Multiplus OFF / Help tweaking a few settings or diagnosing an issue

[gcap]

When I checked on my system this morning, my multiplus was OFF and the low battery light was flashing

I have recently added solar and have been testing it out over the past 8-10 days. Settings I used in the charger are the same as in the MPII as per posts I’ve read.
With not much sun lately I’ve been running my batteries down by methodically adding loads to test and wanting to trigger my “ignore AC input” assistant which is set to 15% and charge till 30%.

I’m confident that the system shut down because of the DC low shutdown @ 48v, restart @49v.

I can easily set my "ignore AC" assistant to turn on at 16-17% if that’s what would be recommended but as I dug a bit deeper I realized that while my SOC slowly declined at a predictable rate over the last week, my voltage took a nosedive overnight and I’m not sure what this could be an indicator of.

I’ve removed my critical loads and have kept fridge and freezer connected to try and see a pattern and it seems obvious that without sun the MPII will simply just continually turn its DC relays off and on at 48 and 49v respectively. I’ve now removed all loads to replenish the battery slowly. I’m thinking I should use the other relay to allow me to manually NOT ignore the ac input general flag

My battery screen shows 15% SOC at or around 48-48.3v when it’s telling the MPII to cut-out.

Is the voltage drop in my batteries normal or signalling something I should investigate? see below
Should I modify the low DC setting or have the ignore AC come in sooner?

Thanks to all of you for getting me this far along.

LAST 7 DAYS ( aside from a few solar days, steady decline in SOC )



LAST 24 Hrs ( steep voltage drop around 5-6am but steady SOC decline )

 

[sunshine_eggo]

When I checked on my system this morning, my multiplus was OFF and the low battery light was flashing

I have recently added solar and have been testing it out over the past 8-10 days. Settings I used in the charger are the same as in the MPII as per posts I’ve read.

What settings?

With not much sun lately I’ve been running my batteries down by methodically adding loads to test and wanting to trigger my “ignore AC input” assistant which is set to 15% and charge till 30%.

The generator start/stop feature of the Cerbo is WAY better than the assistant. Much more flexible.

I’m confident that the system shut down because of the DC low shutdown @ 48v, restart @49v.

While not consistently, you will almost certainly trigger this before SoC, especially when dealing with BMS-based SoC - not horribly reliable.

I can easily set my "ignore AC" assistant to turn on at 16-17% if that’s what would be recommended but as I dug a bit deeper I realized that while my SOC slowly declined at a predictable rate over the last week, my voltage took a nosedive overnight and I’m not sure what this could be an indicator of.

The inverter itself uses power, and you are clearly drawing power. When you're at 50.25V and 18% SoC, you're in the "holy shit, stuff can happen quickly here" zone. Look at LFP charge and discharge curves... in the middle, they're very flat, but at the ends, voltage spikes fast as they near full charge and voltage drops fast as they are near depleting charge.

Have you confirmed the BMS did not trigger low voltage protection?

I’ve removed my critical loads and have kept fridge and freezer connected to try and see a pattern and it seems obvious that without sun the MPII will simply just continually turn its DC relays off and on at 48 and 49v respectively. I’ve now removed all loads to replenish the battery slowly. I’m thinking I should use the other relay to allow me to manually NOT ignore the ac input general flag

With the Cerbo generator start/stop method, you can simply tell the "generator" to run for X time manually.

My battery screen shows 15% SOC at or around 48-48.3v when it’s telling the MPII to cut-out.

This will vary. BMS SoC aren't always reliable.

Is the voltage drop in my batteries normal or signalling something I should investigate? see below

Very.

Should I modify the low DC setting

Yes. 44V max. IMHO.

or have the ignore AC come in sooner?

Your call. Switch to the Cerbo generator start/stop method to allow you to change the parameters without having to reboot.

Recommend you zoom in on charts and show only a few hours worth of data. If you haven't already, set logging interval to 1 minute.

Check Battery Monitor Alarms/Warnings as well.

 

[gcap]

thanks for your detailed response as usual sunshine_eggo

Settings I used in the charger are the same as in the MPII as per posts I’ve read.

What settings?

You had recommended I go with these

So for my scc I did the same, should I open expert mode to set the fixed charging and 1 hr absorption time?

The generator start/stop feature of the Cerbo is WAY better than the assistant. Much more flexible.

I'll move over to that method if more flexible

Look at LFP charge and discharge curves

I was under the impression the drop off was steeper under 10% not 18-15%

Have you confirmed the BMS did not trigger low voltage protection?

No alarms in the battery section nor on the units themselves. I could also clearly hear the MPII relays alternating at 48 & 49V, just as the settings I was recommended. I'll move the DC shut-down to 44V as you say to allow the SOC setting to kick in first.

Thanks, I'll take your other recommendations as well and keep testing.