Solar USB Charger Design?

AmishdudeAmishdude Solar Expert Posts: 29
I have a spare 12v solar panel that I would like to dedicate to charging USB powered devices (cell phones, I-pad, etc.) What do I need to drop the 12v to 5v and get it to an output suitable for my intended purpose? Thanks in advance to the gods of solar here at the Wind&Sun forum. :cool:

P.S. I do know that I need to find a way to limit the charging current to 500mA to be USB compliant. How do I accomplish this? That stuff I learned in electronics school just didn't stick with me. (Alzheimers)

Comments

  • erneerne Solar Expert Posts: 41
    Re: Solar USB Charger Design?

    You can get a small 110 volt inverter with a usb port in it or use the ac plug with a wall wart 100 watt would do. you would need a battery and regulator though.
  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?
    erne wrote: »
    You can get a small 110 volt inverter with a usb port in it or use the ac plug with a wall wart 100 watt would do. you would need a battery and regulator though.
    Yeah...that just seems to be going to long way around. 12VDC --> to 110VAC --> back to 5VDC. If that's the only way to do it, OK, but it just doesn't make sense to me given the losses incurred in the back and forth conversion. I know you can buy junk solar USB chargers that lay on the dash of your car to charge your Ipod, and basically I'm just looking for a way to do the same thing only on a larger scale. Perhaps that's where the problem lies.

    Was hoping to come up with a beefed up version of this circuit perhaps. Problem is getting it to handle the 12-24VDC input at pretty high potential currents while limiting the output current to 500ma.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Solar USB Charger Design?

    Problem is getting it to handle the 12-24VDC input at pretty high potential currents while limiting the output current to 500ma. This makes no sense??? what high imput currents???the imput will only draw enough to supply the 500ma output.. it makes no difference if the input is connected to a 5000a 12v generator or 8x"D"cells in series. it will still draw the same input current.
    Your wanting to use an IC as the voltage regulator is ok only to a point. it cant current limit the output. But having said that it really does not matter if the USB output could provide 50amps the device connected to it will still only draw its designed current."below 500ma"
    Here you can buy 12v input car addaptors that can provive 2a output and its what I use as you can connect a few USBdevices to it and be assured each device will have adequate power
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Solar USB Charger Design?

    Note that 3 terminal regulators are "analog" and not very efficient. That circuit above is, at best only 20% efficient at 24 volt input.

    The rest of the energy goes out as heat--about (~20 volt drop * 1/2 amp=) 10 watts. That is a lot of heat for a small 3-T regulator to dissipate.

    Any of the decent USB converters are going to use switching regulators for the job. A bit more complex and layout sensitive.

    I am not sure this will work (12-24 VDC USB converter). You might have to call them to find out. A 24 volt deep cycle battery system will reach 30-32 volts during equalization. Many car/truck type DC Adapters are not really designed to go much over 14.2/28.4 volts peak.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar USB Charger Design?

    He's starting with a 12 Volt panel, so the biggest problem is keeping the Voltage down to the 13.8 Volt typical of an automotive system. If it's not a very large panel this would be fairly easy, but knocking down 7 Amps of current from a K135 operating at 17.7 Volts is more difficult. Will there be a battery or not? Batteries are nice for leveling out the fluctuations in panel power production.

    Once you've got the 12 VDC steady, plug in http://www.futureshop.ca/en-CA/product/rocketfish-rocketfish-usb-car-adapter-charger-rf-m357-rf-m357-t/10126360.aspx?path=be0adbdaa1cc07a9da3c1fc47eedf2f5en02 and you have your USB power.
  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?
    Yeah...you suppose that thing will survive a 20VDC input from my 12V panel if I get a nice sunny day?? I'd wager it would go up in smoke.
  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?
    He's starting with a 12 Volt panel, so the biggest problem is keeping the Voltage down to the 13.8 Volt typical of an automotive system. If it's not a very large panel this would be fairly easy, but knocking down 7 Amps of current from a K135 operating at 17.7 Volts is more difficult. Will there be a battery or not? Batteries are nice for leveling out the fluctuations in panel power production.

    Once you've got the 12 VDC steady, plug in http://www.futureshop.ca/en-CA/product/rocketfish-rocketfish-usb-car-adapter-charger-rf-m357-rf-m357-t/10126360.aspx?path=be0adbdaa1cc07a9da3c1fc47eedf2f5en02 and you have your USB power.
    I hadn't planned on a battery, but it appears that there will be no avoiding it. Things are just more complicated than it seems they should be. :(
  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?
    john p wrote: »
    Here you can buy 12v input car addaptors that can provive 2a output and its what I use as you can connect a few USBdevices to it and be assured each device will have adequate power
    Did you mean to provide a link to this device? Also, can it handle a large variation in input voltages up to 18-19VDC?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar USB Charger Design?

