Friday, 13 October 2017

Cheapie MPPT Controller further discussed

well we had sunlight worthy of mention today, so I thought I'd extend the testing I did on my cheapie controller and give it a quick whirl with one of my 100 W panels.

Now first up lets say that the panel is specified as:

  • Max Power = 100W
  • Open Circuit V = 21.6
  • Short Circuit A = 5.97
  • and "Rated V" = 17.8 (projecting the MPP?)
  • and "Rated A" = 5.62
which is interesting as it implies (to my limited understanding of Solar Panel Specs) that the maximum power of 100W is at 17.8 @ 5.62 

So I thought I'd wire it up to my system in quick way with the following diagnostics:
  • Volt Meter (Fluke 11)
  • Ammeter (Lexa cheapie in Amps)
  • 150A Watt / Power Analyzer (ebay jobbie)

Knowing that some items can suck more peak power than my MPPT controller may be able to stand and deliver, I thought that I'd wire my load directly to my 120AH battery. So here is that.

and for those who can't quite follow the mumble, the summary position is that less amps were going into the battery than was being sucked out of it. In particular the charger was putting about 1.6A into the battery while the little fridge was sucking out 2.89 A ... a short fall of power.

I wondered why the controller was not putting enough into the batteries to balance the load.

So here are the few more measurements I mumbled about at the end...

So the summary position is that the contoller has no way of knowing what is being drawn from the battery (what load its under) and (I assume) it assumes no load. There are controllers which incorporate this sort of externality with a thing (commonly? occasionally??) called a shunt sensor. This doesn't have one.

So my findings are that with my single 100W panel will give through more power, but interestingly it seems that it won't push in much more than 3Amps (not shown in the video, I turned off the fridge giving more available power) ... which could of course be because charger reckons that's as much power as the battery can handle.

So, where did that power go? Well as I mention in the video the panel got to 69°C which means that we need to re-work the figures (because these things conform to known physics). This is coefficient is about 0.4 per degree variant from standard (of 25C) that the panel temp gets to. In my case its; about 44 degrees above 25 giving about 18% loss or in other words dropping my max A figure to about 4.15A ... or pretty close to what we got.

Where does this leave me?
Well it means that (depending on my fridge) I'm going to need more power input than I currently have or the system will basically just wear the battery down in the evenings which it won't be able to recover in the day time.

So, lets have a look next at what a second panel does for this ...

Wednesday, 4 October 2017

Cheapie MPPT controller (updated)

Well, normally I have the view that you get what you pay for. However often what things cost is a reflection of a complex mix of R&D costs, what the market will bear, profit motive ... A few other things.

Well China is now going very seriously into Solar Energy and it's not surprising that they are making efficient electronic devices to do small scale solar.

So with this in mind I bought a cheapie eBay controller and thought I'd see what it did.

This is it, and unlike ones I've seen reviewed on YouTube, this has two inductors.

It's the model CPS-2420 and it comes adorned with precious little documentation.

So, today I got it, and put it to the test. I attached it to a 12V flooded lead acid car battery and with a DMM (Digital Multi Meter) on it and found that it put my panel to about 17V and pushed 13V into my battery. Rough figures because it was constantly adapting output as the battery took charge and as the light conditions changed.

The little embedded system did a great job of ramping up load and determining the system capacity autonomously and heuristically. Best indicator of its effectiveness was that it put 0.67Amps into my battery when the panel is rated (and I've measured itto 0.55Amps at full short circuit load. This is about a 27% increase in power over PWM.

If you don't know the difference between PWM & MPPT then I suggest you do some reading, alternatively this YouTube link has a great and detailed overivew:

But in a nutshell its a way of getting the most power out of your solar photovoltaic panels and into your storage (battery).

This is the review of another similar model (the CPY version) by Adam Welch, but mine is the CPS version (and 20Amps) and as you can see looks a bit different to his.

So in some ways I prefer mine, and either way its Fukken Amazing for $30


I've  just done a quick test with two multimeters (one for amps, one for volts) and an inline wattage meter (that does both amps and volts) inline with another (bigger) panel...

So, on an overcast time I was getting

0.32Amps @ 12.98V into my battery while the panel was 0.41A 13.88V

now this doesn't take into account the losses in the two meters, which while small won't be nothing. I know for instance that my DMM showing Amps has an resistance (including leads) of about 0.5 Ohm which of course is significant.

Basically its not particularly efficient at very low light conditions.