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Question about how to interpret our Charge Controller numbers

Cheesemaker

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Hi,

We now have a second 12.V 105A "Deep Cycle" battery attached to our 330 Watt solar panel.

After leaving the inverter switched off during the night, we had full sun between 7am and 9am ( we are near the equator, in Nicaragua), and the charge controller went up to 14.7 . V.

We then plugged in our 70 Watt ( Inverter / Linear/ Compressor) fridge, and the Charge controller dropped straight away and showed 12.7 V.

How should we interpret these numberS? If the battery was showing 14.7 V, doesn't that mean it had been charged to that amount and therefore why does it drop so suddenly to 12. 7 V ? Is this normal ? I mean, for the number to drop so quickly from 14.7V to 12.7 V ? Should we leave the fridge plugged in and just wait for the number to go up again?

Since starting this post, it has gone up to 12.9 V.

We also noticed the number drop when there is a bit of cloud overhead.

Sorry for what must seem dumb questions to people with more knowledge, we want to learn,

Thanks, Joe and Maria.
 
Hi,

We now have a second 12.V 105A "Deep Cycle" battery attached to our 330 Watt solar panel.

After leaving the inverter switched off during the night, we had full sun between 7am and 9am ( we are near the equator, in Nicaragua), and the charge controller went up to 14.7 . V.

We then plugged in our 70 Watt ( Inverter / Linear/ Compressor) fridge, and the Charge controller dropped straight away and showed 12.7 V.

How should we interpret these numberS? If the battery was showing 14.7 V, doesn't that mean it had been charged to that amount and therefore why does it drop so suddenly to 12. 7 V ? Is this normal ? I mean, for the number to drop so quickly from 14.7V to 12.7 V ? Should we leave the fridge plugged in and just wait for the number to go up again?

Since starting this post, it has gone up to 12.9 V.

We also noticed the number drop when there is a bit of cloud overhead.

Sorry for what must seem dumb questions to people with more knowledge, we want to learn,

Thanks, Joe and Maria.

If you had removed the charge from the battery and applied no loads at all, you would still have seen it drop below 13V in a few hours.

Voltage is "mushy". To get a "12V" battery fully charged, you must charge to a higher voltage. When charge is removed, the voltage will settle per the above.

Voltage varies with current. When you add current (charger), voltage increases. When you draw current, voltage decreases. Clouds = less solar, fridge = more load; both cause voltage drop.

The behavior you describe doesn't sound abnormal.

The concerns are:

Does your 330W panel collect enough energy every day to power all your load?
Is your 105Ah (52.5Ah usable) battery sufficient to power your loads between charging?

52.5Ah * 12V = 630Wh - this is the amount of energy you can use between charges before you risk stressing the battery and reducing its life.

I picked Masaya, Nicaragua at random:

1638720281099.png

Note the the numbers above also reflect average weather conditions.

Using Dec number:

5.29 hours * 330W = 1746Wh

Your panel can produce about 3X your battery capacity on a daily basis; however, that depends on the panel and charge controller. You may have the two mismatched if you're using a cheap charge controller.
 
Hmmm I would think that a 200ah battery at 12v would need more solar to charge it
I use 500 watts to charge my 230 ah battery’s but it’s no very sunny in my area .
And it would not run a frig .
I doubt your 210 ah battery/300 watt panel would run a fridg even if you where sitting on the sun .
Those are really good solar numbers ? I get half that .
I’m think you will only get 1400 watts with 20% loss maybe more since it’s hot .
Then your frig will run more with the heat .
12.7 is a full 12v battery , the frig plus inverter is a large draw for 2 battery’s .
After the frig is running for a few min the voltage should give you your % of charge .
I would bet that your inverter and fridg would use 1200 watts a day running half the time but in your area the fridge would run more ,it’s hot ?
soooooo if you un plug the fridge after its running for a hour and let it sit with no charging or Current draw
your voltage should be close to accurate.
As it sits you need at least one more 300wat panel to run the frig and charge your battery’s to full. 2 would be better
You will be running your battery’s down to 50% every nite so they will die faster then if you are using only 25% a nite .
3 battery’s would be better but then you would probably need a third panel .
For your next set of battery’s you should be using wet cell , lead acid 6v golf cart battery’s so you can refill the water
and check SG .
27ACB7BC-422D-4C76-BD44-84FFF817298F.jpeg
 
If you had removed the charge from the battery and applied no loads at all, you would still have seen it drop below 13V in a few hours.

Voltage is "mushy". To get a "12V" battery fully charged, you must charge to a higher voltage. When charge is removed, the voltage will settle per the above.

Voltage varies with current. When you add current (charger), voltage increases. When you draw current, voltage decreases. Clouds = less solar, fridge = more load; both cause voltage drop.

The behavior you describe doesn't sound abnormal.

The concerns are:

Does your 330W panel collect enough energy every day to power all your load?
Is your 105Ah (52.5Ah usable) battery sufficient to power your loads between charging?

52.5Ah * 12V = 630Wh - this is the amount of energy you can use between charges before you risk stressing the battery and reducing its life.

I picked Masaya, Nicaragua at random:

View attachment 74643

Note the the numbers above also reflect average weather conditions.

Using Dec number:

5.29 hours * 330W = 1746Wh

Your panel can produce about 3X your battery capacity on a daily basis; however, that depends on the panel and charge controller. You may have the two mismatched if you're using a cheap charge controller.



Thanks very much for your detailed reply, in fact we have two batteries each 105 A. They are connected in parallel. We do notice big fluctuations depending on cloud, and your table is great as we are close to Masaya, in Granada.

We have the cheap blue CMTD charge controller. And we only turn the 2000 W inverter off at night and when not using solar.

