I’ve nearly completed installing a Victron MultiPlus II 12/3000/120 inverter/charger on my sailboat. I’m using 95mm² tinned copper cables, which seem appropriately sized for the system. However, I’m experiencing high temperatures at both the battery switch and the 400A fuse in the setup.
I’m using a BlueSea 300A continuous-rated battery switch. When the MultiPlus is charging at 120A, the cables connected to the switch reach temperatures of 40°C or higher, and the 400A fuse also shows elevated temperatures in the same range (based on FLIR thermal images). If I bypass the switch, the cable temperature drops to around 35°C, but the fuse still runs hot. The crimps appear to be properly done, and the cables don’t get excessively hot elsewhere in the installation.
I initially used a cheap 300A Chinese switch, but after replacing it with the BlueSea switch, the temperatures at the switch and fuse remain unchanged. Is this temperature range acceptable for the switch, fuse, and cables, or does it indicate a problem? Should I take specific steps to address this, such as upgrading the switch or fuse, checking connections, or modifying the setup?
I’ve attached FLIR images showing the hotspots at the switch and fuse for reference (note: ensure your forum supports image uploads or describe the images if needed). Any advice or suggestions for troubleshooting or improving this setup would be greatly appreciated!
This is why I hate (really hate) 12V systems for this amount of power, and hence current. The Blue Sea 6006 switches have a relatively high internal resistance. It’s why I don’t recommend their use for 12V systems. See a post I made here: PV 275A Isolator Switch dissasembly and comment - #9 by OGPS
If we are forced to install a 12/3000 inverter then we use two pairs of DC cables and two MEGA fuses. We use Blue Sea e-Series or HD switches with 12V systems.
In short, 40°C is acceptable given the way you have installed your system. Not great, but acceptable. If you want to reduce the resistance (which is causing your hot spots), then try the suggestions above. Good luck with your project.
Thanks for your reply and help. I will monitor the system and see how it behaves. Maybe install adifferent battery switch later. 40/50C is still considered safe and normal?
Normal? It’s higher than I would prefer, but 40° is acceptable to me and kind of a given in a 12V system. 50°C would not be something I would let leave our shop until it was addressed.
My best advice is to replace the switch and use two fuses with two positive leads in parallel.
