Fuse between solar panels and MPPT controller?

Baffling that you're not getting the point. The fuse would only blow once, prompting the installation to be modified. Without it the boat might well burn to the waterline, prompting a failed insurance claim.
I wouldn't refuse to wear a seatbelt or decline airbags because I intend to drive safely, so why would I choose to not protect a circuit when it's such an easy cheap option?
 
lustyd said:
Baffling that you're not getting the point. The fuse would only blow once, prompting the installation to be modified. Without it the boat might well burn to the waterline, prompting a failed insurance claim.
I wouldn't refuse to wear a seatbelt or decline airbags because I intend to drive safely, so why would I choose to not protect a circuit when it's such an easy cheap option?
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You really don't get it, do you ? You clearly have limited understanding of electricity and an even poorer understanding of solar installations. I have repeatedly posted that the OP does not need a fuse and various other bits of useful information, but rather than read what's been said and actually learn something, you prefer to continually argue, using your flawed understanding of how it all works.
 
whilst we are on the subject , i was looking at increasing my solar panels as mentioned in an earlier post , my question is, i plan to put an additional 40/50 watt solar panel on the fordeck when in hbr/ on anchorage and therefor have a 6/7 metre run to the controller . what size cable would be adequate and as its that long a run would a fuse be sensible and what size ?
 
PaulRainbow said:
You really don't get it, do you ? You clearly have limited understanding of electricity and an even poorer understanding of solar installations. I have repeatedly posted that the OP does not need a fuse and various other bits of useful information, but rather than read what's been said and actually learn something, you prefer to continually argue, using your flawed understanding of how it all works.
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Actually Paul, I did go and read a bunch of things and found that your views are far from shared by the electrical community. The panels can and do supply current in excess of what wiring can handle and this can and will cause dangerous situations. Your reluctance to consider positions other than your own detracts from the view I had of you as an expert. While you are correct that voltage drop will reduce the power available from the MPPT, you are not correct that undersized cables are safe. If too much current flows, the cables will indeed get hot, just as any other electrical cable will.
 
dunkelly said:
whilst we are on the subject , i was looking at increasing my solar panels as mentioned in an earlier post , my question is, i plan to put an additional 40/50 watt solar panel on the fordeck when in hbr/ on anchorage and therefor have a 6/7 metre run to the controller . what size cable would be adequate and as its that long a run would a fuse be sensible and what size ?
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4mm will keep losses below 3 percent (assuming 16v) but 2.5 will do fine almost all the time and at peak it still won’t be at all dangerous.
 
PaulRainbow said:
Because he has two solar panels, each needs a pair of wires. Cables are sized according to two criteria, current rating and voltage drop. On 12v systems voltage drop is a big deal. 1.5mmcable is rated at 21a, so enough current rating for one of the OPs panels, but a 5m run of cable will drop 3.8v at 15a, clearly no good. 6mm cable will drop less than 1v
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Actually MC4 connectors are quite common at the solar end which join cables either in parallel or series, so the question was a reasonable one. You say that 21A rating is enough for one panel which implies it's not sufficient for two, which is interesting that you're considering current rating based on solar capacity while stating it's irrelevant and voltage drop is the only consideration. My statement was actually that 2x6mm would be sufficient for the two panels in any configuration, you suggested 4x6mm which is clearly overrated, which you stated categorically you would not do.
 
lustyd said:
Actually MC4 connectors are quite common at the solar end which join cables either in parallel or series, so the question was a reasonable one. You say that 21A rating is enough for one panel which implies it's not sufficient for two, which is interesting that you're considering current rating based on solar capacity while stating it's irrelevant and voltage drop is the only consideration. My statement was actually that 2x6mm would be sufficient for the two panels in any configuration, you suggested 4x6mm which is clearly overrated, which you stated categorically you would not do.
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As Paul explains the max current rating will usually be way OTT after a few metres so the limiting factor is the voltage loss. A safe cable for carrying the current will be a very lossy cable unless it is big enough.

I am also now interested in your plan for two panels in parallel to use just 2 single core cables? Is the plan to join them near the panels and then down to the controller, so in effect 5 x 6mm cables of different lengths. Could work but will increase the power loss compared to just 4 cables.
 
Now you're just being awkward. The connection of solar panels in parallel is widely understood and doesn't require individual cables back unless you have multiple controllers. If that's the case then you have stand alone panels, not parallel panels.
 
lustyd said:
Actually MC4 connectors are quite common at the solar end which join cables either in parallel or series, so the question was a reasonable one. You say that 21A rating is enough for one panel which implies it's not sufficient for two, which is interesting that you're considering current rating based on solar capacity while stating it's irrelevant and voltage drop is the only consideration. My statement was actually that 2x6mm would be sufficient for the two panels in any configuration, you suggested 4x6mm which is clearly overrated, which you stated categorically you would not do.
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Good heavens! I'll try one last time. I did not say current rating is irrelevant and that voltage drop is the only consideration.

