Basic Solar Wiring - 1 2 Both Switch

[SV Second Wind]

Hi All,

I believe I have wired my new solar setup correctly, but would appreciate bouncing this off the very informative community here

I wired my MPPT positive battery output to the common on the 1 2 Both switch; attached negative to the neg terminal on battery 1 (batteries are connected in parallel)

Since I have not wired the positive output from the MPPT directly to the battery, where do I place the fuse to protect the circuit incase the batteries decide to short circuit? Do I need to place a fuse on each positive battery wire running to the 1 2 Both switch?

Set up:
- Victron BlueSolar MPPT 100/15
- Renogy 50 Watt Mono Panel
- Two deep cycle batteries wired in parallel on a 1 2 both switch

Thank you all for the help!

Brad

[masonc]

Originally Posted by oivivio

Hi All,

where do I place the fuse to protect the circuit in case the batteries decide to short circuit?

You fuse the wiring as close to the power source as possible. One thing people forget with solar, the solar resource is a power limited device, which means that if the wiring is rated for the maximum deliverable current, fusing is pointless as the wire can sustain the short circuit current without issue. that's why we don't fuse single arrays of solar panels.
Your fault current source is the batteries, even though you are sending current to them. In the event of a short, current will flow from the batteries to the short.
You need fusing rated for the wiring of the charge controller, at the battery end of the wire. For a 15A controller, you would use #12 AWG wire and 20A fuse to cover derate for continuous use. The #12 wire is protected by the 20A fuse from overcurrent in the event of a wiring or MTTP controller short circuit.

Chris Mason
NABCEP certified PV installer
Comet Solar
Anguilla

[skipmac]

Yes. What Chris said covers the issue perfectly.

[Capt.Don]

My controller's installation manual made the point to connect the controller to the battery first and then connect the solar panels. I'm concerned if you set your 1/2/Both switch to OFF AND there's current from the panel(s), you could damage your controller. Hopefully one of the experts can confirm!
Don

[pesarsten]

That is an excellent point capt.Don. , I installed a Morningstar sun saver that required the battery connection first, charge controller did not function if solar in power was present before battery voltage. Most battery switches disconnect when switched.

I am interested in the solution. I believe most here have reccomended wiring direct to house bank.

[SV Second Wind]

Thank you Chris for the great feedback!

That is a good call Capt.Don. I left the panel disconnected before I left the boat as to keep solar power from coming into the system. How should I go about wiring directly to the batteries when a 1 2 Both switch is involved? Seems if I wire the charge controller to battery 1, I would get the following scenarios:

1 2 Both switch in the '1' position = Battery 1 to be charged
1 2 Both switch in the 'Both' position = Battery 1 & 2 to be charged
1 2 Both switch in the '2' position = Nothing charges? Could this be damaging to the controller?

How should I wire to ensure both batteries charge regardless of the 1 2 Both switch position? (I believe this would require an automatic charge relay?)

Thanks for all the help!

[skipmac]

My preferred wiring is to send all charging sources: solar, alternator, charger and wind, to one common busbar and from there to a fused connection on the house battery bank.

I had to modify that slightly on my current boat as my charger is a combination inverter/charger which can charge up to 70 amps OR draw up a 200 amps from the same cables. Since that far exceeds the capacity of the wiring to all the other charging sources I ran that to it's own higher fused connection.

[Capt.Don]

If you connect the solar to the house, you can always put the 1/2/Both switch in Both, to charge both batteries.

[Cadence]

Charge to the battery side. The 1/2 both is for draw not charge.

[skipmac]

Originally Posted by Capt.Don

If you connect the solar to the house, you can always put the 1/2/Both switch in Both, to charge both batteries.

This is the easiest, simplest and cheapest way to go BUT if you forget just once to switch away from Both when anchored it is also simple and easy to run down the starting battery.

Three guesses how I know this.

The ideal is to charge the house batteries and have an automatic battery combiner that connects the starting battery (like the Both switch) to the system but only when there is charging voltage in the system.

[knockabout]

solar regulator between panels and house batteries / battery selector switch controls draw from your house batteries


without a regulator you may overcharge your batteries especially on 1 battery setting

[SV Second Wind]

Thank you all for the suggestions! So the easiest approach would be to connect solar controller directly to House (Battery 1). Then I would receive the following?

1 2 Both switch in the 'OFF' position = Charge on House (Battery 1); no load on either batteries
1 2 Both switch in the '1' position = Charge & load both on House (Battery 1)
1 2 Both switch in the 'BOTH' position = Charge & load both on House & Starter (Battery 1 & 2)
1 2 Both switch in the '2' position = No charge from solar BUT if engine is on, Starter (Battery 2) will receive charge from alternator; load on Starter (Battery 2)

- If I am not on the boat all week, keep switch to 'BOTH' to ensure House and Starter batteries remain topped off?

