Electrical Advice

[DaveBMusik]

One of the problems with trying to educate myself out of ignorance is the difficulty of discerning what to beleive when I receive conflicting advice. I hope that my friends here at C34 can help.

I am installing two 100 watt panels above my bimini on two cross bows. The bows have about an 8" rise in the center so each panel is angled away from parallel.
My plan is to connect each panel to it's own Victron 75/10 controller. This should mitigate the problem of shading on one as well as maximizing  the different angles of sun hitting the two panels.
My questions:
1. Is going with separate controllers a sensible way to go or would it be more efficient to go with a single controller?
2. Can I use 10-3 cable for the 25 foot run to the panels and share a common ground between panels and the two controllers?
3. Is there a combination switch / breaker you would recommend between controller and batteries?

Thanks so much!

Dave

[KWKloeber]

Dave,

I'm not experienced to speak to the other questions -- but as to cable, I ass/u/me you chose #10 to minimize voltage loss?  Certainly could go lighter based on amperage output of a panel.

With a 10-3 boat cable, if only one panel is putting out, then you have "X1" current going through both the black feed and the yellow neutral wire.  If both panels are putting out, you have "X1" and "X2" current going through the red and black feeds.  BUT you have "X1+X2" current going thru the yellow neutral wire. So that increases the voltage loss in that wire (potentially doubles it, depending on each panel's output.)  It counteracts your purpose of going with #10 cable.

Remember DC circuits are a LOOP, with the neutrals handling the same current as the hot feeds.  SO, IT'S CRITICAL to always make sure that neutral ("grounds" in the vernacular) cables and terminals are in the same good shape as your hot leads.  They oftentimes get "out of sight, out of mind" forgotten.


Ken

[Sue Clancy]

Dave,

We used a single Victron BlueSolar 75/15 MPPT Charge Controller - 15 Amps / 75 Volts   for our 2 100W panels
The 2 panels are installed in parallel which required us to use 2 branch connectors to combine the positives of the 2 panels together and the negatives of the 2 panels together.  This was also recommended to us to deal with partial shading.

The switch we used as a circuit breaker and switch between the controller and the batteries was the Blue Sea Systems A-Series White Toggle Circuit Breaker - Single Pole   
Also the cover plate for this Blue Sea Systems Mounting Panel for Toggle Type Magnetic Circuit Breakers Panel Blank Single A-Series

It was recommended to us that we use Solar PV cable rather than regular electrical wire between the panels and the controller.  It's rated for outdoor use and recommended by the solar panel companies.  We used Sewell Solar Panel PV Cable UL Rated, 10 AWG, 100 ft. Roll

We used 10-2 cable for the run from the controller (in the hanging locker near the nav station) to the batteries.

I did a whole write up which you may have seen on the wiki. 

http://c34.org/wikiwp/?rdp_we_resource=http%3A%2F%2Fc34.org%2Fwiki%2Findex.php%3Ftitle%3DFlexible_solar_panels   

Sue

[DaveBMusik]

Dave,

We used a single Victron BlueSolar 75/15 MPPT Charge Controller - 15 Amps / 75 Volts   for our 2 100W panels
The 2 panels are installed in parallel which required us to use 2 branch connectors to combine the positives of the 2 panels together and the negatives of the 2 panels together.  This was also recommended to us to deal with partial shading.

The switch we used as a circuit breaker and switch between the controller and the batteries was the Blue Sea Systems A-Series White Toggle Circuit Breaker - Single Pole   
Also the cover plate for this Blue Sea Systems Mounting Panel for Toggle Type Magnetic Circuit Breakers Panel Blank Single A-Series

It was recommended to us that we use Solar PV cable rather than regular electrical wire between the panels and the controller.  It's rated for outdoor use and recommended by the solar panel companies.  We used Sewell Solar Panel PV Cable UL Rated, 10 AWG, 100 ft. Roll

We used 10-2 cable for the run from the controller (in the hanging locker near the nav station) to the batteries.

I did a whole write up which you may have seen on the wiki. 

http://c34.org/wikiwp/?rdp_we_resource=http%3A%2F%2Fc34.org%2Fwiki%2Findex.php%3Ftitle%3DFlexible_solar_panels   

Sue

Thanks Sue!

Victron is recommending to go with one MPPT and to wire in parallel. This obviously would be much simpler...
I did read your write-up but will go back and take another look.

Thanks!

[Dave Spencer]

Dave,
Sue's writeup is very good.  It sounds like you're doing almost the same thing.
I've never heard of going with separate controllers for two different panels in an effort to mitigate shading.  Some research on this internet may give you better information on this.  To my only partially trained eye, it seems like a waste to go with two controllers. 

My oversimplified understanding is that to mitigate shading, run the two panels in parallel as Sue has described.  This means there is lower voltage (say ~18V) but higher current running to your controller so you'll have to size wires accordingly.  To mitigate voltage drop, run the panels in series which results in twice the voltage (or more if you have more than 2 panels) but half the current running to the controller meaning that you can get away with lighter gauge wire than a parallel setup.

