Solar Mobile Phone Charger - DIY

[digimart]

Hi,
Like to ask your opinion / suggestion about Solar Mobile Phone Chargers.

Various brands of these chargers are available in open market, and online stores. Some models have an included rechargeable battery , whereas others just have solar cells in them. My purpose is to have a solar mobile charger, to be used seldomly, in case electricity is not available or not accessible.

Usually nowdays, most of the phones have a micro-USB connector, and the batteries are 5.5V, with varying capacity, such as 1200mA, 1800mA, or 2200mA.

As I be using this charger sparingly, so I think that the rechargeable battery included model might not be suited to me, as during periods of non-use the charged battery will drain itself, and in short term future may need to be replaced altogether.

How about I assemble (DIY) this solar charger without the rechargeable battery. My idea is that to connect 2 or 4 Solar cells, depending on their power rating. So that I get an output of 5.5V with a cumulative power of 8W or 10W or 12W.

Please advise me following :
a. My apprehension about degrading of in-built rechargeable battery in the solar charger is correct or not ?
b. Would I just need to connect the solar cells and attach a USB port OR I need to have some kind of small charger circuit as well ?
c. Without the rechargeable battery, the power being produced by solar cells, be having some variance. Would it be damaging for the mobile phone ?

If you have any other comment regarding the above, please feel free to add.

Thanks

Omar

[Sunking]

How about I assemble (DIY) this solar charger without the rechargeable battery. My idea is that to connect 2 or 4 Solar cells, depending on their power rating. So that I get an output of 5.5V with a cumulative power of 8W or 10W or 12W.

Just about all chargers to day comply with Standard BC1.1 in either DCP format which is just shorting pins 2 and 3 together to supply 5 volts @ 1.5 amps, or CDP format which I will not g into but it communicates with the device being charged up.

It is going to take more than 2 to 4 cells as that only gets you 1 to 2 volts, more like 12 cells or more followed up with a 5 volt regulator.

[digimart]

Just about all chargers to day comply with Standard BC1.1 in either DCP format which is just shorting pins 2 and 3 together to supply 5 volts @ 1.5 amps, or CDP format which I will not g into but it communicates with the device being charged up.

It is going to take more than 2 to 4 cells as that only gets you 1 to 2 volts, more like 12 cells or more followed up with a 5 volt regulator.

@SUNKING, thanks for correcting my mistake, I agree, regarding qty of cells. Usual solar cells available with Amazon, etc are in range of " fficiency Eff (%) 16.7-17.9 Power Ppm (W) 3.99-4.27 Max. Power Current Ipm (A) 7.89 - 8.16 Short Circuit Current Isc (A) 8.49 - 8.73 Max Power Voltage Vpm (V) 0.510 - 0.521 Open Circuit Voltage Voc (V) 0.623 - 0.625 ".

Pls can you guide me about what is "Standard BC1.1 in either DCP format" and how do I go about achieving this format, and where I can get a 5V regulator ?

On amazon I see this link for the 5V regulator , will it work in my case : " http://www.amazon.com/Voltage-Step-u...p+5v+regulator "

Thanks in advance.

[inetdog]

Pls can you guide me about what is "Standard BC1.1 in either DCP format" and how do I go about achieving this format, and where I can get a 5V regulator ?

The good thing about both standards for USB charging is that if the charger does not conform to either standard, the device being charged will just expect a lower current (between the minimum and maximum allowed in the original USB specification.) But some devices like iPhones may not work properly with a charger that supplies too low a current, putting you in the awkward position of having to deliver too much, even though not requested to, or not delivering enough.
The circuitry to do the BCP format is as simple as a current limiter which can be switched by a logic level to either of two current limit values. The CDP format is best handled using a control chip designed for that purpose.

My Droid X will work with a high-current charger and a short modern USB cable but not when I put an old USB extension cable in to increase the length. The communication protocol works just fine, but the series resistance is too high. The phone keeps trying to draw more power than is available and then trying to re-negotiate when the voltage drops too low.

[joannakrup]

A solar mobile phone charger is one such environment helpful product which can be used by people all over the world on an everyday basis and a lot of power can be saved in this manner. Solar cell phone charger is a device which will make use of the solar panel technology offered by the sun and convert it into the needed amount of power which is required in order to cost the cell phone.

mobilesolarchargers co uk

[PNjunction]

A solar mobile phone charger is one such environment helpful product which can be used by people all over the world on an everyday basis and a lot of power can be saved in this manner.

Digimart - for your homebrew project I'm glad that others brought up the negotiation part that might initially artificially limit the charge when it does not see enough current from the supply. This is one reason when using a solar charger, it is best to have the panel fully illuminated FIRST, and then attach the battery so that it hopefully sees the maximum amount of current and not negotiate down to a very slow speed. Of course it all depends on the device. Shadows and clouds may also cause a repetetive renegotiation which may lock the charge at the lower level despite the reappearance of full sun. It all depends on the device, and you have to babysit it. Fun and useful, but still we're talking solar toys for the most part.

Joannakrup - unfortunately, the world is ripe-for-hype when it comes to saving the planet one cellphone at a time.

What most marketers leave out is the total lifecycle footprint it has on carbon displacement. We know that the typical Li-ion (or variant) has a birth to death life of at most 3 to 4 years under the best of conditions, necessitating a repurchase. So how much does it cost in a carbon-footprint to manufacture, house, distribute, market and dispose of the product? Is that "greener" than just plugging it into the wall when all is said and done? Additionally, what about the peripheral infrastructure needed to house and administer the workers? What is the cost on a mere 1-hour lunch break for lighting and airconditioning just to manufacture the 3rd party battery packs?