- If I am at anchor and using electronics, always flip just to House battery. I can start the engine from the Starter battery (Battery 2) the next morning. What happens if it is extremely cloudy the next day and I would like to recharge the House by running the engine? Since batteries are in parallel and I flip to BOTH, the House battery would begin to pull energy from the Starter battery?

Sorry for so many questions. I greatly appreciate the help!

Brad

[ramblinrod]

Originally Posted by oivivio

Thank you all for the suggestions! So the easiest approach would be to connect solar controller directly to House (Battery 1). Then I would receive the following?

1 2 Both switch in the 'OFF' position = Charge on House (Battery 1); no load on either batteries
1 2 Both switch in the '1' position = Charge & load both on House (Battery 1)
1 2 Both switch in the 'BOTH' position = Charge & load both on House & Starter (Battery 1 & 2)
1 2 Both switch in the '2' position = No charge from solar BUT if engine is on, Starter (Battery 2) will receive charge from alternator; load on Starter (Battery 2)

- If I am not on the boat all week, keep switch to 'BOTH' to ensure House and Starter batteries remain topped off?

- If I am at anchor and using electronics, always flip just to House battery. I can start the engine from the Starter battery (Battery 2) the next morning. What happens if it is extremely cloudy the next day and I would like to recharge the House by running the engine? Since batteries are in parallel and I flip to BOTH, the House battery would begin to pull energy from the Starter battery?

Sorry for so many questions. I greatly appreciate the help!

Brad

All is correct except part about charging from engine. If on both and loads are less than charging current batteries will be charged. If loads exceed alternator charge current, all batteries will be drained (reduce loads). Just remember when you turn off the engine to switch back to 1.

[skipmac]

One or two suggestions for the "easiest" but not necessarily the best option.

Originally Posted by oivivio

Thank you all for the suggestions! So the easiest approach would be to connect solar controller directly to House (Battery 1).

Yes

Then I would receive the following?

1 2 Both switch in the 'OFF' position = Charge on House (Battery 1); no load on either batteries

Correct

1 2 Both switch in the '1' position = Charge & load both on House (Battery 1)

Correct again

1 2 Both switch in the 'BOTH' position = Charge & load both on House & Starter (Battery 1 & 2)

Yes but as noted above, if you're on the boat and using battery power, forget to switch to 1 and you could easily drain the starting battery and have no way to crank the engine. Lots of people wire this way and 99% of them at one time or another forget and drain the start battery. If you're close to home and have towing insurance then call for a jump. If you're a long way from home you could be SOL.

1 2 Both switch in the '2' position = No charge from solar BUT if engine is on, Starter (Battery 2) will receive charge from alternator; load on Starter (Battery 2)

Yes, IF you have the alternator output wired to the start battery but why would you do this? Starting the engine uses a very, very small bit of the charge from your start battery. Running lights, plotter and other electronics, AP and other house battery loads use a LOT of power from the battery. Of course you want to keep the start battery charged but it only needs a small top off but the house batteries need lots of recharging. Connect ALL charging sources directly to the house batteries and use the 1 2 Both switch or much much better, use an automatic combiner to charge the start battery automatically anytime the engine runs or solar has output. Then the start battery is automatically and safely isolated when you turn off the engine and will then be fully charged when you need to start the engine.

- If I am not on the boat all week, keep switch to 'BOTH' to ensure House and Starter batteries remain topped off?

Yes, unless you install the auto combiner. Just make sure you turn off all lights and loads before you leave the boat or once again you risk coming back to a dead start battery.

- If I am at anchor and using electronics, always flip just to House battery. I can start the engine from the Starter battery (Battery 2) the next morning.

With a combiner you don't have to deal with this. Just always keep the house batteries connected to the house loads and the starting battery always isolated and protected unless you are charging which happens automatically.

What happens if it is extremely cloudy the next day and I would like to recharge the House by running the engine?

Connect the alternator to the house batteries.

Since batteries are in parallel and I flip to BOTH, the House battery would begin to pull energy from the Starter battery?

Not if the engine is running and the alternator is charging. Both batteries would be getting charge. If your house batteries are very low they could drain the start battery so don't switch to both until the engine is running. CAUTION!! Make sure your battery switch is make before break. That means one battery is always connected when switching from 1 to 2 to Both or any combination except OFF. Disconnecting the battery with the engine running can blow the alternator.

Sorry for so many questions. I greatly appreciate the help!

Brad

[skipmac]

Here are some auto battery combiners.

Catalog Frame

http://www.xantrex.com/documents/Acc...204-01-01).pdf