diy solar

diy solar

Solar for Boat - 2 circuits one panel

ibikealot

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Joined
Apr 23, 2021
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I want to use one 100 watt panel and charge controller to charge my trolling motor battery and my starter battery. Can I use a switch (200 amp) to switch the connection to the charge controller from one battery to the other? They make these switches for people who use two batteries for a trolling motor so you can switch when one battery gets weak on a fishing trip. There is also a selection to have both batteries connected at once. What I would do is have both negative battery leads going to the charge controller and then the positive leads switched by the switch. Shouldn't that work.

Here is the switch: https://www.amazon.com/Ampper-1-2-B...ncoding=UTF8&refRID=H95BVCHKYJDA7NVF5XGN&th=1

Here is the solar panel kit that I bought: https://www.amazon.com/gp/product/B07VJFXBTT/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1
 
Not a good idea on some cheap charge controllers. You're cutting the charge controller off from the battery meaning it loses power while still attached to panels. If you disconnect the batteries while the panels are attached, SOME charge controllers may be damaged. I would be concerned that it applies to your particular controller.

If you go the route you propose, you should disconnect the panel from the controller before switching panels.

Personally, I'd prefer a set it and forget it solution:

Connect solar/charger to trolling battery.
Connect this between the trolling battery and starter battery:

Solar will charge and float the trolling battery.
Trolling battery will float the starter battery. Once the starter battery is full, it will only pull a few watts from the trolling/solar. If you're concerned about draining the trolling battery, you put a switch that disconnects the trolling battery to the converter.
 
Not a good idea on some cheap charge controllers. You're cutting the charge controller off from the battery meaning it loses power while still attached to panels. If you disconnect the batteries while the panels are attached, SOME charge controllers may be damaged. I would be concerned that it applies to your particular controller.

If you go the route you propose, you should disconnect the panel from the controller before switching panels.

Personally, I'd prefer a set it and forget it solution:

Connect solar/charger to trolling battery.
Connect this between the trolling battery and starter battery:

Solar will charge and float the trolling battery.
Trolling battery will float the starter battery. Once the starter battery is full, it will only pull a few watts from the trolling/solar. If you're concerned about draining the trolling battery, you put a switch that disconnects the trolling battery to the converter.
Which one would you recommend? 8-40V to 13.8V 10A? If it sat in trickle mode when both batteries are charged, they should be OK, right?
 
Another thought. When I am using the boat, the trolling motor battery will keep the starter battery at 13.8 V which is not necessary since when I run the boat that battery gets charged. Should I put in a single pole switch to disconnect the DC Voltage Reducer Converter when running the boat?
 
Another thought. When I am using the boat, the trolling motor battery will keep the starter battery at 13.8 V which is not necessary since when I run the boat that battery gets charged. Should I put in a single pole switch to disconnect the DC Voltage Reducer Converter when running the boat?

You could, and there are other times you might want to disconnect. For the scenario you mention, the boat should push the start battery voltage above 13.8V, and there will be no load on the trolling motor at that time.

I see more value in a switch (and it can be a very puny switch due to the low current) any time you might want to remove the load from the trolling batt.
 
Why don't you just fit a twin batteries charge controller that charges the lowest battery automatically.
This may have been simpler. I installed the DC to DC voltage converter but my concern is that the output will continuously feed 13.8V and I am worried about overcharging the second battery. Should I be worried about that? If the DC to DC voltage converter does not work or I destroy one of my batteries, I will buy one of these dual battery solar charge controller and use it. It won't be hard to swap out.
 
This may have been simpler. I installed the DC to DC voltage converter but my concern is that the output will continuously feed 13.8V and I am worried about overcharging the second battery. Should I be worried about that? If the DC to DC voltage converter does not work or I destroy one of my batteries, I will buy one of these dual battery solar charge controller and use it. It won't be hard to swap out.

13.8V is a good float voltage. Lead-acid likes to be held at full charge in the 13.2-13.8V range.
 
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