Where to put the fuses?

[renoman69]

Hello to all. I am new to the forum and somewhat new to solar power. I am putting a solar system on my fifth wheel trailer to extend my battery power. The equipment I am using is as follows. 2 Kyocera 135w panels, Blue Sky 3024 MPPT charge controller with meter and shunt, Xantrex True Charge 2 40amp 3 stage charger, cheapo 600w inverter and 2 6 volt golf cart batteries. I have built the following terminal boxes to conveniently disconnect and remove my equiment when I need to. My question is where do I need to put fuses. I have a 30amp fuse between the panels and charge controller and a 30amp fuse between the charge controller and the batteries. Of course there is also one between the batteries and the house load but do I need any more?


Terminal box on roof.


Terminal box in storage cabinet.

The 2 wires on the left are coming from the charge controller. The black on the right to the shunt then neg. battery post. The red on the right to the pos. on the battery post. the heavy red and black on the bottom from the Xantrex charger and the smaller ones on th bottom to the inverter.

[Mike90250]

Ideally, you want a big fuse right at the battery terminal. This fuse must:
1) protect the wire gauge you have.
2) allow the inverter to draw full power.

Your 600W inverter, can pull close to 800W at full load, maybe more for surges, depending on what you are powering. At 12V, thats about 65Amps. It does not look like your wire size is large enough to handle full power, 12ga is good for 20A. 10 ga is good for 30 A, for 60A, #4ga is just large enough if you have short runs.

And at 12V, 10% voltage drop in a wire, is 1.2V, which is close to the inverter shut-down voltage of 10.5V. voltage drop varys depending on the load.

wire gauge table (scroll part way down the page)

http://www.powerstream.com/Wire_Size.htm

[renoman69]

Thanks Mike. These pictures are just a mock up of what I have yet to install. My plan was to run #8 wire from the panels to the CC which is a 13 ft. run. All other wires are #6 and very short runs (less than 1 ft.) and the 2 wires to the battery will be heavy auto type battery cables. So I have two more questions. Should I use a circuit breaker type fuse at the battery or a "blowable" type fuse and should I run my panels in series or parrallel?

[Mike90250]

If the cold Open Circuit Voltage of the 2 panels in series, is within the acceptable input range of the charge controller, I would wire the panels in series, and let the controller's MPPT magic down convert it to your battery voltage. No fuse needed in the solar PV loop, generally, till you get to 3 parallel panels/strings.

At the battery, install the fuse/breaker at the + terminal, and then attach the charge & loads to the other side of the fuse .

[renoman69]

Mike, The open circuit voltage of each panel is 22.1 and the "PV Input Voltage" of the CC is 57VDC so I guess I am OK. I read somewhere that wiring your panels in series can be a problem if one of them is in the shade and the other is not. Any truth to this? What size of fuse should I use at the battery?

[Mike90250]

Oh yes, series panels, you can not have any shade, it will throttle the whole array back. Some panels have "bypass diodes" whose function is to bypass shaded sections of panels, but you loose about 8 volts each time they kick in, and your array wattage drops.

Fuse, you need at least one large fuse at the battery, to protect the smallest wire you have connected to it. There are many fuse/wire gauge tables on the web. Use the spec for Power Transmission, and size your inverter wire for <1% drop, and your array wire for <3% drop.

[morse]

Hello,

I have a question about my solar installation.
I am a bit confused about current directions.
It is an Off-grid system with 12V solar panels around 140W connected to a charge controller -- battery 80Ah ---inverter 300W
I am planning to install a 20A fuse between the '+ battery' and the '+ charge controller'
My charge controller can handle 20A (I will never use 20A, max 14A) so I think it is OK to put a 20A fuse close to the battery?
Do I need also a fuse between the '+ battery' and the '+ inverter?
Anyway my inverter can handle 300W (350 peak) so that is around 30 amps max at a time. So I will need a fuse between battery and inverter around 35 A? Or do inverters have an internal fuse which will protect them?

The current that is going from the battery to the inverter and to the load, will it not affect the fuse of 20A between the battery and the charge controller?
Or will the current from the '+ battery' only go to the '+ inverter' and not go to the '+ charge controller'? Or does in some way the charge controller prevents current to flow from battery to charge controller?
The reason is that I will also install an analogue amp meter between charge controller and battery to read the amps that are coming in from the solar panels.
If current is going from battery to charge controller that will damage my amp meter, right? (reverse polarity)

Thanks

[Mike90250]

Hello,

I have a question about my solar installation.
I am a bit confused about current directions.
It is an Off-grid system with 12V solar panels around 140W connected to a charge controller -- battery 80Ah ---inverter 300W
I am planning to install a 20A fuse between the '+ battery' and the '+ charge controller'
My charge controller can handle 20A (I will never use 20A, max 14A) so I think it is OK to put a 20A fuse close to the battery?
Do I need also a fuse between the '+ battery' and the '+ inverter?
Anyway my inverter can handle 300W (350 peak) so that is around 30 amps max at a time. So I will need a fuse between battery and inverter around 35 A? Or do inverters have an internal fuse which will protect them?

The current that is going from the battery to the inverter and to the load, will it not affect the fuse of 20A between the battery and the charge controller?
Or will the current from the '+ battery' only go to the '+ inverter' and not go to the '+ charge controller'? Or does in some way the charge controller prevents current to flow from battery to charge controller?
The reason is that I will also install an analogue amp meter between charge controller and battery to read the amps that are coming in from the solar panels.
If current is going from battery to charge controller that will damage my amp meter, right? (reverse polarity)

Thanks

Read the manual with your inverter, it will tell you what size wire, and what size fuse to use.
mine calls for 4 ga wire and 60a fuse. The fuse has to be sized to protect both the wire and the inverter.

[Sunking]

Pictures are worth a thousand words.



Here is a dual fuse battery block.

[Hawaiiankanak]

Ideally, you want a big fuse right at the battery terminal. This fuse must:
1) protect the wire gauge you have.
2) allow the inverter to draw full power.

Your 600W inverter, can pull close to 800W at full load, maybe more for surges, depending on what you are powering. At 12V, thats about 65Amps. It does not look like your wire size is large enough to handle full power, 12ga is good for 20A. 10 ga is good for 30 A, for 60A, #4ga is just large enough if you have short runs.

And at 12V, 10% voltage drop in a wire, is 1.2V, which is close to the inverter shut-down voltage of 10.5V. voltage drop varys depending on the load.

wire gauge table (scroll part way down the page)
http://www.powerstream.com/Wire_Size.htm

Hey Mike, Thank you for this info. Sorry to ninja a question but when you say: "you want a big fuse right at the battery terminal." Is the fuse on the line side (charge controller - battery) or the load side (battery - inverter) ?
Also, would the fuse be sized by the total amperage of the batteries?
thank you in advance!

[Mike90250]

the fuse I like bolts right to the battery

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

You put your 2 different fuse sizes in there and away you go !

DualFuse.jpg

[Hawaiiankanak]

the fuse I like bolts right to the battery

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

You put your 2 different fuse sizes in there and away you go !

DualFuse.jpg

Oh ok. So we can have the charge controller-battery and battery-inverter fuse on the same terminal?

[Mike90250]

The charge controller gets the 30A fuse and the inverter gets the 120A fuse, look closely at the pic, there are 2 separate fuses in the photo. The + buss is the bottom bar, and above each fuse is the connection terminal for the fuse. Pic shows a 200A & a 90A fuses installed.