PCM3012 low proced MPPT tested

[astrayan]

I finally got some good sun to test this Taiwanese MPPT I purchased recently.

http://s1259.photobucket.com/albums/ii548/pcm3012/ <---photobucket album

I had great hopes that it would get better than unity-gain current, but it seems to perform like a PWM, even though it clearly isn't. It's able to transform 24V into 12, but at exactly the same output as if 12V. I've checked the input on a CRO, and it appears to scan for peak power. You can see the input scan between 25-32V (mostly 28.5V), and also see little glitches at 26us intervals. There is very little heat coming from the heat-sink at 15A.

The ammeter is on the output of the MPPT, on a Y splitter, with circuit breakers, and I can switch it quickly back to direct panel input. The test, showing lots of ammeters at 15A, is the result of 3 tests. To obtain 24V input, I went onto my roof with a soldering iron.

Row 1: 12V input, direct from panels, followed by 12V through the MPPT
Row 2: 24V into MPPT
Row 3: 12V input re-test, then 12V into MPPT.

It doesn't really matter which is which, because it's all the same.

[inetdog]

I finally got some good sun to test this Taiwanese MPPT I purchased recently.


The ammeter is on the output of the MPPT, on a Y splitter, with circuit breakers, and I can switch it quickly back to direct panel input. The test, showing lots of ammeters at 15A, is the result of 3 tests. To obtain 24V input, I went onto my roof with a soldering iron.

Row 1: 12V input, direct from panels, followed by 12V through the MPPT
Row 2: 24V into MPPT
Row 3: 12V input re-test, then 12V into MPPT.

It doesn't really matter which is which, because it's all the same.

An interesting observation. Is it possible that 15 amps is the maximum rated output current for the unit? If so you would have to try it with less panel or less sun to see an effect.

On the other hand, scanning to find the MPP load without being able to boost current is ridiculous, since you would get more current by going below the MPP!

[russ]

12 volt from the panels?

[astrayan]

I think what's going on, is that I'm observing it at the break-even point, which is:

13V battery + poly panel @ temp 47C.

The guy who sold me the device on ebay has done a youtube, where he demonstrates running a fridge off the "load" output, and all powered by an amorphous roll-up array. His "watts up" meter was showing 17V coming from the panels. When I look what's coming off my panels, the MPP is around 15.4V, because my poly panel Pmax Voltage has dropped, even in moderate winter sun. The amorphous array he uses, keeps its Pmax at the 17V that all these MPPT devices are supposed to work at. Also, by loading the setup with a fridge, the battery voltage caves in to about 12.5V.

I was looking at the output in cloudy weather today, when the panels were cool, and another amp was being generated. Also, it gets better when I put the toaster on.

Basically, I'm not expecting great performance when the 40C weather hits, because I know the panels get up to about 80C, which at the normal derating of -0.45% per degree, makes a drop of 24%, so the maximum power point will be where the panel was going to charge the battery anyway, so I'll lose the 7% that the MPPT normally chews up.

Maybe I don't mind, because I just need a DC output to power my fridge and computer during the day.

The whole MPPT concept is fried at the moment, because panels are so cheap.

[astrayan]

12 volt from the panels?

The tests are done with 12V and 24V, and it didn't seem to make any difference, because at the temperature and battery voltage tested, there is no MPP that makes things better, after subtracting the 6-8% that these devices normally chew up.

[russ]

You are not charging any batteries at 12 volts.

[astrayan]

You are not charging any batteries at 12 volts.

I'm running 12V batteries.

However, the problem is that I got sold some "grey market" B grade panels on ebay, which degrade in even low heat, pretty badly. I just tried some other monocrystalline panels, and I seem to be getting some reasonable gains using the MPPT, even on 12V input.

So, it's all a bit like I'm suffering foot-in-mouth disease . You might as well delete the thread, or at least change the name to "priced", rather than "proced".

[russ]

Charging 12 volt batteries with 12 volts?

[astrayan]

Charging 12 volt batteries with 12 volts?

Yes.

Some tests today indicate that the PCM3012 actually handles 12V input more efficiently than 24V input.

[inetdog]

*UPDATE*

This really is an MPPT CC. The OP's observation of a uniform output current is explained by 15A being all the battery could take at its current SOC. That is why I out goes up when a load is added to the battery.

[bcroe]

I love your pictures. What might be happening, is your panels have pretty much a perfect Vmp match to what is required to charge the
batteries (15.4V). If so, what goes into the controller is nearly identical to what comes out. I'm estimating the scope shows the MPPT
controller running at 97% on cycle, meaning its close to a simple short. If the panels got shifted to say, 40% more voltage, everything
would change. Bruce Roe

[inetdog]

I love your pictures. What might be happening, is your panels have pretty much a perfect Vmp match to what is required to charge the
batteries (15.4V). If so, what goes into the controller is nearly identical to what comes out. I'm estimating the scope shows the MPPT
controller running at 97% on cycle, meaning its close to a simple short. If the panels got shifted to say, 40% more voltage, everything
would change. Bruce Roe

Note that this is a four year old thread.....I updated it solely because it still shows up high in a Google search on that model number.
Your hypothesis does not completely match the current being identical with two panels in series. In that case the CC would be deliberately operating away from MPP to limit the output power.

[bcroe]

Note that this is a four year old thread.....I updated it solely because it still shows up high in a Google search on that model number.
Your hypothesis does not completely match the current being identical with two panels in series. In that case the CC would be deliberately operating away from MPP to limit the output power.

Oh yea, 4 years. I couldn't figure out for sure if the controller was limiting, or the panel output was. Switching down a 24V panel arrangement
will give the same output current (and power) as a 12V arrangement of the same panels. Bruce Roe