RV system - type and location of combiner box?
vsheetz
Registered Users Posts: 18 ✭✭
On a previous motorhome I installed six 100w panels on the roof - all in parallel wired to a roof mounted combiner / junction box, and from the combiner box ran a large gauge wire down to a Morningstar PWM solar charge controller.
Now have a different motorhome and looking to install a new, and larger, system consisting of sixteen 100w panels and a MidNite Solar Classic 150 controller. I am thinking of having the panels in 4 strings.
The question: Whether to do a roof mounted combiner box setup similar to my previous motorhome *or* to run multiple smaller (#10) wires from each string to a combiner box with 4 DC breakers located near the solar charge controller near the battery bank. The wire run from the roof would be approximately 30-35' long.
Suggestions? Pros/cons? Is #10 wire size ok?
thx!
Vince
Now have a different motorhome and looking to install a new, and larger, system consisting of sixteen 100w panels and a MidNite Solar Classic 150 controller. I am thinking of having the panels in 4 strings.
The question: Whether to do a roof mounted combiner box setup similar to my previous motorhome *or* to run multiple smaller (#10) wires from each string to a combiner box with 4 DC breakers located near the solar charge controller near the battery bank. The wire run from the roof would be approximately 30-35' long.
Suggestions? Pros/cons? Is #10 wire size ok?
thx!
Vince
Comments
What size battery bank (voltage and AH rating)?
-Bill
Even if I were using larger > 200w panels, the question of the combiner box type and location remains the same.
thx
Vince
The actual wiring, number of circuits, awg, etc. depends on how you series/parallel connect the panels. For a 12 volt battery bank, 2-3 of your 100 Watt (Vmp~18 volts) in series, then combine those in parallel (at the box) will be more efficient for your Classic.
You can run your panels in series up to Vmp-array~100 VDC (check Classic String Controller, your local temperature to be sure) if it makes wiring better for you (classic will run a bit hotter, higher voltages into MPPT controller has more losses).
If you have 6 panels, and they are Vmp~18 volts--Your ideal mix would be 3s x 2p or 2s x 3p. The advantage of 3s x 2p is that you really do not need a combiner box... For three (barely) and more parallel strings, you need the combiner box to reduce the chances of fire if one panel is shorted and fed by the other parallel strings.
Many people still like a switch (on combined strings) to turn off the controller for service. Or you still put a 2x combiner box with breakers in so you can turn off one string and see if it is carrying is share of current (easier/quicker debugging).
To get exact answers, need to know the Vmp/Imp of the panels and how many you will use. Note that >200 Watt panels (Vmp~30 volts) are cheaper (about 1/2 the price) of typical 1xx watt panels. And less wiring too.
But you have to make do with the space and hardware available.
-Bill
Thanks
Vince
The Classic does have fans which can be noisy... Need to place near battery bank (short/heavy battery leads to low voltage drop) and good airflow. Having it near your work space (for example) in the RV may be distracting from the fans running during the day.
That is a good size array for a 12 volt battery bank(?). What AH rating will it be?
-Bill
The 4x4 configuration I agree, will provide for wiring ease and economy allowing #10 runs from the roof to the combiner box / breaker box, and fit within the capacity parameters of the classic 150. As well as some shade mitigation. The controller and combiner box with breakers will be located adjacent to the battery bank - with 2/0 as the wiring there.
Good to note about the fan noise of the classic 150 - it will be located below in a storage bay where I don't anticipate this to be a problem.
Thanks for the help,
Vince
Trojan L16RE-2V 1110 AH 2-Volt Deep Cycle Battery $353.00 each
Trojan, as I understand, actually has three cells (three caps) in parallel--Not ideal (I would prefer one cell)--But to give you an idea. 6 of these batteries in series would be your bank (and like 5x parallel 6 volt GT batteries. (note: weight of lead will be about the same--no matter the configuration--I.e. a 12 volt @ 1,200 AH battery weighs about same if a bunch of small GC batteries or single string of large AH batteries).
The next question I would ask you--At that size of battery bank, I would be suggesting a 24 volt (or 48 volt) battery bank. Fewer parallel battery strings and smaller awg wiring (24 volts is 1/2 the current; 48 volts is 1/4 the current of a 12 volt battery bank). More or less, I would suggest any battery bank >800 AH should look at the next higher voltage battery bus (12 volts @ 800 AH to 24 volts @ 400 AH--as an example).
And with that much weight--Perhaps look at LiFePO4 (version of Li Ion chemistry). Smaller and lighter weight.
-Bill