I don't know where to start

Dawud · April 2011

I am sure this question or one similar has been asked, but I couldn't find it off hand and I have been racking my brain over this for a couple of weeks.

My life is very simple. There is no electricity in the house and I am content. I recently gave in and bought a cellular phone for communication purposes. I don't want to tie to the grid just for a simple phone. I do not have a vehicle to charge in either.

I know it charges on a usb port which is 5 volts and .5 amps. I just can't seem to figure out how big of a panel and battery to get. I am figuring, for the sizing, that it would run constant on the Panel and battery when is actuality it would only need to charge. That way there would be buffer to charge the battery. I worked it down to 1.8 kWh. I live near Prescott so a few days in a row without sun is normal for the monsoon and the snow season.

I really don't know where to go. A 12 volt system would allow me to use a simple battery as well as simple usb inverters to get the usb power required.

Thoughts? Help? Questions?

Thank you in advance

mr.radon · April 2011

Re: I don't know where to start

I made a USB charger for my sister's long vacation to Africa. This is a little over kill but would charge your phone just fine. (if it is a Verizon phone you have to add a resistor to get it to charge)
I made a smaller one for my trips into the mountains.

http://forum.solar-electric.com/showthread.php?t=9591

BB. · April 2011

Re: I don't know where to start

Yes, the other way to go would be a smallish solar panel, small charge controller, and a small 12 volt battery... Many times handy (use phone during day, charge at night).

Do you have any other 12 VDC power needs?

The total amount of power you need per day (and based on where you live--amount of sun per day, local weather patterns, etc.) will drive the size of the battery and solar array.

For example, a smallish but capable setup could be:

Solartech 10 Watt Multicrystalline Solar Panel
Price: $78.57

SunGuard 4.5 amp solar charge controller
Price: $30.47

And a 12 volt battery around:

10 watts * 0.77 derating * 1/14.5 volts charging * 1/0.10 rate of charge = 5 AH battery

Around a 5-10 AH AGM or other small lead acid battery.

You would get around 1-3 AH per day @ 12 volts (depending on season and where you live----Sunny or cloudy climate, etc.). That can keep a cell phone fairly well charged (deep winter gloomy days may be an issue).

All this depends on your load... I have a simple cell phone that will last 2-3 weeks on a single charge with light usage, and a smart phone that can be charged 2x, or more, per day if using it as a web browser.

Power usage is a highly personal choice.

-Bill

Dawud · April 2011

Re: I don't know where to start

Thank you. It would be house set, not portable.

Seven · April 2011

Re: I don't know where to start

It sounds like you don't need much. I rigged up one of those battery minder charger panels on a regular car battery for a lift winch at work. It is only used for about 3 minutes a day, but it runs a winch lifting 300 pounds. It has been there for over two years. How long does it take your phone to charge? 1.8kw seems high to me. Get a 12v (cigarette lighter) adapter to charge the phone and run from straight dc. You would be talking about $70 for the entire setup.

Dawud · April 2011

Re: I don't know where to start

I believe I am doing right on my math for the 1.8kWh/month.

5 volts multiplied by .5 amps (500 mah) yields 2.5 watts.
2.5 watts multiplied by 24 hours in a day yields 60 watt hours.
60 watt hours multiplied by 30 days in a month yields 1800 watt hours (1.8kWh). I am still rather new at the electrical conversion process, but I believe that is accurate.

petertearai · April 2011

Re: I don't know where to start

I have seen solar powered radios that include a port for cell phone charging.I think they are described as emergency/ disaster radios .That may be all you need?
Regards Peter

BB. · April 2011

Re: I don't know where to start

There are other losses too, but your math is correct.

Question is do you really need 0.5 amps 24x7?

My droid may use that much of I had the screen on high and browsing the web 24 hours a day.

-Bill

Eric L · April 2011

Re: I don't know where to start

I know it charges on a usb port which is 5 volts and .5 amps.

That's likely just the maximum draw of the charger when the cell phone battery is low. Once the cell phone battery is charged, the current draw probably falls to a handful of milliamps.

If you know how long it takes to charge the cell phone battery from empty, that would give you a better idea of the amount needed. If for example it took three hours to charge it, say, that would be 3 x 2.5 watts or 7.5 watt hours per day, before accounting for solar system inefficiencies, and assuming you need at most one full charge/day.

