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Fluctuating voltage after shutoff by Daly 4s Smart BMS100, Morningstar MPPT45, 2 x 200W panels and 320Ah LiFePO4

ConradPoohs

New Member
Joined
Apr 22, 2022
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3
Hi,

I would appreciate your help confirming that everything is OK with my charging system please.
I have just replaced some old flooded batteries with a LiFePo4 320Ah pack. All balanced, connected and set as recommended on this forum (an YT). The Daly BMS 100 settings are below (14.40/12.00 V cut off). I have customized the Morningstar MPPT45 controller as recommended with max absorption 14.40V (no temperature compensation and equalization). Once the battery is back to 100% SOC the DALY BMS cuts off charging, the bluetooth BMS Smart app shows nicely 0 Ah and solid 13.8V (going down quickly from max 14.4V).
However, the solar controller MSView software shows fluctuating voltage (up to 21V) but no current. I can see similar fluctuations 10 meters from the charging system/battery at my 12V sockets...
1. Is it safe
for my batteries and equipment to ignore it or should install some kind of additional regulator (shunt 14.4V) as a barrier for these voltage
I can physically switch off the connection panels/controller and obviously it stops that issue but it can't be monitored all the time.
2. Another question - the Battle Born Batteries in setting up the MPPT controller at:
changed the Absorption voltage to 14.40V but left the absorption time as 2.5h. Is it correct?

Please let me know what could be done about it.

All the best,

Conrad

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Having the BMS opening the charge path under normal operation is not a good idea. The sollar charge peramerers should control charging, not the BMS. The charge voltages must be lower than the BMS protection values for over voltage.
Increase the BMS cell high volts to 3.65, and pack volts to 14.6.
With the charger, set absorption to 14.0 or 14.2 volts with a short or no absorbtion time, say 15 minutes.
Set float volts ( if this applies for your charger) at battery resting volts, 13.4 to 13.6 volts.

Unsurprisingly the Morningstar gets upset when the BMS disconnects the battery as its trying hard 'pumping' current Into it. The resulting voltage spike may damage other equipment connected to the system.

To sumerise, the charger setting should control the charging process not the BMS.

Mike
 
Thank you Mike.

For how long should the float phase be set please?

All the best,

Conrad
 
If there is loading on the system during the solar day then having the system on constant float is useful to provide power.
Provided the float voltage is not higher than the resting battery volts defining a maximum duration is not critical.
 
Hi Mike,

Many thanks for your help!
I have set up the float at 13.4V only and it keeps it charged up to 75% every day (Daly BMS). It's enough for me as my boat does not take more than 6% from the battery (in the morning BMS shows 69%) and during the day most of my needs is covered directly from the solar controller. I may change it for November-February period to utilise maximum of potential light.
I wonder if the advice given by the Battle Born Batteries here:
isn't actually dangerous?
Absorption 14.4V for 2.5 h everyday and then float phase at 13.6V.
What is your opinion please?

All the best
 
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