Newbie question - small 24v panel

Registered Users Posts: 1
Several years ago, my wife bought me a small (5w) panel to keep my ATV battery charged. I didn't know much about solar charging and she knew less, but still surprised me with the gift. Long story short, things came up, the panel was shelved, we moved, and now I'm finally pulling it out to use it. I'm an amateur and know enough about electricity to know I have a lot to learn.

Having said that, the panel says its 5w, 350mA, and 24Voc. My ATV battery (like a motorcycle batt.) is 12V and is pretty small 18-20Ah, i think). Can I even use this panel to trickle/maintain a charge since it's a 24v?

If it was a 12v, would I need a similar sized charge controller?

Thanks

• Solar Expert Posts: 1,220 ✭✭✭✭
The first and important thing to know about solar panels is that they are current generators, not voltage sources. Thus you can connect that panel to any battery, even a 1.2V battery and it will charge at (about) 350mA. The first and important thing to know about batterys is that they are like, ahem, women. (Hard to please in case you were wondering). They dont like to be undercharged and they dont like to be overcharged. Oddly even a small panel like that can overcharge a battery. Because once its full, the voltage will keep rising and keep rising until it hits Voc. So you dont want to do that. Read, you need a charge controller, (or a vigilent person to supervise it.)

The less important thing to know about solar panels is that while you can charge a 1.2V battery with a 24Voc panel, the effective charging power will be 1.2V times 0.35A (, ie not much, the rest is wasted). If you were charging a 12V battery it would be 12V times 0.35A. Make sense. So the closer the battery voltage the better. Except... not too close, (woman, remember). For a start the panel wont always be capable of reaching 24V, (clouds, heat, wire losses), and on the other side the battery needs something like 14.8V to provide the absorb stage that is important for fully charging the battery. Thus, the ideal panel for a 12V lead battery is one that has a Vmp (not Voc) of between 16 and 17V. (such a panel has 36 cells),That takes care of the losses, and gets most of the power to the battery.

But the really cool thing is that, that battery and panel, in time, will teach you pretty much all you need to know about how to be nice to your good lass. Then you have a happy battery, and a happy wife.
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar