What size fuse ?.

[shadow]

I ordered a 200 watt solar kit from ebay, its nothing fancy but its all I need.
What I need to know is what size ANL Fuse do I need to use between the battery
and charge controller ?.

[Trebor English]

The fuse size depends on the size of the wire.  200 watts can provide 10 amps.  If conditions are right it could be as high as 15.  A fuse less than 15 might blow if it is a sunny day.  The wire really needs to be at least AWG 12 and and the fuse at least 20 amps.  To get good performance if the wire is real short you want AWG 10 or 8.  At 10 feet you might wanr AWG 6.  A 30 amp fuse has less resistance than a 20 amp fuse.  Use a 30 amp fuse with AWG 10 or bigger.

[shadow]

The charge controller that comes with the solar kit is a 30 amp pwm, so I`m
guessing that a 40 amp fuse would be needed ?.

[MN C Van]

Naw, I'd listen to Trebor,

200/13=15.4 Amps

It won't reach that theoretical number, it was explained, so 15 Amps

My 300w would've gotten by on a 10 Amp most days

[shadow]

15 amps it is then.

[sternwake]

The charge controller will usually dictate what size fuse to use.

Keep in mind that fuses are designed to protect the wire, not the device attached to it.

And fuses add resistance to the circuit.

If a fuse blows, it might be able to destroy the charge controller.

So having a fuse just big enough to carry expected current, but which is still well below that of the ampacity of wire, is not extra safe.

not if its blowing takes out the charge controller.

As most olar controller manuals, will say not to disconnect the controller from battery while panels are still making juice.

Which a blown fuse is going to do.

The smoke might escape instantly or after several of these load dumps.

so I'd recommend following the recommendation of the solar charge controller as to fuse size, and if one is not listed then the max ampacity of the wire the fuse is on, or the thinnest wire in the full circuit, in case one uses 4 awg on the + and 10AWG on the (-)

[Trebor English]

15 amps it is then.

No.  

The panel could produce 15 amps.  Have you ever seen the cloud edge effect?  You have a slightly cloudy day.  The sun lights up the back side of the clouds.  The cloud has cooled the panel.  The whole sky is shining on the panel.  A hole opens up.  The sun shines directly on the panel plus all the illumination from the clouds.  Momentarily I get an extra amp with my 100 watt panel.  So your 15 amps goes to 17 and you have a blown fuse.  You want a fuse that the solar panel can't possibly blow.  

Fuses are not precision lab type current measuring devices.  A 15 amp fuse cannot be depended on to hold forever at 14.9 amps and blow instantly at 15.1 amps.  Automotive fuses are favored by Ford and by me because they are cheap.  Figure plus or minus ten percent.  At double the rating it could take a minute to blow.  It could blow in a second at 13.5, 15 - 1.5.

Use a 20 amp fuse.  That requires AWG 12 wire.  You might want a bigger wire.  A 15 amp fuse could work with AWG 14 wire but that's real small.  You don't want that.  The resistance will lessen your charging.  AND, the fuse might blow on a sunny day.  Then you get no charging until you notice that it's broken.  AND, if your controller is sensitive to it, disconnecting the battery at max charge current might smoke the controller.

http://wiresizecalculator.net/calculator...gedrop.htm  

Using the voltage drop calculator, 10 feet of AWG 12 wire, the drop is .4 volts.  14.6 volts at the battery, 15 volts at the panel, it is 2.6% of the voltage.  With wire that size you may get less than 10 amps.  Bigger AWG 10 wire, 10 feet, 10 amps, the voltage drop is .25 volts.  If your wire is 20 feet long you might want bigger.