MC4 Connectors and PV Cable Size Questions

[Rooftop-Special]

Hello,

Thank you for the great forum. I've been watching Will's video and ordered his book. I'm about to tackle my small solar project on my RV with the hopes of educating myself for a large home system on my property in the future.

I just wanted to make sure I understand a few things.

The current system I'm looking to do on the RV is:

(4) 450 watt panels
(3) 200ah lithium batteries
3000 watt inverter charger
(2) or (4) mppt charge controlers
(1) lynx distributor

Batteries are self heating litimes
Components are Victron

I was originally going to do 4 seperate arrays to 4 seperate mppts. Now I'm playing around with parralleling the panels into 2 seperate arrays (2 panels parralleled together). I'm not set on anything yet so looking for input there.

My main question is I'm reading/understanding that both panel wire, and MC4 connectors, can only handle 30 amps. I plan to run 8awg PV wire with the appropriate MC4s. With the initial thought of (4) seperate arrays I was okay. Now that I looked at (2) parralleled panels together it's twice the amps (obviously) and well outside the 30 amp limits of the wire, etc.

It seems I see people parralleling panels and using "regular" pv cable and branch connectors? Maybe I they aren't doing it with 450 watt panels?

I know I can do everything in series but wanted flexibility with shading since its on an RV and half the year I'm in Montana (with trees)

I've been searching and searching, researching and researching, and now I just need to ask!

Thanks for any help and input you have.

Cheers,

Casey

 

[robbob2112]

Post the specs of the panels. And the pv wire you are using.

People put panels in series to increase the voltage and keep the current the same. Pv wire is typically rated for higher current than thhn or romex. It is all about the sheath rating. Generic 450w panel I looked up as example has 40v and 15amps. Put 4 in series and you have 160v at 15 amps. Put them 2p2s and you have 80v at 30amps. Put that on a mppt that can handle it and you are good. Typical 10awg pv wire can do 40 to 45 amps.

Finding mc4 connectors for 8awg can be a challenge. Any connectors it attaches to needs to be rated for the current too.

 

[740GLE]

First of ditch 12v don’t even bother thinking about it. 24v minimum if not 48v.

Def run at least two panels in series, even then you’d be fine with one MPPT.

 

[robbob2112]

First of ditch 12v don’t even bother thinking about it. 24v minimum if not 48v.

Def run at least two panels in series, even then you’d be fine with one MPPT.

On ditching 12v - I agree to a point -

if the OP has most devices including the AC or other expensive large draw devices that run on 12v it isn't practical to use a buck converter to step the higher voltages down to 12v. Many long time RV folks have all hand held and kitchen appliances like the coffee maker at 12v.

If the OP only has lights, and a few other things at 12v and everything else runs off AC voltage then for sure ditch it and go to a higher voltage. Much simpler with everything and you can run the panles in series for higher voltage and all the DC lines are reduced in size to 1/2 or 1/4 the size of 12v lines.... much lower current.

 

[740GLE]

Just another reason to ditch that 12v coffee pot and get that espresso machine you’ve been eyeing!!

 

[Rooftop-Special]

Thank you for the replies. The panel specs are:

450w
42.24 VOC
13.8 ISC

I'll be installing 4 of them.

I thought about going 48v but already purchased (3) 12v batteries. I could buy a 4th but read it's not ideal to wire the batteries in parralel and should have just got a 48v to begin with.

That and the victron multiplus 12/3000 2x120v split phase inverter just seemed like an easier install for the 50amp split phase setup on the rv. This along with needing a dc to dc converter (for the12v)....... it just didn't seem like the juice was worth the squeeze. I understand the benefits of smaller wire.

When I do a larger system I'll definitely do 48v.

Open other manufacturers as well, it just seemed victron had it pretty dialed in on the RV stuff.

I know it'll be more wires but is having each panel seperate to it's own MPPT ideal? I know why people do series or parralel on larger systems, it just seems on this size, with unpredictable shading scenarios this setup would be best.

Thanks,

Casey

 

[Rooftop-Special]

Sorry. Using temco 8awg wire and bougeRV 8awg MC4s.

ETA. I'm a bone head and was looking at max charge amps on an MPPT charge calculator VS the amps from the panels itself wired in parralel. So it seems 2P2S is a decent option as well.

Seems more economical to but (4) 100/30 controlers than (2) 150/60s. Any advantage to only 2 VS 4? I know I'll need a buss bar to connect the 4 to the lynx distribution system. I believe it's not advised to wire all 4 to one post on the distributor?

 

[HarryN]

There is not any obvious advantage to using a lynx for a 12 or 24 volt system in my mind.

It is ok, but I don't see the point.

Here is an example diagram that I use.

For 12 volt systems, double wire the inverter, but for 24 volt systems, there is usually no need.

I am a big fan of 24 volt for DIYers, so if it were me, I would:
- Buy a 4th battery
- Charge them all individually so they are all pretty close charge wise
- Wire them 2S x 2 P and use similar to the diagram.

If you want to keep it 12 volt, just add on the third battery in the same way as the other two that are shown.

 

[740GLE]

Thank you for the replies. The panel specs are:

450w
42.24 VOC
13.8 ISC

I'll be installing 4 of them.

I thought about going 48v but already purchased (3) 12v batteries. I could buy a 4th but read it's not ideal to wire the batteries in parralel and should have just got a 48v to begin with.

That and the victron multiplus 12/3000 2x120v split phase inverter just seemed like an easier install for the 50amp split phase setup on the rv. This along with needing a dc to dc converter (for the12v)....... it just didn't seem like the juice was worth the squeeze. I understand the benefits of smaller wire.

When I do a larger system I'll definitely do 48v.

Open other manufacturers as well, it just seemed victron had it pretty dialed in on the RV stuff.

I know it'll be more wires but is having each panel seperate to it's own MPPT ideal? I know why people do series or parralel on larger systems, it just seems on this size, with unpredictable shading scenarios this setup would be best.

Thanks,

Casey

Just so you’re aware Victron doesn’t make a 2x120v “split phase” inverter. So many people get confused by the marketing.

It only passes 120/240v if you’re on 120/240 shore power, but the inverter (via just battery) only outputs 120v.

It’d be interesting if they’d ever offer a true split phase inverter it I’m guessing the market is too small compared to their core market.

 

[Rooftop-Special]

Thank you for the reply.

I think I understand the inverter correctly. Since RVs don't really use 240v I think having the 120v on L1 and L2 in either shore power or inverter mode is all I need. I know I could use a different inverter and accomplish the same thing I just figured the ease of wiring to the 2x120v in an RV scenario would make everything a little easier.

Easier is good for me right now since I'm learning about all this solar stuff in a relative short span.

I appreciate all the replies!

Casey