help with wiring solar setup

[motion30]

I just purchased 3 275 watt solar panels that will feed an outback controller. I need help with wire sizing
I am installing this on the hard top of my trawler. Large area, no shading
Ok so i figured series and the outback can accept 150 volts. Here are the specs of my panels. 275 watt, maximum power voltage 35.82.
Maxium power current 7.86. Opean circuit voltage 46.98. Short circuit current 8.18. The run from the panels to controller is about 25' run from controller to batteries is about 10' there are many here who know more about this then i.. so. What size wiring do i need?

[model 10]

If you do run it in series I came up with, #8 wire from the panels and #8 from the controller to the buss. This would be for a 3% v drop.

[Nicholson58]

Originally Posted by motion30

I just purchased 3 275 watt solar panels that will feed an outback controller. I need help with wire sizing
I am installing this on the hard top of my trawler. Large area, no shading
Ok so i figured series and the outback can accept 150 volts. Here are the specs of my panels. 275 watt, maximum power voltage 35.82.
Maxium power current 7.86. Opean circuit voltage 46.98. Short circuit current 8.18. The run from the panels to controller is about 25' run from controller to batteries is about 10' there are many here who know more about this then i.. so. What size wiring do i need?

24 or 12 VDC? No matter series or parallel, use bigger wire than you would plan. I have 3 X 220 Watt in parallel with #6 from each one to the MPPT charge controller. Keep the wire from the charge controller to the batteries short & large. BTW, in series, one goes out, they all go out. Also, in series, are they rated for the higher total current?

[motion30]

Which voltage i am i concerned about, maxium power or open circiit voltage ?

[socaldmax]

Open circuit voltage is the one to plan for, both in terms of max. voltage you might see, and the max. voltage that the controller can handle.

i would recommend 6awg, just to err on the safe side and minimize losses.

[motion30]

Thanks guys. I will use 6 awg

[Getweh]

Just curious - I have a little electronic knowledge, but no specific experience with solar systems. Seems to me that in the interest of reliability, going in series is a better bet, as you dont lose charging if 1 panel goes out. Just use diode bridges on each panel to isolate.
Is ther a specific reason for not doing this?

[Moontide]

Putting in parallel means that you keep charging if one panel is shaded. In series you can lose virtually the entire array with a shadow only a bit bigger than a handprint.

There are lots of wire sizing tables available on the net. Handy to have a digital or printed copy on board. Have to remember to use the round trip length, not just one way.

[motion30]

One more question. My boat is 12 volt. what size speakers but I use into the controller and out of the controller assuming 60 amps in and out

[winethief]

"6 gauge. Bigger is better. It's what my electric guy did for my 450 watt system.

[blackswan555]

I do not do "AWG" so I will quote amps and let someone who does translate

A few things to look at, your panels wired 3 in series will give a VOC of just over 140v @ 25c, lower temps will give higher VOC's, The OB cuts out at 140v and is reputed to give the magic blue smoke at 150v ish, Also for best efficiency, they should be wired with an approximate VMP target of twice your battery voltage, So all 3 in parallel would be a better option,

Pro's and cons of either,
Series, Pro's need smaller cable panel to controller, looking at 8 amps max
Con's, dangerously high VOC & working voltage, loss of controller efficiency,

Parallel, Pro's, better efficiency, safer working voltages,
Con's, Bigger cable panel to controller around 24 amps,

The cable from controller to the batteries should be rated for the controller and it's breakers,(you should have DC breakers either side of controller) eg in your case 60 amps (presuming it is MX/FM60)

Other notes, It is very important to install the battery temperature sensor on the hottest part of your bank, About half way down the warmest cell, Also the OB default settings are very generic (safe) refer to your battery manual for advice, Default absorb is 1 hr and battery charge voltage is also too low for most batteries,

Tim

OB forums if you need more help OutBack Power Technologies User Forum • Index page

[motion30]

Tim
what do you feel would be a good program for the
outback? I am charging 12 6 volt golf cart batteries
I finally got everything wired and working today but of course it is overcast and raining.

[blackswan555]

Get yourself a decent hydrometer to start with (maybe two, you will break one ) It is the only real way to tell your batteries state of charge, Also make sure your battery temp sensor is placed about half way up the warmest cell, I like to number cells & keep a log of SG's, With the amount of strings you have, It would be a good idea for you,

What you are looking for is your absorb time, (use a pretty standard 14.4v for absorb voltage) in an ideal world it would be exactly when your batteries are fully charged, in the real world that is near on impossible to get, So to find as close as you reasonably can, use your hydrometer,

A bank is fully charged when all cells stop rising, So start with a long(ish) absorb time, Try 4 hrs initially, check sg's about every hour until you find the time they take, It may be longer or shorter (this is not a fast process, do a few pilot cells to start, when they stop rising move onto the rest) when you find the time, I like to add half hr & that is your absorb time, Cut's down on EQ

Tim

edited to add, What AH Batteries ? What other charge methods do you have ?

[motion30]

I have a 100amp charger inverter. And also a master volt 40amp charger. ,last night was the first night I had the chargers turned off as to lower the state of charge of the battery it has been a little overcast the last couple days, it is currently 4 p.m. and I have put 1.8 kilowatt per hour back in the batteries. I do have a hydrometer but I have not had a chance to check yet. maximum voltage observed so far is 110

[motion30]

Stilll a little cloudy today, I did generate 2.5 kilowattS. I did check the SG around 3 o'clock and they were full up at one 1.275. I knocked my absorption time down to three hours. He how it goes tomorrow if the Sun shines