generator? Do you have something that records the solar output continuously for review purposes? To provide an answer to the question, “should I have run the generator longer” would depend on the voltage converter you have…..is it capable of charging a higher bulk voltage for your lithium batteries? There has been discussion on this forum that some of the voltage converters that are supposed to accommodate lithium batteries, left the manufacturer’s facility properly programmed. Adding a shunt to your system would also help to understand the in and out flow of amperage to the batteries.
Best wishes to get some feedback from experienced 400i solar flex users.

[JRTJH]

Here is a chart that gives you an APPROXIMATE voltage/charge level for lithium batteries. Looking at the chart, if your batteries were at 13.2 VDC after 2 hours of charging, then the generator brought them from "where they were" up to somewhere between a 60-70% charge in 2 hours. It seems reasonable, that with a 70% charge and depending on what you were using that relied on the batteries after charging them, a 70% charge may have been fairly well discharged the next day.

Here's the chart. It might help you with "predicting your charge status"...

I'm also attaching a FLA chart. Notice how beneficial the lithium batteries are at holding a "usable voltage" much longer into the discharge condition than a FLA battery. That "higher voltage" means you can rely on lithium batteries to provide "usable DC power" almost down to the 90% discharge condition while FLA batteries aren't of much use below the 40-50% discharge condition.

[xrated]

Some things to know about LiFePO (LFP) batteries. A single cell is normally considered to be fully charged when it reaches 3.45V. So there are 4 of them in a battery which would equal 13.8 volts if each cell was at the 3.45V level. However, the charging voltage will have to be greater than 13.8 to get the cells to that level. The normal charging voltage is around 14.5 to 14.6 volts. Many of us do not like to push the battery charging voltage all the way to the 14.6 level, as that is the MAX voltage that the battery should ever see, so we use a lower voltage.....say 14.xx. That number is still over the 3.45/cell or 13.8/battery, but it will just take a bit longer to fully charge the battery. The reason for that is to not stress the battery as much as the full 14.6V charging would. You said that your battery, after the two hours of generator run time was at 13.2.....which was obviously not long enough to fully charge the battery.

One of the most important things to remember and know is that battery voltage is a very poor indicator of the State of Charge (SOC) of lithium batteries. I'll give you an example. A LFP battery sitting at 13.00v is at an approx. 30% SOC. That same battery sitting at 13.2V, is at an approx. 70% charge. When you realize that the difference of .2Volts is a huge difference, then you realize that there needs to be a better way to calculate/estimate the battery SOC. A volt meter can EASILY be off my .2V or more

So with LFP batteries, most people rely on a shunt that actually counts the amount of current going into the battery and the amount of current that comes out of the battery after charging. Most of them are very, very accurate at counting what goes in and what comes out. Victron is a very popular brand and that is what I personally use to monitor battery status on my rig.

There is a lot to the LFP battery usage thing, but suffice to say, make sure that you have a charger/converter that is capable of fully charging the battery or batteries...AND that you can accurately monitor how much battery usage (both charging and discharging) that you are actually doing.....and that will be possible from a good quality shunt, specifically made for that purpose. Given all of that, yes, you will have to run the generator longer, depending on how depleted the battery is and how quickly it can restore the battery to full charge. And the best way to know that is not by looking at voltage numbers, it's by monitoring with a battery shunt.

PS: In the chart above posted by JRTJH, you can ignore the numbers in the yellow section completely if you are using LFP batteries. That section is for traditional Flooded Lead Acid (FLA) type batteries, but it does show a good comparison of how flat the charging curve is for the LFP batteries vs. FLA

[Bluie]

It does have the shunt. I’ll be watching it more closely. All that was running was the 12 volt refrigerator, the radio and occasionally the water pump during the day. At night was the 12 volt refrigerator and my Cpap machine on the inverter. Thanks for the chart JRTJH. The batteries are 2 Dragonfly at 100Ah each.

It appears that I just need to watch the output and input more an use the chart that JRTJH provided.

Thank you for all the responses.

[JRTJH]

Originally Posted by Bluie

It does have the shunt. I’ll be watching it more closely. All that was running was the 12 volt refrigerator, the radio and occasionally the water pump during the day. At night was the 12 volt refrigerator and my Cpap machine on the inverter. Thanks for the chart JRTJH. The batteries are 2 Dragonfly at 100Ah each.

It appears that I just need to watch the output and input more an use the chart that JRTJH provided.

Thank you for all the responses.

This is just a hunch, but you might want to focus most of your "suspicions" on that CPAP machine.... If you have the "humidifier turned on" that heating element draws as much battery power in a couple of hours as a coffee maker draws making a pot of coffee. So, by comparison, using the CPAP with humidifier turned on to sleep aroung 8 hours will drain a battery about the same amount of "charge status" as will making 4 pots of coffee.

You might consider turning off the CPAP humidifier and just breathing "cool dry air" for a night on your next trip and see if your battery charge status is significantly higher the next morning....

In short, CPAP's ain't energy efficient and will put a significant drain a battery if you use all the CPAP features.

Also, if you're plugging in the CPAP to the inverter, you're "double wasting" battery power... What you're doing is running the inverter (changes DC to AC) to power the CPAP converter that changes AC to DC. So you're wasting some of your battery charge running the inverter only to change it back to DC for the CPAP. You can buy a DC/DC voltage converter attachment for your CPAP that changes battery power from 12 VDC to 18 VDC much more efficiently than using the trailer inverter and the CPAP converter to get that same 18 VDC

[Bluie]

I forgot about the Cpap humidifier. I did have it on the trip prior because we had electricity and didn’t turn it off this trip. I didn’t even think of it.

[JRTJH]

Originally Posted by Bluie

I forgot about the Cpap humidifier. I did have it on the trip prior because we had electricity and didn’t turn it off this trip. I didn’t even think of it.

BINGO !!!!! "Methinks" that may be the most significant crux of your problem.....

[Bluie]

I did have the adapter for my old Cpap so I could bypass an inverter. I have a new machine and don’t have an adapter yet and the old one won’t work. It’s now higher up on the to do list.

[Cwinch44]

You might want to check your charge controller and shunt settings, I checked mine this last weekend after seeing a post about a new trailer coming from the dealer with the wrong settings. mine was set to deep cycle batteries so I set it up for the lithium batteries that were an upgrade option. Here is the link I used,
It is the solarflex quick start guid from Keystone.


https://keystone-rv-dealer-app.cdn.p...DF_QSG_WEB.pdf

[Kzneft]

Not sure how many batteries you have, but originally I had two 100ah lithium, but found that was not enough. Ended up getting two more, and now all is good.