So a system like B.B. suggested above would probably be enough, in that case (one full three hour charge/day at most).

Dawud · April 2011

Re: I don't know where to start

The phone should be here come Monday.

It is one of those apple phone things.

BB. · April 2011

Re: I don't know where to start

Do you have access to a DMM (digital multi-meter) or something that can measure a few amps of current?

Take the readings every 10 minutes or so, and use the average current and the hours of charging to get:

Amp * Hours * Voltage = Watt*Hours per charge

Figure out how many times a day you charge, or how many days between charges to get an average Watt*Hours/Day of charging power requirement.

Note that Smart Phone usage can really impact charging and power usage... And browsing the Internet/online communications can become very addictive.

And probably double it to allow for errors, and variations in use.

Whether you choose the solar panel/USB charger route or using a 12 volt battery too, your choice.

Typically a 12 volt battery intermediate battery system needs a larger solar array (losses) and more costs (upfront and replacing battery every 1-3 years or so).

Many times a PV Array with 12 volt battery can be very handy... Charging batteries for a flash light, run an LED for a reading light, small fan, etc....

And pretty soon you will be running 400-800 watts of solar array, 2-4 deep cycle golf cart sized batteries, and a laptop with 4G or Satellite modem, reading lamps, and a well/water system pump.

-Bill

Dawud · April 2011

Re: I don't know where to start

I have a digital multimeter that I used for trouble shooting my electric fence. The fence is small and run off a dedicated panel box. When the gets in I will be headed back to the house after getting some charge data. My friend has been very generous for the use of his couch and computer while I wait for the phone.

After Monday, assuming even a temporary charging system can be found, I will be checking this forum a couple of times a week via the library.

Seven · April 2011

Re: I don't know where to start

Dawud wrote: »

I believe I am doing right on my math for the 1.8kWh/month.

5 volts multiplied by .5 amps (500 mah) yields 2.5 watts.
2.5 watts multiplied by 24 hours in a day yields 60 watt hours.
60 watt hours multiplied by 30 days in a month yields 1800 watt hours (1.8kWh). I am still rather new at the electrical conversion process, but I believe that is accurate.

I didn't realize you were talkingnabout per month, I thought you were talking about per day. Like said above, how long does it take to charge the phone. I would imagine no more than an hour. So that would bring your needs for it down to 2.5 watt hours a day times 30 days so only 75 watt hours instead of 1800.

Dawud · April 2011

Re: I don't know where to start

Alright,
The phone can draw up to 1 amp at five volts until the battery reaches 85 percent. At 85+ percent the draw drops down to .5 amps until fully charged. The maintaining charge is 5 volts at .25 amp. It take approximately three hours to charge from a complete dead battery to full. It can function at 5 volts .5 amps but the charging time is increased to 5 hours.

Eric L · April 2011

Re: I don't know where to start

So 5 watts for an hour or two until the load drops down to about 1 watt. Conservatively, you need a bit less than 15 watt-hours/day at the load. So B.B's suggested system combined with a small, inexpensive inverter equipped with a USB charging port (like this one), should work.

The one thing to watch for would be that the inverter isn't drawing power all the time (as an inexpensive one may if it were left on 'idle' continuously), since that could be a bigger drain on the system than the phone. So I would suggest that, after the phone is charged, you unplug it and flip the inverter off (most have a switch for this).

dwh · April 2011

Re: I don't know where to start

http://www.thinkgeek.com/gadgets/travelpower/e193/

jagec · April 2011

Re: I don't know where to start

Eric L wrote: »

So 5 watts for an hour or two until the load drops down to about 1 watt. Conservatively, you need a bit less than 15 watt-hours/day at the load. So B.B's suggested system combined with a small, inexpensive inverter equipped with a USB charging port (like this one), should work.

The one thing to watch for would be that the inverter isn't drawing power all the time (as an inexpensive one may if it were left on 'idle' continuously), since that could be a bigger drain on the system than the phone. So I would suggest that, after the phone is charged, you unplug it and flip the inverter off (most have a switch for this).

It's much more efficient, and inexpensive, to use a DC-DC converter to supply 5V from the battery. A USB car charger would be a better option for iPhone charging.

I don't know where to start

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