Battery Problems

Kelvin8tor

Kelvin8tor

Joined
Jan 2, 2023
Posts
68
Likes collected
94
Location
Cheltenham
Funster No
93,141
MH
Swift Bolero 684FB
Exp
Since 1998
Around about a year ago I upgraded the 12v system on my motorhome changing to a lithium battery
280 amp Fogstar drift battery
Renogy 30 amp battery to battery charger with 300 watts of solar
Renogy 2000 watt inverter
Every thing has been working fine although I only ever used around 50% of the battery
Use is normally microwave kettle and charging bike batteries phone batteries
I have during the last couple of trips powered the fridge through the inverter
I have been away for a few days and decided to get full use out of the battery so during the day I have had the fridge powered through the inverter and when monitoring the apps both Fogstar and Renogy the battery was discharging at around 2.5-3.6 amps due to the solar generated
The battery had dropped to around 42% this afternoon and being as we are heading back home tomorrow I continued to use the inverter then suddenly the inverter alarm came on and the fridge lit up on the gas the Fogstar app reported over discharge and shut down the Renogy app reported the same over discharge of leisure battery
Not sure what happened as the battery should still have plenty of power
The renogy app has shown the minimum voltage today at 8.9 volts maximum today of 13.8
The Fogstar app is allowing discharge at the moment ( could not turn that on earlier ) voltage is currently 11.2 but no sun at the moment so no more charging cell voltage low 2.759 Hi 2.834 Diff 0.075
Any ideas
Thanks
 
How long since the battery was at 100% Soc?
Bear in mind the FS BMS doesn’t accurately detect small (<0.7A) drain which can add up over long periods of time.
 
In theory a 3A draw will deplete your 280 in about 93 hours.
Is it possible that something else used up the power?

Interestingly today I chased down a 3A draw caused by a faulty after market van stereo system. The installer took a feed from the TV wire, and something has gone wrong with the unit.
 
RogerIvy said:
How long since the battery was at 100% Soc?
Bear in mind the FS BMS doesn’t accurately detect small (<0.7A) drain which can add up over long periods of time.
Click to expand...
Hello, is the battery status source of truth on (for example) a Victron shunt based on telling the shunt the battery initially fully charged?

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If both BMS and Smartshunt are correctly set up they will both accurately register a full state of charge. The shunt does it by detecting current flow and voltage, and the BMS does it by detecting individual cell voltage.
 
RogerIvy said:
If both BMS and Smartshunt are correctly set up they will both accurately register a full state of charge. The shunt does it by detecting current flow and voltage, and the BMS does it by detecting individual cell voltage.
Click to expand...
I don’t have a smart shunt I only have the Fogstar app to indicate the soc perhaps this is totally inaccurate
 
Kelvin8tor said:
I don’t have a smart shunt I only have the Fogstar app to indicate the soc perhaps this is totally inaccurate
Click to expand...
When all is well you don’t need a shunt, but I guess when you need to debug it’s really handy. I’d consider fitting one if I was you.
 
I am hoping that the battery will recharge tomorrow on the drive home I do have a lithium battery charger at home that I purchased from Fogstar when I purchased the battery
I do not use the mains charger in the Motorhome as it has no lithium setting
 
Kelvin8tor said:
I am hoping that the battery will recharge tomorrow on the drive home I do have a lithium battery charger at home that I purchased from Fogstar when I purchased the battery
I do not use the mains charger in the Motorhome as it has no lithium setting
Click to expand...
If your charger has an AGM setting it will probably be OK. Not optimal but OK.

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RogerIvy said:
When all is well you don’t need a shunt, but I guess when you need to debug it’s really handy. I’d consider fitting one if I was you.
Click to expand...
Maybe I should purchase one any recommended that would integrate with my current system
 
Kelvin8tor said:
Maybe I should purchase one any recommended that would integrate with my current system
Click to expand...
I’d recommend Victron. The 300A, 500A or the BMV 712 (it has a small round display).
 
Kelvin8tor said:
I don’t have a smart shunt I only have the Fogstar app to indicate the soc perhaps this is totally inaccurate
Click to expand...
When my van is sitting the drive with just low current draw from the batteries the Fogstar BMS can read 20% higher than my Victron shunt, the shunt is the accurate reading.
 
Kelvin8tor said:
Is the Renogy smart shunt any good?
Click to expand...
I bought one and it failed quite quickly requiring to be reset every few days. They were fair and gave me a full refund. I then bought a Victron...

