Charge Controller isn't outputting enough voltage for Lithium Battery... maybe.
I just setup my controller and such last night and got my Renogy lithium battery today. Before connecting the panels, I programmed my controller with parameters that I thought would work, but it doesn't seem to be. At least it's not behaving how I expected.
In short, It's "charging" right now, but my multimeter only reads 13.2V on the battery. My little $18 inline shunt meter reads 13.35V. The controller meter says 13.4V. It's been charging for an hour. If I disconnect the panels and then the battery (both are on cutoff switches), and I read the voltage again (with no charging or discharging at all), it still just reads 13.2V. If it were truly charging the battery, then the voltage would be higher when charging than idle, but they are both the same.
Here's what the controller meter shows:
I'd assume that amperage reading in the middle indicates that it's putting 3.9A into the battery, but maybe that only means what's available.
My only background regarding battery charging is with cars, plus hours of research on here and other forums about solar charging FLA batteries. That's not really applicable with Lithium batteries, so maybe I don't know as much as I need to.
When your alternator runs, it's putting 14+ volts on the battery because that's the only way to get current to flow into it. It has to significantly exceed the battery's voltage. I'd assume the same is true of lithium batteries, so how can it be charging the battery at only 13.4V?
One might assume that maybe it's in float charge mode if the battery is full, but I have the float charge set to 14.4V, so that doesn't make any sense. Renogy just says to charge it at 14.4V +/- 0.2. It says nothing about float, and my research says that it's just supposed to be the same as the charging voltage. The internal BMS will use that voltage as needed to balance cells, etc. Internally, it manages what it actually uses, and whether it truly "floats" at all. It also says it will cutoff charging above 14.6V, which I assume is a safety mechanism. It doesn't want to receive any more than that.
Controller: EPEVER MPPT Solar Charge Controller 50A 150V
Meter: MT50 Remote Meter
Battery: Renogy 12V 170 Ah (RNG-BATT-LFP-12-170)
Here is a photo of all of the settings the controller lists in the manual:
First off. I don't understand all of these settings. I've read other posts on these forums and searched the web, but I still came up short.
Over voltage disconnect voltage - I'm guessing this means that if the controller will disconnect if the detected battery voltage is higher than the value. And then reconnect when it's equal to or lower than the "Over voltage reconnect voltage". I'm not really sure what this feature is for. An FLA battery itself could never output 16V, right? So what does this feature do, and why is the number so high for those types of batteries? I set this value to 14.5, and the reconnect to 14.3, but I have no idea if that's right.
Charging limit voltage - I set this to 14.4. I suppose it could be 14.5, or maybe even 14.6 if the battery cuts off above 14.6V, but I figured setting it to 14.4 is best. I figure this is the absolute highest voltage the controller will send to the batteries.
Equalize charging voltage - not really applicable to LFP batteries, but I set it to 14.4 to effectively disable it. I also set "Equalize duration" to 0.
Boost charging voltage - Is this the same as "Absorption"? I set it to 14.4V
Float charging voltage - Like I said above, I've read it's supposed to be the same as the main charging voltage, so I set it to 14.4V.
Boost reconnect charging voltage - Really not sure on this one. It seems like the voltage it must drop to in order to go back into boost/absorption mode? I could have that totally wrong. It won't let me set it to 14.4; it gives me a parameter error. It defaulted to 13.2. I could set it to 14.2, but that didn't change the behavior of the controller.
Low Voltage Reconnect voltage - I believe this is only used when using the Load side of the controller for lights and other small appliances. The thing is, my model of controller doesn't even have load connections. [EDIT: I'm wrong, it totally has load connections, but I'm probably never going to use them.] I believe if the battery goes below the "Low voltage disconnect voltage", it will cutoff the load, and only reconnect when the battery is back above the reconnect voltage. Seems pointless to bother with these settings, but I set them at rational values. The battery will internally cut itself off at 10V, so I set the disconnect at 11, and the reconnect at 12.
Under voltage warning - I'm assuming this means it will audibly beep and turn on the warning LED if the voltage drops below this value, giving you a chance to deal with the issue. I set it to 11V and the "reconnect" to 11.2.
Discharging limit voltage - Seems like it might be for the load again. Not sure how this differs from the low voltage disconnect.
Boost duration - Seems moot if I set the boost voltage to the same as the charge limit voltage, but I left it at the default of 120 minutes. I'm assuming this is the duration of absorption charging, after which is will enter float charging.
If I'm wrong about the meanings of any of these, please illuminate me! I don't just want to know what settings to use; I want to understand what these things mean. But, primarily, I need to know how to get this thing to actually charge my battery!