Solar Panel set-up

[Shaun]

G'day,

Any battery on my boat seems to have a certain death sentence, with a life expectancy of about 12 months….
I have decided to install a dual battery system on Blue Moon (that’s on a mooring), charged from a 20watt solar panel & the alternator on the inboard diesel, I would like what is probably the standard set-up where the starting battery is charged first from either the SP or engine, then once fully charged the house battery can then be charged.

Sketch of possible solar panel set-up

solarsk.jpg (43.85 KiB) Viewed 5286 times

It would not be good to accidently run down the start battery while using the autopilot etc, so would need to keep the batteries separated.
Currently we have a good starting battery & am looking at buying a 12v AGM battery around the 100a/h for the house battery.
Do I need a diode or something in the system, or does the regulator do that?
For a dual battery set-up do you need a special component &/or a dial like a 1, 2, 1 & 2 or Off switch?
Any recommendations for good panels, batteries, regulators?

Any suggestions on a solar panel set-up & what else am I forgetting?
Cheers
Shaun

[lockie]

Shaun;

You will definitely need a battery switch so you can select A, B, A+B, or isolate both. Leaving aside the solar panel for now, normal operation would be to select your designated start battery and start the engine, and then leave this battery selected for a while, so the alternator can replace the charge you've just used in starting. After a while (ten minutes would be plenty if the battery started off with a full charge), you select the other (house) battery, so it can also get some charge while the engine is running, and so it can supply the "house" loads after you stop the engine.

You can also leave the switch in "A+B" position while the engine is running so the alternator can give both batteries some charge, but never select A+B while the engine is stoppped, as the battery with the higher charge will discharge into the other (which might flatten both if one is crook). The only exception would be for emergency starting where both are run down, and you might need their combined strength to get the engine started. What I've just described is the "default" set-up on most yachts.

Now if you have one solar panel, you'll need to choose which battery it charges, via a plug/socket or switch. Or you could buy a dual regulator which will charge the starting battery first, and then the other one. If your panel is over about 20 watts, you'll have to connect it via a solar regulator to avoid over-charging. This could be a simple one to charge one battery, or a fancy dual one with a display.
I use a 20W panel for the house battery and a little 5W panel for the start battery. Bear in mind that if you only use the start battery for starting, you will only draw a small charge from it, since it is only used for one or two seconds at a time. This charge is then quickly replaced from the alternator, so a small solar panel will suffice just to keep it from self-discharging between uses (assuming we are starting with a fully-charge battery).

This is a very simple summary, and there's a lot to know, so you've got a lot of reading to do. You can glean a lot from the internet, but I'd also suggest you buy a good book on marine electrics. Nigel Calder's books are well regarded.

lockie

[Dolphin]

G'Day Shaun,
that is a good rundown from Lockie.

One other thing to remember is that when the motor is running and the alternator is charging NEVER switch the battery through the OFF position. The open circuit alternator voltage will exceed the Back EMF voltage of the main diodes and short them out.
I use 2 x 2amp diodes that separate the solar panel to charge both batteries. The only drawback is that if I have one weak battery it will take all the charge and the other battery will slowly discharge as well. Thus I have two dead batteries. I don't use a regulator. The solar panels will only give you 6 hours peak output per day. While ever there is light it will be charging.
It would be interesting to see what is in the regulator to see how it works. Does anyone know?
When I had the BMW engine it didn't have an alternator and the panel used to recharge the battery enough to use it every week. Although the engine did have a crank handle!
Batteries now don't seem to come with the Amp Hour (Ah) rating on them rather its just the Cold Cranking Amps (CCA) rating. In the Inox battery conditioner instructions it estimates the Ah by stating that its 6 or 7 CCA per Ah. Thus 420 CCA = 70Ah (Using a factor of 6, or 60Ah using a factor of 7).
I just checked my charging voltage and its 14.5V.

Greg.
Usual disclaimer, take free advise for what its worth!

[Phillip]

Hi All,

The post so far are ok if its weekend sailing but for cruising it won't work. Just not enough capacity.

I will have to investigate this when I get back home as I am sure there is a solution.

Phillip
MacKay Marina.

[Dolphin]

Does anyone have a wind driven generator or any experience with them?

[Phillip]

Greg,

Sailors I have spoken to, who have a wind generator say,

"Well we do tend to anchor in sheltered places out of the wind"
and
"It's apparent wind when sailing and if going down wind that is usally B...... all"

Phillip
MacKay Marina.

[Shaun]

Thanks for the responses

Yes, it seems there is certainly more than one way to skin a cat, & I have been doing a lot of reading (also posted the same question on the trailersailerplace forum, they love discussing technical stuff), iniatially I thought about an automatic switch/relay to manage the dual battery system, but after doing some reading, including the above replies, & armed with a now dangerous amount of info ,I think I can be trusted to manually select which battery I want to be charged etc.

Good point about not leaving battery switch on A+B(with engine off), as one battery could drain the other.
Also good point about not going through OFF, I cant fore-see any scenario's (apart from disasters maybe) where I would want to use the OFF position anyway.??

To be able to select which battery the Solar Panel charges I would have to route the SP through battery switch first right? (is that possible?)

Or alternatively wire up SP(20 or 40w im thinking now) to B, & have smaller SP for A battery as lockie has done.
Still got heaps to think about....
cheers
Shaun

[Shaun]

This is what im thinking of installing, anyone see any problems?
cheers

solarsc1.jpg (50.6 KiB) Viewed 5185 times

[Dolphin]

Shaun, you should always leave your battery switch OFF when you leave the boat. If you don't the batteries can supply leakage currents that will erode (Corrode) some parts.
Can the MPPT (Is that the solar Panel regulator) operate with a diode in the output so that it can feed 2 batteries? It probably can't.
Greg

[Shaun]

Hi Greg,
So as ive shown the drawing, No batteries would be charged if OFF position.
I would have to wire the solar panel on the House battery side if I want it to be charged while not on board, but then start battery gets nothing!, but then I still have the leakage current problem anyway, how do you know if you have current leakage?
Currently I dont have any kind of battery switch onboard, except for the ignition key( if that counts).
So is the idea just to shut off the postive from the battery to the engine(as thats what is in connection to the water)?

Would a seperate one of these https://www.whitworths.com.au/main_item ... lutePage=2 to disconnect any connection to the engine work? (between the start battery & engine)

As far as i know the MPPT, solar regulator can only charge one battery/system.

cheers
shaun

Im sure i'll get there eventually....seems the more you learn the more complicated it gets, rather than being in ignorant bliss