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Kelvin8tor said:
The battery had dropped to around 42% this afternoon and being as we are heading back home tomorrow I continued to use the inverter then suddenly the inverter alarm came on and the fridge lit up on the gas the Fogstar app reported over discharge and shut down the Renogy app reported the same over discharge of leisure battery
Not sure what happened as the battery should still have plenty of power
Click to expand...
Your fridge is a 3-way, able to run on gas, 12V or 240V mains. If set on 240V via the inverter, the inverter would probably be drawing at least 10-12A from the battery. Even in sunlight, you say the solar wasn't keeping up, so if you continued on the 240V setting into the evening, that would be a significant load on the battery.

As others have said, the 42% estimate of SoC could be optimistic, because the BMS can't measure low level discharges reliably. So my suspicion is that there isn't a fault as such - you have just drawn too much from the battery without realising it.

It is possible to have the system switch the fridge to mains power via the inverter automatically when there is spare battery capacity available - and more importantly, switch it back to gas automatically when the battery SoC drops below a level you select. RogerIvy could advise whether such a system might be economically justified in your case, but I suspect it might need a different inverter as well as a shunt..
 
TheCaller said:
It is possible to have the system switch the fridge to mains power via the inverter automatically when there is spare battery capacity available - and more importantly, switch it back to gas automatically when the battery SoC drops below a level you select. RogerIvy could advise whether such a system might be economically justified in your case, but I suspect it might need a different inverter as well as a shunt..
Click to expand...
Obviously the more solar you have the better.
We’ve installed this upgrade where there is a Multiplus 3kva and Cerbo GX, and lots of solar. In these cases we’re already installing most of the equipment so just a few hours and a cable run to the fridge is required.
You can also achieve the objective using a BMV712 shunt and an “inverse” relay to simulate a D+ going to the fridge. You can combine the simulated D+ with the real one using diodes. …. Gets more complicated 🤔
 
TheCaller said:
Your fridge is a 3-way, able to run on gas, 12V or 240V mains. If set on 240V via the inverter, the inverter would probably be drawing at least 10-12A from the battery. Even in sunlight, you say the solar wasn't keeping up, so if you continued on the 240V setting into the evening, that would be a significant load on the battery.

As others have said, the 42% estimate of SoC could be optimistic, because the BMS can't measure low level discharges reliably. So my suspicion is that there isn't a fault as such - you have just drawn too much from the battery without realising it.

It is possible to have the system switch the fridge to mains power via the inverter automatically when there is spare battery capacity available - and more importantly, switch it back to gas automatically when the battery SoC drops below a level you select. RogerIvy could advise whether such a system might be economically justified in your case, but I suspect it might need a different inverter as well as a shunt..
Click to expand...
My 137lt 3way fridge seems to draw around 18amps, I think the 24hr figure quoted in the spec is around 400AH!

One day I'll put a condenser in.
 
We run a little node red flow to turn the MP 3kva on and off depending on the batteries SOC and available solar, but can also use 12v if prefered not yet put the last bits in for the 12v, but it's simpler to do in some ways.
 
TheCaller said:
but I suspect it might need a different inverter as well as a shunt..
Click to expand...
No system needs a 'shunt' to work. A shunt is just a big lump of metal.

However, a shunt based battery monitor will give you a good display of how much of your battetry capacity you have used.

It will also tell you what current you are currently drawing from the battery.
And it will do both more accurately than the bluetooth based BMS in your battery.

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LithiumConvert You have taken my quote out of context. Earlier posts in the thread had already established that a shunt would be desirable, for all the reasons you now repeat - in particular the improved accuracy of the state of charge measurement.

It would have been more long-winded, but perhaps clearer, if I had said:
'As well as fitting a shunt, as earlier suggested, I suspect a different inverter will also be needed.'
Roger mentions the Multiplus, which with its 2nd AC outlet makes this relatively simple.

RogerIvy said:
You can also achieve the objective using a BMV712 shunt and an “inverse” relay to simulate a D+ going to the fridge. You can combine the simulated D+ with the real one using diodes. …. Gets more complicated 🤔
Click to expand...
However, if I understand this last comment by Roger correctly, it sounds as if it might be possible without changing inverter - but I got a bit lost at this point! I think Roger is suggesting using the 12V element in the fridge, rather than 240V from the inverter.
 
The battery monitor and the inverter are two distinct issues.

The orignal wording implied they were related.
 
Last edited:

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