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Beware the cheap MPPT solar regulators

April 13, 2019 — BarryK

...because they aren't, they are PWM regulators.

As posted a couple of days ago, I have ordered a 250W solar panel:

I currently use a very cheap PWM regulator, model CY1220, rated for 20 amps. Took a photo for the 2017 camping report:


An MPPT controller has a distinct advantage, that it draws from the solar panel at it's peak-power point. Say for example, that is 17.5V @ 13A. Whereas, the battery voltage, for lead-acid batteries, would be somewhere between 12 and 13.7V, let's say it is 13.2V. The MPPT regulator will convert to the battery voltage, and charge at a higher current. If the regulator is operating at 100% efficiency, the input power for this example is 17.5x13 = 227.5W (watts). Right, so the output will be 13.2xA = 227.5, where "A" is the amperes. Do the maths, A=17.2.

You see, 13 amps coming out of the panel, 17. amps going into the battery. A PWM regulator cannot do this!

One downside of the MPPT regulator, is that it does draw some idle-current from the battery, even when the solar panel is not charging. Meaning, if the regulator is attached to the battery, it will be drawing this current 24 hours a day.

The bad news is that most of the cheap Chinese solar regulators that claim to be MPPT are not. Tests have also shown that the idle current on those that are MPPT, is much higher then claimed, for example 50mA instead of the claimed 5mA.
Also, they are not 100% efficient. Some cheap ones claim 99%, however, I very much doubt this. I think, one tester on youtube reported getting about 95%.

One of the testers on youtube is Adam Welch. Here he tests one of the cheapest claimed MPPT regulators, model CPY-2410:

...yes, it is a genuine MPPT. Most unfortunately, however, later versions, in the same box, same CPY-2410, have a different internal design and are NOT MPPT! This is the minefield that you have to wend your way through, if you buy one of these.

After Adam had reported the CPY-2410 works great, and getting some negative feedback, here did a follow-up video:

This chap also, ended up being disappointed:

The electronic engineer in me has become intrigued (that's what I used to do, before retiring). So, I have ordered a couple of the 20A versions, the CPY-2420. Ordered two, with different model numbers...

This one, with voucher code, cost AU$46.71, photo shows "CPY-2420" but the specs show "CY1220-MT":


And this, cost AU$48.44, photo and specs both show "CPY-2420":

Keen to test these, and find out if they are true MPPT! And test other specs, such as idle-current and efficiency.

I have a 120W panel to test with. When the 250W panel arrives, will test with that, in fact, that is the one that will be used in future camping trips. But, it puts out up to almost 14A at peak-power point, claimed anyway, which could be up around 18A into the battery ... and perhaps that is flogging the regulator beyond it's capability. 

Ultimately, might have to go for a 30A or 40A rated MPPT regulator, and one with LCD display, and the cheapest is about AU$170. We shall see, will find out what these cheapees are capable of first. 

Tags: light