wires burned up with 4 100 watt panels

[markcouz]

My guess is that the smoke and drama came from the fuse holder - often cheap and nasty junk that make a poor connection to the fuse resulting in lots of heat, then it is a race between fuse blowing (heat, not amps) or fuse holder melting.

[zstine]

Shadowdancer: You have not told us enough information to advise you. What is the panel voltage? Are you using an MPPT controller and what is it rated for? 400W / 13V = 31 Amps. Many panels have thermal protection at the panel. I didn't have a fuse between my panel and the controller, just a disconnect switch. Put a Circuit Breaker between the controller and battery.

Your wire run length is the supply plus return, so your 10ft is a 20ft run. for 12VDC you should be running 6 AWG per chart link below @ 12VDC. If you have an MPPT controller, consider a 2 parallel, 2 series setup. or even all series if you want to be safe with 10AWG. That will increase the voltage, reduce amps and reduce the size needed, but you will still need 6 AWG for the 10ft (20 total) run from the controller to the batteries. That is why I put my controller as close to the battery as possible and ran mine in series. NOTE the chart linked below is a 3% drop. Skimping on wire size increases drop and reduces system efficiency. not smart to pay a bunch for panels and controller and cheap out on wire.
http://www.coastalsolarsales.com/voltagedropchart.jpg

[Dsanduril]

Originally Posted by Cadence

Someone correct me if I'm wrong. My understanding is the panels produce a higher voltage and the controller knocks it down to charging levels. The 10ga. wire would seem more than adequate from the panels of 100W each.

Depends entirely on the panels, about which we only know they are 100W. Based on experience I would guess that 100W panels are delivering 6-7A at mid-teens voltages, but I could be way off. For that, 10AWG for each panel is more than adequate. But where those four 10AWG come together into one (as described by the OP) you now have a 10AWG at ~25A. That is acceptable from an ampacity perspective and may or may not be from a voltage loss perspective.

[markcouz]

Originally Posted by Dsanduril

Depends entirely on the panels, about which we only know they are 100W. Based on experience I would guess that 100W panels are delivering 6-7A at mid-teens voltages, but I could be way off. For that, 10AWG for each panel is more than adequate. But where those four 10AWG come together into one (as described by the OP) you now have a 10AWG at ~25A. That is acceptable from an ampacity perspective and may or may not be from a voltage loss perspective.

All correct, however the smoke is unlikely to be the result of cable size - more likely poor fuse holder quality or loose connection at fuse holder.

[zstine]

Originally Posted by Cadence

Someone correct me if I'm wrong. My understanding is the panels produce a higher voltage and the controller knocks it down to charging levels. The 10ga. wire would seem more than adequate from the panels of 100W each.

The panels are 100W but the Voltage was not specified.. they could be 14V each (100W/14V=7.1Amp) or they could be 20V(?)... running the 4 in parallel sums the amps, but voltage stays the same... so 4 times 7.1A = 29 Amps. Running the same 4 in series would sum the voltage (4 x 14V = 56V) and the current would stay 7.1 Amp. The low amp, high voltage will go through a smaller wire than the high amp low volt. This is why I put my controller close to the battery and put my panels in series.

[sailingharry]

Originally Posted by Dsanduril

I'd question why you have a fuse in that position at all? Solar panels are current-limited sources, there is no way for a solar panel to deliver in excess of its Isc, so there is no need for an overcurrent protection device between the panel(s) and the controller.

A current limited source solves ONE fuse, not both. You have, in theory, TWO sources of fault current -- the panels and the battery. The panels can't exceed their Isc, so as long as you size the wire for the Isc, you can't burn the wire. But you can still have a fault fed by the battery, so you still need a fuse (without the current limited exception, you need TWO fuses --one at each end, for instance an ACR that connects two batteries). In this application, the fuse would be where the controller connects to the battery (or ideally, the bus).

[stevo_002]

Originally Posted by GILow

Something is wrong here. Fuses should not smoke. Generally they fail with a faint click or pop sound.

Sorry to say, I'm going with the view that it's time to bring in a pro. When there is visible smoke there is a very, very serious threat to the boat.

It is possible also that the fuse holder if inline is smaller than 10ga typically or rather often 12ga. I have seen an appropriate fuse melt the plastic without blowing. On a solar feed line at higher voltage. Seems the solar input varies enough not to blow the fuse but in high output (current) do more than momentary heating of the fuse assembly.

[Compass790]

Originally Posted by markcouz

All correct, however the smoke is unlikely to be the result of cable size - more likely poor fuse holder quality or loose connection at fuse holder.

