Connectors

[chemist308]

Bigger systems require thicker wiring. I’ve posted my plans previously, but I’ll do an 1800 Watt system if but will run my panels in series parallel to minimize partial shading effects while still pulling voltage I need. That said, I’m guessing the common solar connectors work for smaller wiring. If you’ve done a bigger system, where did you source solar connectors for thicker wiring?

[brandtb1919]

Bigger systems require thicker wiring. I’ve posted my plans previously, but I’ll do an 1800 Watt system if but will run my panels in series parallel to minimize partial shading effects while still pulling voltage I need. That said, I’m guessing the common solar connectors work for smaller wiring. If you’ve done a bigger system, where did you source solar connectors for thicker wiring?

As far as I know, the MC4s max out at about 10AWG. I put a watertight junction box on the roof with bussed terminals and ran 4AWG wires to the basement. I have 4 sets of two panels in series, so no more than 10A per set going to the junction box. I am a big fan of the series parallel combo.

Brian

[chemist308]

As far as I know, the MC4s max out at about 10AWG. I put a watertight junction box on the roof with bussed terminals and ran 4AWG wires to the basement. I have 4 sets of two panels in series, so no more than 10A per set going to the junction box. I am a big fan of the series parallel combo…

So are you thinking run all the wiring over to a junction box, then do wire ties and bus bars?

[brandtb1919]

So are you thinking run all the wiring over to a junction box, then do wire ties and bus bars?

This is what I did:

https://www.mygrandrv.com/forum/show...827#post428827

Brian

[Butcher]

MC4-EVO2 can accept up to a 10mm wire/8 AWG. If I recall, just under 70A

[acoleman43]

What is the max current from your panel pairs? What is the length of wire from the panel to the junction box?

Assuming your panels are the Rich Solar 200W "12V" panels. Data sheet shows max current (Imp) at 9.8amps (not considering temperature). If you wire a pair in series, it will remain 9.8 amps. Max voltage is 20.4V (Voc is 24.3V). Wiring in series will double voltage for each pair.

Lets assume 10 amps and 50V from each panel pair. Using 2% voltage drop, you can use a 10 awg wire for up to 95' length.

If you are paring the 2 pairs in parallel, you will size a wire for 20 amps and 50v. WIth 2% voltage drop you can use a 10 awg wire for up to about 45'.

All this to ask, why do you need anything larger than 10 awg?

[brandtb1919]

What is the max current from your panel pairs? What is the length of wire from the panel to the junction box?

Assuming your panels are the Rich Solar 200W "12V" panels. Data sheet shows max current (Imp) at 9.8amps (not considering temperature). If you wire a pair in series, it will remain 9.8 amps. Max voltage is 20.4V (Voc is 24.3V). Wiring in series will double voltage for each pair.

Lets assume 10 amps and 50V from each panel pair. Using 2% voltage drop, you can use a 10 awg wire for up to 95' length.

If you are paring the 2 pairs in parallel, you will size a wire for 20 amps and 50v. WIth 2% voltage drop you can use a 10 awg wire for up to about 45'.

All this to ask, why do you need anything larger than 10 awg?

All of your points look correct to me. In my case, it was all about flexibility to reconfigure if I want to, hence the Unistrut under the panels and the 4AWG wire from the junction box. I also wanted to transfer every watt I reasonably could to the MPPT controllers. With my 4 sets of series panels, the theoretical maximum current is just under 40A from the panels. I wasn't willing to accept the (I squared R) loss associated with this current on 10AWG wires to the basement.

Brian

[acoleman43]

All of your points look correct to me. In my case, it was all about flexibility to reconfigure if I want to, hence the Unistrut under the panels and the 4AWG wire from the junction box. I also wanted to transfer every watt I reasonably could to the MPPT controllers. With my 4 sets of series panels, the theoretical maximum current is just under 40A from the panels. I wasn't willing to accept the (I squared R) loss associated with this current on 10AWG wires to the basement.

Brian

That makes sense.

I'm a little jealous that you have room for more solar.

I don't think you really need to have anything larger than 10 awg from solar panels to junction box. Let me explain using my system as an example.

I have 3 pairs of 210W "24v" panels. Each pair is wired in series, and the 3 pairs are then wired in parallel inside a single junction box. Each panel pair has a theoretical max current of 6.24 amps and theoretical max voltage of 39v (adjusting for low temp of -30 Celsius which is very extreme). I have 10 awg wires form each panel pair into the junction box. The longest run of 10 awg wires from the panels to the junction box is a little under 20'. With this I experience less than 0.5% voltage loss with 10 awg wires....virtually nothing.

