Panel to battery matching

Ok so after a lot of help on this forum, well...basically no help at all from the 48 views i researched that for a 40ah battery a 50watt panel is recommended so I purchased a 100w panel and connected it up to my new PWM Souer ST-S-12-20 charge controller in the blazing midday sun and got 2.9amp charge from the rated 5.85A. I then plugged a 140w fan and that seemed to run fine and the battery ran about 12amps and the solar I assume was replenishing the loss. I then reached for the big guns and plugged in an additional 750watt toaster in which pulled my battery down to a level the new 3000w MSW Souer Inverter didn’t like and after a minute or so the inverter gave a warning tone of low battery amps ( i assume) then just as my toast was browned the inverter tripped. The battery is a transpower TGEL 12 -38 that AGM Gel on the label. I turned the inverter off and watched the battery recover over 30mins im not sure but when i tried to run the 140w fan the inverter complained again. There was no boiling of the battery as mentioned in other threads. I was interested to try a double size that recommended panel to see if it would compensate for the dust and heat that Thailand bring as opposed to a bright sunny 10 degree day in Birmngham UK. I shall post back for the interested tomorrow when i see how the panel copes with a constant load all day. Thanks for everyone’s invaluable help it was much appreciated

Sorry no one got back to you.

Based on what you have posted I would say your battery is in trouble. Except for maybe Lithium chemistry type all Lead Acid batteries do not like to be drained below 50% SOC and last very long. Which is probably why even a 140w load will quickly drain it after it has been depleted by the toaster.

Another misconception is the panel wattage to battery Ah rating. Just about all panels never put out their rated Imp rating so having a little more wattage will get you into the charging amp range of the battery. That range is usually between C/12 and C/8 where C = the battery Ah rating. So for the 40Ah that requires between 3.3 amps and 5 amps. And most panels require to be pointed directly at the sun to get even 90% of the output. So a low sun will not get you what you hope even if there are no clouds in the sky.

IMO also a GEL type battery is not really good for solar because most do not like to be cycled a lot or deep. And boiling is not always present unless you really put a high amp charge on a battery.

Dont mistake battery gassing ( bubbling as water electrolizes into O2 and H ) with actual boiling when something really goes wrong and you have a battery in a plastic case with boiling hot acid ( from over charging or some other failure) Bubbling is a normal process in recharging a flooded battery, and weekly/monthly top off with distilled water is normal. But doing something bad that causes a battery to boil at 212F is never good

And remember, Gel and AGM batteries, when overcharged, will turn electrolyte into gas faster than the re-combiners can handle, and then they VENT the gas and fumes. They still need a vented box lust like flooded.

Ok.Thanks for the input. So my findings so far with the 100w Mono panel and 38AH AGM Gel 12v battery are. I tested with a 60w 220v fan on the inverter. I calculated that 60watts /12v = 5A and 38AH / 5 A is 7.6hours but halved for the leadAcid longevity lacking I get to 3.8hrs. The fully charged battery lasted 4 hours so the toaster test episode from previous day had not damaged the battery. Next day the solar panel charged the battery at 5amps at midday and later when I checked the panel amps they were on zero. Confused and looking for a problem I realised the PWM Charge controller had stopped the charge process so the relevance of a matched panel was obselete as I has been controlled to stop. I will have to take the experts word that a big panel would provide a too high a charge rate and damage the battery.

Then I left a fan on all day and watched the panel match the current needed to prevent the battery getting drained. Today I have fitted a 12v output to a fan and light which originates from the Souer Controller and I have provided two switches for my girlfriend's father to independently switch while in his hut out in the Goat farm and I tests noticed that I can switch the battery isolator off and the 12v controller feed is still present ( not a big surprise ) and the fan and light is powered free by the sun. The volts can get as high as 15 volts, I don't know what the effect of high volts on the 12v fan and Led bulb will be or are.

Another anomoli is the the Souer MSWave Inverter is labelled 'Solar Inverter '. I can't understand what this means when Inverters have nothing to do with solar but everything to do with battery's. I'm hoping that the 'solar' part in the description means that if I connect the panel to the inverter input it will output 220v when the sun shines ? You never know ... How could it possibly know the difference between volts off the battery or volts from the Solar array ? I would be interested to connect a 1000w of Array direct to the inverter and see what is produced. Does the ' solar inverter ' care if the panel volts are high ? Or is there away of dumping excess power/volts before it reaches the Souer Inverter ? Trying getting an expert on the net to give a straight answer to that...

