PV Gap

Frederick Said:

Need Help, 12v Solar Panel for Emergency?

We Answered:

The solar panel has a 12 volt output with only 13 watts of power at 700mA.

This is very useful for charging low voltage devices directly, such as a radio, batteries or a GPS unit.

It is not effective to attach an inverter to this to convert the power to 110 volt AC adapters which in turn convert the power back to DC for your personal electronics.

You could use the solar cell set to charge a marine grade deep cycle battery over several hours, attach an inverter (for example this one http://www.batteryjunction.com/marathon-… to the battery and then plug your AC adapters into the inverter and run your devices or chargers.

However, this is an incredibly inefficient waste of power as you convert the power back and forth between DC to AC to DC again. It wastes power as it spills off much of the solar energy collected as heat in the different steps and different adapters.

Connecting the inverter directly to the solar charger will not work well because it doesn't produce enough power in 12 volts (watts) for it to run an inverter.

In short, don't do it, it isn't worth the effort.

In order to make this work effectively you should fine the automobile adapters available for your devices and plug the auto adapters for your devices directly into the female cigarette lighter socket provided with the solar briefcase charger.

Many items only require 5 or 6 volts DC power, so the car adapters throttle the power down to the amount the devices need from 12 volts and smooth out any spikes or drops in power.

If you have a base station, you can also attach the Solar Power Briefcase to 12 volt car/marine battery and charge the large lead acid battery while you are away using your devices and then when you return, detach the solar charger and attach a female cigarette lighter adapter to the battery.

You can then attach your devices to the charged car/marine battery using a female cigarette lighter socket and charge or power them using the car adapters described earlier.

Here is an example of a NiMH or Ni-Cd battery charger with a car adapter http://www.batteryjunction.com/vachulsmc…

Many GPS units that bluetooth have a small USB port and a Cigarette Lighter to USB charge adapter can work for them http://www.ziplinq.com/products/Prod_Ind…

Most radio's have a DC plugin port. You can build or purchase adapters that step down the 12 V power to the radio's power needs.

In short, power your devices directly from the solar cell using the car adapter plugs made for them or charge a larger battery as a power resevoir and plug your car adapters into it when it is dark which allows you to charge devices when you are not using them while sleeping.

Andrew Said:

What size solar panel should I use to continuously charge my 12v battery that powers lights fans etc.?

We Answered:

You need to do research. First find out how much power your items are going to be drawing. Next, you have to research a bit on solar cells. What you are mostly interested in is efficiency and the surface area you are going to be able to cover with them. You will use this information in conjunction with the amount of time you believe your solar cells with be exposed to the sun and the amount of energy the sun will provide to that surface area to determine the efficiency of the solar panel you need. There's more to it, but since you are asking for help on yahoo, that should do.

Monica Said:

How long will it take a 12v 150mA Solar panel to fully charge a car battery?

We Answered:

Hey Powergland, Flash is quite right. That panel will never actually recharge your car battery. A lead acid battery loses about 3% of its charge per week even if it is not used, and more if it stays connected to the car, so the clock and alarm can function. A 150ma of charge, even for 8 hours a day will barely keep up with the normal losses. Turns out that's exactly what those little dashboard top panels are for. If you park your car at the airport for example and go away on a 10 day trip, it is assumed your battery is near full when you plug in the panel, it really just keeps it up until you return, it isn't going to recharge a dead battery even in full sun in the desert.

You could put a larger panel in it's place, or connect several if you like. One is enough to keep the battery up, the next could be a recharger, but will still take several weeks. A third will cut that time down to several days, and so on. There is a good book at the library called, The Complete Battery Book by Richard Perez, you could just read the chapters on lead acid batteries and become fairly knowledgable on the subject in half an hour or so. Good luck, and take care , Rudydoo

Marilyn Said:

solar panel 12V 20 Watts.....what battery / charge controller amperage would be sufficient/best?

