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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Charging a 6 volt battery with a 12 volt solar panel

Sunday, February 1st, 2009

Hi Jeff,

I recently built a small alt-e project with my daughter.  It’s a shelf with a 6v van and a couple of led lites for over her bed.  It’s powered by a 6v 36 amp-hour battery in an ammo can under her bed.  I have a 4.5w, 300mA Coleman solar panel intended for trickle charging 12v batteries.  It charges at about 17v.

Am I right in thinking that with a system this small and with a current that low that I can use this panel with this battery without frying wire or battery, or should I hold out to find a panel that charges at 8v.

Steve Sonntag MD


In an emergency you could temporarily re-charge a 6 volt DC deep discharge battery with a 12 volt solar array, but I would not make this a permanent connection for the following reasons.  This Wal-mart solar charger was designed to trickle-charge a large 12 volt battery, and does not have a built in solar charge controller, which is available as an option from the manufacturer.  Supplying a higher voltage to a wet cell deep discharge battery is typical for periodic equalize charging, but it sounds like you have a sealed deep cycle battery.  If that is the case, over-charging from a high charging voltage will dry out a sealed battery and these cannot be restored.

Also, without a solar charge controller between the battery and the solar module, you have nothing to prevent battery charge from discharging back through the solar module, although this small solar module may contain a blocking diode to protect from this.  You may be able to remove the backing from this solar module and “split” the string into two groups of 6 volts, since many solar modules are made up from separate strings of individual cells like Christmas string lights.  Find the wiring point between two equal sets of cells and cut this wire, then tie the positive side to the positive output wire, and tie the negative side of the cut to the negative output wire.  Now you will have a 6 volt nominal solar module.  Keep in mind that many commercial 12 volt and 24 volt modules have internal junction boxes set up to allow you to do this with these larger units.

If all else fails, buy a 12 volt battery, fan, and light.  They are probably easier to find than 6 volt units anyway.

Good luck,

Jeff Yago

One Response to “Charging a 6 volt battery with a 12 volt solar panel”

  1. Dan Able Says:

    This is interesting, I have been looking into 12 volt power on the road using inverters and those emergency jump start units. It would so great to be having my batteries “re-upped” with solar power.



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