Wiring underway (At last!)

Macboy

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Aug 8, 2014
254
Macgregor 26S Sherwood Park, Alberta
I finally did it. I found time to tear into the Mac and address the wiring so I can add the little creature comforts for my wife and kids (reading lamps, USB charge ports) and relocate the batteries to the V-berth.

My question is regarding the solar panels. I have four 40 watt panels for now that I will connect to a Victron Blue Solar MPPT 75 | 15 charge controller. My question is this - how do I gang the four positives and four negatives off the panels into the charge controller, how close should the controller be to either the batteries or the panels and do I use the panel specs in determining wire gauge (multiplied by four)?

The panel specs are:
  • Maximum power output: 40 Watts and 2.3 Amps under ideal conditions
The controller specs say max battery current 15a, max of power 200w

I have two spare buss bars I could combine the positives and negatives off the panels to. Then it’s just a matter of the wire run either up to the controller near the batteries or from the controller near the panels and then up to the batteries.
 
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Macboy

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Aug 8, 2014
254
Macgregor 26S Sherwood Park, Alberta
I was just continuing my reading on this and the controller says it operates more efficiently at higher voltages so perhaps I want to wire them up paired in series to get to 24v X 2 and then wire those in parallel to the controller?
 

Macboy

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Aug 8, 2014
254
Macgregor 26S Sherwood Park, Alberta
I'm getting myself all confused. If I take the solar out of the mix I get it (I think) but with the charge controller in play does that mean all loads go through the controller? Meaning I take the pos/neg out of the controller "loads" output to my neg bus bar and positive fuse terminal block? But then what about the motor? It serves double duty as a battery charger (connec direct to batteries) AND a load (starter) - connect to the bus bar/fuse terminal. What's the proper way to wire the motor into the system?
 

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Jun 14, 2010
2,081
Robertson & Caine 2017 Leopard 40 CT
@Macboy Don't be confused by the load control feature of your Victron controller. It's use is optional -- its purpose is to allow you to connect an always-on load such as a refrigerator or marker light, and to cut off power to that device if it threatens to drain your batteries flat (to avoid battery damage).
Leave everything else connected as-is to your house and/or starting battery.
Your second post is on target, but keep in mind that if one panel in a series-pair is shaded, it behaves as if they are both shaded. Combining two in series will raise voltage in the wires to reduce voltage drop (loss) in the wires (think of it like a water hose; more voltage = more pressure) and enable the MPPT controller to be more efficient. Putting them all in parallel will make your overall system more tolerant of partial shade, but be less efficient in evenly lighted situations.
As for your engine alternator -- that is also connected to the battery in parallel to the Victron charge controller. They will each read the battery voltage and regulate power independently as needed, according to the programmed settings.
As for wire gauge -- the reason for bigger/thicker wires (lower AWG numbers) is to reduce voltage drop over distance. The minimum size you can use is determined by the amp capacity, but the reason for going larger is efficiency. (Again, think of the water hose analogy -- a wider hose has less internal resistance and can move a given volume of water more easily under a given pressure). There are tables online you can search for (search for "voltage drop wire size table"). The practical limit is cost, ease of routing, and connection size - I would advise you to stay with AWG#10 or 12 for long runs, with #14 or #16 only if for short runs (smaller AWG number is larger wire diameter).
Hope this helps.
 
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Macboy

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Aug 8, 2014
254
Macgregor 26S Sherwood Park, Alberta
Thanks Capt Larry. At what point do I pull the power for the house loads if I'm not using the load output on the controller? The PO wiring pulled all house loads from a dedicated pos and neg off of the battery posts each to their own bus/fuse block. Should I do the same?

I should ask also about the 2-way switch (which I'll just be using as a cutoff, only wired on one side). Where should that insert into the system? Is it to cut off the house loads or the whole system?
 
Jun 14, 2010
2,081
Robertson & Caine 2017 Leopard 40 CT
I didn’t realize that you were starting from scratch. :(
I think you should follow ABYC standards and find a book or online source about basic boat wiring. I don’t think I’m the best person to assist you further.
 

Macboy

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Aug 8, 2014
254
Macgregor 26S Sherwood Park, Alberta
Not starting from scratch, just relocating and adding. So kinda from scratch in that it's all getting disconnected and reconnected ; )