fuse size/type

[fiddlerkelly]

AM planning on making change to my panel array and wondering if I can use the same type fuse after change.

I currently have a 12 volt panel array of 3 -12 volt panels with each panel being 50 watts . These panels are connected in parallel for total 12 volts  with 150 watts. I have a 15 amp inline fuse on the positive wire going from panels to CC.

Now if I double the amount of panels for total of 6- 12 volt panels and wired every 2 in series for 24 volts   with 100 watts  and done the same with the other four panels  when they are all combined 3 sets of 24 volts  100 watts each set   I will have 24 volts - 300 watts going to my CC. Question is can I still use that same inline fuse that I had used when it was a 12 volt system as the amps for both systems is 12.5 amps and I will be using the 15 amp fuse in this inline fuse.

[tecnodave]

FiddlerKelly,


Yup,   But you missed the point......to be properly protected you need a fuse/breaker on each set of panels.......the reason for this is if a panel or wiring fails at any point the other panels will short back through the failed panel. You can do two in parallel with no string protection but not with three strings. The current available is enough to burn ( set ablaze ) the failed panels.  Not good!

At the minimum you need a fuse/breaker for each string of panels and a fuse/ circuit breaker to turn off the whole array.

I suggest a MidNight baby box and one MNEPV breaker for each string and one for the array.

String breakers size is computed by multiplying panel current times 1.25 safety factor rounded up to next breaker size. These breakers are available in 1 amp increments in small sizes
Array breaker size is 1.25 times array total current.

On the cheep and better than nothing is automotive fuses types ATO, ATC, SFE,  or AGC.  These are 32 volts maximum and are to be used in low voltage situations only........they will not protect at higher voltage

Fuses/breakers are way cheaper then not having them when S@&! happens and it will....we just don't know when!

td

[fiddlerkelly]

Even though I never stated it I would also be using a in line fuse also on each positive line coming from each panel going down to the combiner box.  Out of curiosity if I set up  48 volt panel system  with the amperage  12.5 amps would I still be able to use that same in line fuse with the 15 amp fuse in it.

[tecnodave]

FiddlerKelly,

At 48 volts the current would be less but you have crossed that 32 volt threshold.......48 volt system on charge is 56 volts or so........60 volt DC protection is required........nothing that you will find at Home Depot will work at these voltages.

I have searched far and wide for DC rated breakers.......the best deals are the MNEPV  line from MidNite @11.00 each from NAWS.  comparable breakers are $45.00 each and hard to find, they are used in industry, but never in residential.......won't even be found in electrical wholesale houses


My opinion.......BigBaby.....$34........4 breakers@$44.00=Real cheap insurance when things go wrong!

Fuses/breakers are only good if properly sized and rated.

td

[fiddlerkelly]

Thanks , the reason I asked is I was thinking on setting up the battery bank as 48 volts so I would have two large batteries but will settle at having 4 batteries at 24 volts instead.

[Robin]

The Bib Baby can be used as a combiner, but there are some drawbacks to using it over a real
PV combiner.
1`. The Big Baby is not listed as a PV combiner
2. You will need a busbar and output connection after connecting all the positive strings. We do sell busbars, but check the price and fit. Those busbars were not intended for use in the Big Baby. They may hang out the side too far?
3. You will need a PV minus busbar (insulated). We have those too and the Big Baby is designed to accept the short busbar.
4. The Big Baby is not rain proof.
The MNPV3 or MNPV6 is a better choice, but it may cost more. Not much more though.
MidNite ships thousands of combiners each month. We are without a doubt the North American standard for residential combiners. Why? Because they serve every function required and cost less than anybody else. One of these days I should get one of these for my own system. My system was installed before I knew what a combiner was!

[zoneblue]

Yeah, i can atest what Robin says. Many of us start out trying to patch a bit of this and that togther, based on what we know and can get. But sooner or later we usually end up cleaning things up with purpose designed midnite kit.