State of charge

Bessy765

Bessy765

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Hi all, I have a 2019 Burstner on the Fiat 2.3 150 hp. Have a query re the batteries. (Two 95 amp AGM’s) van is stored in my garage so no help from the 100 watt solar panel. If on hook up the batteries never get to 100%. If I let them run down to say 90% plug in ehu the percentage of charge never gets above 93% even less if I let them discharge further. I have set the control panel to tell the system there are two batteries. If I disconnect both the 50 amp fuse and the smaller one right by the leisure batteries. Leave it for say half an hour when putting fuses back in the state of charge will show 100%. Left on hook up overnight nothing on the state of charge now shows 97%. Whilst still on hook up if I Turn all the lights on the display shows 0.00 amps so not charging or discharging voltage is 13.4 but the state of charge still only shows 97% two hours later state of charge now 95% and zero charge or discharge.
 
The Burstner has a control panel when you turn the control knob to check the voltage of the leisure batteries, then press it once you kept the amps in or out, press again you get state of charge. I have checked the voltage at the batteries and it corresponds with the voltage at the panel within a tenth of a volt.
 
Has it always been like that? Even the expensive battery monitors are only estimating the capacity based on their programming, our BM1 monitor sometimes shows 104% when the battery is full, but I know what it means 😏

Not familiar with your system but some don't even have a shunt installed and are even less accurate, relying just on battery voltage.
 
A calibration issue with your control panel perhaps ????

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Richard n Ann said:
Has it always been like that? Even the expensive battery monitors are only estimating the capacity based on their programming, our BM1 monitor sometimes shows 104% when the battery is full, but I know what it means 😏

Not familiar with your system but some don't even have a shunt installed and are even less accurate, relying just on battery voltage.
Click to expand...
As does mine !
 
Thank you for your replies. It’s not so much as to how accurate the % gauge is, its the fact that it reduces over a period of time even when still plugged into the mains and the fact that it never seems to fully charge. But if you pull the fuses wait a bit put the fuses back in it then shows 100% but then begins to fall even when still on hook up.
 
Bessy765 said:
Hi all, I have a 2019 Burstner on the Fiat 2.3 150 hp. Have a query re the batteries. (Two 95 amp AGM’s) van is stored in my garage so no help from the 100 watt solar panel. If on hook up the batteries never get to 100%. If I let them run down to say 90% plug in ehu the percentage of charge never gets above 93% even less if I let them discharge further. I have set the control panel to tell the system there are two batteries. If I disconnect both the 50 amp fuse and the smaller one right by the leisure batteries. Leave it for say half an hour when putting fuses back in the state of charge will show 100%. Left on hook up overnight nothing on the state of charge now shows 97%. Whilst still on hook up if I Turn all the lights on the display shows 0.00 amps so not charging or discharging voltage is 13.4 but the state of charge still only shows 97% two hours later state of charge now 95% and zero charge or discharge.
Click to expand...

13.4V is not enough to charge AGM batteries, it is just a maintenance charge. Your charger needs to have an initial charging phase with a voltage in the range 14.6-14.8V. You will find a guide to charging AGM batteries here.
www.alpha-batteries.co.uk

A Detailed Guide to AGM Batteries - Alpha Batteries

With AGM products becoming more widespread in their use, knowing when you can or should use one and how to look after it properly is all the more important - our guide is here to help.
www.alpha-batteries.co.uk www.alpha-batteries.co.uk
The mains chargers in many motorhomes have a Gel battery setting giving about 14.3V but do not have an AGM setting.

Battery monitors have to know the charging efficiency and peukert’s exponent of the battery to keep proper track of the state of charge. Even then they need to synchronise regularly, which the better ones do by monitoring the tail current having reached a fully charged voltage. An earlier post mentioned a 104% charge which whilst technically impossible demonstrates that there is a difference between what goes out and what needs to go back in to replace it. Your battery monitor may be of a type that gives only a rough guide to the state of charge.

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The voltage when I have removed the main fuse waited and refitted it is 14.6 to 14.8 but once the battery is fully charged the voltage drops down, the % of charge starts at 100 % but gradually drops down and even if I turn on every light and the heating it shows no discharge amps ( it does if I turn the charger off ) and the voltage stays at 13.4.
 
The battery voltage will drop back to near 13V after charging even if the battery is disconnected. The mains charger will supply the bulk of the power whilst in the maintenance phase. A small amount of self discharge is normal in all lead acid batteries which includes AGM. There may also be a small flow of power from the battery if it’s voltage is slightly higher than the battery chargers voltage, this might be too small to register on amps display being only milli amps. However the battery monitor should still be monitoring these small amounts and adjusting the charge level accordingly. Perhaps you are expecting too much precision from the equipment.

AGM batteries are very good as engine batteries for stop start engines because they tolerate heavy rapid bursts of power in and power out. They are generally less tolerant of deep discharge than Gel or LiFePO4.

What type of mains charger do you have?
 
It is not so much about how accurate the equipment is. It is the fact the with the hook up on so battery charger working once the initial full charge, the % of charge will drop slowly down, the voltage stays at 13.4. But if I leave it long enough it will drop as low as 88%. That is with the hab power off. The % of charge reading does fall slower when hook up off hab power off?
 
Replaced the Hella IBS & it made no difference to my percentage charge reading still very intermittent even when at full voltage
Can show between 74% up to 100% if I reset the connection to the IBS it shows 100% but if I power the display panel off/on
The reading drops again.
I’m now thinking of getting a Victron shunt with Bluetooth to monitor
 

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