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.
I had the Victron rotary switch on my 48v system, that was getting to about 70°c and has long since been done away with. I have double pole moulded circuit breakers on the batteries, and MCBs on the solar feed, as well as the various fuses, so other means of isolation is possible.
Very common problem these rotary isolators getting hot, especially if they’ve been operated under load.
ZBeny, I first spotted their name in a SolarEdge document I was looking at, can’t remember the specific item, but it was on a list of suitable items. I’ve also seen their isolators used built in to some inverters.
One on the left is for the battery, one on the right is the battery rack isolator. I do use these in conjunction with T class fuses. To give you an idea of size the mounts in the middle are 1" square box.
Thank you. I found them under ZJBeny. They have several different website domains, but all are the same company. No suppliers in the USA that I have found, yet. I’ll keep looking. They don’t have UL certifications so that’s probably why. NoArk is a brand of Chinese MCCB’s that are quality and UL-listed, but still very very expensive :-o That’s why I stick with high-current DC disconnects and Class T fuses.
To be honest, 40 or even 50 degree C isn’t that hot.
My 18kW system on 51,2V also runs at 50C at the fuses. Victron Lynx has an operating temperature range up to 60 degree C.
No need to worry about temps if they are not above 50C
You can either double up the cables into a single, larger lug to connect to the e-series switch or use the regular size lugs and double up the cables on the studs on the back of the switch.
