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.

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