I think this is getting confusing. Sometimes you guys are stating readings reported by a battery, and then you refer to parameters set within the inverter.
Measuring SoC is tricky. Doing so over long periods of time without re-defining it by charging the battery(ies) to 'full' is nigh on impossible.
Let's assume that the figures you're stating here are within plus/minus 5% almost all the 'inaccuracies' we've just discussed are actually within the range of acceptability.
Firstly, I agree with @ggw that it's the inverter which is 'in control'.
Theoretically it's possible, but I haven't heard of that being implemented.
The BMS in that battery would need to have been pre-loaded with the command-set for your particular model of inverter. It would then need to select the Modbus command from that set and send it to the inverter across the CAN or RS485 connection.
The inverter could then start charging the battery from the grid...
... until something else then happened.
And what is that something else?
Does the battery initiate another command? At what point? How can it know its SoC accurately enough whilst still being re-charged at high current?
Or would the inverter intervene anyway? Might it read its own configuration settings and stop the grid-charge because a particular parameter had been reached?
Matching batteries and inverters is normally not undertaken at that level.
They wouldn't normally send commands to each other. Their 'compatibility' is rarely more than just sending data from the battery to the inverter, which you can then see on the inverter's App.
Our hybrid inverter is a sunsynk, and while it states the SOC monitored by the (Seplos mason) battery I’m pretty sure it uses its own voltage measurement to indicate full/empty, and takes emergency measures based on it. The voltage levels it uses are “hidden” - you have to swap to batt=Pb voltage control, set the levels, then swap back to Li bms. Weird, and when it works (it is), it’s not something I’d like to mess with.
I have been reading all the posts abotu Fogstart 15.5 kwh battery. I would like to get one without solar. Ideally I would like someone to install but I don't see anyone at the moment.
What is the max charge and discharge power from this battery, from the spec sheet it says 200A, but not about peak/continuous charge and discharge power? Somewhere I don't recall it was mentioned that it is under 2kw that seems quite low.
If I want to DIY install can I not go over 3.6kw inverter? Do I have to get G99 prior before if I want any thing higher?
Hi @littlefinger and well done for finding an appropriate topic in which to post 🙂
Firstly, the Fogstar storage batteries have no direct connection to either the grid or to solar panels. You require a separate inverter to achieve that.
That 200A is the maximum sustainable current. It's unlikely that you'd ever want to pull that many amps from your battery.
200A at 52v is over 10kW. I don't know from where you got the 2kW figure. It's not correct.
The limit of 3.68kW and G99 are factors which apply to inverters which export to the grid.
If you wish to do a DIY installation and you don't intend sending power back to the grid, then neither of these issues is relevant.
Tell us a bit more about what you'd like to achieve, preferably without too much technical stuff! We can get more technical when we understand what you'd like to do.
forums can be a minefield of misinformation. So the max input in Kw for a 200A bms is 2.4Kw It's a little over 2.4 as lithium operate at 13.2v (meadan voltage range)
So in answer
2.4Kw (2400w) max charge and discharge.
Hope this clarifies.
Any resources on how to calculate there figures from spec sheet?
At the moment I have install home battery storage at lower cost and came to know about Fogstar battery.
After reading this thread and other online forums it looks like Sunsynk Hybrid inverter is good choice.
My immediate goal is to shift my grid import to off-peak, while keep my options open for future expansion for extra batteries and Solar. There is possibility of getting EV but not right now.
From what I understand, G99 is required even if you do not want to export if inverter is over 3.68kW
I'm thinking of having either 8kW Ecco Hybrid Inverter or 8kW Hybrid Inverter (not sure what the difference, except for one is smaller than other) or Sunsynk-LifeLynk-XL.
Would G99 approval specify how much one can export? That is can I get approval to export without solar so if I add solar later I do not have to apply again.
That reply from Fogstar is in response to a question about a battery rated at 13.2v, which tells me that it's probably four LiFePO4 cells in series.
The Fogstar 15.5kWh battery bundle uses sixteen LiFePO4 cells in series, each rated at 3.2v (nominal):
Power in watts (or kilowatts) = Volts x Amps
Yes the SunSynk 8kW inverter is a good choice for an off-grid system.
The SunSynk inverters do have the capability to export to the grid. So you would still need to obtain G99 consent from your DNO, even 'tho you will configure the export to be Zero.
That's the most common arrangement for SunSynk installations in the UK. You state the inverter model number on the G99 Form, and the DNO will look this up on the ENA Database.
SunSynk's export-limitation feature has already obtained ENA approval to operate with Zero-export. So you will be given G99 approval regardless of the power-rating of the inverter.
