Beginner help, config BMS.

[Merct4]

Hi.

I'm planning on fixing a system on the roof on my canopy (pick-up) and did a lot of research before buying.

I ended up with this;
Victron smart solar 100/20
24v 250w solar panel.
12v 150Ah lifepo4 battery.

The thing is, I didn't plan to bother how the BMS was configurated until I used a lifepo4 wall charger and realized that it was charging with less volts then desired (13.6v) and that led to a snow ball effect.
I ended up buying a better wall changer more suitable for lifepo4 (victron blue smart ip65 12/25) that delivers 14.2v.

I used the xiaoxiang app but it doesn't show much info and I ended up downloading the overkill app.

I read the doc. on this forum regarding voltage/charging/BMS and realized that my BMS doesn't agree on those values.

I have attached print screens from the app above.
I haven't made any changes except the value "total cycle capacity" which was set at 125 000. I set it at 150 000.

My goal is to use 85-90% capacity of the battery but all these numbers seems to be all over the place.

Or should I leave all these values stock for warranty reasons?

Help!

 

[time2roll]

Usually the cell over volt is set to 3.650 and under volt protection is set to 2.500
Balancing can start at 3.400

Charging at 14.2 I would set the "full" voltage slightly under at 3.500. This is just to reset the 100% charge indication.

Using 85-90% will be determined on how the equipment cycles the battery more than the BMS.

 

[mikefitz]

Under capacity config, set cell full to 3450.
Balancing, start volts 3400, balance only when charging -- on.
Protection, charge under temp, trig 0C release 5C
Batt over volts, trig 14600 release 14000
Battery under volts, trig 10000 release 12000
Cell over volts, trig 3650 release 3500
Cel, under volts, trig 2500 release 3000

The BMS settings are 'last resort' to protect the battery, charger and load set up should be configured to operate 'inside' the BMS limits.

It's not really practical to limit the SOC at the 'top end', as the battery has to get near full charge for balancing to occur, over 3.4 v per cell, 13.6 v for a 4 cell battery. My view is that a charge voltage, absorbtion, of 14.0 volts, with 15 minutes absorbtion, and a float volts of 13.4, is a low stress charge profile.
SOC at the low end is easier as there is significant voltage change, consider charging at 12.5 volts and limit discharging at 12.0 volts, (10%).

It's considered stressful on the cells to keep at full charge continually, thus if your vehicle has extended periods of non use, either discharge the battery to a lower SOC, say 13.20 volts ( resting volts) and disable charging, or if there are operating loads on the battery, for example security systems, set up a ' low power' charge profile in the solar charger, charge to 13.35, float at 13.30.
Revert to normal charge profile when the vehicle is in use.

Mike

 

[Merct4]

Thanks guys, much appreciated.

The victron mppt lifepo4 pre-set charges as 14.2 as well (float is 13.5).

I will always have a draw of a refrigerator but if I disconnect that and leave the battery at 50% SOC and disable the mppt controller from the victron app, will the solar panel get damaged? I've heard that they should never be exposed to the sun when not connected.

Regarding "total cycle capacity", what does that really do? Just change the % left or limit the amount of discharge?
For example, if I leave it at 135 000 which is 10% less then 150 000, will it stop discharging when there's only 10% left in the battery?

 

[mikefitz]

With a constant refrigerator load, keep the normal charge values all the time. The preset at 14.2 and 13.5 float is OK, but the absorbtion at 2 hours is longer than ideal. You can keep the preset values or set up user values, I prefer slightly lower charge voltages but that's me being conservative. In practice I suspect there won't be any significant reduction in battery life.
Total cycle capacity only effects the display, it will not prevent discharging.

Having a disconnected panel in the sun won't damage the panel.

Mike

 

[Merct4]

Thanks.

I can adjust the voltage on both the solar charger and the wall charger.
As I said earlier it sits on 14.2 at the moment.

I've heard that lifepo4 needs 14.4-14.7 in order to be fully charged but that's just a thing I heard.

The hard parts are all the voltage numbers, charging numbers, resting numbers and what actually is a fully charged battery.
I'll guess that's something you'll learn along the way

 

[Merct4]

Everything is hooked up and it seems that I really went the safe way regarding panel size/battery size/consumption.

Is it bad for the solar panel if you limit the charge current via the victron app?
Let's say I go from the max current which is 20A on my victron (100/20) to 10A.
Where does the excess current flow? Heating up the solar panel?

 

[time2roll]

The power is just not converted. Same as a wall outlet with nothing plugged in.
No issues.

 

[Merct4]

Thanks for the reply.

Everything has been connected for about two weeks and no matter how little sun there is I'm always above 90% SOC all day.

I realize that balancing happens at full charge but is there a charge profile that stops around 70% SOC?

As long as I keep track of the cells (and do a full charge maybe once a week to keep them balanced) it should be doable, right?

I was advised to charge to 13.35, float at 13.30 by mikefitz earlier if i didn't use the vehicle that much.
Could that be a good setup?

The other solution would be to disable the charging completely from the victron app every know and then but that seems like a hassle.

 

[time2roll]

No real difference in 90% and 70% as far as longer life.

If there is an adjustable equalize function consider setting it to charge to 14.2 maybe every 7 to 10 days.

 

[Merct4]

No real difference in 90% and 70% as far as longer life.

If there is an adjustable equalize function consider setting it to charge to 14.2 maybe every 7 to 10 days.

Should I continue to be at 90-100% SOC all day?
It dips to 90% in the morning and before lunch it's 100%.

There is a equalization function in the expert menu but that's way to advanced for me.


What SOC should I reach with 13.35/13.30?