Sunsynk 5.5kW charging Fogstar 15.5kWh Battery pack - Won't charge to 100%

[GGW]

Unveiling the Future of Solar Storage: A Deep Dive into the Fogstar Energy 15.5kWh Battery

The Fogstar Energy 15.5kWh Battery rewrites the storage narrative, transforming sunlight into a reliable, on-demand energy source, empowering you to break free from the limitations of the grid.

www.fogstar.co.uk

Fogstar lists sunsynk as an acceptable inverter for this Battery pack.

The issue: On first install - I charge my battery pack to 100% (after a sunsynk factory reset, this works on the first night)
Every cycle after this, the sunsynk will charge and 1% lower each day (cycle)

Today was 93%. Tomorrow will be 92%.

If I factory reset the sunsynk it will charge to 100%. The BMS is communication with the inverter - the screen is showing values and the BMS_ERR does not show an error.

The user timer works as described. I changed over the AGM-V and adjust thed voltages - Shutdown works fine.

Voltages are set to 57.6 & 55.2V.
I am at a loss and both Sunsynk and fogstar support have not got a solution...

HELP please

 

[GGW]

@houseofancients

Have read many of your answers. You seem much more knowledgable than myself.
Any thoughts.....

There is a voltage difference between the V-bat voltage and the BMS Voltage, plus the V-bat voltage also reaches the BMS charging voltage value of 56V. This causes the battery to no longer charge.

Please ask the customer to contact the battery dealer to check the battery and to upgrade the battery firmware.

Supporting Images....

 

[kommando]

When in closed loop what canbus protocols are the inverter and battery set to.

Do you know what BMS is in your Fogstar battery, they have used Seplos and Pace.

 

[GGW]

The Sunsynk cannot be set to a protocol that I can see - other than CAN
The Fogstar is set to Pylontech - several others are available.

The BMS in the battery is PACE, I'm lead to believe.

 

[SeaGal]

If I read your graph correctly, you are charging up overnight from 2:00am to about 08:00 am, but only at 2kW. From about 07:40 the battery charge rate reduces, which is expected as SOC goes over 90%.

My first thoughts are that you are simply not charging at a fast enough rate to achieve a charge from (what looks like) about 18% at 2:00 to put a full charge in the battery by the time your cheap rate finishes, bearing in mind that charge rate reduces as 100% approaches.

Can you try to increase the overnight charge rate to something over 3.5kW and see what happens by tomorrow morning?

 

[houseofancients]

Could be a few things..
Could you post an overview of your cell voltages when the battery is at its highest SOC ?

Can you post a screenshot of your lithium screen in the inverter ?
This would show the charge voltage, and if your comms are working alright

Also this BMS has a passive balancer, that needs time to balance, especially when newly or recently commissioned

As @SeaGal already mentioned, your charging time and /or max amps may not be sufficient to do that

I would change your charging voltage to 56.8 or 56 and let it charge overnight, all night untill either the BMS shutsdown charging, or the inverter..

Let us know how you fare with above, after we may be able to make some better recommendations

P.s. , the sunsynk can be set to either rs485 or canbus, but canbus is preferred for BMS comms

 

[Teshi80]

@GGW did you resolve this ?

if so how as I have the same issue.

 

[SeaGal]

So frustrating when we all try to help someone and they never get back - despite being logged in only a week ago

 

[Teshi80]

So I've raised a ticket with Fogstar, gave them some screenshots. I'll update if I get anything back next week,

but at present just after Lunch time, I lose 1% SOC - Sunsynk have given the inverter a once over, updated the software and confirmed it's not their side. and recommended I speak to the battery supplier/manufacturer

and to add to the FUN the Screen has also died after I turned the battery off and back on.

 

[Mongoose49]

So I’ve been having the same issue with mine, but I think it’s some glitch on the fogstar battery, when I switched the sunsynk over to agm battery the battery started going over voltage it wanted and it suddenly jumped to 100% charge, when prior to this it was reading 65% and the day before was 66% and the day before that 67% and so on. So there’s definitely an issue somewhere between the two, which sucks cause that means it’s not charging to the correct 80% charge it should be going to.

 

[houseofancients]

So I’ve been having the same issue with mine, but I think it’s some glitch on the fogstar battery, when I switched the sunsynk over to agm battery the battery started going over voltage it wanted and it suddenly jumped to 100% charge, when prior to this it was reading 65% and the day before was 66% and the day before that 67% and so on. So there’s definitely an issue somewhere between the two, which sucks cause that means it’s not charging to the correct 80% charge it should be going to.

I am pretty sure your cells are out of balance

 

[Mongoose49]

I am pretty sure your cells are out of balance

What makes you say that? It appears to be balancing on the screen, all 16 cells are around the same voltage…

 

[houseofancients]

What makes you say that? It appears to be balancing on the screen, all 16 cells are around the same voltage…

The behavior of your cells at their top voltage, the sudden jump to 100% and charge shutdown

 

[Mongoose49]

What makes you say that? It appears to be balancing on the screen, all 16 cells are around the same voltage…

The behavior of your cells at their top voltage, the sudden jump to 100% and charge shutdown

Well it’s still likely that me and the other guy is having the same issue isn’t it? Also what would I even do to fix it?

 

[kommando]

Balancing is not the same as balanced.

What cell voltage is the balancing set to start at and what is the 'about the same voltage'

 

[Mongoose49]

Balancing is not the same as balanced.

What cell voltage is the balancing set to start at and what is the 'about the same voltage

I’m not sure, do you know if can I access the settings of the battery? I think it’s a pace bms inside these fogstar batteries

 

[Teshi80]

@Mongoose49 if its the 15.5KW it is the Pace BMS.

@houseofancients i've switched on the active balaning and plan to leave it on for the next few days, see if it helps.

I hope Fogstar come back next week as without the screen I have to keep taking the laptop to the battery lol, 1st world issues.

 

[Teshi80]

where do I set the 56V charge voltage on the sunsynk ?

 

[houseofancients]

where do I set the 56V charge voltage on the sunsynk ?

You would have switch to voltage on your battery screen, otherwise you would have to change the settings in your bms

 

[Teshi80]

You would have switch to voltage on your battery screen, otherwise you would have to change the settings in your bms

Job for tomorrow. I'll take the laptop out and see, as the screen is Poked at the mo.....

 

[houseofancients]

You would have switch to voltage on your battery screen, otherwise you would have to change the settings in your bms

If you do change to voltage, disconnect the comms

 

[Mongoose49]

H

If you do change to voltage, disconnect the comms

you guys are really great! Im curious why would this be necessary?

 

[houseofancients]

H

you guys are really great! Im curious why would this be necessary?

Because the BMS communication will override any settings you do in the inverter itself.
Normally this is exactly what one would want for safety, but when keeping the cells at a specific ( and usually a bit lower ) voltage for let's say top balancing, you don't

 

[SeaGal]

and to add to the FUN the Screen has also died after I turned the battery off and back on.

Interesting - that's the 2nd Fogstar screen I read about in the last month that's broken.

So there’s definitely an issue somewhere between the two, which sucks cause that means it’s not charging to the correct 80% charge it should be going to

Why 80%? If you're only charging to 80% you'll never give the BMS a chance to keep the cells in balance.

 

[Teshi80]

OK So update, the unit is going back for repair, they say the Screen and charging issue can both be fixed.

I will let you know when it's collected and returned and the overall results etc.