Once you have DNO consent for Sunsynk inverter(s) operating with Zero-export, you do not need to reapply if
you add solar input
you add another SunSynk inverter in parallel configuration
you add further battery storage
Your off-grid system might then look something like this:
Just wanted to share my experience with this kit, as I feel I need to pay back the help this site gave me. Without it, I would not have taken this step.
I bought a SEPLOS V4 Kit and x16 Envision 315Ah from Fogstar. I have been doing the top balancing of the cells for almost a month.
They advise to get a NANKADF DC adjustable power supply, connect the cells in parallel and charge before assembling the kit. I bought one adjustable bench power supply that is 0-30V, 0-5A. The website says: "Hold at 3.65V Until Current Drops Below 1A ". I set it to a fixed voltage so it gives me a reading of the amps that the cells are taking. That started just below 5 and it went down to 3.55A. It has been at that level for a week!
I now have my 8k Solis inverter all ready and this top balancing has been raising questions. Since the cells are not taking any reasonable charge when wired in parallel, it could only get worse when they are in the cage and wired in series?
Have to say Fogstar have been supporting me over email and phone. They respond quickly, but I wish the answers would be consistent.
My concern is since I am planning to have the cells charging when the wind blows and discharging most of the time, I need them to be able to take as close to the inverter capacity as possible. Otherwise I will get no ROI.
The instructions from Fogstar are correct (as usual!), but they haven't explained the reasoning behind the top-balancing process.
Here's a set of cells I was charging in parallel:
My power-supply was rated at 12A, rather than the 5A unit you're using. Even so, it takes the best part of a week to bring the cells up to the same voltage.
The time taken depends on the State of Charge (SoC) which they happened to have when they left the factory. There is no predetermined value for this.
Note that my supply wires (blue and brown) are connected in the middle of the row of cells.
There is considerable voltage drop along the row. Those closest to the supply wires will get preferentially charged.
I've proved that point by using a secondary voltmeter. The display on the power-supply states that the supply wires are at 3.49v. The (yellow) +ve connection to the multimeter is connected two cells further along (behind the current-clamp meter). That records a voltage of 3.466v.
If I'd checked the cells at far ends of the row, then I'd expect to have seen as much as 0.4v drop!
The quality of your cell connections makes a huge difference when performing Top-Balancing. Use copper wire that is appropriately thick, and ensure the cell bolts are 'tight'.
NB to avoid stripping the aluminium threads in the top of the cells, the definition of 'tight' is dictated by the cell manufacturer's specifications. The cells in my photo are made by EVE, and the maximum permitted torque is 8Nm (8 Newton-meters). You need a decent torque-wrench that can operate at low values.
I use a Wera A6, which retails at well over £100. It can be set as low as 2.5Nm.
These low-value torque wrenches often pop up for sale on Ebay or Amazon Resale because someone wanted a 'normal' torque wrench and purchased one with a low range by mistake. They then want to sell it on.
this top balancing has been raising questions. Since the cells are not taking any reasonable charge when wired in parallel, it could only get worse when they are in the cage and wired in series?
No. The voltage balance will slowly get better once they're in-use.
The BMS (Battery Management System) in Fogstar's enclosure will handle that balancing during charging. But the balancing current used by a BMS is pretty small - typically 2A.
It can take a couple of months to achieve the level of cell balance you should be running at with the cells in series... ... which is why we all do Top-Balancing in parallel first!
I can't answer specific points on what could be taking such a long time with your Top Balancing operation. I'd need more data and some photos to help with that.
But the points you make are quite valid. Top-Balancing is a tricky subject to understand. It's a shame that newcomers need to understand it so early in their first battery-build!
You should continue to post questions and observations here... ... very shortly you'll be called upon to help others!
This post was modified 6 days ago 2 times by Transparent
I am planning to have the cells charging when the wind blows and discharging most of the time
You're intending to link up a wind turbine?
How would you expect that to connect to a Solis inverter? Did you realise that the product name is derived from the Latin word 'sol' which means sun ? That's a big hint as to what the device is intended for.
I can't see any configuration options in the Solis Manual to accept input from a wind turbine.
Contrarywise, I have found primitive instructions in the (older) installation manuals for Sunsynk inverters. They're absent from the latest manual versions, but I believe the functionality is still present.
Running up a wind-turbine has a steeper learning curve that that for solar panels. The concepts are harder to understand, especially the precautions you need to have in place for days when peak-output is achieved. You can't just isolate a wind-turbine by opening a contact breaker for example.
I am planning to have the cells charging when the wind blows and discharging most of the time
You're intending to link up a wind turbine?
