Posted by: @chickenbig

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Anyhow, this Octopus integration is only visible from the Connect app or web interface, and gets turned into the System Mode 1 schedule which is pushed to the inverter. So good luck to me trying to find that stuff on the inverter UI (and one has to think about whether there is a race condition in there). 

I've not tried the web interface yet for that sort of thing, only physically at the inverter, but doesn't sound the best implentation!

Posted by: @chickenbig

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The problem with discharging not happening turned out to be related to the charge voltages (float/absorbtion/equalization), but I got to that conclusion by fuzzing the configured values until it started taking energy from the batteries. There is no visibility about why a decision is made by the inverter.

I thought those settings weren't applicable to the Lithium Battery setting as it got the settings from the Seplos BMS, perhaps not then.  If the battery is in alarm mode due to high voltage, it will take some time for it to come back down before it can restart.  Presumably the solar contributed to the house load today while charging the batteries?  Did the batteries become 100% from only solar?

Posted by: @chickenbig

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Part of the problem was that (unknown to me) the installer set up Octopus Agile integration with zero prices which seems to trigger the charge logic.

So I ought to make two observations here:

1: The software shouldn't allow such a setting, surely?!

If decisions within the inverter are to be based on price, then it makes no sense to allow zero to be entered.
I'd class this as a design flaw.

2: There are two places from where a customer's tariff can be obtained

• their energy supplier
• the communications hub of their smart meter

The first one is difficult to pick up other than by manually reading it. The tariff differs according to your geographical region, and so a generic 'Octopus Agile' figure is no good.
Yes, Octopus have developed their own 'standard' which allows your tariff to be obtained electronically, but when their rivals eventually offer ToU tariffs, they'll create their own methods.

The smart meter is clearly the preferred source of tariff data, but it can only be accessed by a device which is registered as 'approved' by the Smart Energy Code (SEC), like your IHD is.
Moreover, that device must run a secure version of the Zigbee wireless protocol, and be paired with your particular communications hub.

Those hurdles are sufficiently high that it's very unlikely an inverter manufacturer would attempt to obtain a tariff by that route.

The UK smart meter network is very secure.
But the way in which achieves this makes it too difficult (and expensive) to use our smart meters for the tasks they're designed to deliver.

As such the main features of smart meters in the UK have been ignored.
They are used solely by the licenced Energy Suppliers for obtaining consumption data, and for managing pre-payment credits.

That's another point which needs to be made to the House of Commons Select Committee on Energy.

Posted by: @transparent

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it makes no sense to allow zero to be entered

Certainly for export anything less than or equal to zero. Anyhow, I would have expected to see some indication on the UI that it was being actively updated by Sunsynk servers. Rationale is key!

Posted by: @vaugi

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Did the batteries become 100% from only solar?

The batteries have been on a very high state of charge for today, 99.5% or so. We shall see how things work tomorrow. Plenty of cups of tea is the solution to that problem and more. Better check the electricity meters as well.

Posted by: @chickenbig

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We shall see how things work tomorrow.

Progress report. The batteries are at about 98% SoC but charge is disabled due to high cell voltage (as it is charging at 57.6V so some cells are peaking). Interestingly discharge did not work. The more time spent trying to get Sunsynk and Seplos Mason batteries to talk to one another the less value I see.

I reverted to AGM mode and the discharge works fine. Actually it is nice to be able to simply set some values (float to 53.6, absorption to 55.2, disable equalization, temperature coefficient to 0, shutdown voltage to 47) and you are away. Well not quite as changing to AGM changes the system charge/discharge schedule to use voltages… nearly lost about 25 units of electricity down the wires with that.

Granted there is no communication of warnings or advanced warnings of the mosfets switching, but equally there is no need to hope that someone has interpreted conditions correctly.

Will give another progress report by the end of the day.

@chickenbig 

My 5kW Sunsynk works lovely, so I would persevere.  

Did you allow the Mason box to learn it's capacity?  For this you need to charge fully until high voltage level alarms activate, then high level voltage protection activates.  You then do the same for discharge.  To do this you might need to have it set up on AGM rather than Lithium and adjust the low battery % to allow the BMS to do it's protection without the inverter trying to stop it.  Then at this point you can switch it to Lithium mode and let the BMS do everything as intended, I'm not sure why you would want to keep it on AGM mode when the inverter should speak properly to the BMS.

I also changed the capacity to 280AH on the BMS using it's bluetooth function - if you bought it from Fogstar it has bluetooth - or if it's an older box you might need direct connection using the Battery Monitor tool.  I'm not 100% sure if the above capacity learning changes this figure for you, but I set it anyway.

Like I said on above posts, once at high voltage or low voltage protection you need to let the BMS pause for it to come out of alarm mode before the BMS will allow inverter will control charge/discharge again.  A lot of these settings can be seen on the bluetooth app, you can see delays needed etc.

Could you also look at driving it from the main touchscreen, at least that way you aren't getting issues between the app/web and the inverter.  Once it looks like it's set up nicely on the inverter, then play with the app/web and see if issues arise.  That would be my method.

Feel free to post up some screenshots of the touchscreen settings, we may spot something odd.  

Posted by: @vaugi

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the inverter should speak properly to the BMS

Perhaps these are expected integration issues between two manufacturers products in the embedded software world, but it does not inspire confidence in me.

