Solis inverter charging battery from the mains

I have a Solis RAI-3K-48ES-5G inverter connected to four Dyness 2.4kWH batteries. Also 9 PV panels connected to a Solaredge SE3000H grid connected inverter.
The Solis inverter is set in Self Use mode, so that it charges the batteries when there is sunlight and the PV panels are producing power via the Solaredge inverter.

I am seeing though that the Solis inverter also charges the batteries in brief bursts during the night (at 3 or 4 hour intervals). It carries on doing this through the day if there is no sunshine. It must be drawing the power for this from the mains.

I've attached part of a SolidCloud screenshot to show what is happening.

Is this normal?
Why does it happen?

And if it isn't normal, what should I do about it?

It could be that your batteries are dropping below the minimum charge level and the inverter is giving them a bit of a charge from the grid to stop them going too low.
On my inverter (RHI-3K-48ES-5G) the "low charge" level is 15% and when the batteries get that low they will be charged up to around 22% from the grid if there is no solar generation.

Thanks, that sounds plausible. Can you tell me the name that Solis use for the "low charge" level, and where I find it in the config menus?

It should be in the Advanced Settings menu under Battery Select then "Force Charge SOC %". It's usually best to leave it at the default for your battery type.

One question. Do you see any alerts in the Solis App at all? I ask because it seems to be happening more frequently than I'd expect. Once my batteries drop to 20% charge the inverter starts using about 90% from grid and 10% from batteries until they drop to 15% charge, then it tops them up a little. It takes several hours for that to happen.

Also I just got an email from my supplier saying there is an issue with some Solis inverters and Pylontech batteries. Something about an issue caused by a firmware update and batteries being charged from the grid at various times. Apparently Solis are working on it.

Are you referring to the SolisCloud app? It doesn't work well for me at all. The overview diagram only shows power to/from battery, it doesn't show PV yield or grid import/export, although the inverter is picking up this info from the meters and I can see it in the front panel window. As a result I can't see if it is doing what you describe.
My supplier tells me that Solis are aware of the problem with SolisCloud and will do a server upgrade in a few weeks time to fix it.
Thanks for the tip about the problem with Pylontech batteries, however we have Dyness batteries.
To try to fix my problem with the inverter charging the battery from the grid, I have tried increasing OverdischgSOC to 25%, leaving ForceChgSOC at 20%. I'll report whether it makes any difference.

Did you ever get the bottom of this? I have different batteries to you but am seeing the same behaviour. Right now my battries are 3% below my discharge limit and still discharging at 200+250w. They'll continue discharging until they get to the forcecharge limit and then they'll charge from the grid up to 30%..... Very frustrating.

An update on my last posts:
I noticed from the SolarCloud app that the battery was charging every 3-4 hours overnight from the mains, for about 5minutes each time. There were about 6 of these events per day. Overdischg SOC and ForceChgSOC were both set to 20%, so the battery could discharge to 20% capacity, then if it went down a little more the inverter would force charge it from the grid. The inverter would then draw current from the battery, and the cycle would repeat. (Inverter operating mode is Self Use).

On 7/12/22 I increased Overdischg SOC to 25%. The battery stopped supplying power at 25%, but declined slowly to 20% (I don’t know why) before a force charge took place. This was usually at 0440 and lasted 20 minutes (only one per day). This was still an unwanted charge/discharge cycle, so:
On 12/12/22, while the battery was at 34%, I increased Overdischg SOC to 30% (ForceChgSOC still at 20%). That was only yesterday, but so far the SOC has not gone down to 20% and the battery has not yet charged from the grid. (It was sunny here today, so it charged as it's meant to, from the PV panels). Too early to say if these settings have solved the problem or not.

Reply to Billybong's post:
Your problem may be different from mine, as my battery only goes down slowly when below the Overdischg SOC level. (I can't see if it is supplying any power at this point, the inverter is not reporting that it is drawing any).

Two possibilities come to mind (assuming your inverter is the same as mine, Solis RAI-3K-48ES-5G)
- is the operating mode 'Self Use'?
- have you successfully set the Overdischg SOC to your desired figure? The first time I tried to alter it, I somehow failed to make the inverter remember the new figure, and it reverted to the old one. When my inverter accepts the new setting, it displays 'Done!' in the tiny front panel window. (I'm entering the setting using the buttons on the front panel).

RichardMole said:

Reply to Billybong's post:
...<snip>
- have you successfully set the Overdischg SOC to your desired figure? The first time I tried to alter it, I somehow failed to make the inverter remember the new figure, and it reverted to the old one. When my inverter accepts the new setting, it displays 'Done!' in the tiny front panel window. (I'm entering the setting using the buttons on the front panel).

Click to expand...

One thing I've found is that the inverter sometimes says 'done' but when you go back and check, it didn't.
This may be related to the battery vendor you set in the inverter. I have a DIY battery with a Seplos BMS. On the BMS its set to 'Pylon' and on the inverter side it's set to 'Aobo'.

Sorry for the following wall of text, skip to the last paragraph for the point

I was messing with the charge settings yesterday because after removing a circuit from the loads and moving it to the AC backup, it drained the battery to 0.02 SoC without taking any remedial action, even though I have ForceCharge set to 12%. So I disconnected the AC backup loads and reconnected them to the grid.

There is a setting under 'Self Use' to allow charging batteries from the grid or not. Knowing that I had to get the batteries up to a reasonable charge (with no sun) I needed to take some action. 'Allow Charging' was off, so I turned it on. It didn't seem to do anything after standing there looking at it for a while and I got called away to do something else.

About half an hour later I heard a buzzing coming from the consumer unit. Because we have a noisy MCB on the solar grid connection, I suspected the inverter had started pulling from the grid (it gets noisy during the summer when we're pushing 4+Kw from the panels to the grid too). Checking the inverter I see it's pulling 5Kw from the grid to charge the batteries at 93A... this means it was pulling close to 20A through the 16A MCB...

After an hour the battery pack was up to 25% which solved my problem of having a dangerous SoC. But I did wonder why it hadn't stopped at 15% where my OverDischarge setting is at.

If there is no PV being generated (with hybrid) or anyway with RAI, the Solis needs to power itself from the battery. This consumption is about 30W.

So when the discharge limit it reached, the battery will be used at the rate of 30W until either the force-charge limit is reached (in which case grid power will be used to charge the batteries) or the sun comes up

So, at this time of year, if your batteries are not that capacious, you may need to increase the difference between the over-discharge and force-charge settings. Our 15kWh battery only looses 1% every 5 hours.

Coda said:

...Because we have a noisy MCB on the solar grid connection...

Click to expand...

MCBs should not be noisy ... take it out, redo the connection and make sure it is properly screwed into the bus bar. If it's still noisy replace it ! They cost about 5 GBP (in UK) - not worth the risk of... ??‍??

SeaGal said:

MCBs should not be noisy ... take it out, redo the connection and make sure it is properly screwed into the bus bar. If it's still noisy replace it ! They cost about 5 GBP (in UK) - not worth the risk of... ??‍??

Click to expand...

Sure. It's already been out and checked and re-torqued to spec. I've spoken to my Sparky about it and he says the buzz doesn't mean the MCB is bad, it will still trip, more likely earlier rather than later. Plus, there is only the solar on this circuit so 5Kw charging (which I have never used until now) or 4Kw export from the solar in the summer is the most that could go possibly through it.

Anyway, I'm gonna replace the whole lot and rewire the CU (the cowboys that did the original wiring did not split the loads properly, so I've got all the kitchen and ring mains on one side, and lights and low current stuff on the other ). I will probably replace the whole CU with a new one full of RCBOs instead.