Why do 15 watt panels not need a controller but 20 watt panels do? Both produce voltages well above 12v.
controller or no controller
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I think the OP is referring to those small solar trickle chargers that come with a small solar panel that hooks directly up to the battery.
Those chargers put out a voltage just above what the battery needs to be "maintained". It will not be able to re-charge a discharged battery in one day or maybe one week.Comment
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To see an actual test of why even a dinky 12w panel with no controller is a bad idea:
Forunately he didn't totally sacrifice those good test batteries!Comment
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