solar phone charger - Page 1
Forum section: electronics / projects

author: Arcamax
author_rank: Regular Contributor
timestamp: February 01, 2015, 07:41:26 pm
content: I want to know how to do this, as i already tried once with 9 solar panels, i think were 2.5v max/.08mA max each and in a series/parallel combination and didn't work.So i want to use anLM317T 5 volt regulatorand i need some different solar panels that will work for me this time, i was thinking to use 10 volts total and bring it down til 5volts with regulator. So I need a series/parallel combination of either:4- 5v-1W panelshttp://www.ebay.ca/itm/5V-200MA-1W-Mini-Solar-Panel-Mod...or2- 10v-1.17W panelshttp://www.ebay.ca/itm/1-17W-Solar-Panel-Cellphone-Char...or any other suggestions would be appreciated... thank youAlso how much mA would i need to charge my galaxy S3...?

author: Seekonk
author_rank: Super Contributor
timestamp: February 01, 2015, 08:21:00 pm
content: Using a linear regulator not only wastes peak power but greatly overloads the panels in low light. I would use a 2596 regulator module available on ebay for only about $1.50 shipped. Then I would lift pin 5 of the chip and add a transistor so it maintains the input voltage at MPPT for optimal power out. It works great!

author: Arcamax
author_rank: Regular Contributor
timestamp: February 01, 2015, 08:45:58 pm
content: Quote from: Seekonk on February 01, 2015, 08:21:00 pmSo this one be good?http://www.ebay.ca/itm/Buck-Converter-Step-Down-Adjustable-Converter-Power-Module-Regulator-LM2596-New-/251815854466?pt=LH_DefaultDomain_0&hash=item3aa1650182or this one sorryhttp://www.ebay.ca/itm/Buck-Converter-Step-Down-Adjustable-Converter-Power-Module-Regulator-LM2596-New-/271683002872?pt=LH_DefaultDomain_0&hash=item3f4191a1f8which is pin 5which transistor and where

author: poot36
author_rank: Frequent Contributor
timestamp: February 02, 2015, 07:37:56 am
content: I am trying also to recharge a 5V device (a Wii U game pad) from one of those 1.5 to 1.8 watt solar car battery maintainer panels and I have tried using a 5V regulator but I have found that I need a really large filter capacitor on the output or input of the regulator to make the circuit work. It caused the game pad to draw 40 Ma or so. I have also tried it with a buck converter in the form of a cigarette lighter to usb port converter which also needed a large capacitor on the input to even start up. The buck regulator also for some reason could not provide the same current as the standard 5V regulator. I did not get a chance to try it with the game pad as the sun was going down and it only had a mini and micro usb output on it but it could not even power a usb to sata laptop drive converter board without the drive attached so I suspect that it would not be able to charge the game pad anyways. The game pad can charge with as low as 30 Ma of current (it may be able to go lower but I tested this by putting a 33? resistor in series with the standard game pad charger and that is what it drew. The normal draw with a totally flat battery is 650 to 730 Ma with the unit turned off. I am just trying to make a battery maintainer for when the game pad is not in use it will flatten the battery in less then 2 weeks. I suspect it is because the max input rating for the switching chip is 16V and when the solar panel is unloaded it provides around 24V. All my tests were preformed behind a window and the panel was putting out 24V open circuit and 40 to 50 Ma short circuit. It was an amorphous based panel (the brown red colored type) so less efficient for its size but more efficient in low light. Keep in mind that most cell phones need the two data pins of the usb connector to be pulled to a certain voltage or tied together for the phone to start charging.

