Set Max Charge %

[Simonlj]

Hello all, can’t see how to specify charge the battery upto a certain percentage during charge period.

If for example you want to charge up Over Night to 50% charge and then hold it there till the set charge period finishes. How do you do this other than guessing the time it would take to get there.

Simon.

[calum]

In the menu there is an option for this - if you look on YouTube Will Eccles has done a video going through all the menu options on the inverter panel, he explains about it in that video. I don't believe it's something you can do via the app or website.

[ricardo.amado]

Hi,

Option only available directly at the Inverter Menu. Settings -> Battery -> Max SoC. This defines the maximum of State of Charge while being Charge in a Force Charge Window. It still charges to 100% when the Solar as enough energy generated.
As a personal view, since we are having very good sunny days in Portugal, and leaving my battery with Max SoC at 25%.

RA

[graham]

Any recommendations on where to set Max SoC?

I'm running 8 x 445 Watt panels, 4 face NNW and 4 face WSW (the good roof surface is next-door's), into a 16.5 kWh battery.

It looks like my very best expectations from the set facing NNW is 4.1kWh per day and 7.2kWh from the set facing WSW. Worst day so far is 1.3kWh and 3.5kWh. This is based on only a few weeks worth of data though.

I use about 8 to 10kWh most days, but about 15 to 20kWh on a Sunday, when the oven is on a lot and everybody and his dog wants a half hour shower from a 10kW unit (but the battery's inverter only supplies about 5kW of that).

I will be running E7 at 16.8p/kWh overnight (0:30-7:30), and 44.77 p/kWh the rest of the time. I will also be getting 15p/kWh export rate - but none of that applies till Octopus get their finger out. When they do, I think I want max SoC set to 100%. But is there any advantage to me setting it lower?

Changing the Max SoC setting more often than once in a while, like twice a year, will be a pain because of access.

Graham

[calum]

Hi Graham

I don't think there is a one size fits all Max SoC really; in darkest December you want to be able to use the full capability of your battery, in sunny weather in June you want to make the most of the free power.
That said, you will be getting nearly as much for selling what you generate as what you pay to charge overnight, so the penalty for not leaving much room in the battery is not so great.

If you want to minimise the changes to the parameter I'd leave at 100% from mid October to mid March, and maybe 85% the rest of the time. Depends how important self consumption of the solar power is to you, based on the rates you mention you don't have much financial incentive to prioritise it.

We are on Octopus Go and hence get cheap off peak power for a short time overnight, but quite expensive power the rest of the time. Now our array is starting to generate appreciable amounts of power, there is a fine line to tread between charging the battery too much and having to export solar to the grid (we only get 4.1p/kWh on the Smart Export Guarantee), or not charging it enough and having to import expensive grid power at 41p/kWh. Our off-peak rate is 7.5p, rising to 12p in September. Either way, we have a strong incentive to either use off-peak battery power or solar as much as possible!

If your inverter is in an inaccessible place you might want to look into getting an interface box for the COM port, this can then talk wirelessly or via ethernet to a PC running Home Assistant, giving you almost live data on your system but also potentially the ability to update parameters remotely (and possibly even automatically).

The software to do this is under development right now and I don't know if it can change Max SoC remotely yet, but it seems to be planned...have a look at https://github.com/nathanmarlor/foxess_modbus

[graham]

Thanks for the response.

Yes, I'd already decided I should set max SoC to 100% most of the time at least. Maybe after a summer of use, when better I know what the panels will generate, I can work out if a summer level should be lower - I think it depends on what the bad days will be like in the good times. But till Octopus start paying me anything for output, I need to keep it SoC lowish.

I was just wondering if there was something significant I might be missing.

Graham

[calum]

The main thing is that there comes a point where it kinda doesn't matter, as long as the panels add enough juice during the day to get you through to the next cheaper charge window. I have my Max Soc set to 70% just now which seems to be a good compromise between "don't run out of juice" and "don't sell the free power for buttons".

If your hardware is in a hard place to get to, I can highly recommend getting a Home Assistant instance set up to monitor it. Much much better than the FoxCloud portal and not dependent on internet infrastructure either!

[graham]

Hi,

It still charges to 100% when the Solar as enough energy generated.

