So, I was busy routing a board having come up with a basic schematic. I wasn’t going to order the board yet, I wanted to just play around with the design, see how compact I could make this.
One thing that was niggling in the back of my mind, was how the traces would cope with the current. I use 6AWG cable from the solar panels, and 8AWG from the batteries. How wide should I make the traces? One calculator reckoned I should make them about 7cm wide! Another option was to use heavier gauge traces, maybe 3oz copper. A 5cm×5cm 2-layer board would cost a staggering AU$263 for just the PCB!
Okay, so I can work around this by fiddling the solder mask in Kicad and just solder some copper wire along the trace. Not a show stopper. I’ll just make wide traces so I know where to lay the wire and have plenty of area to solder it.
I was making the traces as wide as Kicad would let me, but something didn’t seem right. The inductor, just seemed so, small…
When I did the search on Mouser, their interface allows you to pick a value, then hit the ≥ button to select everything “greater than”. What I missed, is the option right down the bottom:
The “-” option, better known as “we couldn’t be stuffed looking up what the real value is”, is seen as “greater than everything else”.
A check of the datasheet itself, revealed the truth.
In short, there is no way that little tiddler is going to manage the current I was contemplating throwing at it!
What’s the biggest I can get that will handle that current? Well if I take the “-” option out of the equation, they suggest this monster . It’s 10uH instead of 33, so my ripple voltage will increase. At $837.84, it is also a rare exception to the free shipping over $60 offer.
I might need to go play with some numbers to see what I can get away with. The good news is that discontinuous output is not a show stopper for a battery charger. I might have to make do with nanohenries of inductance instead of microhenries.