BMS unresponsive to house demand

[mustjust]

I am hoping that someone can help me with my new Fox ESS which I have monitored closely for the last month. It is in an outbuilding so unheated – I have read with close interest the threads about cold batteries and can echo that mine has come to halt, first in the cold snap in Dec., and then in the last week though not for as long.

My question is can I control or even influence the response of the BMS to supply my fluctuating demand in the house ? For the last few weeks, the battery has charged during sunlight and then discharged at a steady -1.2A until the SoC drops below the preset level I have defined. So I get constant120W or so from the ESS but whenever I use more in the house it only comes from the grid.

Is this the right behaviour ? It means I get the energy from sunshine back but only slowly. On good days I would rather be able to use it for heating food or water when the price of electricity is highest. Can anyone explain how the ESS decides what discharge rate to allow ? Or what I can do to infuence it ?

Thanks

[Dave Foster]

My question is can I control or even influence the response of the BMS to supply my fluctuating demand in the house ? For the last few weeks, the battery has charged during sunlight and then discharged at a steady -1.2A until the SoC drops below the preset level I have defined. So I get constant120W or so from the ESS but whenever I use more in the house it only comes from the grid.

Is this the right behaviour ? It means I get the energy from sunshine back but only slowly. On good days I would rather be able to use it for heating food or water when the price of electricity is highest. Can anyone explain how the ESS decides what discharge rate to allow ? Or what I can do to infuence it ?

Thanks

In short no, it's not what I would expect.

Can I start by asking what your battery Force Charge settings are, you will see 2 time periods each has a start and end time, and 2 switches to Force Charge and Enable charge from grid - If you are using the system normally there shouldn't be a time period set and neither of those must be on.

Also when you look at the app, real time data screen - do you see the correct amount of house load - this is actually updated every 5 minutes so does it correctly show what you have been using in the last 5 minutes and are the data flows moving in the right direction.?

[mustjust]

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[mustjust]

Thanks Dave. Having checked I find I had left a lengthy period on the battery status page to "enable forced charge" but not "enable charge from grid". I reckon I did it from Ian's video to prevent battery discharge. At the time by system was still discharging in cold weather even though it was below the SoC.

I have disabled that time period so we shall see (it's still a bit early since I switched - indeed there is currently still only 60% of the (low) house demand being met from a steady 1.2A discharge of the battery). Maybe the system only looks at midnight for the daily charge periods ?

Maybe someone will explain why the Fox system has such obscure wording to the controls and no guide for the user at all. It is such a relief to use this forum to deal with all the unknowns in management of Fox ESS; thanks again

[Dave Foster]

Ok, no problem i’m sure that’s what would have been causing it

Some of the app/website wording is vague and as you say the user manual only really tells you how to install it, so a bit of a learning curve to go up once you get one installed, i’m sure you’ll soon get up to speed with it - obvs any questions just ask here

[mustjust]

Unfortunately, my system is still unresponsive despite the lack of "forced charge" settings for 24hours. I think it is best illustrated by todays record as copied in below.

During the sunshine in the middle of the day, the battery was charged but the grid was still used to deal with short peak loads of 1.8kW which means the battery reached 100% sooner. Then the excess energy could only go to export to the grid.
Later when the oven was on between 4pm-6pm, all but 0.12kW, came from the grid. The discharge rate remained steady at 0.12kW all through the afternoon (as it had been from midnight until the panels began to generate power).

I have the same data in other forms but I think the image below is explicit. FYI the reported battery temperature is around 13deg C.

What might be wrong ? and can I sort it ?

[Dave Foster]

Could you show me the house load that corresponds to the same time period above , the load is shown on the site overview (first) page when you log in.

And also a couple of things to check in your inverter settings - you’ll have to do this at the inverter panel, go to settings, 0,0,0,0 enter, then work mode it should be set to ‘self-use’

And also from the Settings, go to Battery and let me know what your minsoc, minsoc on grid and maximum discharge current are set to I would expect 10%, 10% and 35A

[mustjust]

Many thanks, Dave - I had already double checked the settings on the inverter and the operating mode has been "self use" throughout. Both min SoC were set to 20%, but I have just changed them to 10%. I am not clear why that would influence the responses so much.

