โApr-05-2022 06:20 PM
โApr-08-2022 08:28 AM
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โApr-07-2022 03:23 PM
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โApr-07-2022 11:21 AM
โApr-06-2022 08:43 PM
โApr-06-2022 08:12 PM
profdant139 wrote:
OP here. Very interesting discussions!!
I will take another hard look at my controller -- I am pretty sure it is molded onto the back of the panels with plastic -- not designed to be removed. It would take a lot of courage for me to cut it out and move it to the battery. What if I mess it up? These suitcase panels are not cheap.
I think I understand, though, why the manufacturer designed a less-efficient "all in one" system. The goal is a consumer-friendly "plug and play" portable solar panel -- nothing to do but just hook up the cable. The more complex the system, the greater the sales resistance.
I know that my 12.7 daily reading is not a full 12.8, but the proof of the pudding is in the eating, as they say. We routinely boondock for a week at a time, using the solar panel to top up the battery to 12.7 every day. We have never lacked for power. (Admittedly, we are very frugal.) So the panel is providing us with more than mere maintenance -- the power system does just what we need it to do.
If it were doing nothing more than maintaining the battery at its then-current charge, we'd gradually run out of power during the week. We don't.
I like the idea of chopping up my cable into pieces and attaching as many segments as needed. But I'd still have to transport all of the pieces.
โApr-06-2022 07:42 PM
MNRon wrote:
Gdetrailer et al - check my math here, good catch on return path:
Simple answer, solar panel placement affects charging more than the difference between 40ft and 70ft of 10ga.
More complex answer:
Based on OP's first post the controller puts out 14v and he measured 13.8v at battery and 13.5v at battery on 40/70ft runs. This would imply with 40f he is getting 2.5A charging current (200mV drop across 80ft (round trip) at 1mOhm/ft); and at 70ft he's getting 3.6A charging (500mV across 140ft...). The reality is that his measurements etc aren't that accurate and I'm sure that he's getting roughly the same current charging with either run, the limiting factor in his charging is *not* the IR drop in the wire, but the internal IR drop inside the battery (if you will, actually more complicated). The truth is that with ~13.5v across the terminals the battery when nearly fully charged is the current limiter and isn't accepting much current.
If he did the same experiment with 50% discharged batteries (12.1v) he will be putting a larger voltage differential onto the batteries and will drive more current. In this case the wire IR resistance might come in to play but I'm guessing second order compared with sun exposure on solar panels. Assuming full 7A charging from his panels he'd be putting ~13v across the battery with 70ft (including round trip) and 13.4v with 40ft; I suspect a 50% depleted battery will draw 7A regardless of 13v or 13.4v across it, and as it charges up the battery internal resistance will be a larger current limiter than the IR drop (as evidenced by his measurements in the first place).
Thoughts?
โApr-06-2022 07:11 PM
โApr-06-2022 04:28 PM
MNRon wrote:
Gdetrailer et al - check my math here, good catch on return path:
Simple answer, solar panel placement affects charging more than the difference between 40ft and 70ft of 10ga.
More complex answer:
Based on OP's first post the controller puts out 14v and he measured 13.8v at battery and 13.5v at battery on 40/70ft runs. This would imply with 40f he is getting 2.5A charging current (200mV drop across 80ft (round trip) at 1mOhm/ft); and at 70ft he's getting 3.6A charging (500mV across 140ft...). The reality is that his measurements etc aren't that accurate and I'm sure that he's getting roughly the same current charging with either run, the limiting factor in his charging is *not* the IR drop in the wire, but the internal IR drop inside the battery (if you will, actually more complicated). The truth is that with ~13.5v across the terminals the battery when nearly fully charged is the current limiter and isn't accepting much current.
If he did the same experiment with 50% discharged batteries (12.1v) he will be putting a larger voltage differential onto the batteries and will drive more current. In this case the wire IR resistance might come in to play but I'm guessing second order compared with sun exposure on solar panels. Assuming full 7A charging from his panels he'd be putting ~13v across the battery with 70ft (including round trip) and 13.4v with 40ft; I suspect a 50% depleted battery will draw 7A regardless of 13v or 13.4v across it, and as it charges up the battery internal resistance will be a larger current limiter than the IR drop (as evidenced by his measurements in the first place).
Thoughts?
โApr-06-2022 02:20 PM
โApr-06-2022 02:15 PM
โApr-06-2022 01:17 PM
BFL13 wrote:
PWM controller passes batt V to the panel so that is the V seen at the panel,less Vdrop not the controller's Vabs voltage of say 14.4
The IV curve for the panel uses batt V
โApr-06-2022 01:14 PM