However there is another question. The charge controller with the 70 W. fridge plugged in solar was showing 13.7 V and there was a small flashing arrow showing that the batteries were still charging. However after three hours of full sun at midday, the charge controller is showing 12. 6 V but the arrow has stopped flashing, and there are only four bars out of five, showing that the battery isn't fully charged. Is this normal? Shouldn't the battery be charging once it drops below the 12.7 V mark? There is still fun sun. It is 12.20. pm

Thanks again.
 
Last edited:
I think at that point your frig and inverter is using all the solar that is coming in to the battery
 
It is 1pm. There is nothing plugged into the solar and the inverter is switched off.

It was showing 12.7 V when we switched everything off, it is 1pm and there is full sun here near the equator, but there is no sign of any charging taking place now.. And there are only four out of five bars showing on the charge controller.

And this morning, it was going WAY up beyond 12.7 V, even though the 70 W fridge was connected.

If 12.7 V indicates a full charge, as you say, why does the charge controller even go up beyond that? Why does it show 13. 6v and 14. 6v sometimes?
 
However there is another question. The charge controller with the 70 W. fridge plugged in solar was showing 13.7 V and there was a small flashing arrow showing that the batteries were still charging. However after three hours of full sun at midday, the charge controller is showing 12. 6 V but the arrow has stopped flashing, and there are only four bars out of five, showing that the battery isn't fully charged. Is this normal? Shouldn't the battery be charging once it drops below the 12.7 V mark? There is still fun sun. It is 12.20. pm

Thanks again.

If you have a cheap charge controller, it may be PWM, and it will not work well with your panel. Your 330W panel may be crippled by the controller and might only produce 100-150W.

I think at that point your frig and inverter is using all the solar that is coming in to the battery

This plus the above use of a PWM controller would certainly describe it.
 
It is 1pm. There is nothing plugged into the solar and the inverter is switched off.

It was showing 12.7 V when we switched everything off, it is 1pm and there is full sun here near the equator, but there is no sign of any charging taking place now.. And there are only four out of five bars showing on the charge controller.

And this morning, it was going WAY up beyond 12.7 V, even though the 70 W fridge was connected.

If 12.7 V indicates a full charge, as you say, why does the charge controller even go up beyond that? Why does it show 13. 6v and 14. 6v sometimes?

This sounds like a improperly configured or defective controller.
 
Sorry, I just saw your explanation above in the first post, about " mushy" voltage .

If the charge controller is now showing 12.7 V after three hours of running the fridge, does that mean we have reached our "quota" for the day?

We had hoped that two batteries instead of 1, would allow us to use the solar for the fan and lamps in the evening.

At what point should we switch the solar off ? When it drops to 12. V ?
 
I didn't see your post there Sunshine_eggo, yes when they installed it , they had a problem with it and called their office, so we couldn't hear the conversation. They went ahead and installed it anyway. Perhaps it is faulty ....

It could well be the cheap PWM controller. Could you recommend a better brand please?
 
I think at that point your frig and inverter is using all the solar that is coming in to the battery


We thought running two batteries with a 330 W panel in blistering sun would allow us a bit more usage than just 3 hours on a 70 W fridge ?
 
We thought running two batteries with a 330 W panel in blistering sun would allow us a bit more usage than just 3 hours on a 70 W fridge ?

The problem with PWM is it forces the panel to work at battery voltage. Assuming a 24V panel, it likely operates at about Imp = 8-9A (round to 8.5)A. When you force it to work at battery voltage, 8.5A * 13V = 110W... 1/3 of the panel's potential.

330W/12V = 27.5A. You need a 30A MPPT controller. Will has several on his site:

 
The problem with PWM is it forces the panel to work at battery voltage. Assuming a 24V panel, it likely operates at about Imp = 8-9A (round to 8.5)A. When you force it to work at battery voltage, 8.5A * 13V = 110W... 1/3 of the panel's potential.

330W/12V = 27.5A. You need a 30A MPPT controller. Will has several on his site:



That's amazing. So they gave us a charge controller which only allows the 330W panel to provide a third of its potential power?
 
Thanks, so if we can get hold of a 30 Amp MPPT controller here, should it be 12V or 24 V?
 
It's not easy to get MPPT here, the guy says he has available the one in this photo below, it says it goes to 60 Amps.
 

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Thanks, so if we can get hold of a 30 Amp MPPT controller here, should it be 12V or 24 V?

It should be the same as your battery voltage.

It's not easy to get MPPT here, the guy says he has available the one in this photo below, it says it goes to 60 Amps.

If that's the case, why does it say PWM on the face of the unit?
 
Sorry, my sentence was badly written, I meant to say we can't get MTTP and he only has this PWM for $60.
 
Sorry, my sentence was badly written, I meant to say we can't get MTTP and he only has this PWM for $60.

PWM of any amperage will force your 330W panel to output 110W. Period. It's the way they work. Your panel NEEDS to operate at about 40V to produce its 330W. PWM forces panels to work at battery voltage.

The only thing that unit will get you is a lighter wallet and lost time.

If you can't get MPPT, then you need to get new 12V panels that operate best at about 17-18V.

Please provide your panel specifications:

Vmp
Imp
Voc
Isc
 
Sorry,. But tttt
PWM of any amperage will force your 330W panel to output 110W. Period. It's the way they work. Your panel NEEDS to operate at about 40V to produce its 330W. PWM forces panels to work at battery voltage.

The only thing that unit will get you is a lighter wallet and lost time.

If you can't get MPPT, then you need to get new 12V panels that operate best at about 17-18V.

Please provide your panel specifications:

Vmp
Imp
Voc
Isc
I will find that information, but does it make any different that we have two batteries, each 105 A ?
 
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