MPPT amp to battery

[wheresthesun]

I have my small 3 X 100W (series) setup in place for a few weeks now and I am just starting to notice some trends that I don't really understand. I discharge lightly enough in the evening and get my 100Ah AGM down to around 12.4 on average. I have noticed that when I get a sunny morning (like today) and I get full beam on the panels the SCC doesn't put maximum amps to the battery. From reading, I thought the controller would try to get 10A into the battery for as a long as it could to charge. However, my controller will rarely put more than 4A at any time. Even if I load the battery with all my appliances I haven't seen it put more than 9A into the battery.

Attached is what it is doing right now.

I have an EPever 30A MPPT and each panel is:
Rated power: 100W
Open-Circuit Voltage (Voc): 21.6V
Short circuit current (Isc): 6.13A
Working current (Iop): 5.78A

Is this normal or is there something I should check on my setup?

 

[gnubie]

Peak of 9 amps is roughly right. 100W nominal / 12V nominal = 8.3A. When your battery voltage, as seen on the controller's battery terminals, is lower the current will go up. When the battery voltage is higher the current will go down.

At 14.58V that 100W becomes a maximum of about 6.8A. There's more to it than just that too. The panel has to be in a position (conceptually and physically) to produce 100W. If the angles to the sun aren't right etc it won't produce 100W. If the cells are hot Vmp goes down a bit and power from the panel does too. If you can find the NCOT ratings for your panel that's closer to what you'll get in real world cases. The 100W figure is the STC rating which is an artificial test to set what the panel can do.

Well forget all that I see it's 3 panels but at least some people might find that informative.

More sensible information below...

300W into a 12V battery is about 25A. That you get a maximum of 9A says something is wrong with your setup or the panels aren't getting square on sunlight when the sun is highest in the sky. I'm assuming that collectively your loads are capable of drawing more than 9A. Do you have a multimeter that can handle the short circuit current of the array - 6.13A? A crude test to see how much power your panels can produce would be to measure the amps with the meter across the + / - lead from the array. That's going to be 70 odd volts open circuit so you should have a way of disconnecting the array from the meter so you'd hook in down stream of your isolation switch.

 

[wheresthesun]

Do you have a multimeter that can handle the short circuit current of the array - 6.13A?

Yes, not sure why I didn't think of that one, thanks. I will run this test and see what we're getting from the array.

 

[HRTKD]

Even if I load the battery with all my appliances I haven't seen it put more than 9A into the battery.

Any load on the system draws down what can be put into the battery. Power doesn't go into the battery and come back out to satisfy load demand. This assumes that both the load and the battery share a common bus bar.

When my batteries are fully charged (according to the BMS), the battery monitor (Victron BMV-712) doesn't see any load. The solar charge controller is putting power at the bus bar and the load (inverter) is taking it right back off without any of it going into the battery.

 

[wheresthesun]

This assumes that both the load and the battery share a common bus bar.

Yep, that is how it's setup.

The solar charge controller is putting power at the bus bar and the load (inverter) is taking it right back off without any of it going into the battery.

That makes sense. Still, I would have thought that after an evening of DOD ~15% that when the sun hits the panels fully - I would get more current into the battery to charge than what I am seeing.

 

[RCinFLA]

Check the voltage drop across MPPT controller from PV input to battery output. You did not say your panel model. Some '12v' panels are only putting 32 cells in series. These low cell count panels put out marginal overhead voltage for many MPPT controllers.

If you find less then 1.5v drop from input to output of MPPT controller it has likely dropped into PWM mode because it doesn't see enough overhead voltage from PV panels when doing its MPPT search. Panel wiring run voltage drop can make things worse. Your battery voltage must be at a state of charge that would accept full charge current during the test.

A panel should have at least 36 series cells to reliably run MPPT controllers on a 12v battery system.

 

[wheresthesun]

Check the voltage drop across MPPT controller from PV input to battery output. You did not say your panel model. Some '12v' panels are only putting 32 cells in series. These low cell count panels put out marginal overhead voltage for many MPPT controllers.

