solar amp calculations

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Bill c112

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Joined
Sep 29, 2021
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Location
Lebanon Missouri
Ok I must be missing something. I need to know how many amps are being put out by my solar panels. They are 200 watt panels...3 of them. 12v and wired in series. So my calculator says they should be putting out 50 amps. Then I checked the actual voltage rating on the panels...says 20.4v. So I redid the calculation...now says 29.4 amps. Sounds more reasonable. However when I check the main line going from the panels to the solar controller, my amp meter only show about 6 amps going through the main wires. What am I missing.
 
I assume you have an MPPT controller, if so then it will up convert amps when it changes the charging voltage. Where are you taking your measurement, before or after the solar controller?
 
I assume you have an MPPT controller, if so then it will up convert amps when it changes the charging voltage. Where are you taking your measurement, before or after the solar controller?
Yes Isaac it's an MPPT an I took the measurements before the solar controller. I'm wondering does the amps only go up on the lines as the amperage demand in the RV go up????
 
Ok I must be missing something. I need to know how many amps are being put out by my solar panels. They are 200 watt panels...3 of them. 12v and wired in series. So my calculator says they should be putting out 50 amps. Then I checked the actual voltage rating on the panels...says 20.4v. So I redid the calculation...now says 29.4 amps. Sounds more reasonable. However when I check the main line going from the panels to the solar controller, my amp meter only show about 6 amps going through the main wires. What am I missing.

the actual amperage will depend on sunlight of course, if you need to calculate the maximum amperage for cable and controller sizing then assume the maximum wattage at Vmpp ( the voltage quoted on the panel at full load at maximum power point. )
for a "12 Volt" panel the Vmpp is usually around 18 Volts, so at full power you will have
200 W divided by 18 Volts = 11 Amps that's a theoretical maximum.
you stated three panels in series, so your Vmpp maximum is therefore 18 * 3 = 54 Volts
and the amperage will be 11 Amps

normally after such a calculation, one would not really be interested in the panel amperage, the more important figure would be the wattage advertised by the mppt controller. most mppt controllers have some kind of output, be it bluetooth, serial, lcd display etc.. and that makes it easy to view the system status at any point in time.
 
To measure 50 amps you have to have a 50 amp load. If the batteries are charged and the system is hooked up you won't measure 50 amps.

Think of amps as flow. In order for 50 amps to be flowing it has to be going somewhere. You could hook up a 600W+ inverter and plug in 6 X 100W incandescent lights as a load pack.

Of course due to efficiency, sunlight and transformation losses you won't ever see the full 600W.
 
here is a different take on your post.

Ok I must be missing something. I need to know how many amps are being put out by my solar panels.

you are interpreting and assuming that the panels will deliver their full rated output and you have divided the panel wattage by 12 Volts to arrive at that 50 Amp value, the value you have calculated is the maximum amperage value used to select an MPPT controller when used in a 12 Volt system.
you don't need to know the panel amperage, I think you meant to say "I need to know how many amps ( or watts ) the MPPT controller is providing"

They are 200 watt panels...3 of them. 12v and wired in series. So my calculator says they should be putting out 50 amps. Then I checked the actual voltage rating on the panels...says 20.4v.
20.4 Volts tells me the panels are not fully loaded, either they are not in full sunlight or more likely, your system is charged and not presenting much of a load. if you were to switch on all your lights and perhaps an inverter with a coffee pot or microwave and load the battery bank, the controller will sense this and increase it's output.
So I redid the calculation...now says 29.4 amps. Sounds more reasonable. However when I check the main line going from the panels to the solar controller, my amp meter only show about 6 amps going through the main wires. What am I missing.
you are using the wrong values for your calculation. the 6 amps you measured at 20.4 Volts equates to
a value of 122 Watts. as I stated in my other post, you do not need to measure these values, the controller does it all for you, just read what it has to say..

additionally, solar panels rarely give anything close to full output. a typical value might be 80% in good conditions.
 
If the batteries are charged and the system is hooked up you won't measure 50 amps.
Just discovered this. Couldn't figure out why my 200 watts of solar was only putting out about an amp in full sun. Then I checked the battery and it was almost fully charged.
 
On the back of the panel is a tag. Look for Isc that’s the max current also look for Imp, max power current.
A 20.4 panel max power current is 9.8 amps. But unlike you will get that, but it’s the max you will see with an mppt controller. But as said, you battery charge will determine how much current they need.
 
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