I could easily write a program and use a PLC controller that switches panels out to match a set point using PID control but I'm sure there is a tried and tested answer and I am trying to reinvent the wheel.

Has anyone used a PSW inverter with a room standing fan and heard it to be silent with no electric hum ?

Thanks for the two replies , gratefully received

Total newbie here as well.
But with regards to the "solar Inverter", I have been working a bit with those on pumps. I'm not sure if this is something similar to the inverter you mention. The ones I have, have a limited given output capacity (for instance 1.5 kW) and also work as VFD. They will also work on things like a fan and some electrical tools. If solar input (W) is enough, the pump will run at full capacity. If not, it will run a bit slower (and continuously vary according to PV input). I'm not aware that there is a specified maximum PV input in Watts beyond anything that makes sense, but there is a clear required input Voltage range. I think in general the word "inverter" refers to the fact it changes DC into AC. That DC could come from a battery (though not for mentioned "solar inverter") or from PV panels. "Solar inverters" usually require relatively high minimum voltage input (a few hundred volt), so for low power output, a DC DC booster might make sense.

In this little video about that set up the Souer ‘ Solar Inverter ‘ is shown. The point of that video is that the controller does stop the array charging the battery when the battery is at the voltage setpoint.

I use normal inverters often in my work in refrigeration and also the goat farm my girlfriends father runs has 3x350w panels in series providing an imagined 39.1v x 3 = 117.3v although unless the sun is over head the red hot 47degC dusty panels will be lucky to provide over a 100v. I may add another panel 350w , temporarily as it will be my own, to prove the lack of volts is the reason his pump is cycling on and off. That 117v array feeds pos and neg to a controller/ speed controller ( it says on the label) that outputs a 3wire 72 volt feed to the underground screw pump widely seen here in asia. Well 2x72v is 144v across two phases. I doubt the 100v average volt provided from the array is getting inverted to 72v per phase ever if at all at the pump. I had originally thought they had been ripped off and sold an undersized for horsepower pump but the array isn’t gonna run a pump of a decent size any way.

Back to the original point why has the 12-220v inverter in my vid got ‘Solar’ emblazoned on it when 95% of the same manufacturer Souer have not ? I’m wondering if upto 17v panel like 100watts panels etc can be connected to the inverter with no battery in parallel? I will try it soon

I think an "ordinary" (non "solar" or "pump") inverter needs a stable Voltage input, so a battery and not PV panels.. To me it sounds like you don't have the solar inverter I was referring to. Is it the one that can be briefly seen in the video ? Other than that, it also sounds like you are talking about a control box, some of the ones I have worked with are similar (PV input and three wires output to pump). I've wondered about the output but never measured it. Can three wires be DC ? Don't see how. So might it be three phase AC with 72 Volts across phases ? That would be an explanation for the description (solar inverter) ? I expect that an inverter that needs a battery has a clear indication of that (terminals), like the charge controller. If it does, I would use a battery, I wouldn't try it without. I wouldn't mind using a very old battery but I would use one. In my head I see them a bit like a buffer for the incoming power/voltage. But I don't know, I guess you probably can't do much harm with 17V, 100W... ?

Hi. Thanks for the reply. Right to be clear. The inverter for the pump is DC 150v solar array to controller which converts to 3 phase DC 72v per phase. I’ll send a link to a YouTube vid tomorrow telling you all about it.

The inverter you saw in the red plastic box was one of many high quality inverters made by Souer China but unlike many including being delivered ro my residence tomorrow a pure sine wave 24v to 220v 500w inverter that they haven’t emblazoned ‘ Solar Inverter’ on for some reason. I believe there is very little difference in a brimming with acid 14v battery supplying you inverter or a cloudy day fed 20v panel giving 15v to possibly a clever inverter that is clever enough to meter 220volts.

I write this in a blackout of 4 hrs so far at 00:07 luckily the ensuing storm has cooled the atmosphere down but I’ll be glad to be self sufficient with the 75ah 24v Lithium NMC set with the inverter and 10amp lithium charger hopefully coming tomorrow and being able to power the house selectively via essential circuits and a contactor relay that hold on the mains when its on but when mains dies the N/C contacts pass the battery fed inverter power to the essential circuits and visa versa when power is restores.

Ok, looking forward to that video.
I think the difference between the PV input and battery input is that the battery voltage would stay relatively stable at between 12 and 14 V. The PV panel voltage but also power output would vary wildly. It might be that the inverter can handle producing 220V output without anything connected but if you also want to draw power from it, I'm not sure if the inverter would be able to handle it the varying input. But others here know a lot more than I.. Especially if you might damage something by trying..