How would you expect that to connect to a Solis inverter?
Oops. What I meant is when the wind blows, and in case the market regs force them to sell, that is the time to charge a battery from the grid, just a proxy for future prices.. I have not found a source for electricity price prediction, Octopus retail prices are only available for the next day. But there´s a data feed of grid greeness forecast available.. I think that is mostly based on wind, solar not being a significant part of the mix.
The instructions from Fogstar are correct (as usual!), but they haven't explained the reasoning behind the top-balancing process.
Yup, when I calculated how long it would take, I thought their instructions are a shambles in this area!!!
To be frank there are far too many holes as they do not provide anything close to step by step. If they wanted this to be truly DIY, they should have a video that matches what they actually ship, keep updating passwords needed for all of it, provide links to the software needed, etc, etc.
I can already say it was not worth the time I spent on it. If Ikea would provide these type of out of date instructions, they would have shrunk and died. I guess people take to this because to some extent they want to learn, but the time required for anyone trying to make sure no mistakes are made is massive.
You need a decent torque-wrench that can operate at low values.
I use a Wera A6, which retails at well over £100. It can be set as low as 2.5Nm.
These low-value torque wrenches often pop up for sale on Ebay or Amazon Resale because someone wanted a 'normal' torque wrench and purchased one with a low range by mistake. They then want to sell it on.
Look around for a bargain.
I got a battery operated one and measured the torque 😉
this top balancing has been raising questions. Since the cells are not taking any reasonable charge when wired in parallel, it could only get worse when they are in the cage and wired in series?
No. The voltage balance will slowly get better once they're in-use.
Ok, but what I saw is that the cells were not even using 5A, which was enerving... Fogstar supply some extra metal connectors, so the setup was not restricting the current flow.
Fogstar now advised to give up this balancing method, so when I built the battery, it is clear that the last cells have slightly different voltage at the moment. But the last ones of the pack seem to have slightly higher than the first, like 0.001V type differences.
The BMS (Battery Management System) in Fogstar's enclosure will handle that balancing during charging. But the balancing current used by a BMS is pretty small - typically 2A.
It can take a couple of months to achieve the level of cell balance you should be running at with the cells in series... ... which is why we all do Top-Balancing in parallel first!
Makes sense, but from what it seemed, this is something that requires manual switching to a balancing mode? If this would happen automatically, perhaps the typical user would be fine to not have the fully capacity of the battery available for a few months and just take this much easier route..
But the points you make are quite valid. Top-Balancing is a tricky subject to understand. It's a shame that newcomers need to understand it so early in their first battery-build!
You should continue to post questions and observations here... ... very shortly you'll be called upon to help others!
It is really something Fogstar do not explain, no mention of how long you may need to wait. And when someone says, "you can build and charge it with the inverter and then disassemble and top balance in parallel", how long would this take, are you really likely to do this quickly as a newbie and how much time can it take you to remove that overtightened screw, etc etc
I hear what you say @batpred but I'm of the opinion that building battery packs is a skill-set which should be passed across to others by self-help groups of enthusiasts.
It's similar thinking to that which you'd find in a model-railway club. I'd happily buy pieces of track and signalling systems from the manufacturers, but I'd be taking advice from my colleagues in the club as to what I can then do with them.
I'm getting ready to offer a hands-on battery build workshop for a group of Young Farmers in my area. Once they've grasped the basic principles, they'll be able to help each other and share the cost of the more expensive tools.
what I saw is that the cells were not even using 5A, which was unnerving
I don't know about your power supply, or the connectors, or how you are reading the current, which makes it difficult to offer suggestions.
Some photos would really help!!
I've previously come across cheap, generic desktop power supplies from China which can't output their rated power. It's possible that you have one of those.
Also, the resistance of the connections really matters at these low voltages.
from what it seemed, this is something that requires manual switching to a balancing mode? If this would happen automatically, perhaps the typical user would be fine to not have the fully capacity of the battery available for a few months
I don't know enough about the (high quality) Pace BMS units which Fogstar use in their enclosures.
I would expect any BMS to perform four basic functions:
measure cell voltages to prevent over-charging any cell in the set
measure cell voltages and disconnect the output if any cell falls below minimum voltage during discharge
provide a low-current balancing operation whilst charging (possibly only for the last 20% of the operation)
measure input/output current and disconnect if it exceeds a threshold curve
It's very likely that a BMS can offer further functionality such as being commanded to implement cell balancing when it isn't at the final stage of re-charging.
Perhaps that mode is what Fogstar are recommending you to try, which is why you are being told to set it 'manually'.
