Jason

On 8/4/2020 at 3:35 PM, Sehc said:

Fusing from panel to controller is not needed, and causes an extra voltage drop. You will need a switch, but that can be sized to little to no voltage drop. I have and used 8 awg uv resistant wire from Windy Nation. But they no longer list any over 10 awg. There are two types of mc-4 connectors. Renogy for one has a different than standard. 

Hi.

Thank you for the information. I was wondering about the fuses available. I will put the switch in

8 minutes ago, oldjohnt said:

Jason, thanks for the update, here's my response:

1) 8 Gauge copper is rated FOR AT LEAST 40 Amps, subject to if jacketed or in conduit or single conductors in open air which makes it even greater, so the possible 15 to 30 amps of current I used above should make it adequate being 15 ft shouldn't cause any excess line voltage drop. HOWEVER AGAIN even bigger wire (say 2 or 4 Gauge) = less voltage drop and I have seen 4 Gauge (even if overkill based on current) used under similar conditions PROVIDED all the connections are suitable for that size wire ????  I don't have any MC4 specs or data sheets handy to see what size wire they can accept.  

2) Ive observed situations where MC4 connectors on open rooftops (it can get hot up there in bright sunlight) have failed, but perhaps that was due to excess current ??? I cant say. I have cut them off and used direct burial rated connections/splices in water tight junction boxes with no problems and believe such to be better then MC4 exposed to water and sun BUT DON'T NECESSARILY DO AS I SAY, DO WHAT THE MANUFACTURERS RECOMMEND. 

As far as multiple panel connections are concerned, in series voltage is additive meaning there's less current down to the solar charge controller, however, in series if one panel is shaded that reduces the net energy harvest. In parallel shading is less a problem but current is additive and as used in the examples above. ALL SUBJECT TO any max input voltage range of your charge controller, although many MPPT have a wide input voltage range maybe even as high as 100 volts or more. 

 You are gonna have a nice system when done

John T

I am very grateful for your feed back. 

Thank you very much.

All of the research done has been on parallel. I am concerned about sun blocking/ shade over panels. Not clear to me. Does the whole panel/ system suffer if one small (example 12"x6' glass)part of the panels are sun blocked?  Everything thing is 12volt in the van also.

1 hour ago, oldjohnt said:

As far as wire size Id consult with the manufacturer for their recommendations lest you risk voiding an warranty. HOWEVER that being said let me run a couple calculations FOR EXAMPLES ONLY AND NOT recommendations.

1) If your two panels were producing full 800 watts (Yeah right lol) at lets use ONLY FOR AN EXAMPLE  24 Volts (even though it should be higher) 800/24         =   33 Amps

2) If your two panels were producing 800 watts at 41 volts, 800/41 =   19.5 Amps 

3) Next there will be a line voltage drop from the panels to your solar charge controller which depends on 1) Current 2) Wire size and 3 ) Distance and if its excessive you would increase the wire size

Okay, that all being said and NOT knowing your actual current (depends on sun and panels etc) and NOT knowing the wire length but ONLY what my training and experience has taught me,  if I were doing it and had NO OTHER instructions to follow, I might use a very MINIMUM of say 8 Gauge (subject to length and larger if necessary to reduce line voltage drop) fine stranded copper conductors, Marine grade moisture and UV rated insulation. NOTE if the manufacturer recommends bigger wire USE THAT, I'm ONLY saying I see 8 Gauge AS THE MINIMUM but larger to reduce line voltage drop and/or manufacturers recommendations. Ive seen people use 4 Gauge in similar current applications since THE BIGGER THE WIRE THE LESS VOLTAGE DROP  

Of course use the necessary moisture rated proper connections and prevent the wire from flopping around on the roof. 800 Watts on a small van with three 100 AH Lithiums should provide a great deal of energy storage and harvest.

 Best wishes

John T

 

Hi John.

Great information. Truly appreciated. Here's another question.

The solar panels come with attached 12 gauge wire with mc4 pre installed connectors. I plan on using mc4 combine connectors with 20amp fuses to combine the 2 panels on the roof. From the roof to the mppt is going to be 8 gauge.

What's your thoughts on the 8 gauge and amps running through it?

Also, can mc4 connectors be attached to 2 and 4 gauge? I was thinking about cutting the mc4 off and connecting the existing solar panel 12 gauge to the heavier 2 or 4 gauge.

The distance from panel to mppt is 15ft.

Thanks again.

Jason

1 hour ago, Al F said:

For the wire size, use a wire size calculator like this one:  http://nooutage.com/vdrop.htm

You are planning on putting the solar panels on a van.  A 400watt panel is about 6 feet by 4 feet.  Do you have room for two?  

With the setup you have planned you should have more power than you are likely to need.

There is room. Extended van. Empty roof. The solar panels come with attached 12 gauge wire with mc4 pre installed connectors. I plan on using mc4 combine connectors with 20amp fuses to combine the 2 panels on the roof. From the roof to the mppt is going to be 8 gauge. What's your thoughts on the 8 gauge?

Thanks for the information and the calculator. 

Hello.

New to the site. And new to solar. Been reading and watching videos on the subject. I'm considering two 400 watt panels (41vmpp per panel with mc4) in parallel for a 12 volt system on a van.  My concerns are amps through the wire and what gauge wire to use. I would be using the Epever 100A mppt charge controller  with 3 100ah lithiums. I would greatly appreciate your knowledge and experience.

Thanks

Jason