Yeah it's 100watt. I was keen to avoid any holes so the bars were ideal from the point view. We never put much up there but there's enough space for a water proof bag or chairs which gives a little more space inside the van when it's full of kids and kit Sent from my Pixel 4 using Tapatalk
If you have two panels in parallel then with series diodes on each you get output if one is shaded. Or you can get panels like the Solbian that have forward diodes built in in parallel with sections. So then a shaded section is bypassed. To make up the voltage to significantly more than 14V you then connect the two panels in series. That means on my setup I see current out of the controller even when the stack of two panels is giving out less than 10 volts a panel. Series stacking means my 20A Epever can take 520W of panel or a series connection (40V in) of two pairs of 120W panels. Or 260W if you have panels in parallel. Both are limited by max current in to the stepdown MPPT regulator..
Hi all. Just getting the bits and bobs read for installing my 100w panel on the front luggage rack and I have a couple if questions? I'm intending to use 6mm² solar cable (about 5m) to join up to the controller, is this the right size? I'm also looking at the attached gland (photo), any thoughts... Thanks
You wont see that much voltage drop with 6mm2 solar cable and that length of run : quick check says that cable is good to about 70A or so. The solar cable also has the advantage of tough insulation rated to hundreds of volts that is UV proof so it doesnt go hard and crack in the sun. That gland is nice and neat - once bonded to the panel you are feeding the cables through, you can still slacken the nuts to release the pressure on the rubber grommets that seal the cables , so you can install or replace the cables easily, and the wires come out basically horizontal. I made something out of two bits of 5mm rubber sheet , two bolts and some drilled stainless steel strip that works in a similar way to seal the solar cables going through a 2mm aluminium panel on my poptop.
I should have checked my panel to remind myself what a 100w panel produces and it produces a wapping 5 ish amps max and has 2.5mm² cable ends. So I'm wondering if it is worth while getting the thicker cable for my run to the back to minimise voltage drop? The cost difference is small (2.5, 4 or 6mm²) so it's more about getting it right and learning at this point. My cable run from the front to the back mostly inside if that makes a difference. Thanks as ever.
Something I dug up on the web as an estimate If you take the number 19 the divide by the cross sectional area of the cable this will give you the resistance over a kilometre. (This works for copper cable) So 19/2.5 = 7.6 ohms/km or 0.076 ohms for a 10 metre loop (5 metres there and back again) . At 5 amps that is 0.38 volts or 1.9 watts loss. 19/6 = 3.16 ohms/km or 0.0316 ohms/ 10 metre . At 5 amps that is 0.158 volts or 0.8 watts loss. I really wouldnt worry, the losses are less than the effect of the shadow of a twig or a guy rope on the panel... Its also a good reason why if your controller can support series or parallel connected panels you connect them in series using the same wire - 10 amps through the same wire loses 7.6 watts through 2.5mm2 or 3.2 watts through 6mm2 .. Or you bring each panel's output to the controller through a separate wiring loop.
However, @Chrisd if you want to do your own calcs here's a link to a piece I wrote a few years ago. I've linked it here before but stuff gets lost in the anus of time. I try and keep stuff simple, coz, well I am... https://www.thefitoutpontoon.co.uk/electrics/voltage-drop/
And I've just realised by strange coincidence the example I gave is very close to your proposed installation
The good news is the cable I went for works out well both ways. My main draw is under 6m from the solar panel via the battery. So I think I happy with the 4mm² size I went for....
About to connect my new panel via the controller to the battery. I have two questions that I'd appreciate some help in. The controller suggests connection order as battery to controller and then controller to panel. I do seem to remember reading somewhere that there may be different methods including keeping the panel covered until it's all connected. Peeps thoughts in this would be useful. Secondly, is it better to earth the wire from the controller to the body or the battery? Thanks
My negative is controller to battery. I always try and cover my panels when connecting and disconnecting Sent from my Pixel 6 Pro using Tapatalk
Run all your cables with a direct connection to the battery. I initially had them going to a bus bar,but it's more efficient to the batt terminals. As Matt says, cover them up. They are producing voltage. A mini in line fuse and holder in the positive cable will allow you to quickly connect and disconnect without disturbing MC4 connectors or battery terminals if you need to do maintenance in the future
That's what I mean @Chrisd . That's a 20amp fuse. The cables will handle way more, but our panels will max out at about 12 to 14 so 20 is plenty.
@theBusmonkey, thanks for the idea about the fuse, is this in the positive or negative run, I assume on the negative (earth)? I also don't quite understand your point "Run all your cables with a direct connection to the battery". I will have wires from panel to controller, then from controller to battery and finally battery to loads (fridge etc). Do you mean something else? Edit :- after engaging brain, I now think you were answering my question about controller earth to battery or body!
