Hello,
I have a Victron Smart Solar charge controller MPPT 75/15. The operating manual explicitly state that a 20-25A fuse should be used for the cable from the battery to the charge controller.
However, I could not find any information on how the load output must be fused. The charge controller has a maximum output of 15A. So should I use a 15A fuse or would it be better to have some reserve, e.g. 20A, so that the fuse is not operated in the limit range? I use 6mm² cables so this isn’t the limiting factor.
Additional: A 20A car fuse is already installed in the charge controller. What does this fuse protect (load output, battery, PV)?
Fuses are there to protect the cables not the equipment.
So your choice of fuse for the load output is dependent on the cable size used. The feed out of my load output is 0.75mm and is fused at 3 amps as it’s only used to charge a mobile router.
My main out is 6mm and is fused at the battery end at 20amps well within the capability of the cable.
Ok, I understand.
Can you explain what will happen when I connect multiple consumers to the load output, turn them all on accidentally at the same time and the load exceeds the max. of 15A that the solar charger can provide? Will this damage the solar charger and can I avoid this when I use a 15A fuse?
To be honest no I can’t.
I will say that most users don’t use the load output unless, as in my case, it’s for a particular item that needs specific timings for it’s use.
Most loads are connected directly to the battery then the problem is avoided.
If you try and draw too much current you could damage the FETs that switch the load on and off. Fusing the load output will not help because a 15A fuse can take several seconds to blow with a 20A load by which time the FETs could fail.
If you van draw more than the 15A then you should be connecting to the battery direct. If you want some control of the loads then use a Battery Protect operated from the load output. See Section 3.8 in the manual.
I do not plan to draw more than 15A but it could happen if I add a device sometime in the future and do not think about the max. ratings of the solar charger. So, I want to be prepared for this.
So with your explanation it would be better to use a 10A fuse to have a buffer to the maximum load output ratings. I will check the fuse spec to get more information when it blows.