When does a Fogstar battery shut down?

[Andy MacD]

Currently in the south of France and been off grid since Tuesday.

The Fogstar app for my 280ah Drift battery states charge at 25% and voltage at 13.1v.

My SmartShunt has state of charge at 50% and voltage at 13.14v.

I believe the SmartShunt as Fogstar previously told me the BMS was to protect the battery rather than provide info through the app which not accurate as it did not record current draw under 1amp. I don’t think the Fogstar app is recording the solar input correctly.

On the basis of the voltage and the SmartShunt readings I’m happy to go for another couple of days before charging but when does the Fogstar shut down on the basis of cell voltage or the state of charge reading? I’ve asked Fogstar the question but they’ve not responded yet and are probably closed for the weekend.

Does anyone know the real answer?

My guess is that it’s the cell voltage that determines shut down but I’d be interested to know if any of the electrical experts know the answer.

Thanks all.

 

[Jev88]

Has my Fogstar down to 5% (inverter accidentally left on) and shut down. The shutdown level is adjustable I think?

 

[Andy MacD]

Thanks Jev88 , any idea what the voltage was at that point to establish if it shut down because it was at 5% or voltage at that time?

 

[Derbyshire wanderer]

Lithium batteries should be put on charge at 10% capacity or above.
The BMS will shut down at a critical level (0%) but prompt charging will reset it without any problems.

 

[Raul]

A bms will cut out discharge at low cell voltage, and cut out charge at high cell voltage. If it cuts out at a SOC value, it may be an additional setting to stop discharging at a certain setable threshold.

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[Andy MacD]

I think I may be able to answer my own question, according to Chat GBT.

My question was
For the Fogstar battery the state of charge is unreliable as it does not record draws of less than 1v. In that case does it shut down based on the state of charge or does it shut down at 10.0v

The answer is
Great question — and you’re absolutely right. The Fogstar Drift batteries use a smart BMS that does not rely on state of charge (SoC) estimates for shutdown, especially since, as you mentioned, low current draws under 1% (around 2.8A on a 280Ah battery) may not register accurately in the internal coulomb counter.

So to answer directly:

The Fogstar Drift 280Ah battery shuts down based on voltage, not SoC.

Specifically:

BMS Low Voltage Cutoff: ~10.0V
Regardless of what the SoC reading says, if the battery voltage drops to 10.0V, the BMS will shut off output to protect the cells.


Why SoC isn’t reliable on its own:

• The SoC is calculated based on current going in and out, but the BMS ignores currents below ~1% of rated capacity (to avoid noise and drift).
• Over time, small loads or trickle drains (e.g., standby electronics) can deplete the battery without the SoC reflecting it.
• This is why voltage remains the fail-safe method for shutdown, and why Fogstar and other LiFePO₄ manufacturers recommend using voltage-based monitoring rather than SoC for critical limits.

If you’re depending on SoC for system management, it’s worth supplementing it with:

• A shunt-based battery monitor (like Victron SmartShunt or BMV-712), which tracks all current accurately.
• Or keep a close eye on voltage under load, especially as you near the end of usable capacity.

I recon at 13.1v I have a couple of days at least to go, I’ll be interested to see how Fogstar’s response compares to AI.

 

[jwells]

This may be of help hopefully! It is directly off my 280 Fogstar!

 

[Lenny HB]

The Fogstar app for my 280ah Drift battery states charge at 25% and voltage at 13.1v.

My SmartShunt has state of charge at 50% and voltage at 13.14v.

That is very unusual as you say the BMS is often out because it can't measure small currents but I've never seen it that way round.
I often see my BMS at 80% but shunt which I know is accurate is at 50%.

Can you post a photo of your shunt settings.

 

[Raul]

BMS Low Voltage Cutoff: ~10.0V
Regardless of what the SoC reading says, if the battery voltage drops to 10.0V, the BMS will shut off output to protect the cells.

Only half true, and if all cells are equally balanced to the last millivolt at 2500mV each, then the above its true.
However, it can shut down discharge much sooner, and at any voltage the moment one cell reaches 2500mV-2.5V.
If one cell reaches 2.5v it will stop discharging.

 

[Andy MacD]

That is very unusual as you say the BMS is often out because it can't measure small currents but I've never seen it that way round.
I often see my BMS at 80% but shunt which I know is accurate is at 50%.

Can you post a photo of your shunt settings.

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[Andy MacD]

My intention was to let it run to around 12.25v then get EHU for a day to charge it fully.

 

[Cush]

Is your discharge floor not a bit low? Thought FS recommended 20%. Not that it will affect the battery turning off. Just jumped out at me.

 

[Raul]

That would be my lowest too, but, not under load voltage. The problem is, being at 12.25v and turn on a large load, it may trigger the bms.
Also your shunt settings look good to me, except one, I would change peukert value from 1.05 to 1.02.

 

[Lenny HB]

One thing I would change is the Battery SOC on reset best to change to Keep SOC.
I think that could be your problem.

 

[Peregrinator]

Currently in the south of France and been off grid since Tuesday.

The Fogstar app for my 280ah Drift battery states charge at 25% and voltage at 13.1v.

My SmartShunt has state of charge at 50% and voltage at 13.14v.

