Question about power discharging too quickly

[Cheesemaker]

Hi, thanks for accepting me, we had our system installed yesterday but have a question. We live in a very hot country, Nicaragua and 3 days ago had installed a 330 Watt solar panel plus 12.V 105 AH battery ( Deep Cycle) and a 2000 Watt converter. Today we left it charging up to 1pm and the controller showed it at 13.2 volts, but as soon as we plugged in a lamp and a laptop, this dropped very quickly to 12.3.V. Is it normal for it to drop so far and so fast? When we used it yesterday on its first day after installation, it was holding its charge around 12.9 V with 5 lamps and a laptop and a fan plugged in for three hours....now today it already seems wiped out. Is there anything obvious could be causing this? Thank you! Joe and Masha
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[MichaelK]

I'd say your battery is too small for your application.

First off, you don't have a converter, you have an inverter. A converter changes DC of one voltage to DC of another voltage, say, from 24VDC to 12VDC. An inverter converts DC power of one voltage into AC power of a typically higher voltage.

Let's look at your numbers first. Say 5 lamps draws 125W of power? These are compact flourescents, or standard incandecsent bulbs? Your laptop charger might be drawing about 100W, and the fan also 100W. Totally, that 325W for ~3 hours, or about 0.98kWh of power. Your inverter also draws power, how much depends on the inverter. Mine draws ~30W per hour, while others, such as the MPP series draw about 100W/h. So, with a MPP inverter added in, that's about 1.3kWh of power.

Your battery is 105A, which at 12V works out to be 105A X 12V = 1260Wh of power, or about 1.26kWh. So, basically you are draining your battery each and every day.

Maybe these numbers are not exact for you, but you determine the real values and plug them into the math I described to you above.

Now, what do you need? Assume you don't want to deplete a lead-acid battery more than 50%, and you want power to cover at least 1 cloudy day, so the math works out to be (1260Wh X 2 X 2days)/12V = 420Ah, or about 4X what you already have. But, don't make the mistake of just adding one more battery. Assuming you increase the battery capacity, you'd want to also increase your panel wattage. For 420Ah of battery, you need (420Ah/8) X 13V charging X 1.175fudgefactor= 803W. Well, since you already started out with one 330W panel, most likely you can get by just fine by adding just one more 330W. That would bring you up to around 52A of charging current, so what is the current maximum of your charge controller.

 

[Roswell Bob]

I expect maybe your battery may not be full charged or maybe even sulphated. Is the battery brand new? Has it been sitting for any time without a full charge?

 

[Alice2021]

I agree with Michaelk, you'd better add another 100Ah battery at least.And charger your battery to 14.5-15V , and use the shortest cable between inverter and battery,in order to save the battery voltage lost on the cables.

 

[Cheesemaker]

Hi

Thanks for the time you took to reply. I would like to reply to your points and ask some more questions if that's ok?

The make of the Inverter is OXD - SSK 2000 @ 110V. It says DC 12V to AC 110 V and 50 HZ.

We have LED lamps, each about 5 Watts, total 10 hours per day and evening.

1 Laptop = 65 Watts , at 5 hrs in the daytime.

1 Fan, 60 Watts, at four hours in the evening.

Electric piano= 20 Watts, 1 hour per day in the afternoon

= Total approx : 735 Watts usage. ( plus Inverter, but I don't know how much it uses).

If I number my short questions, it will make it easier I hope.

1) Now that I have given the appliances and their output, is the conclusion still the same, that we need another 330W panel and four extra batteries? Your suggestion tallies with what our provider said we would need, but he said it included our fridge too ( Also Inverter/ 70 Watt economy model).

2) What is the minimum value on the charge controller, that we should not go below? Up to now, when we go to bed around 8pm ( I have to be up at 5am to teach), it is showing 11. 5 V on the charge controller.

I don't want to overload you with questions, this is really useful for us, to have people who know their stuff, as our provider/installer did not explain much at all to us.

We are on a budget and can't afford to buy the best system straight away, but we do want to add as we go along, and build our capacity up steadily, one panel here, one or two batteries there, as and when we can afford it. In this case, it would be very useful if you could tell us the best place to start.

Thanks again...

Joe and Maria.

 

[Bud Martin]

Are those numbers in Watts or Whr (Watt Hour)?
I.E. if your laptop power consumption is 65W, then in 5 Hours you will be using 65W X 5Hr = 325Whr.

 

[Cheesemaker]

Hi yes, our total usage is approx. 735 Wh/r per day.

 

[MichaelK]

OK, let's take another look at the numbers. I could not find any reference for your inverter, but did of another 12V 2000W inverter, which was 2amps. Assuming the inverter is left on 24/7 it's self-consumption is 2A X 12V X 24hr = 576W

LED lights...25W X 10h = 250Wh
Laptop..........65W X 5h = 325Wh
Fan...................60W X 4h = 240Wh
El piano.........20W X 1h = 20Wh
Inverter..........24W X 24h =576Wh

Total = 1411Wh of power. So, if your inverter has the same rate of consumption, your actual consumption is double what your prediction is.

Now, to answer the numbered questions,

1) Not four extra batteries, 4 batteries total. Did you see the math I did for you above, 105Ah battery X 4 batteries =420Ah

2) Here is a battery "state of charge" table. You are grossly depleting your battery down to almost zero. I would make the cutoff 50%, or 12.1V


I would completely forget about the frig right now. It uses 70W? Is that 70W on and off all day long? Assuming a 50% duty cycle that's 70W X 0.5 X 24 hours = 840Wh. No way your system, as is, will handle that. Assuming your consumption right now today is ~1400Wh, adding the refrigerator will bump that number up to ~2250Wh. Realisticly by then you'd need at least 3 or maybe four of your 330W panels. Also, sticking with 12V once you reach these power levels, you are really better off with a 24V system.

