Since a couple years I've been messing around with a raspi and some motors. Building random stuff with dc-motors and such. I now want to power a self driving boat-robot with some solar power. For this I imagined using a solar panel, a charge controller and a li-ion battery. I chose li-ion because it's light-weight, but not as explosive and difficult to charge as lipo.

So I was thinking of ordering the following:

So I thought of connecting the 3 solar panels in series so that they make for 18V input to the charge controller (the input voltage is up to 28V). That can then be hooked up to the battery.

I have 2 questions about this:

1) Would this be a reasonable setup?

Furthermore, once I can charge the batteries I want to build this into my robot and simply connect the load (raspberry pi and some very small dc motors) to the battery connectors. That means the battery connectors are connected to both the charge controller and the load.

2) Would this work or am I thinking too simple?

After this I want to add a voltage sensor to the battery and read that out from the raspi, so that I can limit power usage when the battery power is going down too fast, or shut the whole thing down if the battery juice is critically low.

  • \$\begingroup\$ Unless you're using protected batteries, you'll want a battery overcurrent/undervoltage protection circuit. Make sure it's included in the pack or get a board for it. \$\endgroup\$
    – K H
    Mar 29 '19 at 0:16

Regarding (1): Your proposed set up will work, but the MPPT is rated significantly higher than your solar panels. You might want to rate them closer for a more optimal design.

Regarding (2): Attaching the load and the MPPT to the battery is not an issue. That is how most marine and RV solar systems are wired.

  • \$\begingroup\$ Thanks! Two questions about your first remark. What do you mean with "rate them closer"? Do you mean that the 5 Ampere of the MPPT should be lower or do you mean something else? And what do you mean with a "more optimal design"? Will it be more efficient with a "closer rated" MPPT? Or do you mean something else with "more optimal"? \$\endgroup\$
    – kramer65
    Mar 30 '19 at 4:30
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    \$\begingroup\$ @kramer65 Your 3 solar panels in series are going to supply (are rated to) 6W. Your MPPT is capable of supplying (is rated to) 5 amps at 12V or 60W. So there is a lot of excess capability of the MPPT that you are not using. You could either go with more solar power (like 10x as much) or find a smaller, maybe cheaper, MPPT. Also, K H is correct. You will want Under and Over voltage protection on your cells if you care about them. It is not clear that the MPPT you have selected provides that capability. \$\endgroup\$ Mar 30 '19 at 5:15
  • \$\begingroup\$ Alright thanks. I just asked the seller and this board does not have under/over voltage protection. So I'll need to measure the voltage on the battery and build some logic there. But what does it need to do when the battery is full? Simply (electronically) disconnect the wires from the MPPT to the battery? Or between the solar panel and the MPPT? \$\endgroup\$
    – kramer65
    Mar 30 '19 at 7:30

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