author: Arcamax
author_rank: Regular Contributor
timestamp: February 02, 2015, 08:30:13 am
content: So i understand that the2596 regulator moduleshould work for me, just that i still want to know if thelm317t regulatorwould work. I ordered a pack of 3 lm317t's awhile agoand had them resend them due the fact that they took way longer to arrive than they said, meanwhile the first set came so now i have 6 of them and i need something to use them.Thanks

author: Seekonk
author_rank: Super Contributor
timestamp: February 02, 2015, 01:56:00 pm
content: Those 2596 modules are quite handy though I would be leary of drawing much more than a half amp from them. Pun #5 is the one on the far right and it goes to common neg. That pin is lifted and a circuit is added as in the TI/National May 2002 data sheet figure 22 Undervoltage Lockout. Change the base resistor to a pot so it is adjustable. A typical 12V solar panel has an open circuit voltage of 21V and a power point of 17-18V. The ideal zener should be about 2V below the power point, The power point is usually around 80% of open circuit voltage. It is not too critical, a 12V would work fine.It is harder for me to come up with a zener than a TL431, an opamp with a 2.5V reference. These are found in about any PC power supply near the opto and in many older wall warts. Use that in place of the transistor. They switch at 2.4V so a 10K and 100K pot divider circuit would be adjustable to 25V. The 431 can only clamp down to 2.5V so a 15K to 4.7V divider is needed to feed pin #5 to get the ON voltage below .6V. In order to insure it turns off the 47K collector pullup has to be changed to 10K to get a high enough OFF voltage.The input power (solar panel) to the module has to have at least 1000uf added to it to store the panels current for short periods during the off periods. Set the voltage pot to 5V or whatever charge voltage is needed. That insures the maximum voltage. Place a resistor on the output so the converter is slightly overloaded, output voltage under set point. Then adjust input voltage for maximum output. Pane power point voltage does not vary with light intensity. Only panel temperature changes that voltage, it increases with colder temps. Even then a summer setting would work fine in cold temperatures.

author: Arcamax
author_rank: Regular Contributor
timestamp: February 02, 2015, 06:16:16 pm
content: so for that 12volt solar panel, can i use 2 - 6volt ones.

author: Seekonk
author_rank: Super Contributor
timestamp: February 02, 2015, 07:54:09 pm
content: Yes. OR THREE. You can not exceed 35V on the input because of cap voltage. Pin 5 can not exceed 25V, the reason a voltage divider is often included on that pin. A good read for you,http://www.egr.unlv.edu/~eebag/Solar%20Cell%20Shading.pdf

author: Arcamax
author_rank: Regular Contributor
timestamp: February 02, 2015, 09:30:33 pm
content: so yeah i need phone charger to have 5volt output (kind of obvious i just). so you think 2 - 6volts= 12v for solar or do you recommend 18v.

author: Seekonk
author_rank: Super Contributor
timestamp: February 02, 2015, 11:16:03 pm
content: I would certainly recommend more as long as the panels are matched. With switching supply voltage will be converted into more current. Are you considering the mod with the zener or 431?

author: Arcamax
author_rank: Regular Contributor
timestamp: February 02, 2015, 11:30:05 pm
content: Quote from: Seekonk on February 02, 2015, 11:16:03 pmim considering it yes. what was the difference of thezenerthan the 431so do mean more voltage input converted be more current on output or input

author: Arcamax
author_rank: Regular Contributor
timestamp: February 03, 2015, 07:49:11 am
content: what was the difference of the zener and 431 modifications

author: Seekonk
author_rank: Super Contributor
timestamp: February 03, 2015, 09:24:36 pm
content: It depends on how many zeners you have sitting around. The TL431 is preferable, easy to find in an old power supply. Any opamp or comparator would do as long as you have a reference voltage and it is set up for the output to go low when input exceeds the reference. A diode would do as a .6V reference. Temperature variation would work in the circuits favor.

author: Arcamax
author_rank: Regular Contributor
timestamp: February 03, 2015, 10:45:19 pm
content: if i use this buck convertor should i still mod it with either twohttp://www.ebay.ca/itm/DC-DC-Buck-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-/160995621268?pt=LH_DefaultDomain_0&hash=item257c163994Also does it matter what the input current of the solar panels are to this converters output