Since it appears that the inverter itself is the single biggest load, you might be able to save a bit of power in the short term by shutting off the inverter when not in use. What you need to focus your attention on first is getting your battery charged back to 100%. Assuming it's already been repeatedly drained to <10%, your battery has likely already suffered some permanent damage, and might not be able to be brought to 100%. You'll just have to wait and see.

 

[Bud Martin]

Hi yes, our total usage is approx. 735 Wh/r per day.

That cannot be right.
Are you saying that for example, your laptop only consumes 13W of power (so 5 hours will be 65Whr)? My Laptop consumes about 45W.

 

[Cheesemaker]

OK, let's take another look at the numbers. I could not find any reference for your inverter, but did of another 12V 2000W inverter, which was 2amps. Assuming the inverter is left on 24/7 it's self-consumption is 2A X 12V X 24hr = 576W

LED lights...25W X 10h = 250Wh
Laptop..........65W X 5h = 325Wh
Fan...................60W X 4h = 240Wh
El piano.........20W X 1h = 20Wh
Inverter..........24W X 24h =576Wh

Total = 1411Wh of power. So, if your inverter has the same rate of consumption, your actual consumption is double what your prediction is.

Now, to answer the numbered questions,

1) Not four extra batteries, 4 batteries total. Did you see the math I did for you above, 105Ah battery X 4 batteries =420Ah

2) Here is a battery "state of charge" table. You are grossly depleting your battery down to almost zero. I would make the cutoff 50%, or 12.1V
View attachment 73538

I would completely forget about the frig right now. It uses 70W? Is that 70W on and off all day long? Assuming a 50% duty cycle that's 70W X 0.5 X 24 hours = 840Wh. No way your system, as is, will handle that. Assuming your consumption right now today is ~1400Wh, adding the refrigerator will bump that number up to ~2250Wh. Realisticly by then you'd need at least 3 or maybe four of your 330W panels. Also, sticking with 12V once you reach these power levels, you are really better off with a 24V system.

Since it appears that the inverter itself is the single biggest load, you might be able to save a bit of power in the short term by shutting off the inverter when not in use. What you need to focus your attention on first is getting your battery charged back to 100%. Assuming it's already been repeatedly drained to <10%, your battery has likely already suffered some permanent damage, and might not be able to be brought to 100%. You'll just have to wait and see.

Thanks very much for answering my questions, it's very much appreciated.
Our fridge is an " LG Inverter Linear Compressor"= 75 Watts.

We have managed to cut our consumption down, thanks in part to being more aware and careful with our usage, and in BIG part to your advice about not using the Inverter when not using any appliances.
We switched off the inverter when we went to bed last night, and today noticed that after 3 hours of laptop use for my lessons, with a lamp and fountain pump, the charge controller was still showing 13.7, and stayed at that number without dropping.

Here is an updated list of our usage, after buying a smaller ( 35 Watt) table fan.

1) Laptop - 65 W - 6 hours - 390 W/hr
2) Fan - 35W - 2 hours - 70 W/hr
3) Pump - 5W - 6 hours - 30 W/hr
5) Piano - 20 W - 1 hour= 20 W/hr
6) 1 lamp- 5 Watts - 6 hours- 30 W/hr

7) INVERTER - 10 Hrs, Wattage unknown.

= total 540 W/hrs + INVERTER.?

Thanks for telling us the lower load limit for the charge controller, of 12 V, this is very useful.

However, today when we switched off the inverter after using my laptop for three hours, the charge controller figure jumped up to 14.5. V

Can you tell us the upper limit please for our controller, and should we program the upper and lower limit amounts so that the controller will prevent the battery from under or over charging?

Thanks again for your help,

Joe and Masha.

 

[Cheesemaker]

That cannot be right.
Are you saying that for example, your laptop only consumes 13W of power (so 5 hours will be 65Whr)? My Laptop consumes about 45W.

Hi, my laptop is 65 Watts and I use it for 6 hours per day = 390 W/hr ?

 

[MichaelK]

However, today when we switched off the inverter after using my laptop for three hours, the charge controller figure jumped up to 14.5. V

Can you tell us the upper limit please for our controller, and should we program the upper and lower limit amounts so that the controller will prevent the battery from under or over charging?

Yes, the numbers are starting to make more sense now. Yes, it appears that your single largest load is the inverter. Since you weren't factoring it into your calculations, your consumption numbers were far off. The 13.7C and 14.5V numbers are not making sense though? Was it still daylight when you shut things off. A resting 12V battery should not be at more than ~12.7V when fully charged. It is only charging at13to14+V when the charge controller is receiving solar power.

You set the charging specifications into the charge controller. Depending on your battery, it should be set to somewhere between 14.4V and 14.8Vmax. The manufacturer's literature will tell you what the exact voltage should be. The floating setting should be somewhat less, ~13.5V.

You set the discharge specification into the inverter. I'd set it for 12.1 to 12.0V, so you don't drain the battery less than 50%.

 

[Cheesemaker]

Thanks again Michael, yes the 13.7 V and 14.5.V was when we switched off the inverter in daytime. We will make your suggested adjustments , thanks again. Joe