Forum Discussion

rexlion's avatar
rexlion
Explorer
Mar 13, 2017

solar panel hooked directly to battery

I've heard of some folks hooking a small solar panel directly to the battery to charge or maintain it. But some panels (my 70W, for instance) can peak its output as high as 17V. My question is, how does a 17V input at low amps play out when hooked to a 12V battery? Is it healthy or unhealthy for the battery, and if the latter, what can it do?

(Side note: I do use a properly sized controller with my panel. My interest is academic.)

(EDIT: ) :) Let me rephrase/refine my question. For a short time of charging a non-full (depleted) battery, would the direct connection at 16-17V charge the battery harmlessly, and would it charge more quickly than a panel with a controller that knocks the voltage down to about 14V?
  • time2roll's avatar
    time2roll
    Nomad
    Mar 13, 2017
    Plays out same as any 17v charger on a 12v battery. Voltage will steadily rise to 17 volts. Your panel is maybe 4 amps so the effect will be slow. So slow you may never get above 13 volts while in use. Monitor the voltage rise closely the first few times. Best to have a controller in storage.

    Unless it has a diode, best to disconnect as the sun drops.
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Mar 13, 2017
    Controllers are inexpensive. I use one on my solar battery tender as well as big old WindyNation system. What others do....hmmm
  • MrWizard's avatar
    MrWizard
    Moderator
    Mar 13, 2017
    if the battery is fully charged, sitting in storage
    then that 17v could damage the battery by drying it out, same way the old magtec converters

    you can buy a $10 controller for that 70w panel and be safe

    which is more important to you, the $10 and a little time involved to install
    or that battery ?

    if your going to use solar then you should use a charge controller

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