Solar powered battery chargers???

[SemiMan]

No worries Norm. If Sub would like to change feet that's okay but a little bit of Google goes a long way. There was a ton of research on this 4-5 years argue then it stopped being discussed because its a non issue as anyone who has done the research knows. As I am not the one trying to refute the common knowledge on this I dont really feel a need to defend my position since its not really a position its fact.

Semiman

 

[harrycolez]

Solar power for charger

Hey sorry if this is the wrong place,
So I have this charger:
http://www.amazon.com/gp/product/B004AWE2L2/?tag=cpf0b6-20
and I noticed it has a power input of 12v 1a which is 12w correct?
Since im looking for a portable solar charger would I need one that has an output of 12w?
Also are there any or is it ok to under-power the charger?
Thank you for your time.

 

[ChrisGarrett]

Re: Solar power for charger

Hey sorry if this is the wrong place,
So I have this charger:
http://www.amazon.com/gp/product/B004AWE2L2/?tag=cpf0b6-20
and I noticed it has a power input of 12v 1a which is 12w correct?
Since im looking for a portable solar charger would I need one that has an output of 12w?
Also are there any or is it ok to under-power the charger?
Thank you for your time.

That looks like my Xtar WP2 II charger that I use with a solar charging system.

The problem that you'll have is, is that by going straight from a solar panel to that charger, you'll have erratic voltage swings. Assume that you have a 20w 12v panel. That panel can have an open voltage of ~15v-22v with no load and that might wreak havoc on your Xtar charger, possibly burning it out.

Some here fell that unless you want to be there for a month, charging at 300mA, you'll want a starting point of 20w. The 10w foldable panels output about 600mA on a laboratory test bench, so less in the real world.

What you really want to do is get something in the 20w range for panels, either two 10w panels daisy chained together, or a single 20w panel. You'll then want to get a digital solar controller, that acts as a buffer between your panels and your load, modulating/regulating the panel(')s voltage. Most of us run a 12v SLA/AGM mother battery in between and then charge off of that, back at home base.

The panels will send amperage into the controller, which will then charge the battery AND power the load.

Here's my setup from August of '12. That is the Xtar WP2 II on the bricks and you can see the small 12Ah mother battery there as well. The black thing on the white signboard is a Morningstar SS 10-L controller and that allows the 12v cigarette socket to get power from the battery, which is being topped off by the PV panels (2x30w.)

You can go smaller on the battery, if you want.

Here's the link:

http://www.candlepowerforums.com/vb/showthread.php?342073-Portable-solar-charging-setup-I-just-built

 

[hiuintahs]

Re: Solar power for charger

........ I noticed it has a power input of 12v 1a which is 12w correct?
Since im looking for a portable solar charger would I need one that has an output of 12w?
Also are there any or is it ok to under-power the charger?.....

You can power that charger with less power as long you're not charging at the max rate. It's a function of

Total power input = power output + power lost by the charger's electronics.

As an example, suppose you are charging only one battery at 500mA and the battery currently is at 4.0v in the charge cycle........well that is 2 watts. That is the output power.

Assuming that the charger is utilizing switching power supply technique (not linear) for best efficiency, then let's assume a 75% efficiency. That means it will be drawing 2w / 0.75 = 2.67 watt requirement for input power. So the 12v supply needs to source at least 0.222 amps with this example. (12v x 0.222a = 2.67w)

The issue is that its not a good practice to go straight from solar panel to charger because the solar output can swing all over the place based on clouds and sun movement.

There is 3 areas of caution when going straight from solar to lithium ion charger:

1) Can the charger handle input voltages up to 22v which would be worst case high voltage from solar panel?

2) Be prepared for numerous resets if voltage drops too low on your solar system due to clouds, night time, changing sun angle.

3) Solar panel needs to be sized such that its rated maximum output is say 3 times greater than the maximum load you intend to draw from it. This accounts for the variance as described in #2 above.

 

[harrycolez]

Re: Solar power for charger

So if the input for the charger is 12v and the output to the battery is 4.2v at a peak of .5a but it was unable to provide the current it would just scale down? So long as it was able to provide the voltage needed?