From what I've learned so far, which is that volts x amps=watts. Does this mean that watts divided by volts=amps? If so, I have a few questions based on it. If a solar panel (or a series of panels) have 28 watts, and output their power through a USB port rated at 5 volts, that comes out to 5.6 amps being produced. Based on that, here's what concerns me: Let's say I'm using this solar panel to charge batteries in a 4AA battery charger. If each AA has a capacity of 2,000 Mah, or 2 amps, then 4 of them totals 8 amps. If the solar panel is producing 5.6 amps into the 4 batteries which have a capacity of 8 amps, then they'd all be fully charged (assuming they were fully drained to begin) in well under 2 hours. That sounds a little too quick to be safe. But to drive the point home even better, let's say I was charging a smartphone with a battery capacity of 3,000 Mah, which is 3 amps. The solar panel would have it charged in slightly under a half hour, by my calculations. So what I'm thinking now is that if all I'm going to be using with a solar charger is a 4AA battery charger and a smartphone, then would it be best to get a smaller solar charger with a lower watts rating, maybe closer to 10 watts rather than 28, even though the higher watt panels seem to get better reviews?
If you don't use a charger for most modern batteries, you are going to kill them sooner or later. The usual charger for most batteries charges at a constant current after the first few seconds and then when it reaches some desired voltage transfers to a sustaining voltage that will prevent over charging. In my limited exposure to solar chargers there are two options, a very expensive light weight, folding panel that may even be flexible, usually sold for back packing etc and a heavier solid panel and electronics that may be 10 times heavier, but not very expensive. Once you have made that choice, then you can start looking. I went with cheap heavy 100 w system, with small used sealed battery and proper electronics, seems like I find a new use for it every week. In my experience a 12 v and 100 w panel, will day in and day out have a current into the battery etc of from about 2 amps when cloudy, early in morning, late in afternoon, to about 6 amps at 12 noon on clear day in July. With the proper electronics, the 12 volts can be converted down to about 5 volts and the output current about doubled, in a lot of cases they go for cheap and that doesn't happen. Two major voltages, 12 v lets you use all RV and auto equipment, lights, refrigs, pumps, LED, computer and tool automobile chargers, 12 volt batteries, etc, the 5 volt ties into the now almost standard for phones, LION batteries and their chargers and a lot of computer stuff. I usually try to pick a system that puts out both voltages from the charge controller.
An inexpensive DC to USB module is very cheap on Amazon. I bought 5 of them to use with both solar and batteries... Your USB device will take care of itself as far as charging goes... I would suggest you just buy a 12 volt AA/AAA charger to use with your solar panel. That way your charger will handle charging rates and voltages. Power available isn't necessarily power used. BTW if you are on west coast you will be lucky to get 800STC from sun. So take panel ratings and figure you might get 80% on a real good day. Just finished with a 6000watt array and we get just under 5000 on a bright sunny day. We consider ourselves lucky. Charging an electric car. A battery is a battery....
I guess I should have been more specific when I was talking about solar panels. I was referring to a folding unit such as this one: https://www.amazon.com/dp/B01EXWCPLC/?tag=survivalmonke-20 which I read in a review is able to put out 8 watts under cloudy skies. To narrow down what I was asking about--Is 28 watts of power from the solar panels too much power for charging AA batteries or a phone? If that's all I would be doing, should I be looking at a solar panel unit that's smaller?
Simple answer is no... Use a simple USB charger with your panel and it could be a 250watt panel (12volt) and it won't be too much... I use a 65watt panel for USB and small gell cell battery. A bigger panel will just maintain voltage better under cloudy conditions. The important thing is to use with a charge controller of some fashion that does the work of conversion for you. Available cheap from may suppliers. Power meters of all sorts are available from USB to RC car models. I love my little RC meter. Gives me my solar voltage, current and watts allinone small
https://www.amazon.com/dp/B08MCZNYZN/?tag=survivalmonke-20 Example of a usb charger that will take whatever your solar panel will put out and give you multiple ports
Keep in mind that you need to consider VA as well as Watts if you are going to power AC devices. Watts are the actual power, where VA is the apparent power. If you are only working with DC like batteries and tablets then they are the same. This is why you will see both VA and Watts listed for come devices. If you are just looking at a small system you use to charge batteries, tablets and the like you can safely ignore most of what follows. If you are thinking lighting, refrigeration, etc,, then you need to plan more carefully. With both AC and DC you also need to account for efficiency loss. AC power supplies consume more power than they produce with efficiencies typically running between 50% to 90% depending on design. In DC you can run into power losses due to circuits that convert from one voltage to another or otherwise regulate voltage and current. To understand what you need to need to have outline every component in the system including the powered device and identify it's consumption and except for end devices the output. Be thorough to avoid disappointment and add a fudge factor to cover anything you missed or any portions that aren't exactly as the manufacturer specs describe. I suggest workign back from the endpoints and working back to the panels. Here is a decent explanation if the difference between the two: Difference Between VA and Watts | Difference Between A more detailed explanation is here: AC power - Wikipedia
VoltAmps are all that matters to an inverter. I have a whole post about lowering VoltAmps on larger machines. Once you get to a certain size it's better to run bigger stuff straight off an engine if possible.
That's because VA is always equal to or greater than Watts. In DC they are always the same since there is no reactive component to worry about.
This also looks like something I could clip to my car battery and get power from that instead of a solar panel. Interesting! Might be my best option. I've been doing so much research on solar panels and running into complications with them, so maybe this way would be better.
Even easier you can get adapters that plog into your car's accessory outlet/cigarette lighter. I have one with three connections and you can get higher densities, https://www.amazon.com/dp/B07D9WK6VT/?tag=survivalmonke-20
[ The main reason why I posted the clip on device is that it will handle 30volts just what you need for solar panel open circuit voltages. Cigarette lighter plug ins don't like much more than 16volts and can have an untimely death. FWIW
Something else I could mention in relation to clip ons versus plug ins is that if there was an EMP strike, the plug in might be less likely to operate because it depends on the car's wiring to make a connection to the battery, while the clip on would be connected directly to the battery. Just a thought.
