Portable (suitcase) solar "install" question
I've gone back and forth on solar panels on the roof or portable. Well, due to a tight budget, portable is the only way I'm going to get solar for now and it makes sense for me to try it out 1st as we...
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When it comes out of bulk doesn't make much difference. It's when it changes from absorption to float when charging really slows to a trickle (pun intended).
If the controller simply switches to float as soon as the absorption voltage is hit (like the infamous WFCO converters), then all bets are off - it's not charging right to begin with, and you've got bigger issues than which end of the wire to connect the controller to.
Quality controllers tend to use time and/or current to end the absorption stage (they also tend to support remote voltage and temperature sensing). Most cheap controllers don't document how they work, but I found one which did (LMS 2420). It says "When offline voltage of battery is close to constant regulated voltage, the battery is fully charged." So, it's stopping to measure the short term resting voltage vs. the desired voltage. So, the change from absorp to float would be unaffected by voltage drop.
50 feet of 2 conductor 12 gauge copper has a resistance of about 0.16 ohms. By the time you get to the late absorption stage (say, <0.5 A), the voltage drop will be <0.1 V. 100 ft of 10 ga will do similar. Mice nuts. The fixed setpoints on most cheap controllers have a greater difference than that vs. what the battery really wants. I've seen them come with fixed voltages from 14.2 to 14.7, and that's making the unwarranted assumption that they even measure that accurately.
If the controller simply switches to float as soon as the absorption voltage is hit (like the infamous WFCO converters), then all bets are off - it's not charging right to begin with, and you've got bigger issues than which end of the wire to connect the controller to.
Quality controllers tend to use time and/or current to end the absorption stage (they also tend to support remote voltage and temperature sensing). Most cheap controllers don't document how they work, but I found one which did (LMS 2420). It says "When offline voltage of battery is close to constant regulated voltage, the battery is fully charged." So, it's stopping to measure the short term resting voltage vs. the desired voltage. So, the change from absorp to float would be unaffected by voltage drop.
50 feet of 2 conductor 12 gauge copper has a resistance of about 0.16 ohms. By the time you get to the late absorption stage (say, <0.5 A), the voltage drop will be <0.1 V. 100 ft of 10 ga will do similar. Mice nuts. The fixed setpoints on most cheap controllers have a greater difference than that vs. what the battery really wants. I've seen them come with fixed voltages from 14.2 to 14.7, and that's making the unwarranted assumption that they even measure that accurately.
