24V Pannel with 12V system wire size???

Re: 24V Pannel with 12V system wire size???

Welcome to the forum.

Shall I mention that the battery bank is a problem waiting to happen? You've done about the best you could for wiring that, although the wire size looks rather small. A 1kW inverter on 12 Volts can draw 100 Amps or so at maximum power/minimum Voltage. That would require 4 AWG minimum, and would be better with 2 AWG. But you probably don't use it at full power. There does not appear to be any circuit protection (fuse/breaker) on it either.

On to the next wire! Your panel probably is rated around 8 Imp @ about 30 Vmp. The distance will make a big difference: 50 feet would have about 2% Voltage drop on 8 AWG wire. At 75 feet that drop goes up about 1%. Could be just over 3% then, which is around the limit you'd want. Less is better.

The output of the controller: 30 Amps is large for 235 Watts - planning on adding a second panel? With one it's likely to be about half that. Again, distance makes a difference here as you don't want too much V-drop to the batteries. 10 AWG can handle 15 Amps @ 12 Volts for 5 feet with only 1-2% Voltage drop. If you are planning on adding a 2nd panel you might as well wire for it now. The same wire size will suffer an additional 1% drop if you double the current. This is another line that should have some form of circuit protection on it.

Your battery bank is theoretically 7 * 50 = 350 Amp hours. That 15 Amps of current won't be too much for it. In fact it won't be enough; only 4% peak charge rate. You should probably re-evaluate your load requirements, adjust the battery bank capacity accordingly, then change the charging to suit. Three or four of those batteries will charge very nicely from that much panel, and would supply up to 900-1200 Watt hours, a fair size system.

Re: 24V Pannel with 12V system wire size???

Panel to Controller is the least critical for circuit protection. The panel can only produce its Isc rating in current, so it is highly unlikely anything can go wrong in that section if there's only one panel. More than two in parallel and this becomes a different situation. At any rate, you are looking at <10 Amps there (it will not change with two panels in series).

If the controller is rated for 30 Amps output then the circuit from the Controller to Batteries needs to be wired and protected for that. Batteries can kick out a lot more current than the controller will, and that is the danger here; something shorts in the controller and the batteries can feed a huge amount of current through the wires and start a fire. Usually the controller will have a recommended fuse rating for its output. If not, just figure the wiring and fuse/breaker based on the peak continuous current of 30 Amps. NEC formula would put this at 50 Amps, but it could be scaled back to 40. The controller manual should also recommend a wire size, in this case probably 10 AWG minimum or more likely 8 AWG.

The heaviest current will be from the Batteries to Inverter, because as I mentioned before it is capable of 100 Amp draw. This is the place to put your 75 Amp breaker, although that will limit your inverter to around 900 Watts (@ 12 Volts) max. More current and the breaker will trip. This is not necessarily a bad thing. But do always use wire size capable of handling more current than the fuse/breaker on the line: the basic idea is that the circuit protection is the weakest point current-wise and will give up before anything else does should something go wrong. That way the failure will be controlled and not left to some random section of wire burning up.

(Not too sure I covered everything in this post as I suddenly was "off-line" due to the on-going snow storm and only had some of the content "auto-saved". :roll )

Re: 24V Pannel with 12V system wire size???

We have a whole section here full of information/sources: http://forum.solar-electric.com/forumdisplay.php?14-Solar-Information-links-amp-sources-event-announcements

You might particularly want to look at the thread about battery system Voltages and equivalent power.

It will be a while before our British Columbia snow storm reaches La Belle Provence!

Re: 24V Pannel with 12V system wire size???

They're both 15 Amp panels so on a 12 Volt system that one 230 Watt panel could max out either.
The Blue Sky you may find has some weird limits on it like "if either the system Voltage or the panel Voltage is over 'X" output is limited to 'Y'".
My choice would be the simple Morningstar 15 MPPT. It's also slightly cheaper.

Probably the best would be the new Rogue 3024, but as far as I know it's not available yet.