Posted by: @vaugi

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I also changed the capacity to 280AH on the BMS

Did that a few days ago, before connecting both batteries to the inverter. This data showed up (560Ah) in the battery info page.

Posted by: @vaugi

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the Mason box

Note that there are two Mason boxes; I think Off Grid Garage Andy had issues with two batteries and charge sloshing between them as they disable and re-enable charging when at a high SoC.

Posted by: @vaugi

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driving it from the main touchscreen

I have been using the touchscreen throughout as the installer has not yet given me permissions to make changes from the app or internet …

Posted by: @vaugi

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You then do the same for discharge.

This bit is proving difficult to do, since taking power out of them is a tad tricky, and finding out why is challenging.

So, the “AGM” batteries have reached 100% but now it looks to be taking charge out of them when the sun is still charging. The picture shows 1kW of solar plus 140W of battery being used to support 286W of home use, with 846W going back to the grid. Therefore I am not sure why the ~3A is being drawn from the batteries. Also I am not sure where 53.7V is coming from as the batteries are around 53.15V (IIRC).

Are my expectations too high?

Sorry, I forgot you were using two batteries.

It's hard to say whether the 140W is normal or not, I just checked back on a day when I had 100% for a few hours and it varied from couple of W to around 100W, however going into the battery, not from it.  My inverter is set to zero export at the moment though, so it's different setup there.

I think I would be trying to wind back a few things to see if you can pinpoint the problem(s), as at the moment it seems like there are a few things  (e.g. is it an inverter setting, is it the BMS, is it two batteries as you mentioned) and some need eliminating.

What happens when there is no solar at all, I presume no discharge.  I also assume you CT clamp is the right way round as from your flows look right - e.g. solar is generating and it's going to grid.  It could be worth turning the solar DC off though for half an hour so you can get no solar addition intefering.

Then could you turn off one of the BMS, leaving it simply as grid importing and one battery.  I still think you could send the other screen shots and it would help - definitely the system mode screens, but the others would help - Battery screens, LiBMS screen etc 

If you can get all that sorted (discharging), then try adding in the second battery after.

A number of issues are being discussed here, about which I have reservations...

1: I don't like the sound of using a setting for AGM batteries (4x 12v nominal) when you actually have LiFePO4 cells.
The way in which the 'float voltage' operates isn't the same.

With Lead-acid AGM cells, must inverters will assume that the float voltage will be 54.4v (13.6v per 12v battery).
But for most types of Lithium based batteries, it is the end-user who sets the three relevant parameters:

• max voltage, prior to allowing the battery to drop to float voltage. Usually set at 56v-ish
• float voltage at which the battery will be held following a 'charge cycle'. Usually 55v-ish
• peak voltage at which point the BMS will interrupt charging and show a 'fault' on an App or LCD monitor. Usually 57.6v (3.6v per cell)

In practice it's likely that the 'fault' condition is more complex because most BMS units will interrupt charging if any one cell in the battery exceeds 3.6v
You sometimes find this happens before the inverter charges the overall battery to 56v, which can be quite puzzling the first time you meet that situation!

2: I'm wary of 'communication links' that are made between a BMS and an inverter - usually by CANbus.

Each manufacturer has their own idea of why they want to do this.
In many cases the only outcome is that the BMS status and cell-voltages get displayed within the App for the inverter.
In practice that's pretty useless.

The inverter and BMS unit(s) will still let you enter stupid values for max/peak/float voltages for each of them, and not tell you that you've made a mistake! 😲 

What most of us would like is a more intelligent approach.
Eg if a cell in one (of two) batteries goes duff and it's capacity falls to a much lower level, then the BMS for that battery should disconnect it, warn you, and not allow that battery back into service until you've swapped out the cell.

But I haven't found any such intelligence built into inverter/batteries connected together with CANbus.

Consequently I no longer make any such connections.
If they won't do something sensible under fault-conditions, then what's the point?!

3: Most hybrid off-grid inverters take quite a lot of electricity to stay 'live'.

When you're drawing little from the battery(ies) to power a load, the current taken by the inverters is very noticeable.

This is fundamentally down to such inverters using an integral transformer.

You can buy inverters with solid-state MosFET switching handling the 'shape' of the sine-wave output. They cost more and are lighter of course.
So if you want higher efficiency, then you need to look out for 'transformerless' inverters.
They can often be identified by having TL in the model number.

I’m using 210aH CALB prismatic cells but my absorption/float numbers are:

55v absorption, balance starts at 3.45v, 1.8a maximum balance current, 20 minute absorption timer, 53.8v float.

Been running those numbers for about 5yrs now and everything works well. Panels will cover the loads on the AC side perfectly when the sun is out with the batteries resting nicely at that voltage.

I think my re-bulk is set to 52.8v

That sounds a very 'safe' set of parameters to me @hughf

There's very little additional energy being stored by taking cells right up the theoretical limits.
It's far better to back off, and then allow plenty of space in which the cell-balancing can occur.

@transparent my cells are old and I could use actively cooled balance resistors as although my bms can request a reduced charge rate when balancing, it doesn’t support my mppt controller communication protocol. As such I like to keep things conservative.

When I first set this up I ran 3.65v/cell for absorption and the balance resistors couldn’t keep on top of things and they started thermally throttling and backing off.

For reference I use batrium blockmon balancers/bms and outback power systems inverter/mppt/etc.