I believe the SmartShunt as Fogstar previously told me the BMS was to protect the battery rather than provide info through the app which not accurate as it did not record current draw under 1amp. I don’t think the Fogstar app is recording the solar input correctly.

On the basis of the voltage and the SmartShunt readings I’m happy to go for another couple of days before charging but when does the Fogstar shut down on the basis of cell voltage or the state of charge reading? I’ve asked Fogstar the question but they’ve not responded yet and are probably closed for the weekend.

Does anyone know the real answer?

My guess is that it’s the cell voltage that determines shut down but I’d be interested to know if any of the electrical experts know the answer.

Thanks all

Yes they don't work weekend. You can tell the app when to shut off, You can set the cell undervoltage protection to 2.5 volts per cell, but I keep mine at 2.8 volts per cell, you may have a setting called Power off Voltage, you can set that at 2.5 volts.

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[Raul]

One thing I would change is the Battery SOC on reset best to change to Keep SOC.
I think that could be your problem.

Agree, I missed that setting.

 

[Andy MacD]

Thanks all. I’ll get EHU in the morning to get back to 100%

 

[Jev88]

Thanks Jev88 , any idea what the voltage was at that point to establish if it shut down because it was at 5% or voltage at that time?

Sorry I didn't measure, just put it on mains charger.

 

[Andy MacD]

So this morning the voltage was 13.1v, the Fogstar SOC 8% and SmartShunt 38%.

Mark from Fogstar responded and asked me to go into advanced settings and change the Cell Full Voltage from 3.55v to 3.50v. Once battery fully charged sync the SmartShunt to 100%.

I’ve just taken a day of EHU so we’ll see if the Fogstar app tracks more accurately over the rest of the week.

Mark confirms shut down based on voltage only. SOC is for info only so relatively unimportant.

 

[headlight]

So this morning the voltage was 13.1v, the Fogstar SOC 8% and SmartShunt 38%.

Mark from Fogstar responded and asked me to go into advanced settings and change the Cell Full Voltage from 3.55v to 3.50v. Once battery fully charged sync the SmartShunt to 100%.

I’ve just taken a day of EHU so we’ll see if the Fogstar app tracks more accurately over the rest of the week.

Mark confirms shut down based on voltage only. SOC is for info only so relatively unimportant.

How many cycles does the app say you have completed ?

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[Andy MacD]

40

 

[headlight]

40

 

[G-RMPS]

Any advance on 4%? :-(

 

[Raul]

Any advance on 4%? :-(

View attachment 1046521View attachment 1046521

Charge it up, there's not much left on there and it will be much harder to bring it up from near zero.

 

[G-RMPS]

Trying. Still have problems.

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[Raul]

Trying. Still have problems.

Can you expand?

 

[Andy MacD]

So the plot thickens.

I’d not noticed but the capacity of the battery on the app was showing as 210ah, not 280. No idea when that changed or how as I’d never used the advances settings till Fogstar told me to change the max cell voltage from 3.55 to 3.5v.

So they said simply go into advance settings and change the nominal capacity back to 280ah.

I did that so now my fully charged battery is sitting at 60% with 168.1/280.

I’ll see what the advice is now, don’t understand how the settings can just change.

Meantime I’ll believe the SmartShunt.

 

[G-RMPS]

Hopefully the last reply in this thread from me. Troubleshooting the "B2B problem" revealed two problems. The Fogstar battery wasn't being charged by the solar panel/controller. And there was a continual 2.2 - 2.4Ah drain on the battery.

The first problem was a loose/disconnected wire on the Victron solar controller. That prevented any charging, even though the controller was showing a battery voltage of 13.5V and in "float" mode. The 15A fuse between the battery and the controller was blown. Possibly due to intermittent current from that loose wiring connection, or possibly at the point of reconnecting the wire?

At the time of purchase I got the dealer to add a heater to the grey water tank. But I never found how to switch it on. While troubleshooting the above, I found a rocker switch on the back of the passenger seat base. When I switched it (to off!), the battery drain disappeared.

So I have been heating the grey water tank continuously for three months, Fortunately on EHU for most of that time.

Battery is now slowly recovering thanks to some solar radiation in Scotland

PS Sorry, I gatecrashed this thread. I should have posted the above as the conclusion to "Is B2B working?"

 

[BouncyBoatFolk]

Hopefully the last reply in this thread from me. Troubleshooting the "B2B problem" revealed two problems. The Fogstar battery wasn't being charged by the solar panel/controller. And there was a continual 2.2 - 2.4Ah drain on the battery.

The first problem was a loose/disconnected wire on the Victron solar controller. That prevented any charging, even though the controller was showing a battery voltage of 13.5V and in "float" mode. The 15A fuse between the battery and the controller was blown. Possibly due to intermittent current from that loose wiring connection, or possibly at the point of reconnecting the wire?

At the time of purchase I got the dealer to add a heater to the grey water tank. But I never found how to switch it on. While troubleshooting the above, I found a rocker switch on the back of the passenger seat base. When I switched it (to off!), the battery drain disappeared.

So I have been heating the grey water tank continuously for three months, Fortunately on EHU for most of that time.

Battery is now slowly recovering thanks to some solar radiation in Scotland

Neon/LED switch replacement for the rocker switch?
Mike.