We Answered:

If you are running the 15W pump continuously, the 20W solar panel won't be big enough. 15W x 24 hours = 360 watt hours (wh). Since the solar panel is generating electricity only during sunny hours, it can't keep up. Let's use 5 sun hours as an example, which is the total number of hours the sunlight is equal to the standard test rated power. 20W x 5 hours = 100wh. You're 260wh short. You need around 95W to do what you want. (360wh / 5 sun hours + ~30% inefficiencies) http://www.altestore.com/store/Solar-Pan…

For the battery, you'll need a deep cycle battery that is designed to be drawn down to about half way and recharged, repeatedly. They are rated in amp hours, (ah), not cca. Since you only can use half the power in it, you need it twice as big as you calculate. If you need 360wh, that's 30ah usable power, 360wh / 12v = 30ah. 30ah x 2 (only using half of battery) + 15% (battery losses) x 1.19 (50F temperature compensation)= 82ah battery. http://www.altestore.com/store/Deep-Cycl…

The charge controller is rated based on the current output of the solar panel. That 110W 12V panel is rated at 7.5A. Add 25% safety margin, you need at least a 9.3A charge controller. If you get one with a low voltage disconnect (LVD), you can have the pump automatically shut down if the battery gets low, saving the life of the battery if you've had a day or two of clouds or rain. http://www.altestore.com/store/Charge-Co…

You can run the numbers through a calculator like this to see for yourself, http://www.altestore.com/store/calculato…

.......Update based on asker's update............. If you just want to run it for as long as you can with your 20W solar panel, you can size it based on your potential output from the solar. Let's say 1.3A output, 5 sun hours, so 6.5ah. Multiply by 2 since we're only using half of the battery, so at least a 13ah battery, figuring you'll be using the power about as fast as it'll be putting into the battery, so it's really just acting like a buffer. I suggest rounding up if possible, since I didn't figure in any inefficiencies or losses. http://www.altestore.com/store/Deep-Cycl… . Or if budget is more important than running duration, then http://www.altestore.com/store/Deep-Cycl…

I still recommend a charge controller with a LVD to turn the pump off when the battery is low. So, while the panel requires only about a 2A charge controller, the smallest charge controller I can think of with LVD is the 6A, http://www.altestore.com/store/Charge-Co…

Joan Said:

12V Solar panel directly to 12V inverter...and restult.?

We Answered:

12v (12v nominal) is a descriptive term, not an actual voltage figure given. it serves to identify components that will work together in a system. your 300w inverter needs to see a constant voltage supply likely between 10.5 and 14.5 volts in order to function. a 12v battery (hopefully a deep cycle one) will remain at these voltages in day or night. your pv module (aka solar panel) is designed to work at 15-17 volts. why? because you have to be at a higher voltage to charge the battery which may not be full until 13 or 14 volts.

your pv module is not intended to be wired to the inverter,and the inverter manual will only describe wiring to a battery for this reason. not only will unregulated pv be too high a voltage, but it is also variable based on sunlight so it wont work at nigh, and is also only 5% of your inverters capability. the other answerer is correct, solar module to charge controller, charge controller to battery(s), battery to inverter, inverter to appropriately sized load. if your installation is permanent rather than mobile, you would be subject to national electric code, and also have to include appropriate grounding, overcurrent protection and disconnects.

very few loads can "run" directly from solar (aka pv direct). these are often things like fans or pumps that can handle variable voltage and power outputs.


james
altestore.com staff

Leonard Said:

12V Solar panel: how do I drop the voltage to 6V without just wasting the power?

We Answered:

The only way to not throw away more than half the power is to use a switching regulator.

There might be off-the-shelf 12V to 5V DC-DC converters, intended for use on motherboards. Certainly, there are 12V to 3.3V ones made.

If you wanted to design your own, you would find a part like the AP34063 or the LM5020, and build your regulator around that. This is a non-trivial exercise, though. Email me if you need more information.