If we only consider current rating, the OP needs something that will carry 9a, which would be 0.5mm cable, rated at 11a. a 5 m run of that will have a voltage drop of over 3v, clearly not acceptable. So we need to install thicker cable to combat the voltage drop.If we used 6mm cable the voltage drop would be about 0.3v, that'll do nicely. So i haven't used overrated cable in case the next owner fits more panels, i've used a cable that's suitable for the installation, taking into account both current requirements and voltage drop. There is no need for a fuse in this installation.

If, as you suggest, the parallel connections are made externally the 6mm cables now have to carry twice the current, so voltage drop increases to just over 0.5v, which is borderline, so the cable should be increased to 10mm. Rather than use bigger cables and risk leaks in connectors, i'd make the parallel connections inside the boat and stick with 6mm cables.

Let's say someone comes along and adds another panel, something you claim will melt the cables and "burn the boat to the waterline". Firstly, where are they going to connect this panel to ? The only join is below decks, let's say they make it there, so the less than 2m run of 6mm cable now has to carry a maximum of 27a, the cable is rated at 53a, so it is not going to be overloaded, even if that was possible. What will happen is the voltage drop in the <2m cable will increase from 0.2v to 0.3, which is still well in specification for both current capacity and voltage drop.

What if they decided to join the panel outside the boat, go the 6mm cables from one of the existing panels ? That cable now has to carry 18a instead of 9, but it's rated at 53a, still not over loading the cable, but the voltage drop increases to a borderline acceptable figure, but no melting cables or burning to the waterline.
 
Paul you're causing yourself problems here. First you say there is literally no way a solar panel could overload a cable and now you say it is possible. Make your mind up before posting because it's an important distinction that you can't argue both ways. If a cable can be fed too much current then a fuse is a small but very wise investment. You're too hung up on planning new installations and what the installation rules are to even acknowledge the potential issue. You're now extending your story to back up your reality just so that you don't need to acknowledge the issue. You've invented a whole load of details to your scenario which back up your stance without considering that those details might be different in a real world scenario.
4x6mm is more overrated and more expensive than 2x10mm. You're literally arguing with your own arguments.
 
Consider this, if the guidance changes you'll be first in line to tell everyone they need a fuse and quote that guidance at them. Not all safety measures are included until enough humans have shown they can out-stupid common sense.
 
lustyd said:
Consider this, if the guidance changes you'll be first in line to tell everyone they need a fuse and quote that guidance at them. Not all safety measures are included until enough humans have shown they can out-stupid common sense.
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You have absolutely no clue what you are talking about and just like to argue for the sake of it. I've wasted enough of my evening trying to explain it to you.
 
No I don't enjoy the argument, it's extremely frustrating that you're unwilling to consider the problem, and more so that you've contradicted yourself so many times. I genuinely consider your advice to be excellent in most threads but in this instance that view has been tarnished.
 
lustyd said:
No I don't enjoy the argument, it's extremely frustrating that you're unwilling to consider the problem, and more so that you've contradicted yourself so many times. I genuinely consider your advice to be excellent in most threads but in this instance that view has been tarnished.
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Consider what problem ?
 
Never mind. You're clearly not interested in any scenario not covered by the guidance. Personally I prefer to consider the outcomes so will sometimes go further than recommendations if I think there is an advantage, especially if the cost difference is negligable.
 
lustyd said:
No I don't enjoy the argument, it's extremely frustrating that you're unwilling to consider the problem, and more so that you've contradicted yourself so many times. I genuinely consider your advice to be excellent in most threads but in this instance that view has been tarnished.
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If only there was a facepalm emoji.

Paul has made it as simple as possible for you and you still are arguing because one sentence explains current capacity and one explains voltage drop so you think that’s a contradiction.
 
lustyd said:
Never mind. You're clearly not interested in any scenario not covered by the guidance. Personally I prefer to consider the outcomes so will sometimes go further than recommendations if I think there is an advantage, especially if the cost difference is negligable.
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It's not guidance, it's physics, there is no need, advantage, or point in fitting a fuse in the PV cables in the OPs installation. Note the previously posted Victron schematic and the lack of a fuse.

Do you fit fuses in the cables going to your anodes ? No, because they serve no purpose.

You adopt the typical armchair expert pose on here, you don't understand how something works, or you dream up some oddball idea of how it works and then everyone else is wrong and i'm a shit electrician because you can't grasp what i'm trying to tell you. Fortunately, the vast majority of PBO readers can tell who's who.
 
Paul, stop digging. You literally said there is no danger to the cable. You then acknowledge that there is a danger if the cable is too small for the current (which is obvious to us "armchair experts"). Just stop.
 
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