I purchased a 20 watt solar panel to be mounted to the hardtop of my boat to charge my batteries. The directions say put the controller within five feet of the batteries and the solar panel can be up to 20 feet from the controller. The wires that came with it we're not 20 ft long. I extended them with 12 gauge stranded wire and used the proper waterproof butt connectors. I do not see either of the lights on the controller lighting up if I move the controller back two within five feet of the solar panel the lights light up as they should I have solid continuity through the splices but the controller lights do not come on when I put the controller back by the batteries. My question to you is can I reverse the connection and leave the controller in the overhead box and run the wires back to the batteries and have the solar panels still perform is proper function.
Electronic – the distance I can put between a 20watt solar panel and a controller and still have enough current to make it work
batteries
Related Solutions
Don't even think about creating the setup you just described. It is bloody dangerous.
If you wire the "solar cell pack" and the two battery packs in parallel without connecting the Raspberry Pi, you'll get a loop. Kirchhoff's second law explains that the sum of voltages around a loop must be zero. In this case, if you start going around the loop in one direction, you'll encounter the two power sources with opposite directions, so now their difference must be zero - so they must be at an equal voltage. Will this be 6V (dictated by the solar panels) or 3.7V (dictated by the battery packs)? The following will happen:
- Initially, without sunlight, the common voltage will be 3.7V. No current flows, since the solar panel does not let current flow backwards (its resistance goes near infinity). All is well for now.
- Then you apply sunlight. The solar panels try to increase the voltage to 6V, but at this voltage the batteries would allow through much more current than they can supply. So the panels drop their voltage to 3.7V, but still begin to charge the batteries with the couple hundred milliamps they can supply, until the voltage in the battery packs reaches 6V. And there's a pretty good reason the batteries are rated at 3.7V.
- If I learned anything about Li-ion and Li-polymer batteries is that they are very easy to upset. And they especially don't like being overcharged. If they are indoors, they will blow up your desk and burn your house down. If they are oudoors, they'll happily ignite the grass around them. Then burn your house down. Li-ion and Li-polymer batteries are not toys. Don't even think about putting them in a circuit where there's even a slight chance they'll get overcharged.
Connecting the Raspberry Pi before the detonation wouldn't work out well either. The 3.7V combined power supply is not enough for the Pi, which will then do one of the following (I'm not familiar with the Pi's power supply circuit):
- Pull a lot of current overheating the battery, the solar panel and maybe even its own on-board voltage regulator. It will not boot, or even if it does, it will frequently crash and reboot because of the inadequate voltage. This goes on until one of the components fail: if it's the solar panel, you're safe. If it's the Pi, it's the time bomb scenario all over again. The battery packs also don't like being over-discharged, but as far as I know, they don't burst out in flames then. They just don't work anymore.
- Don't pull any current at all. Then it's like you didn't connect it at all. Time bomb again.
Creating a circuit which safely combines solar and battery power requires advanced electronics skills and dedicated circuitry. In your case, I would follow S.J. Becker's advice (+1) and buy a (solar powered) power bank from eBay. The circuitry is there, pre-made for you and it can power your Raspberry Pi longer than your setup would have even if it worked. I know they are not as cheap as using things from your parts bin, but they are definitely cheaper than replacing your burnt furniture.
Additionally, does the thing have to be solar powered?
Edit: Some battery packs have built-in protection circuitry that shuts the power off if the battery is overcharged, so there's a chance your setup won't actually ignite but just not work at all.
There are many reasons why the current from the solar panel would vary.
First, let's look at the solar panel in isolation, ignoring any effects the batteries could have. When a manufacturer says that a panel is rated for some amount of power, it's done under specific, not entirely realistic conditions called Standard Test Conditions (STC). You probably aren't getting exactly 1kW/m^2 of sunlight and aren't cooling your panel to exactly 25C for your test, so the rated power won't match exactly.
Next, let's consider how your solar panel behaves when connected to a load.
The range of possible output voltages and currents under specific conditions can be plotted as an "IV curve," usually done by connecting some controllable load to the panel at STC.
Here's an example IV curve for a single cell under some particular amount of light:
From this example with a single cell, you can see that depending on the output voltage when the load is connected, the power delivered to the load will vary. The point where the maximum power is delivered is referred to as the maximum power point. Your Vmp and Imp figures refer to the expected voltage and current when the panel is operating at its maximum power point.
If your charge controller directly connects the panel to the batteries, the panel voltage will follow the battery voltage, so the panel may only briefly operate at its maximum power point (or never, depending on the curve).
Controllers that can adjust the operating point to stay near the maximum power point all the time are known as maximum power point trackers (MPPT).
To summarize:
- Your panel's output power will vary depending on ambient conditions, which are probably not the same as the manufacturer's test conditions.
- Even if they are the same, your charge controller might not have MPPT functionality, so the output power/current varies with the battery voltage.
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Best Answer
Congratulations on doing it properly as you can in your situation, on adding an extension in a competent manner and in thinking about other ways to achieve your requirement.
Fortunately, it is likely that you have done something wrong with your extension cable. I say "fortunately" because it shoul be possible to make what you have done work.
Perhaps the polarity from panel to controller has been reversed when you added the extension. Check the polarity with a voltmeter, with the cable connected to the panel and disconnected at the controller.
12 gauge wire from panel to controller should be VERY adequate and cause no problems at all. Resistance is under 0.1 Ohms and voltage drop at 20 Watts is probably around 0.1 - 0.2 V.