question about fuse size on aolar panel string

[ray]

im at a loss my current panel string fuses are 12V 10 anp AGU fuses. I dont think that is the right rating for my panel string. The string is make up of 4 100 watt solar panels rated at 5 amps at 83 volts each string.

What is the right fuse to use on each string?

 

[gnubie]

How many 4x100 strings do you have, and just checking, the panels are arranged in series? If you only have 2, there's no point in a fuse as there can't be sufficient current to blow the fuse with 2 identical strings of panels. Check your local regulations, but that is likely what they'll say too. If you have more than 2 strings, a fuse on each string is important.

Let's assume your string's Isc (short circuit current) is 5 amps. You'd want at least a 6 amp fuse. The fuse should be rated to not blow on the short circuit current of the string being protected, but should blow on the current from 2 strings. If you could get it, 7 amps would be a good fit IMO but MC4 fuses only come in certain values.

 

[ray]

mc4 fuses will fit in the AGU fuse block. MC4 fuses and AGU fuses are the same length and diameter as each other. But a AGU fuse is rated at 12 Volts and the MC4 fuses has a 1000 VDC rating.

Should i use the MC4 fuses? the 10 amp is what i understand,

 

[gnubie]

Regardless of the fuse shape you use, be it a ceramic cartridge fuse, or an inline MC4 fuse, it definitely needs to be rated for the voltage that can appear across it. If you have 4 panels in series (I'll take a stab at them being 12v panels) the open circuit voltage of the string would be around 76v. MC4 style fuses are rated at 1000V (I've not looked for different voltage ones, so they might exist) as a typical solar panel is rated (supposedly) for a string up to 1000VDC.

A fused rated for 12v use would not be able to break the current safely, if at all.

The question is, are your panels arranged as parallel sets or series sets. When people talk about a string of panels, they usually mean a number of panels connected in series but there can be confusion on that point with people new to the game.

 

[ray]

they are in series and are about 80 V at 5 amps

 

[gnubie]

OK, then those 12v fuses are no good. You need fuses rated to handle the Voc of the string, and then some. MC4 fuses are usually a convenient way to do it since you can plug them inline with the string being protected. The only problem there would be the current rating of your string vs what is available in MC4 fuses. Can you post the specs for the panels (the label on the back or a link to the manufacturer's web page for the panel).

 

[ray]

 

[gnubie]

OK, the current rating of those panels puts it in a difficult area to get a MC4 fuse that will blow under less than full light conditions. You already have a fuse block I think, so you could put higher voltage rated fuses in. Do you have a link to your current fuse holder?

A fuse something like this is what I'm thinking of but it doesn't indicate if its good for 250VDC. Zephyr does make HV DC fuses, so a quick enquiry to them should clear that up.

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