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203 posts

Master Geek
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Topic # 123225 29-Jun-2013 13:23
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I have had an off grid system running 1 x 90watt panel, has been running great for the past 2 months or so.

Have finally gotten the budget to add a 2nd panel, I have added it in series - so keeping the 12 volts, but doubling the amperage...

However for some reason its not increasing and I cant figure out why.

I have tried googling, as i thought for some reason it may not work...and I came across things like this:

http://cleangreenenergyzone.com/solar-power-panels-or-cells-in-parallel-circuits/
http://au.answers.yahoo.com/question/index?qid=20100120064759AA8YgR8

now that says exactly what I was expecting. 90 + 90 = 160.
I have tested them singularly, and they are both putting out 4.5 amps. (which being sunny today, is about right)
but when they are both connected, they still only put out 4.5amp.

I have double checked the fuses, I have checked to make sure I got positive and Negative around the correct way,
With both connected 4.5amp
with panel one connected 4.5amps
with panel two connected 4.5amps

why doesnt the amperage increase after they join?

When I setup the system, it was done for there to be 5 panels eventually,

How they are wired:
Panel ---> Positive ---> 6way fuse box with 10amp fuse ---> distribution bar ---> 1 fat cable to solar controller positive
panel --> Negative --> distrution bar ---> 1 fat cable to solar controller negative

I dont think the fuse box is needed, but I added it anyway to make sure the panels didn't try to fry each other.


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  Reply # 847117 29-Jun-2013 13:33
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Shouldn't 90 + 90 be 180?



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Master Geek
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  Reply # 847118 29-Jun-2013 13:34
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yes, sorry. my math was wrong there.

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  Reply # 847119 29-Jun-2013 13:38
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And you describe a parallel circuit yet say its wired in series.




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  Reply # 847121 29-Jun-2013 13:41
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"Have finally gotten the budget to add a 2nd panel, I have added it in series - so keeping the 12 volts, but doubling the amperage..."

You need to add them in PARALLEL to keep the voltage at 12V and combine the current.
Adding them in series will add the voltage - not the current. Hope your regulator is rated for greater than 24V input otherwise you may have damaged it too.

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  Reply # 847126 29-Jun-2013 14:05
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How did you attempt to measure the amperage output? Did you just measure the actual current drain with a meter or did you calculate this based on the watt rating of the panel and then the realtime voltage and resistance which will give it's actual output?




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  Reply # 847128 29-Jun-2013 14:17
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Hmmm, yes there is a couple words round the wrong way, sorry about the confusion.

they ARE wired parallel, thats my writing being dumb - along with my math.

I have tested the voltage, it remained at 20 as it should in parallel.

I measured the amps using a meter,

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  Reply # 847132 29-Jun-2013 14:26
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KennyM:I measured the amps using a meter,


What exactly did you measure? I'm guessing it was the actual draw at that time, not the actual potential total amperage output which would require a mathmatical calcultion using ohms law.

  



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  Reply # 847136 29-Jun-2013 14:52
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I measured it straight off the end of the panels, so both cables connected to nothing but the meter
now this could be the wrong way to do it? does it have to be under load when i do it? cause thats easy enough to do, ill disconnect it from the solar controller and put the amp meter inbetween, then draw some power from it?

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  Reply # 847145 29-Jun-2013 15:26
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Short circuit current of the panels should have doubled with 2 panels. but if you are measuring the current into the charger, that may not want to take any more current than you have available.

Is it a dumb charger or a max powerpoint tracking one?




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  Reply # 847149 29-Jun-2013 15:32
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KennyM: I measured it straight off the end of the panels, so both cables connected to nothing but the meter
now this could be the wrong way to do it? does it have to be under load when i do it? cause thats easy enough to do, ill disconnect it from the solar controller and put the amp meter inbetween, then draw some power from it?

You need to measure the current under load. Likewise voltage should really be measured under load. Nothing wrong with the maths, just the way you are measuring.


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  Reply # 847175 29-Jun-2013 16:41
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KennyM: I measured it straight off the end of the panels, so both cables connected to nothing but the meter
now this could be the wrong way to do it? does it have to be under load when i do it? cause thats easy enough to do, ill disconnect it from the solar controller and put the amp meter inbetween, then draw some power from it?


And did you cook the meter?

An AMP meter is not built to put directly across negative/positive of a power source. It's designed to go between the source and load only on one leg and measure the flow of current.

Your charge controller may only suck 4.5 or 5 amps and therefore won't draw the extra current the second panel is capable of. In this case you'd need a greater capacity charge controller and battery rated for the extra charging current.

So you'd need a 8amp load to start with before the AMP meter will show 8 amps (keep in mind if using cheap digital multimeter with DC current mode they're only designed for about 10-20 seconds use before they need a good time out).

I remember my first attempt at figuring out how to use an AMP meter, I put it straight across the power source, I saw a flash of lighting and had one black charred AMP meter left in my hand, I was extremely lucky. Hence my question, did you cook the meter?





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  Reply # 847177 29-Jun-2013 16:42
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And if you are measuring the current, check you are in the right terminals of the meter, many even pricy ones dont beep at you when the probe is in the wrong hole for current when you have the range selector on current but the probe in the voltage terminal.




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  Reply # 847182 29-Jun-2013 16:51
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kiwirock:
And did you cook the meter?

An AMP meter is not built to put directly across negative/positive of a power source. It's designed to go between the source and load only on one leg and measure the flow of current.


Thats assuming a non current limited power source.

A solar cell has a short circuit current printed on it, at which point it is delivering almost no power because you are taking close to zero volts off the panel. Put the meter across a 50 watt solar panel, and you will see about 5-6 amps or so in full sunlight.

That is why its important to get a charge controller that can track the maximum power the cells can produce. If the charge controller is still acting as if it has a single panel on it, then it will not try to pull more current as that would cause the voltage to sag and make less power.




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  Reply # 847218 29-Jun-2013 19:18
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KennyM:  does it have to be under load when i do it? cause thats easy enough to do, ill disconnect it from the solar controller and put the amp meter inbetween, then draw some power from it?


All that will tell you is the current drain in amps at that moment in time, one can presume you're wanting to know the maximum available current rom the two panels. As I explain above to do this you'll need to do some basic math - you need to know the size of the panels in watts, measure the resistance across the panels and then use ohms law to calculate this.


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  Reply # 847223 29-Jun-2013 19:32
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Except you can only measure the resistance of an ohmic load, which a charge controller will be far far from.




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