Someone Check my Math

[Paul Elliott]

Originally Posted by bluegreen

Not some random connector. The wires from the pannel itself are not very big. My 30 volt 9 amp panels are in series. So i have 66.7 volts of pannel with rather small wire from them to the controller. At that point it goes to 24 volt system where i run the heavier guage to the batteries. In all the research ive done, the wire size seemed to be the very least of all the powerloss problems ive ran into. And if i want to add more pannels in series it dosent affect the current on the pannel side. Same amps just volts increase. The controller does the rest. So traveler having roughly the same pannels with a mppt controller swapping 60v 9a to 12v 50a, his controlers efficiency is far more critical then the pannel wire size. Thats all im saying. The 1.5 volts lost will only account for 10 watts on either side. Having a small shadow pass over the pannels will effect it more then that. Its just how i see it. Electronics is a lot more rough n dirty then i would have thought prior going to electronics engineeringin college back in 1998. Its getting foggy for sure so i like reading this thread and voice an opinion when i can.
Maybe i will try heavier wire and see if it makes any difference. I however believe the batteries internal resistance make the bigger difference. But let me know how this works out. Im interested for sure. And good luck to all.

In your situation, since you have your panels wired in series you have a higher voltage and lower current (than the parallel case). (As you noted above.) And yes, you can add panels in series, using the same wire, without increased loss as long as the controller can handle the voltage.

In the OP's case there were two "30V" panels, with independent wiring to two MPPT controllers. Do the math -- there will be a 5% loss with the #14 wires, but a 2% loss with #10.

As for shadows, etc., being a bigger problem than wire loss, that may be, but that's still no reason to throw away power. We advocate using MPPT controllers because they give us a 5 or 10% gain (and for other good reasons).

At the end of the day, we are arguing about finding the point of diminishing returns when choosing wire gauge. Neither of us would use #18 wire for this 30-ft run, even though it could carry the current without getting too hot. I say that #10 gives a 2% voltage drop and so it the smallest I would prefer to use.

I also am saying that the connector size should not determine the wire gauge. If the connector is too small for the proper wire then an adaptor of some sort is called for.

[bluegreen]

That brings up a good point. Are dual parrell systems more effective then a single, higher voltage system when using the same equipment?
Provided your peaks are within specs of course.
Thanks for the conversation guys. Have a great adventure!

[travellerw]

Originally Posted by bluegreen

That brings up a good point. Are dual parrell systems more effective then a single, higher voltage system when using the same equipment?
Provided your peaks are within specs of course.
Thanks for the conversation guys. Have a great adventure!

I haven't been out there yet, so I can't answer it with actual data.

However, I left out part of my install as I'm not changing it. The boat originally came with 300W of shell solar panels (3X75W). They are installed WAY back on the Bimini and never get shaded. Within 2 days of taking possession, I wired those panels in series at 80V running on 14AWG wire. In the 7 months I have owned the boat, that array has put out more than I expected. Over the summer I seen it hit the rated 300W multiple times. If there is no shade, I think series is the way to go.

The reason I'm running 2 home runs for the new panels is that will give me 3 individual strings, with a controller for each. Any one failure can only take out 1/3 of the array. I also carry a spare controller.

[Paul Elliott]

Originally Posted by bluegreen

That brings up a good point. Are dual parrell systems more effective then a single, higher voltage system when using the same equipment?
Provided your peaks are within specs of course.
Thanks for the conversation guys. Have a great adventure!

If you can keep the panels out of the shadows then series lets you use smaller wire so it's "better" (as long as your controller can handle the voltage and power). On a boat it's hard to find shade-free locations so you might do better with parallel-connected panels, or better yet, with per-panel MPPT controllers.

Panel bypass diodes can somewhat mitigate the shadowed series panel issue, but this will depend on the particulars of the panel design. Per-cell bypass diodes would be best, but I'm not aware of any panels that use these. It's been a while since I've looked.

[bluegreen]

Please post again after you get set up with multiple mppt controlers on the same battery bank. The way my Midnite 200 works is it does a battery test every 3 min and checks the voltage, determines which charge to apply (absorb , float ) and applies the set voltage. When you have multiple mppt systems, what happens when one is on an absorb state, putting 14.4v across your banks, and the 2nd or 3rd controllers do a sweep and decide to float or rest because they think the source is max? This was something i need feedback on causethis controller was $900. It can do 200v in outputting 79 amps. So i may take yours and pauls advice and go with 2 parrell pannels and get 250 watts more often then 500 sometimes. Shadows kill series current! Its horrid. Sounds like you have a sloop.

[twinboat]

I think at that point you don't need both controllers charging anyway. The batteries will only accept so much in absorb state.

[travellerw]

Originally Posted by bluegreen

Please post again after you get set up with multiple mppt controlers on the same battery bank. The way my Midnite 200 works is it does a battery test every 3 min and checks the voltage, determines which charge to apply (absorb , float ) and applies the set voltage. When you have multiple mppt systems, what happens when one is on an absorb state, putting 14.4v across your banks, and the 2nd or 3rd controllers do a sweep and decide to float or rest because they think the source is max? This was something i need feedback on causethis controller was $900. It can do 200v in outputting 79 amps. So i may take yours and pauls advice and go with 2 parrell pannels and get 250 watts more often then 500 sometimes. Shadows kill series current! Its horrid. Sounds like you have a sloop.

I have no idea how the Midnite controller works but the controllers (Chinese) I use have no problem. I have tested it using 2 controllers, 1 to the solar array and 1 fed with a 30V bench supply. There was no problems.

Morningstar also has a whitepaper on it as well.
Parallel Charging Using Multiple Controllers With Separate PV Arrays » Morningstar Corporation

My boats a Catamaran so I have tons of space.

[travellerw]

Bluegreen - The information you are looking for is here...
Can two Midnite Solar Classic 150 be used in parallel? - northernarizona-windandsun

[bluegreen]

Thanks guys. Good input. I will look for your advice in future posts. Take care. Got some reading to do!

[ramblinrod]

Originally Posted by travellerw

The boat originally came with 300W of shell solar panels (3X75W).

Interesting math, and per your other post, you have no problem calling other people stupid?

[travellerw]

Originally Posted by ramblinrod

Interesting math, and per your other post, you have no problem calling other people stupid?

You seem to have a problem with reading comprehension.. I never called anyone stupid. What I said, was I thought they were stupid. I can't help it if you stepped up and claimed the title!

[ramblinrod]

Originally Posted by travellerw

You seem to have a problem with reading comprehension.. I never called anyone stupid. What I said, was I thought they were stupid. I can't help it if you stepped up and claimed the title!

Seriously?