How do I increase 3A fixed output current of a buck converter?

Basically I am making a solar inverter without any battery or charge controller that will directly convert the dc output coming from solar panels (6 connected in parallel) into 220V AC.I am using solar panels 50W each, having an open circuit voltage of 20V and the voltage varies between 15-20V during the entire day provided a minimum amount of sunlight is there. Next, I am using a 12V buck converter circuit using an LM2576 (here is the datesheet of lm2576)and few more components to get a stable output voltage of 12V out of the panels. Now this 12V DC is fed to an inverter circuit which converts it into a square/modified sine wave 220V AC at approximately 50Hz. But, I am not getting desirable power output. From 6 panels, all I am able to power is a 45W LED bulb along with a small 3W LED bulb.

Probably, one problem is with LM2576 buck converter IC. This IC although providing a constant 12V output but it is rated at a 3A fixed output current. And I think probably this is the reason why we are unable to drive more loads. Is there a way to amplify current in this case? Or something else should be done which I am missing here ?

-max-4 months ago

I assume you have 6, 50W 12V solar panel.


Why you should definitely use a battery:

Without a battery to act as a buffer for energy, then you will very rarely get reasonable efficiency from a "direct-to-inverter setup". The issue is that solar panels only produce their rated output under very specific amount load, assuming full sun (about 1000w/m^2 and no half sun does not mean half power!), the perfect orthogonal angle, and a good uniform amount of solar radiation on all cells. Basically it's a bullshit rating and you need to take it with a grain of salt.


Importance of load matching:

If you try to draw too much current, the voltage will collapse to 0V and you get 0 power. Likewise if you have a very light load, the voltage will climb up close to it's maximum rating and your setup will again be very non-optimized.

Also, if your open circuit voltage is only 20 volts, the MPP voltage (maximum power point) is likely only going to be around 12V or so. Maybe less when less light is available. Keep this in mind when choosing a regulator.


That regulator sucks! well, at least for this application:

From what I can tell, the LM2576 you picks is pretty much shit. The 5V version is only 77% efficient at the full 3A and w/ 12V input. This is likely with an ideal setup, so your milage may vary. (hint: it will be less!) In general, switching regulators efficiency drops with increasing current and larger Vin to Vout ratios, too.


Cheap / easy solution:

If you are looking to get up and going as quickly as possible, Downunder35m's suggestion of hacking a UPS does not sound half bad, especially if you can get one cheap. You will most likely end up with a standby UPS, which is fine. I would seek out a online UPS or standby-online hybrid UPS, because with these, the inverter is engineered to power a device continuously and not for short and very infrequent periods of time.


"best" solution:

If you want the most optimized design, and then try to design it such that voltage is only stepped up, that is, try to avoid stepping down to low voltages before stepping up to the 110v or 220v AC output. less total voltage conversions = less power losses. I'd shoot for a 48v or 96v battery configuration, a 48v or 96v inverter, and an MPPT capable of charging such a pack. pay close attention to min / max voltages of the inverter, your chosen battery configuration, and the MPPTs. Make sure under no conditions can the inverter over-discharge the battery, burn up due to the battery being at the fully charged state, etc. If you are using lithium batteries, then the use of an additional BPS or BMS is going to be critical for safety.

Downunder35m4 months ago

1. Are your panels rated for a parallel connection?
E.G.: do they have protection diodes build in?
2. 50W is a figure from the seller based on maximun sunlight at noon with the panel aligned correctly.
This means on a normal day you might only get about 30W if lucky.
3. Using a limited buck converter not only introduced a lot of interference but as you noticed 3A just won't cut it.
Better use a solar charge regulator rated for 30A that offers a direct output for a load and not just the connection for a battery.
If you really want to get good use I recommend to connect a decent battery anyway and to drive the inverter from it - this will prevent your stuff from blowing up if the clouds come while you need a full load.

Even if you assume no losses anywhere a 12V/3A input for the inverter will only have less than 40W and you won't get more on the output side.
Might be easier to modify an old computer UPS for your needs....