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Solar Charging Lithium Batteries


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Hello, I’ll make my long story of my first world problem as short as possible…and Thanks in advance for any advice or guidance members of the community will share.

I have a little fishing boat and a 24v trolling motor. My research is telling me to make the investment in lithium batteries.

My issue is that I have no electric at the dock and need to create a solar solution to charge the batteries. The batteries I’m planning on purchasing are 12v 80 or 100amp…haven’t decided on what size yet. The batteries will be wired in “Series” per the manufacturer. The trolling motor has an 80 lb thrust and max amp draw of 56.

The boat will only be used on the weekends and the dock has full access to sun, so solar charging will not be an issue. My questions are as follows:

Can I use a single solar panel to charge both batteries at the same time? The batteries are wired in Series…will it harm the batteries to charge them in this fashion?

What size solar panel will I need? 50w? 100 w? 200w?…I have no idea

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35 minutes ago, halenajulie said:

The boat will only be used on the weekends and the dock has full access to sun, so solar charging will not be an issue.

I'd seriously consider staying with lead acid batteries for this application... Li Ion's advantage is size and weight, neither of which are especially problematic for a small boat (ballast is good, right?).

Since your boat will sit all week, the battery system will be on 'float' charge for extended periods of time unless you have a charge control system to turn the charger off when the battery is topped up. Time spent at full charge is time that reduces the lifespan of a Li Ion battery, but doesn't bother lead-acid.

As a bonus, off the shelf solar charging systems are quite common for 12V lead acid batteries. You should be able to purchase a system that's ready to go—Li Ion charging systems might be a bit more difficult to source. Check into the off-grid RV sites, they'll have a load of information and sources for 12V systems.

35 minutes ago, halenajulie said:

What size solar panel will I need? 50w? 100 w? 200w?

That depends on how quickly you need to charge. If you use the whole battery on Saturday, you'll get a late start Sunday if you can't charge quickly enough. A larger panel will allow you to charge more quickly, but you may not be able to do a complete charge when the sun isn't 'strong'. More is generally better, but more also means bigger and more expensive! If you stay with lead-acid, you can leave 1 set of batteries on shore charging while you're punting about on Saturday... they'll be all set for you on Sunday. Size your panel so that it'll charge your batteries in 1 day. Car batteries aren't cheap, but they are quite a bit less expensive than similar capacity Li Ion.

Edited by Tawpie
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