Harvard
newbie
Reged: Oct 21 2009
Posts: 3
Loc: Canada
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First timer, nice site, love it!
I need a 5V Supply in S. Arizona and I have one Siemens M5 (5 Watt 12V) panel. I am thinking of using this panel to connect directly to ONE 6.3 Volt Golf Cart Battery (BA220 or equivalent) WITHOUT a regulator. Can anyone see a problem with this obvious miss match? I am anticipating a max supply current of 0.86 Amps into the 6.3 V battery when the sun is shining. My load, a temperature monitoring device, will only be a few millamps at 5.0 Volts. This is a hobby project so "industrial strenght" is not a criteria.
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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Wait a minute, you have a 12v solar panel and you will be using it to charge a 6v battery? A golf cart battery is a big one. The 5 watt solar panel will pump about 300ma of current into the battery. In time, the battery will be fully charged and the excess voltage from the solar panel may damage the battery, if kept in that state for a long time. If you only need 5v at a few milliamps, why such a big battery? Have you considered using four AA NiMH rechargeable batteries instead?
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David Johnson, PE
www.discovercircuits.com
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Harvard
newbie
Reged: Oct 21 2009
Posts: 3
Loc: Canada
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The big battery idea is part of the logic "how could such a little solar panel damage such a big battery?"!!! Using the same logic, if I use smaller batteries then I should use a 12V battery (bank) with a regulator!!!
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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You have a huge energy mismatch here. Your solar panel generates watts of power yet the sensor load may only be 0.025 watts. For a typical 6 hour sunlit day, the 5 watt solar panel would crank out 30 watt-hours of energy. The sensor may only need 0.6 watt-hours per day. Your big 6v battery might store 1,300 watt-hours. It all seems like a waste. But, if you want to do this then that big battery stores enough juice for operating the sensor for a long time. You could connect the battery up to the solar panel every 6 months or so to charge it back up.
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David Johnson, PE
www.discovercircuits.com
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