    Don't panic yet. :D
    The plug-in adapter won't handle 17.5 Vmp from a panel, true. But you may be able to regulate that lower without too much difficulty. The question is, how big is the panel?

    In essence you want to "lose" about 4 Volts. When you do this it turns into current, and so heat. If you have a small panel (20 Watts) it can't put out much current (a little over 1 Amp max). If it is a large panel it becomes more difficult. Like Bill said, those little IC regulators aren't good for 10 Watts.

    Ultra-simple circuit: dropping resister, 12 Volt Zener, filter capacitor. May/may not work depending on the adapter's power needs and the USB device's draw (up to 500mA).
  • RCinFLARCinFLA Solar Expert Posts: 1,393 ✭✭✭✭
    Re: Solar USB Charger Design?

    Solar panel is an illumination based current source. The best solution is an active buck switcher to take the panel voltage down to 5vdc.

    Remember the panel is not a voltage source. Most switchers, like a cigarette lighter charger will not work properly when the input is from a high impedance current source. You may be able to add a large value electrolytic cap between the panel and regular cigarette lighter charger and make it work, at least when the panel has good illumination. You can buy a $5-$10 cigarette lighter charger and try it with a 1000 uF cap or more across the panel.

    If you are talking about a larger smartphone with 1200 mAH to 1850 mAH battery, almost all draw more then 500 mA USB limit when on their own charger, not a regular USB data port. They have a manufacturers' specific resistor setup on the USB data lines in the wall mount or their cigarette lighter charger that the phone senses to know it is okay to draw more then 500 mA of current. For smartphones this is in the 700 mA to 1000 mA range. Sometimes these resistors go between the 5th 'ID' pin on the mini or micro USB plug to ground pin. The resistors are in the USB plug end, molded into the connector plug.

    Most desktop computer USB ports allow you to draw more then 500 mA's from their USB ports.

    The phones have a linear regulator that runs as a voltage limited, constant current source to the Li-Ion single cell. On a generic USB computer port that delivers 5 vdc there is a USB protocol that starts out at 100 mA draw then gets permission from host USB via data lines to go to 500 mA. Some laptop computers may not allow a 500 mA draw on USB port when they are running on their internal battery pack.

    You don't want the phone to see more then 5.5 vdc as it adds more heating within the phones linear regulator. Most phones will not even allow a charging connection if the USB voltage is too high. They want to protect their internal regulator.
  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?

    As usual, you guys have been a veritable fount of wisdom and knowledge. It appears that the only "simple" solution is to build another complete system with charge controller, battery, inverter and use each device's unique proprietary charger since this is a 135W panel. Not what I had hoped to hear, and outside of my financial capability at this point, but probably the best solution nonetheless.

    This is what I was hoping to accomplish: http://www.ebay.com/itm/Portable-Thin-FIlm-Lightweight-Solar-Battery-Chargers-40-Watt-Panel-w-USB-/280828462435?pt=LH_DefaultDomain_0&hash=item4162ae4563 but only using my spare 135W panel.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar USB Charger Design?

    Oh well, it was a nice dream while it lasted eh? :p

    Handling the current from a 135 Watt panel (converting to Voltage and regulating it) requires more expensive components than it would for a 20 Watt panel. The whole charge controller-battery thing would be the only sure-fire way to keep the Voltage from spiking and frying any USB adapter equipment I fear.
  • mike95490mike95490 Solar Expert Posts: 9,359 ✭✭✭✭✭
    Re: Solar USB Charger Design?

    I use my Monolith to charge a 12V battery, and then use a regular 12V car/usb adapter, which seems to have worked fine (phone is charging in the lower photo)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • AmishdudeAmishdude Solar Expert Posts: 29
    Re: Solar USB Charger Design?
    Oh well, it was a nice dream while it lasted eh? :p

    Handling the current from a 135 Watt panel (converting to Voltage and regulating it) requires more expensive components than it would for a 20 Watt panel. The whole charge controller-battery thing would be the only sure-fire way to keep the Voltage from spiking and frying any USB adapter equipment I fear.
    Yeah. If I get bored, I might pick up a small panel and tinker with this idea some more, but would have been nice to use that odd panel I had.

    I did find this item intriguing though:
    Attachment not found.
    http://www.ebay.com/itm/Dual-Output-12V-5V-Dc-Dc-power-module-LM2596-Input-7v-40V-Good4-Solar-/350521587367?pt=BI_Electrical_Equipment_Tools&hash=item519cb6f6a7
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar USB Charger Design?

    Nice unit.
    Maybe they have plans for connecting it to solar? Panel output still has to be converted to a relatively stable Voltage rather than a current.

    Ah, the fun we could have if only we had the time (and money) to have fun! :D
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