Location of battery cut off switch with solar panels. Small boat Hunter Minstrel.

[noelex]

A PWM controller, will probably charge to 100% given long enough. This is because the voltage reading is an average, whereas the output from a pwm controller is a series of pulses at the full panel voltage, hence over time, the battery state will be higher than expected going by the voltage.

The better PWM controllers use the same charging profile as the better MPPT controllers so there is no difference in the ability to ultimately charge the battery to 100% . The MPPT controller is likely to extract slightly more power from the panels (around 5-15% typically) so the batteries will get to 100 % slightly quicker but there is no gain in output from MPPT controller over a PWM model when regulating so the speed difference to 100% SOC will be very small.

An absorption voltage of 13.8V is too low a setting for either a PWM or a MPPT controller.

Fuse the controller as close to battery as possible. The fuse rating should protect the wire, but in practice this will be much higher than highest possible output of the panels so you can afford to be very conservative. For a 45w panel typically you will be using wire rated at 15A + (to reduce voltage drop) so a 5A fuse would be fine. Most solar companies also recomend a fuse between the controller and the panels. In practice this does little, but if a circuit breaker is used it is also an easy way to shut down the panels, while leaving the controller powered, which can be useful.

 

[PaulRainbow]

My panels are wired from the controller to the battery with 6mm 50a cable. If any of that shorted it could easily start a fire. It's fused at the battery end with a 20a fuse. The fuse is over rated for the panel output, but well under rated for the cable and it's the cable it is protecting. I find that fitting fuses too close to the panel rating results in blown fuses.

If there was a problem at the controller or panel end and the fuse didn't blow, the panel doesn't have enough power to set fire to 50a cable. I would expect the controller fuse to blow or some of the more delicate electronics to go. I don't think there is much, if any, danger that the panel output could start a fire. If, however, undersized cabling was used, that would of course be a different story.

Edit : Typed while Noelex was posting his reply.