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PCB's Back & functioning unit!

A project log for Open MPPT

Open Source MPPT for Solar charging.

Ben BrownBen Brown 07/21/2017 at 13:440 Comments

PCBs!

I received the PCB's back from SeeedStudio this morning and naturally had to build up one to test the design.

As I was populating the board I realised my main mistake on the design, which was to use a completely too tiny diode package, which is why there is a large wire across the PCB.

I'm also completely out of the XT30PW connectors I need to populate the board, having only been able to find one so far. So I have run a wire for the input side for the mean time.

The boards turned out perfectly otherwise, which is very nice to see after waiting for them to arrive.

Testing

The unit was setup for an MPPT voltage of approximately 18V and output voltage of 12.3V. 

This allows the use of a standard 3S lipo with the common 19V laptop power supplies, as well as most solar panels.

On the first power up the unit did not work straight away (wouldn't it be nice if it just worked).

The Schottky diode used for the bootstrap circuit needs to be a decent model, and the first one I used had too low of a breakdown voltage (I think) which allows the voltage at the REGN pin to go up to around 9V. This resulted in the main IC getting very hot quickly.

Once this was replaced with the larger diode (seen above), the main IC was still drawing a large amount of power, so it was replaced with the spare main IC. 

After replacing the main IC the unit powered up much more stable and now appears to work... Mostly.

Running the unit at 2.5A input (4A output), the main IC runs cool and stable, and the switching MOSFETs are staying nice and cool as well. However the input filter caps that I used are not rated for the pulse current the unit is drawing, and get hot after only a few minutes of runtime.  I plan to replace these with better-rated capacitors and then test the unit for a longer period of time.

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