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Solar charging a laptop, and issues with amps.

I want to charge my laptop from solar power without an inverter. The transformer supplies DC 12V, 3A output; but most (affordable) solar panels only output 50-200mA at 12V. Does this mean it will take a long time to charge, or will it not charge at all unless I supply it with 3 amps? Is there a better way I can solar power my laptop?

frollard8 years ago
Solar is a niche that unless you can provide MORE than what the application needs, often it wont work - The laptop sees power, and says "I'm plugged in, so I'll run the cpu off this input power, and charge the batteries" - but if you input less than the cpu needs, it gets very mad at you - because it stopped using the batteries... to have a secondary battery setup with the solar charging that - and intermittently use the battery pack at the rated power of the charger. Can be used with or without an inverter - and offers the ability to store power while you're not plugged into the laptop.
MoeIsMe7 years ago
You are correct. A 20 watt panel will charge faster than a 10 watt panel. Most laptop batteries are now in the 60 Watt-hour range, so a 20 watt solar panel should be able to produce enough power for a complete 100% charge (from dead) each summer day. Similarly, a 10 watt panel will be able to easily offset about 1 hour of laptop use per day (summer months, deployed for most of the peak-sun hours).

Laptops present an "either/or" power scenario. By this, I mean that unless they see enough power at the source, they will ignore it completely and just operate from their internal battery. For example, let's say you have a 20W solar panel that on a particular afternoon is producing 15 watts for you. If your laptop is 'running', then it will likely need something like 30 watts, so it will consider the solar panel as effectively a "brown-out" and will ignore the panel and continue to drain its own internal battery. Laptops are not designed to take 15 watts from the source and supplement with the extra 15 watts needed from its own battery. They prefer to protect themselves. This is NOT a very good use of your solar investment!

There are two ways around this:
1. Only charge your laptop when it is turned off (so it doesn't have the same power requirements)
2. Use a solar storage battery between the panel & your DC adaptor. These batteries operate like a black-box power source, and will be able to take the 15 watts from your panel and add the extra 15 watts your laptop is wanting. This will also let you store power during the day for use with your laptop anytime, day or night. Effectively doubles your run-time too. Look at the Voltaic Generator Battery or the Brunton SOLO 7.5 as good examples.

One last issue to watch out for... Make sure that your DC adaptor does not have a minimum power input requirement, or you will not be able to go solar-direct from the panel to your laptop. For example, I have used a 65W DC laptop adaptor with solar, and it continually switches on & off if the solar power is weak.

There is an article on the solar laptop subject for further reading on the ModernOutpost.com website.