Solar-Panel Voltage at 2420 RC and LC

Hey everyone,

I’m interested in the libresolar project. I want to help engineering and developing the software, as far as I can go with it. But first i have an important question.

For which solar-panel-voltages for 12V Batteries (car) and which panel-voltages for 24V (also car) batteries ist this system compatible?

I like the design, but why don’t you use an interleaved buck converter? Would not this increase the effeciency of the whole system? I know, it’s also developed for min. prices but i think, this few usd would be worth?

Greetings Ben!

PS: Nice to meet you all and I’m looking forward to work together :slight_smile:

Hey Ben,

welcome to the project, happy to hear that you’re interested!

The LC variant allows for around 55V maximum solar input voltage (but I don’t recommend to build up that one anymore, as the newer designs feature several improvements). The RC variant allows up to around 80V (uses 100V MOSFETs). This works both with 12V and 24V batteries. However, according to first tests, the heat dissipation inside the very compact housing doesn’t seem good enough for the full range up to 20A supported by the board. So the MOSFETs would have to be attached to a larger heat sink (e.g. at the bottom of the board) if 20A output current is needed.

You are right, an interleaved design would increase efficiency and also reduce the ripple current for the input capacitors. I think that up to 20A inductor current the single phase design is sufficient and any charge controller beyond that should have an interleaved design. Would be quite interested to develop an interleaved design in the future.


Wow, 80Volts sounds good for me!

Okay, then i will go for an 20Amps MPPT with an interleaved Buck Converter to increase the efficiency of the whole Charger.

That’s true, we need TO-220 MOSFETs and have to cool them down via Cooling-Backcover , so we have the case and the connection to RC for cooling down. In will implement a connector for active cooling for my prototype, just in case :sweat_smile:

Is there any chance to get the schematic for eagle? It looks like it’s only for kicad :see_no_evil:

Not sure if Eagle has an import tool for KiCad.

Nope there is none, but no problem, then we have also eagle design for Eagle users.

Good morning Martin,

what efficiency can we achieve with the current hardware and software? I think that we can achieve about 96% efficiency with an interleaved buck converter. If the difference to the current efficiency is not too serious, I would leave the design as it is. The additional costs when measured against the entire product are relatively low. So, if the current efficiency is under 90%, i would integrate this converter.

Just thoughts:
At the moment 85% -> 96% -> 11% growth of efficiency. 20€ For the interleaved buck converter > 2€ per percent excluded sw-development. I think it’s worth…

What are your thoughts?

Here is an efficiency graph of the MPPT 2420 LC. It gets up to almost 99%.

The 2420 RC has MOSFETs with higher voltage rating and thus, higher Rds(on). But it should still be above 96%.

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