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Combinerbox

DIY combiner box

Most grid tie systems put 10 or 12 panels in series to have +350V DC at the input of the inverter. This approach doesn't work for my off grid system. The charger takes only 145V so I have to create several strings and combine them to a single DC feed towards the charger, the PCM60X. There are a few commercial units available but I preffered to built one myself. It's pretty easy but you need some hardware, it's all listed at the bottom of this page.

Check your junkbox, you might have a metal case or other hardware and save some $$$.

Layout combinerbox

This is the layout we're working too. At the bottem left you see the PV fuse holder. above you find the blocking diodes. The device with the blue cover are just simple termonal blocks. The red item is a surge protection device. The breaker with the yellow lever is a DC breaker. Don't worry we'll tackle this step by step. Good luck.

Case

Let's start with a watertight case. Dimensions are W/HD 30/35/25 cm. Ideally you have a mounting plate.

MC4 connectors

This design can combine 5 solar stings. At the left I drilled 5 holes for the +/- MC4 connector, at the right the same for (+/-). I have 25cm 2,5mm stranded copper wire connected to the MC4.

Blocking diodes

Get an aluminim cooling plate to line up the blocking diodes. The diodes have a notch on both sides. put a mark

Preparing cooling place

In previous picture I asked to put 6 marks in the notches of the diodes. Drill 6 holes -> 3.5mm and tap M4 thread. I mounted the alu cooling plate to the mounting plate.

Thermal grease

Before mounting the diodes to the cooling plate add some thermal grease. These diodes work way below there specs and they don't get hot.

mounting rail

Install the mountingrail for the fuse holders, DC breaker and lightning protection.

Before welding the cells make sure they're fully charged. If everything goes well, this is the last time the cell sees 4.2V
If they don't have the same voltage, then current will flow from one cell to another during the building process.

Line up

The most challenging job is done. You only need to connect the MC4 connectors to the fuses, the fuses to the diodes, the diodes to the combiners and as final step the DC breaker and the lightening protection.

Wiring

Connecting all parts. All wires are 2.5mm2. from the combiners to the DC breaker/lightening protection I used 6mm PV cable. The green connector at the bottem is the earth connection.