Wiring up a basic solar system

[bcripps]

I've got a typical small boat electrical system: two 85amp batteries charged from the engine's alternator and connected to the boat's distribution panel through a battery switch. Battery1-Battery 2- Both- Off.

Someone gave me a 50W panel. How do I wire this up with a controller? (I have a MPPT controller on order), I want to charger both batteries. I know I need a fuse on a battery post to protect against a dead short across the terminals. And what part does the battery switch play in all this? Do I have to leave it in the “Both” position? And what happens if it is accidentally switched to another position?

I don't see much info on a basic small boat system and would appreciate help getting it right from the start.

Thanks all...
Bry

[jeepbluetj]

There are lots of ways to do this.

Simple:
I assume you have some sort of fuse panel?

Wire the panel to the controller. Wire the controller to a fuse/breaker in your panel. This breaker/fuse satisfies the fusing requirements (assuming that the batteries are wired to the A/B switch and panel correctly)

Solar now charges whatever you have the battery switch set to. Keep them both at the same charge point and keep the switch on both. Or use only one of the batts, keep the switch on that one.

[Stu Jackson]

You might also want to learn more about how & why 1-2-B switches work:

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings | SailboatOwners.com Forums

What are ACRs, Combiners & Echo Chargers? (by Maine Sail)
Battery Switch Question ? | SailboatOwners.com Forums

[bcripps]

Thanks guys. This is exactly what I needed.
Bry

[bcripps]

jeepbluetj:

I was re-reading Calder's book last night, about Solar. He doesn't provide much information on the subject but one point stood out... a fuse should be wired as close to the battery post as possible to prevent a dead short across the batteries. Wiring to a panel breaker in my boat adds considerably more unprotected wire to the circuit.

I love the simplicity of your solution but is there a way of doing it, keeping the fuse on a battery post. My objective is to charge both batteries, but once again, I'm not sure how this affects operation of the 1-2-Both-Off switch.

Thanks again for your advice,
Bry

[barnakiel]

If the 1/2/both/off switch is wired onto batts positives, then you simply connect the solar regualtor out onto any of the batteries. In the both position you will be charging both, in any other position you will be charging only the bat that has the sol reg connected.

This is likely the simplest but not always the simplest is the best.

---
e.g.

I our boat (one bank for starter, separate house bank):
- NO 1/2/both/off switch,
- relay from engine batt to house batt (charges house when the alt is running),
- sol reg neg wired to batt neg, pos wired with a (house/start) selector,

So we manually select which bank is being solar charged and both get charged from the engine as soon as the alt kicks in.

With no 1/2/both/off switch, we never fry the alt. If we were to jump start the engine, I keep a neatly coiled and tied down jump cable next to the batteries.

---

Your options are endless. See what you have, think what you want, adjust your set up. Done.

PS If your sol reg has two outs, you do not need a selector switch either.

b.

[jeepbluetj]

Originally Posted by bcripps

jeepbluetj:

I was re-reading Calder's book last night, about Solar. He doesn't provide much information on the subject but one point stood out... a fuse should be wired as close to the battery post as possible to prevent a dead short across the batteries. Wiring to a panel breaker in my boat adds considerably more unprotected wire to the circuit.

I love the simplicity of your solution but is there a way of doing it, keeping the fuse on a battery post. My objective is to charge both batteries, but once again, I'm not sure how this affects operation of the 1-2-Both-Off switch.

Thanks again for your advice,
Bry

The argument about unfused wiring between the panel and the batteries applies to everything on the panel. Nav lights, waterpump, whatever. You should have a fuse on the batteries that fuses the wiring between the batteries -> A/B switch -> panel.

Lots of boats don't. But that doesn't make the wiring the solar into the panel a bad idea. Just means you need to fuse each battery with a ANL or MRBF fuse rated for the wire sizes you have.

Stu's links are all really good.

I'm in the camp of "Main" and "reserve" battery banks. For my little boat I have 2 CG6's as the "Main" bank (A on the switch) and a dinky little G24 as the "reserve" bank. Since I'm on shorepower 90% of the time the chargers keep both banks up fine. My A/B switch is always on A unless I kill the main bank. Solar feeds the panel, which always feeds the A bank. When I'm at the islands, I do run the fridge which is a pretty sizable load. 160W of solar keeps up mostly, but it is pretty sunny in socal.

Bry: since you have two smallish batteries I'd recommend always leaving the switch on "both" and treating it as a single 170 AH bank. Maybe have a portable jumpstarter around to save your butt if you kill the main bank (or be careful).

85AH per batt is pretty small. But you didn't mention the loads. You did say in another post that your engine is a 15hp, so I'm not envisioning a 50 foot boat here.

[bcripps]

Lot of good stuff here, thank you...

The boat is a 34 and very basic. At anchor (all the time), I pretty much use only a cabin light or two (LEDs), anchor light, and maybe play the car stereo. No refrigeration or fancy stuff. Underway there is the GPS and AutoHelm but I usually have the engine ticking over.

The battery switch is wired to the positive battery leads. And there is a fuse wired next to the switch for the supply to the breaker panel inside the boat.

My thought (maybe wrong), was to wire the positive lead from the Solar Controller (10 amp), to the positive post on one battery using a post-mounted fuse (15 amp), and the negative lead to the negative post on the opposite battery. I figured that would charge both batteries.

But I was wondering if the whole thing would short out if I changed the position of the Battery Switch from All to 1 or 2.

Am I out to lunch here?
Again, thank you,
Bry

[newhaul]

You need a way to isolate the panels from the controller via a properly rated breaker or switch.
If you ever disconnect the battery side of the solar charging circuit without disconnecting the solar panels first you will likely damage the charge controller. ( Calder doesn't mention much about DOD due to the technology being in its infancy when the book was written )

[jeepbluetj]

Originally Posted by bcripps

My thought (maybe wrong), was to wire the positive lead from the Solar Controller (10 amp), to the positive post on one battery using a post-mounted fuse (15 amp), and the negative lead to the negative post on the opposite battery. I figured that would charge both batteries.

But I was wondering if the whole thing would short out if I changed the position of the Battery Switch from All to 1 or 2.

Am I out to lunch here?
Again, thank you,
Bry

Your initial thought of Pos to #1 batt and Neg to #2 batt will not cause both batts to be charged. Really doesn't matter where you hook neg up - it's all connected together.

If you DO connect the solar controller to batt #1 pos, you will have:
1/2/B switch OFF: Solar charges batt #1
1/2/B switch 1: Solar charges batt #1, loads on batt #1
1/2/B switch 2: Solar charges batt #1, loads on batt #2
1/2/B switch B: Solar charges batt #1 and #2, loads on batt #1 and #2

So that's not doing what you want. If you want to charge both but only draw on one, you need an ACR (combining relay). Look thru stu's links to understand what that is and what it does.

[bcripps]

Ok... I'm out to lunch. No surprise there.

But I think I know what I'm doing now so thanks everyone for the solid information. I need to go through things carefully and then proceed. Anyway, everything is fused so there shouldn't be any smelly wires.

My MPPT controller and all the bits: wire, clips, connectors, are in shipment and I'm looking forward to the project. I'll certainly be back here it a question arises.

Thanks so much for all the help...
Bry

[Notus]

Good primer.