Sizing fuse for MPPT Charge controller

[nharrisonclay]

I am building a 200W 12v solar system with a 40A MPPT charge controller. I am trying to figure out what size fuse to use between my solar panels and my charge controller. I already have a 30A in-line fuse – could this work for my current setup even though my charge controller is 40A?

 

[time2roll]

Don't really need a fuse between panels and controller. It will never open. You can short the panel wires and no harm will come of it.
Although you may want a switch to easily remove solar input power to the controller for service. Removing a fuse could serve this function.

Otherwise you need a DC rated fuse 10% to 20% above the Isc rating of the panels as wired.

 

[mike95490]

200w @ 12V is only going to yield 17A at most, a brief cloud lens event is not likely to push anywhere past 30A, so your fuse is safe. And with a 30A fuse 10 ga wire is the smallest you can go.
( edit - sorry - didn't see the "between panels and controller" . I agree with time2roll, no fuse needed with only 2 panels on the PV side.
However - you then need a switch or circuit breaker there, because MPPT controllers need to boot up from battery power first, and then apply the PV power to them. mix up that start up sequence and you have a good chance of frying the controller [ maybe not with only 200w of panels ] )
Many fuse holders are not rated to make/break the circuit, and they rely on the fuse cartridge , not the user unplugging the fuse, so be aware of that before you buy.

 

[nharrisonclay]

Ah okay, thank you! So what I am hearing is that I don't need a fuse between my panels & charge controller but that it would be good to have a switch there instead so that I don't accidentally damage the controller.

I have one switch and was originally planning to put it in between my battery & my positive bus bar. Would it be adequate to just put this switch in between my panels & charge controller instead? Because that would just turn off my whole system and ensure that charge doesn't run from my panels to the charge controller when it's not connected to battery, right? Or, would you recommend having two switches, one between the panels & charge controller, and one between the bus bar & battery? (I am on a budget so would rather not buy another switch unless it's necessary)

 

[Bud Martin]

What is the DC Voltage and current rating of the switch?

 

[nharrisonclay]

12v and 275A

 

[sonny93]

What switch did u get