Solar panel question re OC voltage

[GeoffL]

FWIW, I've recently upgraded to a hybrid system and recognise some of the troubles described in this thread. In my case, it's a Victron SmartSolar 75/15 with a Polarmax 100Ah LFP in parallel with a 110Ah FLA and I have 2 x 100W panels in series (so full sun in this country gives OC voltage greater than 40V). The thread I started is at https://wildcamping.co.uk/threads/lifepo4-issue.100992/.

If you're having the same issue, it could be an unfortunate combination of a smart BMS and smart MPPT! I suspect that what's happening to me is that cloud or shade temporarily reduces the available solar power, which causes the charge current to drop below a threshold, which causes the BMS to switch to standby mode [i.e. stop accepting charge], which causes the MPPT to switch to float! From that point, the MPPT needs to send a higher charge current than float provides to 'wake up' the BMS to resume accepting charge. However, the BMS is shut down and the FLA only needs float voltage... so the LFP won't get more than a short charge window even though there's 'room for a lot more energy'!

I've got a work around -- but with a huge caveat: the Victron app tells me I might damage my battery via overcharging by doing this... So you do the following only at your own risk!

1. Go into the Settings page of the Victron app and choose Battery;
2. turn on "Expert" mode.
3. Scroll down until you get to the setting for Absorption Time.
4. Change this setting from Adaptive to Fixed.
5. In the next setting item down, adjust the duration as appropriate.

I've done this, making a rough calculation of how long it should take to reach 100% SOC and then set an alarm on my phone to remind me to revert the absorption time setting back to "Adaptive" once the LFP is charged. It's a PITA, but the only way I've thought of this far to get a decent charge into the LFP.

 

[Alberto]

Hi
My solar panel is not charging my battery, all appeared fine until a few days ago. (9 months charging lipo battery with no issues, 7 years charging FLA before this).
Victron mppt 75 15.
100w solar panel probably 8 years old.
Mppt says solar voltage is 12.94v 0A and unit is Off ( blue led flashing indicating no charge) multimeter agrees it's 12.94v
lipo battery is 80% charged so room for more.
Removed + wire from mppt PV pair and voltage reads 20.24v - reconnected and it drops to 12.94v
Checked panel OC voltage on roof at panel connectors and it is 20.24v, no corrosion on connectors.
Tried a new victron 75 15 and results are same

Looking at specs for new panel they claim OC voltage of 23/24 volts,

Have tried removing and reconnecting cables as per the install instructions
Does this mean my panel is faulty? I don't have access to a spare to try.

Regards
Al

Just to close, issue turned out to be faulty solar panel, broke down when very wet, ok when it dried up.
Thanks for all the suggestions.
Al