Bms or scc

[Tyler702]

Basically I have wills 24V/2K setup. But I cant seem to get my pack up to full capacity. My single pv is 250W. MT50 shows 29-32V @5A+/- 1 charging during the peak day. 3 days now, and still not full here in southern nevada. Yesterday, CC battery led flashes green (full charge) but pack displayed 27.2V, then a solid red led, then CC completely powered off. I suspect the bms and CC are at odds with eachother. Heres my params, I'd love feedback to see what I'm missing. Btw, haven't even connected the inverter yet. Thanks
Tyler

 

[Samsonite801]

Well, you're almost up to Will's minimum recommendation, as he calls for at least 400w of solar (up to max of 2000w) in that recipe. I might start by checking with voltmeter and amp probe to figure out actual volt and current states throughout the entire system. I would think you need at least 2 solar panels in series to get your Voc up high enough to be more useful in providing the MPPT charger enough juice to keep the voltage up enough on charging a 24v bank...

You didn't mention what kind of batteries you're using in your pack (which helps us decide what the optimal bulk charge voltage should be)... You should check voltages and current flows at every point and look for voltage drops (it's like finding a leak in a water pipe), and even every cell (if you have individual cells), to get an idea where the problem is. What are the cell voltages at charge and at rest?

This is a general answer until could collect more details about the configuration, like exact solar panel model, exact battery/cell model/condition, cells top-balanced, etc. If LiFePO4 cells aren't top-balanced, there could be one cell at high SOC and one cell at low SOC, causing the BMS to shutdown because of the one cell hitting high...

 

[Tyler702]

Cell's= new LifePo4 3.2V100Ah and BMS are both from Overkill Solar. Steve there said they are all balanced before shipping and the bms shipped programmed for the pack. All 8 arrived and metered: 5@ 3.295 & 3@ 3.294. Their Android app and BT functions fine. All readings look normal. Individual cell readings are pretty spot on compared to my Fluke meter readings, but I cant get them above that 3.5V range. Not one cell! And Yes, my pv panel could be bigger, but for now, it's all I have. That, and time. I'm in no hurry, I just want them topped off so I can connect my inverter, and begin running a few things and cycle the pack and get a feel for what I can run, and for how long.

 

[Tyler702]

Btw, Pv panel is a SolarWorld
250W 60cell
Voc=37.8V
Vmpp=31.1V
Isc= 8.28A
Impp=8.05A

 

[Samsonite801]

Btw, Pv panel is a SolarWorld
250W 60cell
Voc=37.8V
Vmpp=31.1V
Isc= 8.28A
Impp=8.05A

Well, if your volts out of the charger is up high enough, and amps are flowing in, keep in mind LiFePO4 has a fairly flat charge curve, so if the batteries were delivered at 3.295v then that's maybe roughly 65% SOC. Do you have an amp probe to check how many amps you're charging at? If it's going in at a low amp, it could take a much longer time to get the cells up. The volts won't start really jumping fast until near the end when SOC hits the 'knee' on upper end in the curve.

Do you have a bench power supply where you can set constant voltage and try charging that way as a test?

 

[Tyler702]

I havent actually metered the amps going in. I'm not comfortable doing that with my 10A fluke meter yet, however the display for the CC and the app for my bms both are pretty much in sync. Peak sunny day, both report anywhere from 3.5A to 5.5A going in. My ground mounted panel is both X and Y axis adjustable, so I've been out adjusting it throughout the day, when I'm home. I was able to get it up to 6A briefly a few days ago, before the clouds rolled in, so I'm fairly sure I'm getting a charge. I cant help but think the issue is somewhere in either the bms settings or the cc settings. I'm concerned why my CC shut down too, after the battery led indicator went solid red for a few minutes. The manual says that's an overcharge status..
I'll keep at it!