+ 1 for this,
We have had problems with "quality" fuse holders from guess where.

[Apollo366]

First Q; Why are you running only 100W panels? On a 42 ft sailboat you should be able to mount the very latest 300-400W 28V panels.

When I made my solar setup the installed insisted on one MPPT controller for each 300W 2-28V panel for safety & redundancy in the overall installation.

Next; What is your house battery capacity? For a 42 ft boat it should be at lest 400 AHh, unless you're only using the solar to keep a charge on the battery when you're not on board to run the gen set.

And yes, your fuse holder needs to be capable of handling 30+ amps, what is it rated for?

Just some thoughts on what's going on here,

Wayne

[John De Bree]

Correct me if I'm wrong but the solar panels put out over 110v and I'm thinking that you are using a 12v fuse this maybe your problem

[philcun50]

Originally Posted by markcouz

My guess is that the smoke and drama came from the fuse holder - often cheap and nasty junk that make a poor connection to the fuse resulting in lots of heat, then it is a race between fuse blowing (heat, not amps) or fuse holder melting.

This is the elephant in the room. You are all diving in at the deep end.
Markcouz is so correct about “cheap nasty junk” and as another said why have fuses at the solar panel end? I’m a retired electrician, so many years experience. Fuses are joints and joints equal potential bad connections and thus heat. Circuit protection is needed but in the right place. It is better to use circuit breakers. Solar panels are a current source but can’t exceed the Isc and probably never even get anywhere near it. At the battery end you must have a solar controller which would block that end as a current source so now only a small argument for fuses on each panel. Mind you having all the panels in parallel probably not a very good grouping either.
My panels, 100watt flexible have an Isc (short circuit current) rating 5.7amp and a nominal voltage rating of 18volts thus 100watt but they never ever do that. So all the talk about exceeding the current rating of your 10g (6mm2) cable is ridiculous. 10g is rated 30amp cable dependent on how and where it is installed, heat dispation. The main factor to consider is voltage drop. Your panels should be connected in series/parallel so you up the volts and lower the current and therefore less voltage drop.
Bigger cable presents problems with getting plugs to fit.

[mjscottinnc]

Originally Posted by John De Bree

Correct me if I'm wrong but the solar panels put out over 110v and I'm thinking that you are using a 12v fuse this maybe your problem

110v? Only if they are attached to microinverters and then it’s AC. Native solar panels put out 6 to 36 volts DC depending on the number of cells and cells wiring configuration. You could get to a higher DC voltage by wiring multiple panels in series.

[KP44]

I used 10 ga marine wire for a 12 foot run with 540 watts of solar. Since the panels are at 18 to 21 volts that is about 30 amps at optimal output. (At the nominal 21v it is about 25 amps.) Everything works well. From the controller, where voltage drops to under 14v, I have a 6 ga wire to the battery buses. Current can get as high as 45 amps if the battery bank is low.

I would check the crimps and terminals at your fuse. If those are sound, check all terminals. A bad crimp or any loose connection can cause arcing, heat, and everything you don't want.

[facciatosta]

There is no way current produced by the solar panels can burn wires. The panels have internal resistance that limits the current. The spec for the panels should tell maximum short circuit current. more likely the panel(s) have short and this short shorts the battery through the controller.
That's why I installed the fuse at the battery because the battery is the source of available high energy not the panels.
I have almost the same setup and same wire sizes and so far it worked OK.

[Sailing Ohm]

Originally Posted by Dsanduril

I'd question why you have a fuse in that position at all? Solar panels are current-limited sources, there is no way for a solar panel to deliver in excess of its Isc, so there is no need for an overcurrent protection device between the panel(s) and the controller.

With four panels in parallel there is some argument to be made for having a fuse in each panel's line so that if one panel faults (or shades a great deal, or...) and becomes a current sink the other panels can't feed into it. A 10A fuse in the lead for each panel would prevent the other three panels from dumping their 20+A available current into a faulted panel. Diodes can also be used in this position, with their attendant voltage drawbacks.

This is bad advice and could burn your boat down and get you killed. You should always fuse or better yet put a fast acting breaker designed for solar between your solar panels and their charge controller for no other reason than to protect your charge controller.
This is standard advice from both the solar panel company and the charge controller company.

In theory a panel shouldn’t produce more than its rating but my rated 660 watts of solar routinely puts out 740 watts on those perfect days. Lab ratings are at a certain set temperature and lower ambient temperatures can cause higher output