Also missing capacity...

[tinnerdxp]

Hello everyone.
Jump to the bottom for questions

Bit of history first:
22/04/2022 - 5.2kWh solars installed + H1-3.7-E Fox inverter
somewhere in 2023 - I have bought 4 x HV2600 v2 batteries - total capacity around 10kWh
Finally around early November 2024 - I've purchased yet another 3 x HV2600 v2 batteries - total capacity after is 17.9kWh
So currently have:
BMS v2: firmware 1.001
4x HV2600-2: firmware 1.04
3x HV2600-2: firmware 1.06

When I had 4 batteries - the overall numbers did add up - the house uses roughly 15kWh of energy a day and full battery lasted roughly 3/4 of a day.
The idea was that with 7x batteries we could survive the whole day easily on a single charge when the electricity is cheap (in winter).

But... The numbers don't add up somehow...
I have the system set up to charge between 1am-6am and on self-consume setting, min soc: 15%.
Example yesterday:

Charging started: 00:57am @ 3.6kW
Charging stopped: 04:27am.
Grid consumption stopped: 06:01am
Total energy stored within the battery: 3.5h * 3.6kW = 12.6kW
Battery consumption started at around 6am then...
Now the idle consumption throughout a day is 700W (it's mostly 500-600 but spikes to 800 so let's say average 700W)
Counting spikes (and really rounding it up) throughout a day:
08:17-08:32 - 2.4kW - kettle
08:47-08:57 - 3.6kW - kettle
11:12-11:22 - 3.6kW - kettle
14:57-16:07 - 3.6kW - hot water cylinder (1h at full power)
17:32-17:42 - 3.6kW - kettle
18:07-18:17 - 2kW - no idea
19:17 - battery discharged to 15% - grid consumption started...

So let's summarise:
Between 04:30 and 19:17 I have used ALL of the energy stored...
17920Wh theoretical capacity at SOH 100%
SOH is 95% at the moment - so max capacity is 17920 * 0.95 = 17024Wh
Min discharge level is set to 15% - so 17024 * 0.15 = 2553Wh
So usable energy capacity is 17024 - 2553 = 14.471kWh (theoretical)

Now let's sum up the usage between end of charging and depletion to 15%:
19:17 - 06:00 = 13 hours and 17 minutes - let's round - 13h at 0.7kWh = 9.1kW
then the spikes:
10 minutes at 2.4kW = 0.4kW
10 minutes at 3.6kW times 4 = 2.4kW
10 minutes at 2.0kW = 0.3kW
that's total of 3.1kW
Total consumption of 12.2kW MAX (and it is heavily rounded up).
So, I'm missing a couple of kWh here and that doesn't take into account the production from solar 1.3kWh for this day that usually just tops up battery anyway.

Data export from essfoxcloud for this day:
PV yield(kWh) 1.29999999999927
Charge energy(kWh) 10.7000000000003
Export energy(kWh) 0
Import energy(kWh) 19.1999999999998
Load consumption(kWh) 17.8999999999996
AC output energy(kWh) 12
Discharge energy(kWh) 12.9000000000001

Batteries sit in a garage and are NOT insulated...

And finally questions:
1. Battery insulation - obvious point to do to improve things...
2. Is there a change-log for firmware versions for both BMS and batteries? If so - where?
3. Are any of the versions listed above - known to cause problems?
4. How do I upgrade firmware on both BMS and batteries?
5. How do I balance the batteries? Do I have to do other than just deplete to 10% and charge to 100% few times?
6. Is there a way to export more detailed usage from the inverter itself?
7. These inverters don't support more than 7 batteries right? (the Dial on BMS set to 5)

[Dave Foster]

Interestingly your Fox cloud stats say that your discharged 12.9kWh in the day which is close to your calculation of 12.2kWh you calculated - so that would appear to be correct.

Fox says your charge energy for the day was 10.7kWh and your batteries were charging for 3.5 hours at 3.6kW so without taking losses into account that's 12.6kWH - but your charge power is automatically reduced by the BMS when it passes 94% to approx 1kW (this would be the last 30 minutes of the charge cycle) - so 2.5 * 3.6kW (+1kW) = 10 kWh which is there or there about what Fox cloud says so that also stacks up.

In effect this appears to be a capacity issue as you appear to be getting 12.9kWh between 100% and 15% whereas you would expect on brand new batteries ~15.2kWh as they are with a 95% SOH ~ 14.5kWh.

Before I go any further, just a couple of things to say about LFP batteries and the FOX BMS system - the Fox batteries are rated capacity when at 25C, below that the capacity reduces (albeit temporarily until warn again) so if you batteries are stored 10-15C that's a probable cause of the reduction you are seeing.

Many people build insulated enclosures - nothing much more than 50mm Kingspan around them, although if you can get insulation below them that also makes a big difference, typically with a fully enclosed insulated battery the heat generated whilst charging / discharging keeps them at a comfortable ambient.

Second thing to say is that it is never a good idea to run your batteries with different firmware as the BMS may struggle to get adequate balancing done one the pack - each battery is responsible for keeping their own cells balanced and the BMS keeps the pack in line by broadcasting the pack statistics to all batteries so they can adapt to stay in balance.

There have been quite a few changes in battery firmware since the versions you have which are now in LFP battery terms 'very old', Fox do not publish release notes but we do know the majority of updates are to improve pack and cell balance and often low temperature balance and SoC tracking - I would strongly recommend that you email fox service with your inverter serial number and ask them to update your battery firmware.

Once you have the latest firmware installed the best way to improve pack balance is to do full charge / discharge cycles i.e. down to 100% all the way down to 10%, this is because the BMS learns the most about the pack when it is getting towards the limits and much of the balancing is done at the top, and bottom.

Unless the pack is in a very bad state of balance (and yours doesn't sound like it is) a few cycles like this is all it takes to probably balance the pack - but always allow the pack to charge and leave the charge period enabled for an hour afterwards, and when it gets to minSoC allow it to stay there again for an hour at least to enable any inter pack/cell balance to take place.