MT50 normal voltage but with sad face

pianoboatdogs · August 2021

Hi, newbie here.

I've had solar power for a few years and worked most of the issues out, but I'm stuck with something.

This is the system:

300W x 2 panels > Epever 60A MPPT > Trojan 110A x 3 > 1000W Inverter

The whole system worked beautifully. It charged easily, was often 13.0V, and we could charge two laptops and power tools without running out of power. There's also a 12v fridge freezer running 24/7.

Then the original 500W inverter stopped working, so I replaced it with a 1000W one. Now the batteries don't seem to want to charge as well as they did. MT50 constantly has a sad face, even if the voltage gets up to 12.5V

I can't work out if it's the inverter swap, or that's just a coincidance and something is up with the batteries. I've checked the water levels, and there's still 150W and 12.5V coming in off the panels on a bright day.

Anything I'm overlooking?
Thanks a million.

mike95490 · August 2021

Your larger inverter consumes more of the solar power when idle, and therefor the batteries never get fully charged (13.8 - 14.2V )
Switch the inverter off for 2 days and see if the battery recovers. 12.5V is not a full battery

priyanshi_786210 · August 2023

Hi, priyanshi here.

I've had solar power for a few years and worked most of the issues out, but I'm stuck with something.

This is the system:

300W x 2 panels > Epever 60A MPPT > Trojan 110A x 3 > 1000W Inverter

The whole system worked beautifully. It charged easily, was often 13.0V, and we could charge two laptops and power tools without running out of power. There's also a 12v fridge freezer running 24/7.

Then the original 500W inverter stopped working, so I replaced it with a 1000W one. Now the batteries don't seem to want to charge as well as they did. MT50 constantly has a sad face, even if the voltage gets up to 12.5V

I can't work out if it's the inverter swap, or that's just a coincidence and something is up with the batteries. I've checked the water levels, and there's still 150W and 12.5V coming in off the panels on a bright day.

Anything I'm overlooking?
Thanks a million.

littleharbor2 · August 2023

Refer to the post right above yours.

Your batteries could be getting tired but usually in that case they will appear to charge up rapidly but also discharge just as fast.

BB. · August 2023

Check the "Tare Losses" or the power draw of the inverter when "on" but no loads.... A smaller inverter may draw 6-10 Watts, a larger/different inverter may draw 10-20 Watts.... Looking at "worst case" example math:

6 Watt tare losses * 24 hours per day = 144 WH per day
20 Watt tare losses * 24 hours per day = 480 WH per day

Again, this is a worst case example... Need real data and/or measure the current draw yourself.

And for your solar array... Typical best case harvest (mid day, cool/clear weather, battery bank below ~80% load and/or you have other loads running), you should see:

600 Watt array * 0.77 panel+controller derating = 462 Watt "best case" peak harvest
462 Watt / 2 = 231 Watt sort of "worst case typical" harvest (less than clear weather, hot days, etc.)

You harvesting 150 Watts peak--If your bank needs charging, that sounds low (panel/wiring issues?).

Guessing you are somewhere around Madhya Pradesh, India. Just to get an idea of how many "hours of sun" per day you get with a 600 Watt array tilted 23 degrees from vertical, fixed array facing south:
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )	AC Energy Off Grid 600 Watt system ( kWh )
January	6.31	53,882
February	6.61	49,739
March	7.44	60,227
April	6.97	54,074
May	6.77	53,583
June	5.46	42,679
July	3.54	29,162
August	3.15	26,046
September	5.18	41,958
October	6.28	51,724
November	6.14	50,097
December	5.85	49,663
Annual	5.81	562,841

Now August (Monsoon season?) for an off grid solar power system:

600 Watts * 0.52 off grid system eff * 3.15 hours of sun (August) = 982.3 WH Per day

Note this is a long term average. Some days you will get more, others less... And if, for example, you where living off the grid, then you should plan on only using 50-65% of "predicted" harvest above.

Things to look at... Check wiring and solar array voltage and current... If you are using a "working" MPPT type charge controller, you should be seeing around 17-18 volts or so... 12.5 volts on the solar array (Vpanel-input) (MPPT will "adjust" Vpanel-input voltage to optimum voltage Vmp--Voltage maximum power... You should see 17-22 volts depending on sun/weather, charging loads, etc.).

With 300 Watt panels, need to know the Vmp and Imp rating of the panels. It would not be unusual to see 17-36 volt Vmp panels.

Also, for MPPT controllers, ideally you would probably put the two panels in series--Better for MPPT harvest (need to check Vpanel-max input voltage, array Voc-cold max voltage, etc. so as not to ruin the MPPT controller with too high of array voltage).

Otherwise, you are in a period with almost 1/2 the hours of sun per day, and 1/2 the Watt*Hours (battery Amp*Hours) of harvest from a couple months ago. Also a new (and larger wattage) inverter can draw more power too...

-Bill

MT50 normal voltage but with sad face

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