You will definitely need a fuse or breaker between the controller and the batteries... just like you would have a fuse between and alternator or a shore power charger and the batteries.  I'm installing my solar over the next two weeks and I'll be putting a fuse between the panels and the controller also.  This is the fuse holder that I'll be using for both panel to controller and controller to battery protection.
http://ca.binnacle.com/Electrical-Fuse-Blocks-and-Holders/c58_580/p2674/Blue-Sea-5006-Fuse-Block-Maxi-Fuse-System/product_info.html  It's likely overkill but I have that fuse holder elsewhere on my boat.

The conflict between solar panels and shore power or alternator charging is interesting to me.  I found this website has a very good writeup on the issue.  http://roadslesstraveled.us/charging-rv-marine-batteries-solar-power-shore-power/

Good luck with your installation.

[KWKloeber]

... just like you would have a fuse between and alternator.........  and the batteries. 

So the loaded question is.... where does the fuse go in the circuit above?

kk

[Dave Spencer]

Hi Ken,
I didn't know the question was loaded but I have my alternator fuse and shore power fuse right at the batteries.  Perhaps I'm missing something. 

[KWKloeber]

Hi Ken,
I didn't know the question was loaded but I have my alternator fuse and shore power fuse right at the batteries.  Perhaps I'm missing something. 

Dave

Exactly. Some would put a fuse at the alternator end. Not!

Ken

[Sue Clancy]

Dave,
Just be aware that the Victron 75/10 controller is probably not enough for the 2 panels.  Not sure what the rating is on your panels but we needed to get the 75/15 for ours with Amps on the panels combined.

Sue

[J_Sail]

Controllers are now pretty inexpensive and there are distinct advantages of putting a separate controller on each panel if they ever might see different degrees of shading. For a panel to operate at peak efficiency (max wattage output for a given strength of sunshine)it  requires a load of a certain resistance.* (see footnote).

An MPPT controller adjusts its resistance as needed to keep the panel in its sweet spot, and then converts the panel's voltage to the appropriate battery-charging voltage.

The problem is that the ideal load varies with the amount of sun on the panel. Simply paralleling or series-connecting two panels that are seeing differing strengths of sun will result in one (or both) of them operating at less that peak efficiency.

For the modest one-time cost of a second controller, you can have both panels operating at peak efficiency all the time. Note - you simply parallel the outputs of the two controllers.

For my install, I used two Genusun GV10-12v modules at ~$115 ea
https://genasun.com/all-products/solar-charge-controllers/for-lithium/gv-10-li-lithium-10a-solar-charge-controller/

It seems to me that $115 is a reasonable price to pay to get optimum output from panels that frankly will never provide quite as much power as you'd like. :)

You can get them on Amazon, but BruceSchwab is a great supplier and seems really knowledgeable.
https://www.bruceschwab.com/genasun-gv-10-12v-mppt/



Footnote * Too high a resistance load and the panel hits peak voltage before its output current hits max; too low and the panel's voltage droops because the panel's max current can't generate sufficient voltage into the load.

[DaveBMusik]

From Victron:
"A single panel producing 17.2V on our MPPT will likely charge very little if at all. The MPPT requires battery voltage +5V from the solar to start charging. If you have bad weather or partial shading it likely will not work. My advice would be to connect them in series (17.2 x 2). This will be much better in terms of voltage production."

I liked the idea of using the Victron for their phone App for charging info and settings.
A 75/10 would be ok in series as my two panels are 17.2 VDC and 5.81Amp thus 34.4 VDC @ 5.81

Do the Genasuns require a +5V?
Is wiring in series with two panels at different angles too serious an issue for one controller?

[Dave Spencer]

Dave,
Be careful with the amperage rating.  I'm fairly certain that the 10amp rating on the controller you're looking at is 10 amps to the battery, not 10amps from the panels.  Given the situation you outlined above and assuming 100% conversion efficiency, you would be delivering 13.8 amps at 14.5 volts to the batteries.

[J_Sail]

From Victron:
"A single panel producing 17.2V on our MPPT will likely charge very little if at all. The MPPT requires battery voltage +5V from the solar to start charging. If you have bad weather or partial shading it likely will not work. My advice would be to connect them in series (17.2 x 2). This will be much better in terms of voltage production."

I don't know for certain, but I suspect that the Genasuns do not require the panels to output a voltage anywhere near 5 volts above battery voltage to turn-on or operate. I think it's a great question though, and one that Genasun should answer. There is also a chance that MaineSail might know.

[britinusa]

Yet another post that hits my button.

While reinstalling the fuel tank, I took the time to follow the power lines from our solar panels as they enter down about 6" foreward of the fuel fill cap
As far as I can see (without trying to rip out the wiring to see if something is installed where I cannot see it) There is no fuse on our Solar Panel to the Blue Sea controller.

So I was researching fuse options and looking at the Blue Sea Systems 285-Series Circuit Breakers.
Amongst other projects, I'm in the process of replacing the existing Alternator with one of Mainesail's 100A Alternators and have to disconnect the battery +ve's as a safety step during the installation.
Then it occurred to me that perhaps I should replace the battery fuses with the same series breakers.

Watching this thread to see how it turns out.

Paul

[sailaway]

  I see there was some talk of series the panels. A lot of people in the Caribbean are going that way you get more charging time. 8 am you get 14v at noon 24+v, 4pm 14v an on cloudy days it will charge. But at 1/2 the amps so it's a trade off longer charging time less amps. Fuses or breakers need to be as close to the power source as possible the panels. Charlie