Using Solar Panels to Recharge Boat Battery

[whitebassman]

I have a 24 volt system.

Living on a lake, my boat sits on the boat lift 99% of the time during the summer. So was thinking about running solar panels to recharge my trolling motor batteries rather then running 100 ft of extension cords from the house to the boat lift. (Which over that distance, using just regular orange extension cords, something tells me is prob not a good idea. Doesn't the voltage drop as distance increases? Prob need a heavier duty extension cord?)

So my question is how does the solar panel plug into the 24volt battery bank? I have a onboard charger.

So do I need to use an inverter to convert the solar output to 110v for the onboard charger, which then converts it to 24 volts? That sounds inefficient to me.

Or can I hook it up straight to the battery terminals, and how would I do that? With 24volts, I assume the two 12volt batteries are hooked in series.

I know a larger solar panel would be needed. I might start with 15 watt panel and add panels one by one, up to 45 watts, which should be more then sufficient. Not looking for a quick charge, but just would be nice to get a charge during the sunny days when I'm at work.

I'm not familiar with how the solar panels are rigged for connecting with the device to be charged.

[LightningBG]

I dont know how it would need to be hooked up, but there are solar charger controlers that will output 24v. might need to bypass your onboard charger all together.

seen some listed as...

15A 12V/24V/48V PWM Solar Charger Controller Intelligence PV Regulator LCD Display for Solar System

[marine_man]

No reason you couldn't charge at 12V either... just connect the individual leads to each battery.

marine_man

[delcecchi]

And the better chargers deal with voltage drop in the AC line input.

[CAMAN]

running 100 ft of extension cords from the house to the boat lift. (Which over that distance, using just regular orange extension cords, something tells me is prob not a good idea. Doesn't the voltage drop as distance increases? Prob need a heavier duty extension cord.

With a standard 14 gauge extension cord over the 100 foot distance, and the charger pulling a pretty standard 5 amps max, you are looking at approximately 2.5% voltage drop which is acceptible, 5% is normally the limit, granted you have 115-120 volts coming into the recepticle. If you are only getting 110 or so volts into the recepticle, you will be on the edge. Going below the 110 volt mark under load is what you want to avoid.

[gofishingtom]

going to need alot more then 45watts to recharge ur batteries at any rate if there low 15watt panel i believe is less then a trickle charger..now if u dont fish up there weeks at a time it might charge up..but i would check into it closer and i believe someone on here has done the math in the past on how much watts u would need to charge a deep cycle battery and i think u would be surprised and it cost over 1000$

[fivebucks]

I have just one panel and my batteries keep charged. BUT - it is usually a couple weeks between trips.

[et600]

I have had solar panels on my lift for 2 years now. I have a 15 watt 12 volt that charges and maintains my starting battery and lift motor battery, and a 24 volt 22 watt panel that I use for my 24 volt trolling motor system. I had 250 feet of dock and about 300 feet from there to power so panels were the way to go.

You can pick up good panels for $80 -90 bucks that will keep your batteries charged if you use them on the weekends and charge the rest of the time. I recommend controllers for them though as they keep the batteries from over charging and also have a maintenance mode. I can give you more specific info of you'd like.

As to hooking them up, on the 12 volt it is positive to positive and negative to negative. On the 24 volt, red goes to the first positive in the series, and black to the second battery in the series on the negative post. You can look at how they are wired for the trolling motor and match that with the wires from the panel.