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Old 10-10-2010, 14:16   #1
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Solar Panel Circuit Breaker Wiring

I've got some new panels I'm installing, each is around ~7.6 amps (Kyocera 135's). It says the short circuit current is 8.37 amps and the "series fuse rating" is 15 amps.

Now these aren't like batteries in that they can only produce a maximum (I'm guessing) of 8.37 amps in full sunshine with no wiring other than enough to short circuit.

So I guess my questions are:

a) What's the "series fuse amp" rating of 15 amps for?

b) I want to get a breaker like this one, for each panel (they're running in parallel to a bus before going into a charge controller):

10 Amp Din Rail Mount Breaker - Circuit Breakers @ AltE

Is a 10 amp circuit breaker going to cause excess resistance on something that regularly can be hovering in the 7.5 amp range, and if so based on the numbers here what size breaker should I use?

There's a second bus after the charge controller (combining the outputs of all the charge controllers) that also runs through a 50a breaker on its way to the battery terminals.

I've done some pretty cheap solar installs before where I've just run the wires directly from the panel to the battery posts, but I'm trying to do this the right way.

Where I'm at so far:

Rebel Heart - Sailing, cruising, liveaboard blog and website - Eric's Blog - finally mounted the solar*panels
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Old 10-10-2010, 14:26   #2
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I just a 20 amp auto fuse holder & fuse. Just goes in line.
$4





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PS I wonder what grief I will cop for this? I DON'T use Paper charts either!
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Old 10-10-2010, 14:35   #3
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Don't feal bad mark. I died last week because I use something like this. Yours should work just fine. Wow you did something right. Now about that anchor...
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Old 10-10-2010, 14:39   #4
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I'm fine with something like that too, but I'm just trying to get the numbers right. If the panel wiring will be destroyed at 12 amps, I don't want to put a 15 amp circuit breaker in, you know?

I can't even find anything online about damage coming from a short circuiting solar panel. I guess it's only going to be able to generate a fixed amount (in this case 8 and some change amps), so as long as everything internal to the panel can handle 8 amps, there's no risk of "damaging" the panel with a short circuit.

?
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Old 10-10-2010, 14:50   #5
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You might check what the manufacturer says. but if max rated out put is 8 amps the 10 amp breaker would be fine. I like marks solution if the wire leads are in line with the wire sizes for the run. If the 10 amp blows you up to a 12 amp. I dont think that will happen if you wire everything with good awg.
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Old 10-10-2010, 15:22   #6
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Reb,

Why not wire them in series to a controller that can handle the 24v, and then fuse them on one wire right before the controller, and then 8 inches from the batteries? Simpler, more efficient.

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Old 10-10-2010, 15:28   #7
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Quote:
Originally Posted by rebel heart View Post
I'm fine with something like that too, but I'm just trying to get the numbers right. If the panel wiring will be destroyed at 12 amps, I don't want to put a 15 amp circuit breaker in, you know?

I can't even find anything online about damage coming from a short circuiting solar panel. I guess it's only going to be able to generate a fixed amount (in this case 8 and some change amps), so as long as everything internal to the panel can handle 8 amps, there's no risk of "damaging" the panel with a short circuit.

?
I have 3 solar panels, 2 32 watt flexible (one on each ama) and a 120 watt on the arch. They all feed a BlueSky MPPT controller which then goes through a 20 amp marine circuit breaker to feed the batteries.

The other day I noticed no charging at all. The starboard flexible panel had been damaged and had water intrusion.

After disconnecting it, everything worked normally. The panel measured zero volts output and depending on where I pressed on it, measured between a few hundred and zero ohms. Water and a little rust could be seen under the clear plastic cover.

Unisolar no longer makes them, but for direct replacement reasons I found one reasonably priced on Ebay.
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Old 10-10-2010, 15:31   #8
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Use the auto-style fuse like Mark says. "Series fuse rating" means the 15 amp fuse is in series, aka in-line. I installed my two Kyocera 135's a year ago, here is a pic of how I did it:

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I have my wind gen using the same charge controller so there are some extra things here. The two red boxes are auto-style fuse holders, the top left is for the wind gen and the bottom right for the solar panels. For the bottom bar on the bus bar, the port panel comes in on the left and the stbd panel comes in on the center. They both leave on the right, go through a 30 amp fuse, and enter the top bus bar on the top right.

The wind gen comes in from its fuse on the left of the top bus bar. Both solar and wind leave the top bus bar from the center and go to the charge controller. I also took the cover off the negative stud so you would have a complete picture - the three skinny wires are the two panels and the wind gen, and the fat wire goes to ... well, it gets complicated after this because I set things up so that I can separate the battery banks.

BTW, the wiring is hugely over-sized to keep resistance to a min. The skinny wires are 10 AWG.

So for your set-up, if you want to use two 15 amp fuses, put them in-line on each panel, then you can either cram both wires into your charge controller, or use a step-down butt connector or a post and just send one wire to the charge controller.

