Settings for my custom LifePO4 (charger, battery protect and BMS)

missoo

New Member
Joined
Dec 1, 2020
Messages
42
Hi all,

I made my own LifePO4 battery from aliexpress raw cells. It is a 280ah.
For it, I bought the overkillsolar BMS and the epever tracer4215BN for my 2 solar panels 215 W in parallel (total 430 W).

I'd like to check with you what would be the good settings to begin with, as I have few knowledge in this domain ...

After doing some research on the forum, here are the parameters I am thinking of for my epever tracer.

1619603030947.png
In yellow, some settings I am not sure of.
Boost reconnect charging voltage, should it be higher ?
Low voltage and under voltage reconnect voltage : these are recommanded by epever. Do they seem correct ?
Discharging limite voltage , I am totally unsure of this one, as epever recommand 10,6 V , I have read it could be too agressive ... What voltage would you recommand ?
Boost duration : As my battery is 280ah, I believe with 430W solar panel I will have a low charge current. I have read in this case I could reduce the boost duration. What could it be ?

For my BMS, I used Steve's recommanded settings , for instance :
Full charge voltage / cell : 3,5 V
End of dischage / cell : 2,8 V
Discharge rate 0,2 %

For my battery protect, I am still hesitating between 10 V and 12 V for discharge limit voltage. Should it be the same settings used for my solar charge controller ?

Thank you so much for your help!
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
860
The settings for the Epever controller relate to charging parameters that need to be considered for charging and the settings for the load outputs of the controller. In many applications the load output of the controller is not used, for example if an inverter is in the system, and all loads will be connected direct to the battery.

Parameters concerned with charging.

Equalize charging voltage, this is not used for lithium, set to 14.1 volts
Boost charging voltage, this is the target voltage for the controller, it will produce maximum current from the panels into the battery until this voltage is reached, any voltage over 13.6 will charge the battery to almost full. Voltage up to 14.6 volts is OK, but for long battery service in a hobby application, 13.8 to 14.2 is considered less stressful. Once the boost voltage is reached the controller maintains this voltage for a preset time, default boost duration180 minutes.
Float charging voltage, once the boost duration is completed the controller drops the volts to the float value. If its required that the solar power is to augment the load once the battery is charged then 13.6 volts. For standby a lower voltage should be selected , less than 13.4.
Boost reconnect charging voltage, if due to solar conditions or load on the battery, the battery voltage falls below this voltage, the controller restarts the charging process, putting maximum power into the battery until the boost charging 'target' voltage is reached. This will be lower than float, typically 13.3 volts. Once the system is operational you may need to adjust this for best performance.
Equalize duration, not used set to 0
Boost duration, with fractional current charging this can be set to a low value, perhaps even 0. With the target charging voltage you are considering, 14.1 volts, the battery can be considered to be fully charged when the charging current falls to below 8 amps. You could evaluate this under test and adjust the time. However due to variations in solar conditions and thus charge current, having a short time say 15 minutes would be OK.

I would use 12v as the low voltage limit in the BMS.

Apart from the voltage settings I have discussed above all the other settings relate to the output port , the load port, on the controller, they have no effect on the charging of the battery.

If you have moderate loads and no inverter then you can use the load outputs of the controller, max current 40A, and use the load out protection settings ( as in the table you indicated).

Mike
 

missoo

New Member
Joined
Dec 1, 2020
Messages
42
Hi Mike,

Thank you so much for your answer !

I am not using the load outupts of the charge controller so I guess I don't have to modify any of the load output settings.
Here is an update of the settings I am going to use according to your comment.

1619626583787.png
For the low voltage limit for the BMS you are speaking about, is it what I called "end of discharge/cell" ? Should I set 3 V per cell then ?

Or maybe you wanted to say "low voltage limit for the battery protect" ?
 

DThames

Photon Sorcerer
Joined
Nov 22, 2019
Messages
1,431
Do you plan to use the system every day? I have build an emergency stand by system. For a stand by system, I would rather charged the battery, then let it settle and not charge again unless power is used from the batteries or it self discharges a little bit. I have been playing with the numbers to see if I can make it act the way I desire. It is 24v system, with 8 Eve 280Ah, Tracer, and Overkill BMS.
Boost set to about 27.2v (lower then full charge because this battery is parallel to 2 used BYD batteries)
The battery bank settles to about 26.6v.
Float is set to something like 26.55v
Boost Reconnect set to something like 26.50v
So after fully charged, it just sits there for days, at about 26.6v. If it discharges below 26.55v, it will float and hold there with a very low current. If I turn on the inverter and use more than a little power, it goes back to Boost and charges back to my "full" value.

If I was using it daily, I might do something differently, but I am not sure.

I have the RS-485 to USB cable and use a PC for Tracer settings. I have a 40amp and also a 60amp Tracer....fairly familiar with the settings interface program.
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
860
For the low voltage limit for the BMS you are speaking about, is it what I called "end of discharge/cell" ? Should I set 3 V per cell then ?
yes, 3v per cell, its a bit conservative and the 2.8 volts suggested would be OK. I see that 3.5 was suggested for the BMS as a top limit.(14v for the pack). I missed that.
If you use this, the charger settings should be lower or the BMS will protect.
So with a BMS limit of 14 volts set the boost and equalize volts to 13.9, with a relatively low charge current compared to battery capacity this will still charge fine.

Just to throw in a further issue. If cell balancing is important, then most BMS are set to enable balancing over 3.4v per cell, 13.6 volts per pack. You should be OK with the values discussed but once everything is running it may be the balancing period needs to be longer, that would need a longer boost duration or a higher charge voltage.

With the Overkill BMS this will be easy to evaluate how things are working out. ( its an excellent BMS)

Mike
 
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