Here is the Load graph for Sat. I have added for comparison that graph along with the Grid Consumption which follows it very closely - the latter is less the 0.12kW of battery supply apart from when the sun is shining. I can confirm these numbers relate well to the figures I see on my smart meter IHD of instant reporting of grid consumption.
FYI I know about the regular demand 1.7kW peaks throughout the day - they come mostly from our instant boiling water unit which heats up for about 30secs approx every 40 mins or so - of course with the strange snapshot reporting of Fox, the chances of it being spotted depends on whether the snapshots are or are not in sync.

Load Graph

Load v Grid Consumption graph

I'd be delighted to hear your opinion or from anyone else who has worked out how the BMS is supposed to match house demand

[mustjust]

Oh yes, apologies I forgot to add the max discharge current on the inverter is set to 35A,

Mustjust

[Dave Foster]

Ok, very strange - can you have a look at your ‘real-time’ power flow, is the direction of power flow what you would expect i.e. towards the house for load, and away from the grid for consumption

[Dave Foster]

I should have added, looking at your graphs assuming the battery is sufficiently charged (> minsoc) the inverter/BMS will respond to demand almost instantaneously and so you would not expect any pull from the grid.

When a large load such as kitchen hob, kettle or heat pump turns off there is a small window of time where the inverter will dump the excess power from the batteries to the grid before it corrects so you should expect demand to be met by your batteries and the occasional short peak of export when the load turns off - that’s not happening at all which makes me wonder as to whether your inverter is correctly measuring the direction of flow.

[mustjust]

Thanks again, Dave - in terms of your first question, yes I believe the flows are all in the correct directions. If I understand correctly, the image you want to check (as just captured) is:

I have never seen an error in the directions of energy flow in such views, also the currents reported, eg Battery, all line up with direction of charge v discharge etc.

I am encouraged that the system is potentially able to be responsive to demand - any thoughts how to fix this or do I need Fox to attend site ? I had only wondered if low temperatures are causing other current limits to kick in ?

As always, ideas from the community are most welcome - i.e. I wondered if I have a rogue setup.

[Dave Foster]

Thanks for posting that, it all looks fine - we’ve checked all the obvious things and they are correct, as for the temperatures, unless the temps are -10C if the BMS/battery will allow charge it would also allow discharge but your discharge seems limited to 120w which is puzzling.

Have you done a full restart on the system recently?, if not can I suggest doing that - you can see how to do that in video guides to isolate the system, basically it is switch the PV off, turn off AC, turn off the batteries, open the battery isolator - wait 30s and then reverse the order.

The inverter will perform checks and restart, if there are any errors reported please make a note and post them here, but once restarted the inverter should have a green light on the panel and mode should be ‘normal’.

Then see if it is behaving normally, as I said if the batteries have charge they will fill in any house load without drawing from the grid - if they are still not meeting the load, I would suggest calling your installer/Foxess for support as there may be an internal fault stopping it which will need Foxess to diagnose. - I’d be grateful if you could let us know how you get on please.

[mustjust]

Will do, Dave. I know the sequence and will try it later today when home.

FYI the behaviour is perlexing in other ways. Just now there is sun and some demand from the house but it chooses to charge the battery and only slightly meet the house demand, drawing the rest from the grid ! See below:

Many thanks again for your checking it out and the advice - I'll report more this evening

[mustjust]

I rebooted the system as suggested at 4:45pm - so far no change in behaviour, and still a steady 120W only feed to the house. see graph below:

No errors on reboot except as expected at time of turn off, see below:

Further, I see the behaviour at midday was to keep feeding the battery even when excess was going to the grid rather than meet the house demand. It seems to me the priority is battery before self-use - how can that be ?

Apart from getting FoxESS directly involved, has anyone any other thoughts ?

[Dave Foster]

It’s not normal behaviour at all - the power flows and loads look correct, yet the battery isn’t meeting the demand - It’s possible that the CT clamp is in the wrong place but not obvious from the energy flow.

If you can’t get your installer back to check over the system, I would definitely contact Foxess support - they can remotely connect to the system and check all of the install parameters.

[mustjust]

I can report the fault is resolved and I have learnt quite a bit along the journey - much rejoicing this end !

