Help Please with new Solar Generator and LiFePo4 Batteries

Hello,

This is my first post and I am full of questions. But first some specs on my build. I am building as a hobby a solar generator with a 12V, 20 AH LiFePo4 battery. It is housed in a rolling tool case (about 25 gallons). The outputs will include several USB ports, two car 12V ports and eventually 2 120v ac (I have an oversized 1500 watt inverter though I know that is probably far too large for this project as it stands right now..

Here is my current problem: At the moment I have my entire DC side hooked up (I am ignoring the inverter for the moment). This included all the USB ports (some with their own volt meters--to be explained), the car ports, the Solar Charge input, the Charge Controller (that can be set to LiFePo4 batteries), a battery meter and of course, the battery itself.

When I first hooked everything up a week ago, the Charge Controller indicated 13.6 volts on the battery, so a full charge. The little USB volt meters read 13.3 volts but I expected some voltage drop and not everything was perfectly tightened down yet--I am still finishing things off. I decided to try a little test and run my cell phone off the device and after only less that a minute of running on the LiFePo4 battery, it was (according to the Charge Controller) down to 12.2 volts! The battery itself was not remotely warm, and in fact was actually cool, I checked. Weirdly, the little USB voltmeters dropped also but showed 13.1 volts and continue to as of right now, and when I used a separate, dedicated volt meter to read right from the battery terminals, I got a reading very close to 13.1 volts (just a little over).

Making matters stranger, I installed a battery meter with a little shunt, but it reads as all 8's, meaning that every bar of the little LCD display is activated. The instructions say this indicates a full battery which made sense at first and I thought maybe it needed some measurable current to show an actual reading, but even with the battery reading 13.1 volts, even the volt meter portion of the battery meter does not function.

I am baffled. I would love to hear the experience from anyone with more experience than I have. For background, I have already built a little 12v 15AH battery box with only USB and car 12v output based on a SLA battery. This was simple. Originally this build was going to be built on a 100 AH SLA battery but I got convinced to go the LiFePo4 battery route. Are LiFePo4 batteries that much more tricky? Also, I can give a parts list and provide pictures if desired, but all my parts came from Amazon and I am pretty sure they were the lowest bidder parts so that may be a factor.

Again, sorry for the length but thanks in advance for any help you can provide

If you only charged the battery to about 13.6V it may have settled down to 13.1V. LiFePO₄ should be fully charged to 14.4V until the current drops to 0A. Then floated at 13.5V. That should all be part of the LiFePO₄ settings for the solar charge controller. That will be 100% SOC for the battery. After some use, if the voltage (as measured directly at the battery terminals) gets down to about 13.1V then the SOC is down to about 60%.

So I suspect you never actually fully charged the battery. Also be sure all connections are properly tightened. You do not want to test the system with anything loose.

rmaddy,

I am using the battery as it shipped, so have not actually charged it at all. But as you suggested, I put it on a little charger I specifically bought for the occasion and the charger indicated that the battery was at 60%, suggesting that it did not actually ship with a full charge. The battery is charging right now so we will see how this changes things.

Thanks. I am sure I will have more complications but thanks at least for the moment.

LiFePO₄ batteries are never shipped at full charge. Typically they are shipped closer to 50% so what you experienced is typical. LiFePO₄ batteries should not be left sitting around unused at full charge for long periods of time.