Another pic because it is Sunday.

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Old 10-10-2010, 15:46   #9
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Rebel, I think I see what you're asking... Not how to do it but why is there a series fuse rating of 15 amps and what happens if you put two fuses instead of one.....correct?

Ok serries fuse is there to protect three or more panels. With two you are fine.

heres how that wokrs

1 shorted panel.... = no amps
2 panels 1 shorts out the other sends over 8.37 amps ( the specs on your solar panel ISC ) the other panel sends the short max of 8.37 amps.. the same as the panel was designed to handle so no worries yet.
If you install a third panel now the short gets 2 x 8.37 = 16.74 amps. This exceeds the rating on the panel and needs the 15 amp breaker for protection... so with only 2 panels you don't need a series fuse.
Heres how that works....

http://www.nmsu.edu/~tdi/pdf-resources/CC125.pdf

Now for the fuses... you ned one between the controller and the batteries.... you only need 1 for every string of solar panels inline....at the end of the positive wires between the last panel and the controller. If you put two little fuses you will be able to trouble shoot the system if there is a problem, but you will get more drop than just putting one bigger breaker for both panels.

Most MPPT controllers have a fail no flow sensor and system that acts as additional protection.... for future reference.

Hope that helps mate!
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Old 10-10-2010, 15:57   #10
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I would go with a fuse over a circuit breaker.

In a general (non marine) sense, a fuse is far more robust to short spikes and surges (in the boating application, not necessarily from the panels but elsewhere on the boat).

Again in the general sense and this also applies in marine applications the advantage of a circuit breaker is that it requires no skill or knowledge to fault find and reset. The downside of this is that it will be prone to trip on a spike that a fuse would be unaffected by and worse still a circuit breaker is far slower to trip than a fuse is to blow in a worse case scenario.

Since you are fitting it on your boat (and hence know what is where and why) put a fast blow fuse in.

To answer your questions as posted (and opinions here may vary)

a) Sufficient margin to not blow from the panel at
i) Maximum amperage from the panels and or "single fault" in the controller or wiring giving a short to ground (not a problem for the panel but the charge controller or other current source (e.g. battery) connected in the circuit
ii) Maximum amperage and the fuse being derated for temperature

b) If you want to go with the circuit breaker the unit that you posted would work in theory. But you have touched on a point that is fairly key, that amperage output given for the solar panel manufacturer is when the panel is operating on the "knee" in the voltage vs amperage graph of the panel, whatever is connected to the panel has to (ideally) present a resistance which is such that the panel is on that sweet spot. Hence the market for MPPT controllers (worth a wiki search/quick read).
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Old 10-10-2010, 17:19   #11
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I hate inline fuses I remove all of them from my boats equipment I use suitably sized breakers instead. The last thing I need is to trying to remember where all those hidden inline fuses are.
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Old 10-10-2010, 19:18   #12
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I have to agree with goboating now. Fuses are old tech. At night in a dark boat, pitching and rocking at sea, it sucks to look for a fuse and replace.... its easy to throw a breaker back on.......sorry but all key systems on my boat have a breaker and no fuse.....The only fuseable advantage generally over a breaker is its cheap....
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Old 10-10-2010, 19:39   #13
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My Plan

Is to use a Bluesea http://bluesea.com/files/images/products/5028.jpg

and bring my solar and wind regulating devices through the fuse block to the battery, as well as feed the battery monitor.
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Old 10-10-2010, 19:47   #14
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To clear up a point: Fuse does not have to mean an inline fuse holder tucked away where you can’t get to it. This is bad engineering! Fuse panels put the fuse out where you can get to it and that is the professional way to install. For what it is worth, circuit breakers tend to drop more voltage across the protective device than a comparably sized fuse.

The over circuit protection protects both the wire and the device. In most low voltage dc the wire size is usually jacked up to prevent excessive voltage drop so the current handling capacity of the wire is quite high compared to the other weak links in the system. If you are using #10 wire in your runs you have a wire that will take 30 amps intermittent and 24 amps continuously, much higher than the panels current limits.

In the case of the Kyocera panel the maximum short circuit current is 8.37 amps and they want it protected at no more than 15 amps of reverse current in the panel. So how many panels do you have in parallel? If you have but two panels the maximum reverse current that could flow from an operating panel into a non operating panel is 8.37 amps, so there is no way you can hurt anything.

I still believe in fuses between the panel and controller to help protect against transients even if the potential reverse current is not an issue. Also a Schotke diode in each line to limit the current drain of a partially shaded panel. I don’t know if the panel is diode protected or not as it comes from the factory.

If you can wire the two panels in series and utilize the new type controllers, you will not only realize a higher power out but it gets easier to troubleshoot because the output is all or nothing, not so in the parallel circuit where a degraded condition is a more common occurrence.

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Old 10-10-2010, 20:04   #15
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Rebel Heart,

I feel for you.

This stuff is complicated.
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