If you find less then 1.5v drop from input to output of MPPT controller it has likely dropped into PWM mode because it doesn't see enough overhead voltage from PV panels when doing its MPPT search.

A panel should have at least 36 series cells to reliably run MPPT controllers on a 12v battery system.

Thanks.
Can you see that in the image I provided earlier or should I look for something else? ~ 65-70V in, down to 13.80-14.40 (depending on stage). Is this what you mean?

 

[RCinFLA]

Thanks.
Can you see that in the image I provided earlier or should I look for something else? ~ 65-70V in, down to 13.80-14.40 (depending on stage). Is this what you mean?

Sorry, did not see you had them in series.

 

[wheresthesun]

So I have made some observations and it seems the amps/volts coming from the panels are correct. The MPPT seems to be regulating what it puts down to the battery. Perhaps this is correct but I , naively, thought that if there is (for example) 20A availble to the SCC and the battery is low on charge that it would put the max amount of charge into it. But as I say, it appears to be throttling it to a much lower current.,

 

[HRTKD]

Is the solar charge controller configured to know the Ah of your battery?

 

[wheresthesun]

Is the solar charge controller configured to know the Ah of your battery?

Yes. It is configured for a 200Ah battery (I did ask here on another post before about that and it was thought this wouldn't affect it).

Not sure it this helps:
Settings Data
----------------------------------
00 Battery type: 1
01 Battery capacity: 200Ah
02 Temperature compensation coeff.: 3mV/°C/2V
03 High voltage disconnect: 16V
04 Charging limit voltage: 15V
05 Over voltage reconnect: 15V
06 Equalization voltage: 14.6V
07 Boost voltage: 14.4V
08 Float voltage: 13.8V
09 Boost reconnect voltage: 13.2V
10 Low voltage reconnect: 12.6V
11 Under voltage recover: 12.2V
12 Under voltage warning: 12V
13 Low voltage disconnect: 11.1V
14 Discharging limit voltage: 10.6V

 

[sunshine]

What brand are your 100w panels?
You need to 1/2 ebay watts to get real watts and looking at the posted photos 5.2 amps to the battery seems more than can be expected.
Why does your pv meter only goes to 200w?

 

[wheresthesun]

What brand are your 100w panels?
You need to 1/2 ebay watts to get real watts and looking at the posted photos 5.2 amps to the battery seems more than can be expected.
Why does your pv meter only goes to 200w?

They are Eco Worthy 100W panels.
5.2 Amps from 3 x 100W in series should be easily do-able, no?
The meter goes to 200W because I initially had 2 panels and I didn't re-write my app to show the limit!! - Lazy programming really. The data will display correctly though

 

[sunshine]

The photos show the battery 4.02 amps 14.48v (18w)
The only way you can increase the amps is by increasing the voltage to the battery but the MPPT controls that irrespective of available wattage.
You are using the other 40 watts( as per photo) for other loads and this will be at that same 14.48 voltage.

Edit: all things being equal if you add another battery the charge would be 8.04 amps

 

[wheresthesun]

The photos show the battery 4.02 amps 14.48v (18w)
The only way you can increase the amps is by increasing the voltage to the battery but the MPPT controls that irrespective of available wattage.
You are using the other 40 watts( as per photo) for other loads and this will be at that same 14.48 voltage.

Yes. The image is confusing. I need to grab a better one to show the problem. If you suppose the battery is at 12.4V with full sun on the panels with zero load on the battery. Should the SCC put more than 4-5A into the battery, if it has up to 20A available?

 

[sunshine]

Yes. The image is confusing. I need to grab a better one to show the problem. If you suppose the battery is at 12.4V with full sun on the panels with zero load on the battery. Should the SCC put more than 4-5A into the battery, if it has up to 20A available?

At 12.4 v the rate is probably similar to the higher voltages.
Really low voltages like 10v is when I see the high rates, Probably because at that voltage it no longer has the usual battery resistance characteristics and will soon need replacing.

PV only produces what it is asked for. 4 amps requested from your agm seems about right from other info,
Just look at the battery as any other resistive load.