Adding a 2nd battery and 50w solar system

[thomm225]

Originally Posted by Aviationcanada

Thank you all for helping me out on this issue and accepted me out on this forum! ��....
Here is enclosed my short electrical circuit...(actual, and what i want)....

I understand, my battery is more than enough to start and day sail cruise with my actual setup! But i'm planning on spending few nights on boat with kids, which will require more electrons available for lights, and ipad/iphone recharge!!!

This is why i want add a second deep charge battery, hooked up to a (what i think)!!! 50w solar panel!....
But i see now how I can plug both batteries in parallel....hooked up to a solar and is controler! But i read somewhere that i might need a switch to kill the power coming from alternator (when engine running) to protect solar panel?? Or is MPPT will be enough to protect the system?...

Multiple charging sources are fine.

The MPPT Controller will "protect" the batteries from being overcharged by the solar panel.

The alternator will charge them when the engine is on until it's regulator stops the charge

Also the MPPT Controller is between the batteries and the solar panels. The alternator will have no effect on the panels since it is hooked to the batteries

I knew a guy once that hooked up a solar panel to his car battery when he planned to be away for months then left it hooked up after starting the engine with no problem from the alternator.

[Aviationcanada]

Ok thomm....i was not sure about this....thanks a lot...����

[thomm225]

Originally Posted by Aviationcanada

Ok thomm....i was not sure about this....thanks a lot...����

Btw, I have three charging sources for my batteries.

One from two solar panels (65 watt on aft lazarette and 20 watt on cockpit lazarette post #10) thru a Victron 75/15 MPPT Controller defaulted at 13.8 volts Float Setting

Another from a 50 watt panel thru a PWM controller set at 14 volts Float Setting. (when out sailing) Tied to stern railing in post #10.

And sometimes a third from a 20 watt panel hooked straight to the two 12 volt batteries in parallel directly with no controller. (when voltage is low in the am and the batteries need extra charging at anchor or sailing early)

[ramblinrod]

Originally Posted by Aviationcanada

Good day,
Just bought a 1985 KELT 7.6 sailboat (25feet day sailor), and this vessel only have a single battery for start (outboard honda 9.9 with alternator) and accessories (autopilot, few LED's lights, deph sounder and VHF).
PROBLEM, sailboat stays at moorage the all season (only way to recharge that battery is to park few hours at shore or when engine runs!).
SO...i want add a second battery and a 50W solar panel...but i have no idea how to plug everything all together!!!
I know that I will need a panel, MPPT, 3 ways battery switch....
BUT any help with wiring, diagram or so ???
Thanks in advance....

Congrats on the vessel purchase.

Sometimes what forum members may recommend for bigger live-aboard cruising boats, doesn't work well for smaller weekend day sailors.

The first thing we need to know is your use case.

So your vessel sits on a mooring (no shore power).

How much do you intend to use the boat?

If you sail it all day, every day of the weekend, your energy requirements will be much greater than if you go for a 3 hour day sail every other week.

If we assume 3 hour daysail every other week, what you have is fine, add a 50 W panel, cheap PWM controller, and the sun will replenish what you use for your odd day sail, no problem.

If we assume sailing for a 2 day weekend (Sat and Sun) every week from May to October, that's a different story.

You daily consumption will likely be < 20 A-hrs. So for a 2 day weekend, 40 A-hrs total.

So if you had a 12 Vdc 100 A-hr DC battery, that would be more than enough.

If you have a 50 W panel and cheap PWM controller, you will produce about 15 A-hrs every sunny day, or 10 A-hrs on avg. day.

So on your weekend, your net loss is about 20 A-hrs total, for an 80% SOC, and return to 100% SOC by Tuesday, most weeks.

At this rate, your single cheap 12 Vdc DC27 East Penn (Deka Marine) battery should last 8-10 years (as long as you keep it on float over winter).

Frankly, you will likely sell the boat, because you don't use it, or you do use it and you want something different, within about 6 years, so buying more expensive batteries simply isn't worth it; no payback.

I would not recommend going golf cart batteries.

First, you would have to install two in series.

This would give you about 225 A-hrs of capacity.

Way more than needed, and your batteries won't likely last any longer.

Even your little outboard alternator wouldn't be able to deliver full output, as the batteries would usually be at 90%+ and only capable of drawing a few amps.

Even though you have spent more than necessary on two batteries, if one goes bad, your house bank is completely gone until it is replaced.

If you increased your loads and wanted ~ 200 A-hrs capacity, then I recommend 2 x Grp 27s. Then if one goes bad, you still have a 12 Vdc 100 A-hr house bank until you replace the bad one (or both if old).

The other reason for not going 6 Vdc golf car batteries is that if you wish to increase capacity, you are forced to do so in 2 battery increments, instead of just one, if you use 12 Vdc Grp 27s.

We normally consider a 4 x 6Vdc golf car battery bank (2S2P), if the daily A-hr consumption is ~100 A-hrs. Even still, if the one battery goes down, you loose 2. 6 vdc golf car batteries really shine at 2S3P, for a ~150A-hr per day consumption.

For you weekend only consumption, and all week solar replenishment, I would recommend a 50W panel and cheap PWM controller. If you find this doesn't quire do it for you, then add a second 50 W panel. (You will be far better off with 2 x 50W and PWM, than you will be with 1 x 50W and MPPT, both scenarios being about the same money.

[JimsCAL]

I would just add the solar panel and controller. You really don't need a second battery. No need to worry about running both the engine alternator and solar at the same time. I do it all the time.

[Aviationcanada]

Thanks again for all of your replies...
I tried to keep the best for what i might need from your recommandations and here is a draw of what i think should work for a cheap cost!!!
BUT is it ok to plug a 2 way switch on “PLUS” side (between MPPT and batteries)?? In this case, i will be able to choose witch battery i want solar recharge (either 1, 2, or both). If ok to plug “plus” side this way, is it fine to hook up both batteries together on “negative” born? (To close the loop!)...
I didn t draw yet fuses and battery monitor.
I hope to get close to what i think will be my best option for this vessel 😒.

Magenta is the plan!
Red and black...actual wiring.
Thanks again...
Franck