Hey folks, I have a similar set up to the post here.
The main difference: I have is a single large 360amp/h battery from expion also internal BMS.
Using the latest Multiplus firmware applied via the android app.
I'm seeing similar behavior where the multiplus will bulk (90amp limit) to 14.2 (my setting) and start absorption. tested with discharge to 95% so I'm not watching the output all day.
The voltage will then creep up to 14.3-14.4 (multiplus perspective) which is above my set desired set voltage (confirmed with multimeter). Near the highest sustained voltage I see a similar amp spike as the related post followed by a voltage spike (~16.1v) for less than a second. (See attached video of the system return to pre spike voltage). Note the V drop from the multi plus to the battery is 0.08-0.09v.
The manufacturer has confirmed the BMS will cell balance at top of the charge and has recommended 14.2 - 14.4 for 1 hour in absorption and doesn't believe I should be seeing this behavior.
- They suggested removed all temperature cables. Temperature is provided by the lynx shunt, and lithium profile is selected for no temperature comp on the multiplus. Can this be the issue anyway? I would rather not remove the temperature sensors.
- Would lowering the voltage further have a benefit e.g. 14.1 vs 14.2? as it seems the multiplus allows voltage to exceed the settings.
- Out there idea: any issues fitting an Alternator protection device in series to prevent these voltage spikes if the BMS is exhibiting normal behavior?
Next steps I'm considering
- Call the battery manufacter again and confirm cell balance behavior
- Repeat testing without multiplus and let mppt do the charging to see if the issue is isolated to the multiplus. Note: during the above discription the solar panels were off.
- Lower voltage to 14.1 if acceptable
- Other...??? Any other ideas from the community to test?