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The simplest way to limit the current is to size the panel to your battery. When the panel gets attached to your discharged 5a battery, it will gobble up as much current as it can. Since you have a panel capable of 3.6A output, this is too much initially for the battery. You can either modify your panel, or even easier, use a larger battery, such as a 10A agm which can now handle your panel's maximum output.
The "C" rate is typically the amp-hour rating of a battery under a 20-hour load. That is, your 5ah battery should sustain 250 milliamp load for 20 hours until the battery is considered fully discharged. Note that fully-discharged does NOT equal zero volts. We're talking 10.75 - 11v for the most part. Going below that voltage is going "past" dead.
This tells you right there that with your 300 milliamp load you should be able to get into the ballpark of 5 / .3 = 16 hours until totally discharged. BUT you don't want to use up more than 50% of your battery capacity, so cut that figure in half to 8 hours. In other words, you essentially only have a 2.5ah capacity to cycle with if you want long life. Use your load for less time, and the cycle life improves. (less depth of discharge)
But you are exceeding the initial current rating with your existing panel. Again, the easiest mod here is to upgrade to a 10ah battery. Guess what? Now you CAN go 16 hours with your 300ma led lights and only reach a 50% DOD state for cyclic use.
Sounds like your Arduino is only measuring things, and not controlling them. You need some sort of control. Current control without hacking up your panel is as simple as upgrading to a larger battery that can handle the current. But now you need VOLTAGE control to not exceed 14.7 volts as measured at the battery terminals. In a solar application, leaving it at 14.7 for the rest of the day until the sun goes down or dropping to a float voltage is a decision you'll want to make depending on how you want to handle it.
With no voltage control, I suppose the best you can do is fire off a klaxon-alarm warning you to pull the clamps.
The "C" rate is typically the amp-hour rating of a battery under a 20-hour load. That is, your 5ah battery should sustain 250 milliamp load for 20 hours until the battery is considered fully discharged. Note that fully-discharged does NOT equal zero volts. We're talking 10.75 - 11v for the most part. Going below that voltage is going "past" dead.
This tells you right there that with your 300 milliamp load you should be able to get into the ballpark of 5 / .3 = 16 hours until totally discharged. BUT you don't want to use up more than 50% of your battery capacity, so cut that figure in half to 8 hours. In other words, you essentially only have a 2.5ah capacity to cycle with if you want long life. Use your load for less time, and the cycle life improves. (less depth of discharge)
But you are exceeding the initial current rating with your existing panel. Again, the easiest mod here is to upgrade to a 10ah battery. Guess what? Now you CAN go 16 hours with your 300ma led lights and only reach a 50% DOD state for cyclic use.
Sounds like your Arduino is only measuring things, and not controlling them. You need some sort of control. Current control without hacking up your panel is as simple as upgrading to a larger battery that can handle the current. But now you need VOLTAGE control to not exceed 14.7 volts as measured at the battery terminals. In a solar application, leaving it at 14.7 for the rest of the day until the sun goes down or dropping to a float voltage is a decision you'll want to make depending on how you want to handle it.
With no voltage control, I suppose the best you can do is fire off a klaxon-alarm warning you to pull the clamps.
Like I said, I ordered a DC-DC converter to regulate the voltage at 14.7, so I should be fine on that front, but the 3.6A scares me, since neither the battery nor the converter likes it.
In fact, the converter specifically states that it should operate to a maximum of 2A, and up to 3A with a heasink, so I somehow need to dissipate any current above 2A.
Is there some obvious way to do this that I am missing?
I am using the Arduino to control relays (that act as electronic switches in this case, with one output being open circuit) and light simple leds (charging / charged) based on the readings.
Thanks for the C rate explanation, it seems to make more sense now.
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