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I have a 160W solar panel that has a built in regulator that I have hooked up to a 100Ah 4 cell Lithium Ferro Phosphate battery.
When I connect them the panel starts charging anywhere between 5 - 7 amps and get the battery to full without issues. The problem I have is once night time has passed, the panel will not charge the battery unless I unpug it from the battery first. The battery box voltage meter sits at 13.4v when fully charged, and with the 12v fridge running on it through the night it got down to 13.1v. I waited till midday and the voltage remained at 13.1 even though the panel was in full sun by that time and my inline amp meter displayed 0amps the few times I checked it though out the morning. Strangly with the fridge still running the battery voltage did not drop further either though it only used 0.3 V for the whole evening proir and night. When I disconnected the panel and reconnected it immediately, it started charging at 6 amps. While it was charging, I then covered the panel and it went to 0amps as expected. When I removed the cover, it started charging just fine. I am at a loss as to why it wont start charging by itself in the morning.

The inline amp meter when running properly

The solar regulator when running properly

EDIT After a comment about the potentially non standard battery voltage got me a little worried, I have added the information I could find.

The battery spec sheet

Regulator specs

Panel Specs

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  • \$\begingroup\$ I wonder if the charge controller itself has a battery in it that completely discharges over night, but not if there is a brief pause. I doubt it, though, because you have a pretty typical sounding use case. What is the model number of the controller? \$\endgroup\$
    – KD9PDP
    Mar 8, 2021 at 5:04
  • \$\begingroup\$ What type of 'Lithium" battery is it? \$\endgroup\$ Mar 8, 2021 at 5:32
  • \$\begingroup\$ Try running a heavier load over night and see if the charger starts automatically if the voltage is below 13.0 V. \$\endgroup\$ Mar 8, 2021 at 6:37
  • \$\begingroup\$ Looks like the comment about the non standard 13.4V level has been removed as I was adding the extra info. Is there anything that looks like I might have an issue on that front? \$\endgroup\$ Mar 8, 2021 at 7:50
  • \$\begingroup\$ What evidence do you have that the charge controller is intended for LFP? Most are for lead-acid only. Some (like Epever) can be set up for LFP by changing parameters, thresholds. \$\endgroup\$ Mar 8, 2021 at 20:34

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As described, This is a normal operation. But I think the charging profile is not suitable for Lithium batteries.

In fact, there are different charging profiles.

When you first apply the solar power the battery will be charged to a threshold value which is 13.4V in your case. Then the controller will wait till the voltage drops below another threshold (which is below 13.1V in your case).

Charging profiles change depending on the type of the battery. The following is for instance the profile used by Deepsea chargers (not designed for lithium batteries):

enter image description here

the float voltage definition fits with your 13.1 V.

To find out if it is really working as needed, apply a continuous load and wait to check below which threshold it will restart charging.

the following graph is an example of a charging profile for a lithium battery that is not voltage float charged and where the current is kept constant instead of the voltage (here the voltages are different than in your case) :

enter image description here

Some battery chargers are profile configurable either by software or simply by a button like the following:

enter image description here

Choosing the right profile increase the lifetime of the battery.

Since you edited your post to add the battery type. Here is one of the suitable profiles included also in a Deepsea charger for Lithium Phosphate:

enter image description here

In fact in this case the float charge is terminated when the charging current is too low and then after either the charge termination timer elapses or the battery is discharged the cycle will restart.

Concerning your controller, it is clearly mentioned in the manual that the battery type is "any 12V DC battery that is used for cars, boats, motor cycles, etc..." so it is mainly a lead acid battery. The charging profile suits these kind of batteries. But this is not to say that it wont work for your case. However it is not the optimal profile for the lifetime of your battery.

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  • \$\begingroup\$ That makes alot of sense, I'll give it a test tomorrow. With the other comment about wierd float voltage, I'm now a little worried I have a missmatch in components. \$\endgroup\$ Mar 8, 2021 at 7:35
  • \$\begingroup\$ @JohnPetrak I edited to include your new added information. \$\endgroup\$ Mar 8, 2021 at 9:03
  • \$\begingroup\$ This was exactly what is happening. The Battery does seem o sit around 13.1V for quite a while. I will try and source a better suited controller. \$\endgroup\$ Mar 9, 2021 at 7:01

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