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!
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
2
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?
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
4
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.
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
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What do you use for moulded case circuit breakers? They are super expensive for good ones here in the States. Thanks!
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.
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
11
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
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
15
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.
I’m currently installing a 10kVA Multiplus 2 and I will run a parallel of 70 mm2 cables to the DC bus bar.
I would like to install a MCCB switch breaker to provide protection and disconnect the DC to the inverter (for maintenance as example) only in the plus parallel.
My question is: do you know if I can use a double pole MCCB like ZBeny to connect the plus parallel cables? The idea is to use each pole of the MCCB for the plus cables only.
Andy of Andy’s Garage and other solar people say Dahools are fine and fairly cheap on Amazon US. I haven’t used them, so I don’t know. I had some Noarks for batteries especially made for me in the US. But those were fairly expensive. They have survived many switch offs under load. They seem to work well.
Meanwhile I have send this question to several MCCB manufactures and Dihool send me this reply:
“Hello, this is not recommended. Parallelizing two positive poles and having current pass through both poles: the current distribution is not average, and the voltages may also be unequal, resulting in a voltage difference between the two sides, which poses potential safety hazards. It is recommended that after parallelization, the current pass through the positive pole together. If the 160A rating is insufficient, a molded case circuit breaker of a larger specification needs to be selected.”
I’m using a 48V 10kVA Multiplus 2. I know that always will be some imbalance on the parallel of the cables and therefor the voltage will also be unequal but the voltage rate of this equipment is 1000V. (send the link below)
Despite the answer from Dihool I’m not seeing why this is not a possible solution for the parallel. Their concern about the voltage unbalance is legitime with such a huge margin (48V to 1000V)?
What technically could go wrong that I’m not seeing?
I’m not qualified to give a definitive answer, if your running parallel cables then there is potential for more voltage drop anyway on one or the other, adding the circuit breaker would increase the chances of a difference, but when the cables are joined at each end is it really going to make much difference, I don’t know.
I built my battery rack to take four batteries, I currently have two, each battery is wired through a fuse and an MCCB, then to a common busbar, where I run 120mm cable to another MCCB via a fuse to the Lynx Shunt, when it comes out the other end of the Lynx Power In there is 2 x 70mm2 cables to the Quattro, each run off a seperate fuse in the Lynx Power In, no switches between the Power In and the Quattro as I removed it due to getting hot.
