Solar panel maxes at 1A, but expected 3.6A?

I ordered a DIY kit from amazon. They are super flimsy and easy to break, but I was careful.

Each cell was supposed to be 1.8W and .5V, ergo 3.6A by the math. But all put together now (in series) I get 5-5.6 Volts and about 1A max (with meter leads directly on each panel terminal). Voltage seems right, but current seems low. I'd expect somewhere in the area of 10%-15% over/under the estimated max, but this seems very wrong.

I am guessing one panel in it is bad or cracked and I can't see it, and is limiting the whole deal. Does that sound right? Can I test the panels using the volt meter on the in/out leads on each cell, or do the other cells interfere after they're connected?

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You'll only get a true reading, if you run the panels into an electrical load and measure the current and voltage simultaneously.

Phoenix17 (author)  steveastrouk3 years ago

Thanks. I need to try this way. I connected a 5V .25A computer fan to it and it whirred at full tilt in the direct sun. In theory it would power several of those in parallel. But I don't have a lot of 5V equipment.

I could try resistors? Is there a method to testing with resistors?

I'm seeing now why people go straight to 12 or 13V with panels they build. that's a good number that can be used to invert, use straight out, or step down.

Resistors are the best idea really. I'd use a piece of resistance wire - lets say a resistance of around 5 ohms, ideally a good long length of wire. Get something you can clip one end to the cell, and something you can slide on the resistance wire, and connect to the other end of the cell. Measure the voltage across the cell directly, and one across the resistor. Slide the wire on the resistance wire until the voltage on the cell, and the voltage on the resistor are identical. The maximum load is then equal to the resistance of the wire between the cell and the slider.

I'd make the resistance wire a metre long, and I'd measure the resistance of the whole metre as I started. The load is then (distance from cell to slider)* resistance of wire / 100

Phoenix17 (author)  steveastrouk3 years ago

What I ended up doing to get max power was to get a second multimeter (the freebie from harbor frieght) and connect the leads together, then touched the output wires of the panel with one reading current and one reading volts, and multiplied. Doing this I can see real world power with different appliances. IE phone charger cutting into the USB wires.

I think one test was averaging about 10W for the whole panel looking like 3.something V and 3.something A.. In that realm. Iphone drew up to .9A at the most and averaged about 4W charging through the cable.

Phoenix17 (author) 3 years ago

It's all good now. I hadn't switched the multimeter leads. Got to looking at it and realized moving from mA to 10A required lead port switch. Duh!

SC voltage reads .56 at the highest, and SC current reads 3.6A at the highest!

Tried to hook up a phone charger to it and charge my phone, but no go. I cut an iphone charger that I knew worked. put the red on the positive and the black on the negative and checked them with diode drop at 5.3V, but my phone did nothing. Might try it with the rechargable battery, maybe it's a more simple circuit.

Then a tiny little stick fell off a tree and cracked one of my cells... MF!

First when you wire in series the voltage increases but the current stays the same. Now the open circuit amperage of each cell may be 3.6A but if you put any kind of lead on the cell or panel the current will drop drastically.

Did you measure the current from the cells before soldering them?

Your getting 5V out so you have 20 cells wired in series?

Can you provide a link to the kit you got?

Phoenix17 (author)  mpilchfamily3 years ago

-max-3 years ago

The 3A max is likely the short-circuit current, when the voltage across the cell is nearly 0V, meaning very little power. On the other extreme, open circuit, you can get the maximum voltage rating of the cells, but only when the current draw is practically nothing. Again, meaning very little power. There is a sweet spot somewhere in the center where the voltage and current will multiply together to yield the highest amount of power.


rickharris3 years ago

What they say they do may well be different to actual practice.

You would need to know the conditions under which they made their measurements.

My Solar panels will vary from a few 100 watts on what looks like a bright day to my eye up to the full 3.8Kwatts in direct summer sunshine.

You wouldn't get the right voltage if a cell was damaged.

A solar cell is not a battery the amount of sun will influence the output.

Try midday, full sun, no cloud, and at a 90 degree angle to the sun.