Taken as a one-off product like a single pack, this may not seem like much. But now toss in the footprint of the manufacturing plant, container-loads of ship / train / trucks needed to distribute the packs, light and aircondition the wharehouse -- all the while the footprint savings gets smaller and smaller.

This problem scales right up to our larger solar projects that claim to save the planet. I am reminded of it every time I set out my backyard full of panels, wiring, agm batteries, controllers, and whatnot. Batteries need repurchasing eventually. Manufacturing and distributing cost the planet as well and will do so again when/if the products fail.

Back to the smaller scale - this issue is one reason that Sanyo Eneloop AA batteries have that name - the "Energy Loop" problem was recognized and attempts are made to make it smaller by doing the initial manufacturing charge from solar. Ok, maybe that's not going to save the world, BUT it is a recognition that one has to take the TOTAL lifecycle cost into account before declaring a product a world-saver.

[shayanjameel08]

Its great thing simply plug your cell phone into the charger when it is in direct sunlight for the amount of time you've calculated based on the battery of your phone and the power output of your charger.

[PNjunction]

Omar - back to the DIY effort:

The regulators used in most external packs are either linear-regulators, or can be up/downconverting switcher supplies. The linear ones are the easiest, but not the most efficient if the difference between your desired 5v output and the internal battery pack voltage is very high.

See the 3-terminal regulator video on the afrotechmods . com site. It explains it in detail from a practical DIY standpoint.

The question a consumer faces is: Does the 5v output have enough current capability to charge my device in a reasonable amount of time? Is that current enough to actually convince the charging circuit that it is ok to charge? 5V pack current outputs vary from the standard 0.5A, to 2.4A on the high end. Small devices may charge adequately with the lower 0.5A, but larger devices like tablets may refuse to charge at all from such a weak output and demand 1A or more to sustain a charge cycle.

The consumer will have to also decide if the overall capacity is enough to provide the amount of charge necessary. Some want an occasional top off. Others want to fully charge a fully depleted battery. When choosing capacity, add at least 30% to your needs. In other words, if you determine that you want to fully charge your existing fully-depleted 7000mah internal device battery, an external 10000mah battery would be the best bet since there are losses in the transfer of power from one device to another.

Note that fully-depleted is not actually fully depleted, as safety circuits inside quality units should not let a pack go lower than 3v under load. Critically, despite packs being typically only charged half-way for storage during retail, a consumer should first charge the pack before attempting to do their very first device recharge. This will help balance the dormant cells. Far too many try to recharge a device straight from the shelf without an initial first charge because they *think* the pack has a valid charge from the factory. This can lead to an imbalance in the cells that may be too far out for the internal balancing charge circuit to handle - again for quality units. An initial first charge is highly recommended no matter what the indicators display when first purchased.

Usage - storing a pack for emergency use usually means charging the pack fully. Unfortunately, LI batteries do NOT like sitting fully charged for great lengths of time. Thus, fully charging your emergency pack and throwing it in the drawer will net you the least amount of cycles. However this may not be critical if you are only going to use it a few times a year. This is one reason manufacturers only supply these batteries about half-charged. The battery has less stress during retail dormancy, but is enough that the small amount of self-discharge should not be a problem.

For the consumer, if they receive a pack that has barely anything in it, that means that the pack is practically new/old stock sitting in retail forever, and one or more internal cells *may* have triggered the disabling internal safety switch. These packs perform poorly, if at all. So getting fresh stock is vitally important - no more than 1 year old. It is quite common for a consumer to get a very old pack that may survive if they charge it first, but unfortunately the tendency is to try and charge a device first, and with the very low charge levels in the pack from retail dormancy, they push the cells well below the 3v cutoff, and typically trigger the charge-disabling safety cutoff rendering the pack dead.

Occasional use - here, unless the consumer absolutely needs top capacity from their external pack, it is best NOT to store them in a fully-charged state, but leave them sitting at only at a half-charge, and then fully charge when the need arises, such as for an upcoming event. I personally do not like leaving an occasional use pack sitting at full charge for more than a week.

Charge times - one should be aware of the maximum input the pack will accept for charging. Small packs usually will only charge at the old usb standard of 0.5A. Others may accept a charge rate of 1A input. If your pack will accept a higher current input, then choose a charging device be it commercial or DIY that can actually accomplish this. For example, some solar panel 5V outputs are only 0.5A and for a device that will accept 1A input, this doubles your charging time. So check the specs of your charger's output to get close to the capability of the chargers input - especially if you are using a solar panel in an area or season with limited solar-insolation.

Of course, for those just doing a top-off, this may not be so critical.

In the end, search out quality manufacturers and components. Cheap manufacturers are unsafe with poor quality components and engineering. Also note that any indication of "grade-A" cells is a completely irrelevant standard made up by marketers. Choose a high-quality manufacturer if you want to retain customers. One example is Anker.

[brokejame]

Such a great concept...But how much it costs? Any idea??

[digimart]

Such a great concept...But how much it costs? Any idea??

I guess it will cost something around USD 30 to USD 50, or max USD 100

[inetdog]

I guess it will cost something around USD 30 to USD 50, or max USD 100

Just FYI, the folks over at Candlepower, who love flashlights and rechargeable batteries, would like to see two key features in what you propose.

1. A micro USB port to which you can connect an external USB charger when you have AC available.
2. Some sort of LED light source for emergencies. Especially if you phone does not have a light of its own.