SOC monitor issue?

[goeasy123]

How do I tell the true SOC when the battery monitor has lost its way?

I have 2 x 140Ah 12v wet lead acid batteries. The battery monitor is an oldish Mastervolt Combi Control Panel. On Med sunny the batteries are at 100% by early afternoon (4 x 115W PV, 2P2S = 460W). 2 x Victron Smart MPPT 100/20's. After a few days of grey weather I think the battery monitor loses its reference. The load is two fridges, LED lights and nav kit drawing not more than 10A.

After running the generator for 2 hour this morning and motoring all day the monitor gets stuck at 75%. It is safe to assume this is 'the new' 100% charge or close to it? The Victron app says the batteries are in float. At the moment (late evening) there are no charging source and the batteries are sitting at 12.55V with something (probably fridge) drawing 5.5A. Any help much appreciated.

 

[CapPugwash]

I have inherited a similar setup, albeit 24v and without solar (yet), and am just starting to get my head around it. Mine gets to about 85% SOC on generator and then seems to jump to 100%

I don't think you should worry about the 12.55 under load. For a true reading you need to disconnect any load and let it rest for a while.

 

[Mistroma]

Battery capacity of 280Ah when new sounds very low for 2 fridges in med., even if water cooled. Probably well below 280Ah if a few years old.

I assess SOC with Smart gauge and temp. compensated SG. However that doesn't give capacity and I use Coulomb counter for that. You should get to 100% with amount of solar installed.

450W solar and 450Ah bank with 1 fridge.
100% mid. afternoon when sunny. Still reaches 90% when cloudy.

Showing 12.65V just now with fridge, anchor and saloon lights on.

I'd suggest a capacity check. Does your old system self adjust capacity over time or rely on manual input?

 

[KompetentKrew]

The battery monitor is an oldish Mastervolt Combi Control Panel.

Does this have a shunt?

Because what you haven't written here is "none of the charging sources are connected the wrong side of the shunt".

Did you add the SmartSolars yourself to the existing system with the Mastervolt monitor? Where did you connect them?

 

[goeasy123]

Battery capacity of 280Ah when new sounds very low for 2 fridges in med., even if water cooled. Probably well below 280Ah if a few years old.

I assess SOC with Smart gauge and temp. compensated SG. However that doesn't give capacity and I use Coulomb counter for that. You should get to 100% with amount of solar installed.

450W solar and 450Ah bank with 1 fridge.
100% mid. afternoon when sunny. Still reaches 90% when cloudy.

Showing 12.65V just now with fridge, anchor and saloon lights on.

I'd suggest a capacity check. Does your old system self adjust capacity over time or rely on manual input?

Sorry, didn't finish the sentence. 460Ah in total. (2 x 140Ah in parallel) x 2 in series. The batteries are 6 month old. The old system self adjusts over time, but it needs 3 days on shore power to do that and it does it with PV normally on a string of sunny days. I get roughly the same balance as you, but I should be able to run 2 fridges as I run the generator in the morning for a hour... when the batteries can take the charge, I also make water at the same time.

Does this have a shunt?

Because what you haven't written here is "none of the charging sources are connected the wrong side of the shunt".

Did you add the SmartSolars yourself to the existing system with the Mastervolt monitor? Where did you connect them?

Yes. All the charging source are on the right side of the shunt.