# How-To: Charge 12v batteries with a Voltaic 15-watt panel

MAKE contributor Mikey Sklar has posted a how-to on Voltaic about using the solar power company’s 15-watt panel to charge a 12v battery, for use in camping, festivals, powering personal electronics, etc.

Charge Car Batteries with a Voltaic 15 Watt panel

## 22 thoughts on “How-To: Charge 12v batteries with a Voltaic 15-watt panel”

1. Tercero says:

What’s the AH output on a solar charger? This doesn’t make sense. He’s charging a car battery (144ah). You would have to have more amp hours in, to actually recharge the battery so what’s the output on this charger. I’m confused.

1. Jason Doege says:

A car battery stores energy. A Watt is not a measure of energy. Please review your electric theory and re-write your how-to. While this may work for you now, this kind of misinformation could be costly or dangerous for you and your readers. This is really very fundamental. Please do not write this off as pedantry.

I’ll help you in the right direction. A car battery stores energy. This might be described in Watt*hours (Wh). Your solar panel might produce 15W in full sunlight. That 15W times one hour would give you 15Wh of energy. Battery capacity is usually described in Amp hours, a unit of charge. A Watt = 1Volt * 1Amp. A car battery, for argument’s sake, is a 12V battery and stores roughly 50 Amp hours of charge, meaning it stores roughly 600Wh of energy. From dead, that solar panel would take 600Wh/15W = 40 hours to charge that battery.

Of course, that is completely idealized and is only just enough information to get you into trouble. It completely disregards the odd characteristics of battery charging (charge rates and over-charge prevention) and some of the real world concerns with charging lead-acid batteries (such as the production of a explosive gas.)

Anyway, that is just a pointer in the right direction. Confusing power and energy is very common but potentially very dangerous. Please take some time to educate yourself before trying to educate the internet.

2. Anonymous says:

I see a sealed lead battery (perhaps 8+ amp hour) in the photos. Not a car battery.

1. Anonymous says:

Ah. Bottom pic.

3. Gareth Branwyn says:

I changed the title of my post to 12v battery, so as not to mislead people. Even tho he uses “car battery” in his title, for most of it, he’s talking about charging a small 144Whr SLA battery.

4. Makes no sense says:

You can’t run anything on a single 12v SLA. Seriously. Even the most basic UPS would run a series of AGM/SLA batteries (4X12v 12ah SLA for example) at the most give you 20 minutes of power.

1. Anonymous says:

“You can’t run anything on a single 12v SLA.”

Nothing? Nothing at all?

I’ve designed products specified to run 12 YEARS on a single CR2032.

1. what the heck says:

He’s talking about running camping, festivals, powering personal electronics, etc. Unless you’re running pocket calculators, LED flashlights, or your IPOD.
It’s a crappy article. Get over yourself.

1. Anonymous says:

He specifically says “easily charge a laptop / cell phone / ipod, inflate an air mattress, power a boom box, recharge AA batteries, run lights and charge power tools.” If you can’t do that with 12V/12AHr, then you must have one of those early vacuum-tube iPods.

I can see a lot of applicability in having an always-charged 12V source while in a tent/RV (anywhere away from mains/AC) even if it doesn’t have enough power to run major appliances.

Obviously people will find fault in ANY article and use it as an excuse to spread the hate. Perhaps the Make blog should only list perfect articles that everyone loves? I’ll be the editor for that. Wake me up in a couple of years.

Get over YOURself. The article shows how to recharge a battery using a solar panel and a charge controller. If it doesn’t fit your purpose, go complain that the motorized beanbag char doesn’t have blinkers, or find some other aspect of the blog that doesn’t meet you expectations and whine about that.

Or how about make something yourself?

1. what the heck says:

“Or how about make something yourself?”

I already won an instructable first prize. What have you done lately. Chump?

5. Gareth Branwyn says:

Please, let’s try to keep the conversation civil and not be calling each other names. Thanks.