Solar Panel Fusing

[The_Lad]

Ok so I have a CTEK 250 from travelvolts and I’m now looking to hook a solar panel into it,

when installing the ctek Martin provided 2 long solar cables which I have ran from the front seat down the side of the van and out through the back lights and these terminate in 2 connectors that I presume will plug into the solar panel.

My thinking is though that I should have a fuse just after the panel to protect against the cable from the panel to the controller shorting if it rubs through to the van chassis for any reason as it’s a long unprotected run, Is this correct? I haven’t seen this in any installs but in my mind it’s needed?

Secondly I want to mount the solar panel on the roof rack between the 2 bars so I guess I’ll need a solid panel? Or is it best to get a semi flexible one and mount it on a sheet? I don’t want it to vibrate at speed.

On the travelvolts site I only see a flexi panel so thought I would ask here first before contacting Martin again

Cheers
Justin

 

[Phil_G]

I would suggest that theres no need to fuse a panel, in fact the short-circuit current is one of the panel specifications. A panel isnt like a battery - its internal resistance is relatively high which inherently limits the current it can supply.
Cheers
Phil

 

[The_Lad]

Cheers Phil so you are saying that in full sun if I disconnected the wire from the ctek and shorted it to the bodywork that wouldn’t be an issue ie it wouldn’t cause a fire or spark etc?

 

[Phil_G]

At what rating would you propose to fuse it? To be effective you want a panel to give its maximum current. If you fuse it above that,the fuse will never blow, there is no more current to be had. The purpose of a fuse is protection where excess current flows, and a panel is incapable of providing 'excess' current - its max is its max
You could argue that at the point of maximum power transfer the current is slightly lower than the short-circuit current, but conventional automotive fuses are not sufficiently granular to happily pass mpp current but blow on isc current, neither of which are fixed but change widely with exposure
Cheers
Phil

 

[The_Lad]

When you put it like that it makes sense thank you.

Now just to find a suitable panel and work out if I need solid or semi-flexible

 

[Dellmassive]

Fusing panels is normally more important for fixed Building installs as they run at higher voltages and currents, though not commonly used in a small mobile solar install.

blocking diodes and in-line fuses are used to prevent backflow though large panel arrays when they are connected in series or parallel or both.

you can get fused MC4 connectors, (thats what i use.) (to protect the panel in case of a "solar controller" fault that could feed battery current to the panel and possibly cause damage to the panel or feed cables)

my panels do not have internal blocking diodes, so i use a MC4 Y branch connector and MC4 Blocking Diodes with MC4 fuse.

the fusing rate would be about 25% higher than the panels max current so that the fuse would not heat up during normal use, but would blow in the event of catastrophic failure..

.............................................................

Renogy quote:
The second fuse between your solar panels and charge controller is a little bit different to figure out. The size of this fuse is dependent on how many solar panels you have and how they are connected (series, parallel, or series/parallel). If the panels are connected in series, the voltage of each panel is added but the amperage stays the same. For example, if you have four 100W panels connected in series, each producing 20 volts and 5 amps, the total output would be 80 volts and 5 amps. We then take the total amperage and multiply it by a safety factor of 25% (5A x 1.25) giving us the fuse rating of 6.25A or 10A if we round up. If you have a parallel connection, where the amperage of the panels is added up but the voltage stays the same, you would have to add up the amperage of each panel and then we add a 25% industry rule to figure out the fuse size. For example, if you had four 100W panels hooked in a parallel connection, each panel produces about 5 Amps, so we would use this equation (4 * 5 * 1.25) = 28.75 Amps, so in this instance we would recommend a 30 Amp fuse.

...................................................................

again this would apply to a larger system.



More solar info here>

Caravans and motorhomes :: 12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

How to Fuse your Solar System

how-properly-fuse-solar-pv-system - Web




Renogy MC4 Waterproof In-Line Fuse Holder w/ Fuse
Renogy MC4 Waterproof In-Line Fuse Holder w/ Fuse



MC4-COMPATIBLE ADAPTOR WITH 10A BLOCKING DIODE FOR CONNECTING MULTIPLE SOLAR PANELS TO THE SAME SOLAR CHARGE CONTROLLER

12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

 

[Dellmassive]

FYI

https://www.ctek.com/storage/ma/b21...9E21271E091489ACEF47A/D250SA-manual-UK-EN.pdf

The Install book shows a 30A fuse on the input side Alternator / Solar

But it doesnt show a fuse on the solar side of the diagram,



.



.

 

[Phil_G]

Each pv cell has a reverse-voltage degradation point of over 13v and you have many cells in series so even in the highly unlikely
event of a controller fault mode which directly connects the leisure battery to the panel, ie distributed across many cells in series, no damage
should result. Without blocking however it would ultimately drain the battery and in very small systems this is usually prevented
with a series schottky diode, but in larger, controlled systems the reverse-current blocking is inherent in the controller design.
If in doubt, other than a small voltage drop, an additional series schottky will do no harm. None of this however helps with the
question of fuses though, Ctek dont show a panel fuse as its not necessary though it is of course harmless if you're happier to fit
one, at least it gives you a convenient test & measurement point.

Cheers
Phil

 

[The_Lad]

Wow great info guys lots of knowledge shared here.

If anyone has a recommended panel to use with the ctek and a 110ah battery suitable for mounting between 2 roof bars let me know

 

[travelvolts]

Yes, what Phil says.

 

[The_Lad]

Thanks Martyn

Do you sell a suitable solar panel for my requirement?

 

[travelvolts]

When you say mounting between roof bars, I assume you are thinking of a rigid panel rather than a flexi one?

 

[The_Lad]

I presume a rigid one would be best unless mounting a semi flexi one on a sheet of something provided any benefit.

I wasn’t sure how a rigid panel would deal with the vibrations, flex and air flow of being between 2 bars.

My plan is to use some angle brackets to mount a single panel (again I presume no benefit of having 2 panels with the ctek) to the cross roof bars of the van which In turn are mounted to the long length way roof rails

 

[travelvolts]

Yes, that will work fine. We have a Victron 100 watt panel that will do the job. £145.00 plus vat delivered.

 

[solarenergy5]

Maybe you are interested in learning a little more about fuses in other fields, here is a good tutorial just in case you are interested. Good luck

or this blog would help you, too (Fuses in Solar panels)