Firstly though a big apology to Dave Foster and thanks for his persistence. In a word his first thought was correct and the "Forced charge" "Switches" were set in error. I don't know how my cancelling failed; I assume that after I chose to save the changes it did not stick, plus I didn't see the failure and subsequently never went back to check.

I thought I might list the learning I have obtained (the hard way) with the help of Forum contributors.

a) Enabling a period of forced charge (but not the corresponding switch for "from the grid"), does indeed limit the discharge but not prevent it entirely - it seems (for my system at least) to allow 1 to 1.2A to flow continually from the battery, sometimes even when below the SoC.
b) The setting of these switches is immediate, except if the on period for the time settings has passed in which case the option described in (a) will wait (presumably for the next day). Unsetting the switch appears to work in real time.
c) It is important to ensure the change has saved successfully. I will ask Fox to add a flag to the battery status which shows if any of the time periods are set (just like they show the presence of recent errors against the inverter status.
d) No surprises here that the knowledge and experience of the Forum goes way beyond my installer (whose support has been next to zero) , but also when I finally contacted Fox directly on their service phone no on the website, I was pleased to be called back within the hour by a technician who immediately saw the issue once he had logged on. It's a shame we can't allow guest logons to allow others to see what is what.
e) The technician reckoned something in the grid settings wasn't spot on and I believe adjusted it, but I know this wasn't the cause as I have gone back to reproduce the problem since he loggged out.
f) I am left wondering about firmware versions as I don't believe any of mine have been updated in the last 2 months, but I can go back to Fox on that. Does anyone know if the behviour I have had would be different with more recent versions ? Mine are 1.38, 1.02 and 1.29 (in order).

Once again I am truly grateful for all the support. No answer from Fox as to how to avoid the system more or less shutting down in cold weather to protect itself, but I appreciate there are simple physical steps I can take to protect its environment from temperature below 8 deg or so.

[Dave Foster]

I’m glad you got it sorted out in the end, after we had tried all the obvious things I really thought you had a fault - and good to hear Fox support were on the ball..

With the charge switches a common mistake is to press the save button at the bottom of the page (which only saves the minsoc settings) - seen that happen dozens of times

On the firmware, they are slightly older versions but as Foxess don’t produce release notes for firmware releases I tend to work on the if it isn’t broke don’t fix it method with this equipment

[mustjust]

Very good, Dave - that all makes sense as to how I got it wrong, and I had already concluded on the Firmware only to change if I have a clear problem.

Hopefully my experience and your advice will be of use to others.

[MattBW]

I am having a very similar issue, two weeks after install and suddenly I am using grid power and the battery is not discharging. I can see the force charge is enabled and no matter what I do it will not stay disabled. Is there something I am missing?

Seems odd to have the ability to enable Force Charge but not disable it. Inverter is set to self use.

Waiting for a call back from my installer but not sure what else I can do.

[Dave Foster]

I am having a very similar issue, two weeks after install and suddenly I am using grid power and the battery is not discharging. I can see the force charge is enabled and no matter what I do it will not stay disabled. Is there something I am missing?

Seems odd to have the ability to enable Force Charge but not disable it. Inverter is set to self use.

Waiting for a call back from my installer but not sure what else I can do.

There seems to have been a change recently the force charge switch used to turn off, and when it did both times reset to 00:00 - it doesn’t seem to turn off anymore but the important things are the times - if you want it off make sure the start and end time are both set to 00:00

[MattBW]

Thanks, that is useful to know, it is indeed set to 00:00 for everything so that seems good.

Everything seems to be going to load, even when the load is lower than what is being generated. My smart meter shows export however so it seems something is off.

[MattBW]

Seems my CT somehow got disabled, not sure how as I hadn't accessed any settings until the battery stopped responding.

Now using battery power and not grid power again.

[H5272196]

Thank you for this post! Was scratching my head on this for a while but easily solved.

[ramsden187]

Hi. You say the issue was your CT clamp in the end, is a CT clamp mandatory for the system to work properly? My system which has never worked since I moved in a few months ago (battery doesnt discharge, just sits there fully charged), does not seem to have a CT clamp anywhere?? And the setting is disabled. I do have a sneaky suspicion the system has never worked properly since installed and the previous owners weren't aware but I cannot prove that.