RA

There's a caveat to this, however. If my battery is already charged to over 95% when the output from the solar starts to exceed the load power, the excess is exported, and the battery is not charged.

I have yet to exactly understand what happens if the battery is below 95% when the solar starts to exceed the load power. I think it will then charge to 100%, but if the sun goes in for a bit, and the load draws from the battery to bring the SoC down to say 97% when the sun comes out again, the batter will not be charged and the excess power is exported.

None of that will matter to me much, once Octopus get their finger out and start paying me for export - that will be 15p/kWh compared to 16.82p/kWh night rate. So if I overcharge the battery overnight, it will only lose 1.82p.kWh plus whatever the inefficiencies in the inverter add to that (most of which will heat the loft space).

But until Octopus do start paying me, my solution is to open the electric fan oven door and turn it on till the battery is drained a bit. That's taking some load off the gas central heating at the moment. But it won't be an option in the summer.

[calum]

Weird, this is not the behaviour I see - excess solar power (in excess of house loads) goes into my battery until it's absolutely fully charged.

[graham]

I assume it's a property of the inverter. Mine says Inverter Model : AC1-5.0-E on the Windows app. Perhaps there's a control parameter for it somewhere? If there is, I think I'd prefer it set so the battery always charges to closer to 100% before power is exported.

Graham

[calum]

There is a Max SOC parameter, but that only applies to grid charging. If the Work Mode is set to Self Use, the batteries should charge to full from solar output before exporting.

[graham]

There is a Max SOC parameter, but that only applies to grid charging. If the Work Mode is set to Self Use, the batteries should charge to full from solar output before exporting.

Yes, but is there a separate parameter for controlling this threshold? That is, the value of SoC above which the battery does not start charging when the solar power begins to exceed load power, i.e. in my case, 95%.

My system only charges the battery to 100% from the solar panels if it starts charging from them when it's below that threshold SoC, and solar remains above load until it gets to 100%. If solar starts to exceed load when SoC is already above 95%, the excess is exported rather than going to the battery. In which case, the only way to get the battery to 100% is to increase the load to draw SoC down to below 95% and then let it charge.

Graham

[calum]

Yes, but is there a separate parameter for controlling this threshold? That is, the value of SoC above which the battery does not start charging when the solar power begins to exceed load power, i.e. in my case, 95%.

Not to my knowledge, no.

What I see is that if the battery is charged to 'full' (99% in my case) and then slightly discharges to say, 98 or 97%, once there is excess solar it will again charge the battery to 99%. This cycle can repeat multiple times if the circumstances allow / cause it.

I don't know what is causing the behaviour you're seeing, but I don't believe it's the way it's "meant" to work.

[graham]

I don't know what is causing the behaviour you're seeing, but I don't believe it's the way it's "meant" to work.

When I first noted that the battery appeared to have stopped charging, even though it was below max SoC, I rang the support engineer from the co that installed the system. He immediately said it would do more or less as described - that there was a threshold above which it wouldn't start to charge -, though he wasn't sure if this threshold was 95 or 90%. I don't remember discussing the reason it should be like this or where he'd seen it before. Next time I ring him, I'll ask.

But I can see that there might be an issue if you try to start charging an almost full battery, if in that special case there's a lag before the system recognizes the battery is full. Presumably, it's not like a dumb charger that just self limits at the charging voltage, i.e. where the battery's internal voltage just goes up asymptotically to the charge voltage, with ever decreasing charge current. I think the DC dynamo regulator on my 1971 Triumph Herald drop-head was smarter than that - till it broke and I swapped to an alternator with an internal reg and converted the old DC reg to a fuse box.

So, if he already knew about this threshold, is it possibly a feature of the battery charger-inverter I've got: AC1-5.0-E? I'm assuming he wasn't just lucky enough to make something up on the spot and happen to be right first go. I know that happens, but it's rare.

Graham

[graham]

I've just noticed that this threshold value of battery charge level, above which, when there starts to be excess solar power over load the excess is exported not used to charge the battery, is now 97 percent, not 95.

I don't think I've done anything to change that, but there may have been a firmware update.

Graham

[calum]

It might be the BMS getting better at knowing the limits of your battery bank.