Now that we have a good sense of comfort the Xuba cell/ battery capacity is good (I haven’t read anyone really say otherwise). Moving on to determining Solar Charge Controller (SCC) setting options.
After a good amount of tinkering today. I’m gonna see about using the solar charge settings below as a base-line. Gotta start somewhere, ha ha.
The hope/ desire is to see if I can set reasonable solar charge settings for just above the upper knee (upper limit) of the typical LiFePO4 graph (as opposed to going for the usual full 100% charging settings). The upper knee seems to curve up from the flat-line at around 3.35V per cell or so (or 26.8V). Aiming more for the middle 80 – 90% usage range. Don't know til we try, ha ha. Preliminary tests seem promising.
Quick Side-Note
I ended up hooking back up my cheap 15A BMS’s. Apparently, they do work. After my last capacity test with no BMS’s, the cells did get a little out of balance (~180mv) and never recovered after I charged them back up. Once I hooked up the BMS’s, the cells gradually balanced to less than 20mv. I guess I needed to disconnect them to see they were working after all.
Solar Charge Controller (SCC) - EPever Tracer 4215BN 40A with MT50 Remote Meter
Experimental settings: Subject to change!
Description | Setting | Per Cell (V) | Notes |
Battery Type: | User | | |
Battery AH: | 560 AH | | |
Temp Comp Coefficient: | 0 mv/C/2V | | Should be zero for LiFePO4 |
Rated Voltage: | Auto | | 24V (12V or 24V) |
Over Voltage Disconnect: | 27.8V | 3.475V | Cannot be lower than Charge Limit |
Charge Limit: | 27.3V | 3.4125V | Cannot be lower than Equalization Charge |
Over Voltage Reconnect: | 27.3V | 3.4125V | |
Equalization Charge: | 27.3V | 3.4125V | Cannot be lower than Boost Charge or higher than Charge Limit |
Boost Charge: | 27.3V | 3.4125V | Cannot be lower than Float Charge or higher than Equalize Charge |
Float Charge: | 26.9V | 3.3625V | Cannot be lower than Boost Reconnect or higher than Boost Charge |
Boost Reconnect: | 26.7V | 3.3375V | |
Low Voltage Reconnect: | 23.0V | 2.875V | |
Under Voltage Reconnect: | 23.1V | 2.8875V | Cannot be lower than Under Voltage Warning |
Under Voltage Warning: | 23.0V | 2.875V | Cannot be lower than Low Voltage Disconnect |
Low Voltage Disconnect: | 22.0V | 2.75V | Cannot be lower than Discharge Limit |
Discharge Limit: | 21.5V | 2.6875V | |
Equalization Time: | 0 minutes | | Disabled |
Boost Time: | 165 minutes | | I’ve heard about 30 min per 100 AH |
NOTE: Some settings are dependent on other settings. A Parameter Error means one or more other settings need to be adjusted first.
Observations so far:
- I still had the Battery AH setting set to 280 AH instead of 560 AH. Not sure if the SCC uses this setting or not for its charging algorithm. The SCC didn’t seem to be charging right lately. Could be because I had this set wrong when I recently doubled the battery from 8 to 16 cells (8S2P).
- From past experience, in User settings, I had only seen the highest voltage go to the Float Charge setting. Today, I just saw for myself, the Boost Charge (Absorb) is for a limited time only (Boost Time). When testing, with solar charging, and using a Toaster oven, I’d get the voltage to drop below the Boost Reconnect setting, turn off the toaster oven, then watch the voltage charge back up until it got to the Boost Charge setting (ie. 27.3V). After 90 minutes of testing, all of a sudden the voltage wouldn’t go above the Float Charge setting (ie. 26.9V) during peak Sun hours. The Boost Time was set to 90 minutes at the time. I ended up physically disconnecting/ reconnecting (power off/ on) the SCC to reset the Boost Time. Then it would charge back to the Boost Charge setting (ie. 27.3V) until it would time out again. Probably considered a Rookie mistake in my case. It makes sense now. Figured I’d mention this as this may be considered a given for some, but not for others (like myself). Guess I never really paid attention to this until now.
- Apparently, the Boost Time begins once the voltage reaches the Boost Charge voltage. After the time runs out then the voltage won’t go above the Float Charge setting. Click!
- I was using a coffee maker, microwave, and toaster oven in various tests today (Intentionally forcing a big enough drop in voltage to trigger the various upper knee/ upper limit SCC charging settings). The voltage would drop below Boost Reconnect setting and the SCC would bulk charge until Boost Charge was reached.
- After the Boost Time timed-out, voltage would only go to the lower Float Charge setting. Depending on how low the voltage went during discharge tests, the charging Amps (current) would adjust accordingly. The bigger the gap between the discharged voltage and Float Charge setting, the higher the charging Amps. The charging Amps would gradually dwindle the closer the voltage got back to the Float Charge voltage setting.
- Reading the Drok meter, I could see I used 600 Wh, but as the discharged voltage bounced back some and was still close to the Float Charge setting, the solar charging current would be low Amp-wise. Meaning, as quick as the power was used by my various tests, it took longer to replenish. So, the closer the discharged voltage is to the Float Charge setting, the longer it takes to level-off back to the Float Charge voltage.
- I don’t think this is a big deal as the battery had hardly been discharged at these settings. When the voltage gap was bigger, though, it would bulk charge (higher current) until it got close to the Float Charge voltage again.
.......snip......
Constructive criticism, suggestions, recommendations welcome. If you see any obvious no-no’s, please chime-in. Even if these settings are way off, perhaps they could still be used as a comparison to improved settings. Worst case, know what not to do, ha ha.