From junction box to MPPT I see a theoretical max current of just under 19 amps with a theoretical max voltage of around 117V. I have 8awg wire from my junction box to the MPPT charger. With the theoretical max, the 8 awg wire (with 2% loss) can run 190'. I see less than 0.5% loss with 8 awg wire into my MPPT.

All my wiring is much more robust than industry standards (2% to 3% voltage loss) and I do not see any real voltage loss.

In my opinion, I would connect all panel pairs wiring at the junction box. That way you can minimize wire size from your panels to junction box. Also, expanding solar array will not affect any current wire size into the junction box - it will just add more wires into the junction box. Where you will want to increase wire size for expansion will be from junction box to charge controller(s).....where no MC4 connectors are needed. at 40 amps and 60 volts you can still run 20' with 8 awg wire at just 1% voltage loss. With 4 awg you can go about 55' with 1% voltage loss.

[brandtb1919]

That makes sense.

I'm a little jealous that you have room for more solar.

I don't think you really need to have anything larger than 10 awg from solar panels to junction box. Let me explain using my system as an example.

I have 3 pairs of 210W "24v" panels. Each pair is wired in series, and the 3 pairs are then wired in parallel inside a single junction box. Each panel pair has a theoretical max current of 6.24 amps and theoretical max voltage of 39v (adjusting for low temp of -30 Celsius which is very extreme). I have 10 awg wires form each panel pair into the junction box. The longest run of 10 awg wires from the panels to the junction box is a little under 20'. With this I experience less than 0.5% voltage loss with 10 awg wires....virtually nothing.

From junction box to MPPT I see a theoretical max current of just under 19 amps with a theoretical max voltage of around 117V. I have 8awg wire from my junction box to the MPPT charger. With the theoretical max, the 8 awg wire (with 2% loss) can run 190'. I see less than 0.5% loss with 8 awg wire into my MPPT.

All my wiring is much more robust than industry standards (2% to 3% voltage loss) and I do not see any real voltage loss.

In my opinion, I would connect all panel pairs wiring at the junction box. That way you can minimize wire size from your panels to junction box. Also, expanding solar array will not affect any current wire size into the junction box - it will just add more wires into the junction box. Where you will want to increase wire size for expansion will be from junction box to charge controller(s).....where no MC4 connectors are needed. at 40 amps and 60 volts you can still run 20' with 8 awg wire at just 1% voltage loss. With 4 awg you can go about 55' with 1% voltage loss.

As a point of interest, I technically have more capacity in the solar panels than I have in the MPPT controllers. I have a total of 1600W theoretical max from the panels, but I have two of the 100/50 Victron MPPTs that are rated at 700W max charging at 12V. This was a conscious decision to save about $500 to the next size of MPPT and figuring that I will probably never see the max output from the panels unless I am boondocking on the equator. It gets pretty sunny here in CO, and so far I have never seen anything above about 1250W of solar charging, so the bigger MPPTs may have been a waste. I figure even if I hit the max output of the MPPTs at 1400W, that is still more than one of my ACs draws.

Brian

[brandtb1919]

That makes sense.

I'm a little jealous that you have room for more solar.

I don't think you really need to have anything larger than 10 awg from solar panels to junction box. Let me explain using my system as an example.

I have 3 pairs of 210W "24v" panels. Each pair is wired in series, and the 3 pairs are then wired in parallel inside a single junction box. Each panel pair has a theoretical max current of 6.24 amps and theoretical max voltage of 39v (adjusting for low temp of -30 Celsius which is very extreme). I have 10 awg wires form each panel pair into the junction box. The longest run of 10 awg wires from the panels to the junction box is a little under 20'. With this I experience less than 0.5% voltage loss with 10 awg wires....virtually nothing.

From junction box to MPPT I see a theoretical max current of just under 19 amps with a theoretical max voltage of around 117V. I have 8awg wire from my junction box to the MPPT charger. With the theoretical max, the 8 awg wire (with 2% loss) can run 190'. I see less than 0.5% loss with 8 awg wire into my MPPT.

All my wiring is much more robust than industry standards (2% to 3% voltage loss) and I do not see any real voltage loss.

In my opinion, I would connect all panel pairs wiring at the junction box. That way you can minimize wire size from your panels to junction box. Also, expanding solar array will not affect any current wire size into the junction box - it will just add more wires into the junction box. Where you will want to increase wire size for expansion will be from junction box to charge controller(s).....where no MC4 connectors are needed. at 40 amps and 60 volts you can still run 20' with 8 awg wire at just 1% voltage loss. With 4 awg you can go about 55' with 1% voltage loss.

I just re-read your comment about the wires from the solar panels to the junction box, I do have 10AWG wires there, the 4AWG only runs from the junction box to the basement.