My inverter insists on trying to get the last few rays, even when the inverter is really seeing 0A. With the lithium battery things are worse, in that the custom "back to grid" settings are unavailable and no amount of fiddling has helped.

So, I'd rather just cut the panels at 4pm daily and put then back on at 8pm (no sun).

I know that the DC from the panels can be severe, so AC breakers are often not recommended, so don't want to size things wrong since it must be somewhat set and forget. For 1.5KW worth of panels (4 x 550W), what automated option could I use. Would the Sonoff Pow2 be an option? With a relay perhaps? Pool pump timer?

As recommended the panel details:

Jinko (https://www.inverter-warehouse.co.za/collections/solar-panels-1/products/jinko-solar-panel-tiger-545w-mono-facial)

Nominal Max. Power (Pmax): 545W Opt. Operating Voltage (Vmp): 40.80V Opt. Operating Current (Imp): 13.36A Open Circuit Voltage (Voc): 49.52V Short Circuit Current (Isc): 13.94A Module Efficiency up to: 21.13%

Put in 2 parallel strings of 2 (4 panels) : +- 80VDC Average @ 26A

Inverter is a 3KVA (2400W) with a maximum limit of 1600w Panels.

Battery is a 2KW Pylontech 48V Lithium battery.

Updated: 20220519

11AM PV1/PV2 Voltage: 84.3V PV1/PV2 Recharging Current: 21.3A

12AM PV1/PV2 Voltage: 82.8V PV1/PV2 Recharging Current: 22.3A

1PM PV1/PV2 Voltage: 82.4V PV1/PV2 Recharging Current: 19.3A

Then goes downhill from there

2PM PV1/PV2 Voltage: 81.4V PV1/PV2 Recharging Current: 4.9A

To clarify, I am asking if there is a SAFE way to automatically (smart timer or Pool Distribution Board Timer) to disconnect the panels from the inverter without annoying the inverter. My best guess, based on @FreeMan is to put a shelly 16A switch on each string of panels (there is 2 strings of 2 panels)

  • 3
    What kind of problem is it causing? Why do you care if the inverter is "trying to get the last few rays?" The solar panels I've got produce 600VDC at 10A. You need current and voltage ratings, not power ratings to figure out which relay can safely switch the power.
    – JRE
    May 17 at 13:53
  • 1
    Please edit in some details about make/model voltage/amperage of panels and switching equipment if you expect to get a good answer. I will suggest that (last I looked) the Sonoff equipment was not UL listed, so might not be your best option. If you've got smart hardware, I know that some of the Shelly switches are UL listed.
    – FreeMan
    May 17 at 14:08
  • @JRE The problem is the battery gets drained at the end of the day. It is trying to gather the benefit of the rays, but one ends up with a 50% battery at sunset, which given our load shedding (google it), is less than optimal. I'd rather let it start charging using the grid for the last hour of the day and start the evening with a 100% battery - in case. May 17 at 15:47
  • @FreeMan I have a automated provider 1 kilometer from my house that stocks both Sonoff and Shelley - so a good recommendation. May 17 at 16:05
  • The change to Li-ion batteries has me concerned. Did you change the charger to one that supports them? If not, you have a potential fire starter sitting there (attached to your house?).
    – FreeMan
    May 18 at 14:07

2 Answers 2


This really sounds like an XY Problem.

The Inverter is an all-in-one sine-wave inverter and solar charge controller. It has an option to take standard float, Gel and, less integrated, the lithiums. The lithium option removed most of the custom settings, reverting to a few % options. Most inverters do that, since they don't natively support lithium (yet). I, not subject to this, have an Axpert 5KVA that gets super confused with the lithium. After a complete shutdown, the inverter is sure there is no battery, keeps on resetting and eventually realizes there is a battery. Annoying, but the Lithiums have good warranty.
-- From a comment on the original question.

It sounds, then, like your charging equipment marginally (at best) supports the new lithium batteries. If you weren't having this issue before the change to Li-Ion batteries, then I'd suggest that is the problem. Either return to the previous batteries or upgrade whatever other pieces of equipment are necessary to support the new Li-Ion battery pack.

If you really want to stay with the Li-Ion batteries and "most" inverters don't support Li-Ion batteries well, then maybe you need to get a stand-alone battery charger that does support them and feed it from the inverter. Or come up with some other combination of equipment that will do what you want.

It seems that trying to cut off the solar panels from feeding into the inverter isn't the optimum solution to the problem.

  • I know it is not optimal, but it is where we are now. If I can find an way to stop panels from charging, it will be a help for many in similar situations. May 19 at 15:12

Given that you have a charge controller with a battery, there is no possible benefit to disconnecting the solar panels. You are always better off with the charge controller adding energy to the battery instead of "not". So the idea you are raising is simply incorrect. You are misinterpreting the data you are looking at.

The product, [on paper][1], looks like the right thing for the job. I'm never a fan of "all-in-one" units because you get mediocre everything and you cannot choose the best solar charge controller, battery charger and inverter.

So it appears to me the equipment is not doing the job it is designed to do. Now typically these "all-in-ones" have parameters to change priorities: e.g. use solar to reduce utility costs vs. using it as a UPS. If you set the wrong parameters, you get the wrong behaviors. This is a huge opportunity for "pilot error" - setting the wrong priorities will get the wrong result.

I, not subject to this, have an Axpert 5KVA that gets super confused with the lithium.

OK, well that's an equipment problem, and you need to either sort that out with the manufacturer, or get other equipment that is made to do what you are doing. Still, the workaround you're trying to do isn't going to fix anything!

Or it may be a pilot error issue, again, best to sort out with the manufacturer.

With the lithium battery things are worse, in that the custom "back to grid" settings are unavailable and no amount of fiddling has helped.

You are trying to use lithium batteries with equipment that is not properly designed for lithium batteries. That's a huge problem. Lithium batteries have completely different charge curves that must be respected. If the charge controller (and line charger) are not correctly set for the battery type, of course they will not adequately fill the battery.

Lithiums are not like regular batteries and require a competent BMS to protect them from a variety of conditions which will cause fire. I gather that you used "commercial product" lithium "12-volt"-ish batteries, which would have an onboard BMS. If not, it's vital you address the BMS issue.

It's possible the lithium BMS is limiting charge current because the battery is in a state of discharge where it cannot absorb large currents, because of the mismatch.

Most people need to continue working, many from home, but cannot afford a significantly priced off grid solution. The included, which retails for +- $2500 allows the use of available electricity when available, save a few $$ during the day and tries to top the battery up as close to full before he end of the day, so unexpected lack of power is mitigated. The energy crisis is not expected to be indefinite, but will likely continue for another year or two, so a full-scale expensive solution is not viable. This works, but could be better.

Well, unfortunately, the reality is that technology isn't going to "give you a break" - you need to have skill or hire it. It is not going to work if you don't.

  • Firstly, thank you for all the effort put into this. I think the extra information I have added has not really clarified or helped and seems to have muddied the problem - the question didn't start out that way and was on stack.elec initially. For that all the effort, I have upvoted both answers. I would still like to know if there is a safe and automatic way to disconnect a 82.8 VDC Input with a current of 22.3A, cheaply. For now, setting the inverter from Solar to Utility at 4PM every day solves the problem - but is not automatic. May 20 at 10:46

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