Turning an AC/mains battery charger into a USB charger - help wanted

Discussion in 'The Projects Forum' started by scootley, Nov 6, 2010.

  1. scootley

    Thread Starter New Member

    Oct 27, 2009
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    Hi,

    I have a regular AC/mains charger for the G-series battery for a Sony camera.
    I would like to turn it into a USB charger.

    The charger lists input as 100-240V AC, 50/60 Hz, 4.5-8.5 VA, 2.6 W, 0.06-0.05 A, and lists output as 4.2 V, 0.25 A

    It is not an authentic Sony charger but an Asian fake.

    Here is an image (also attached) of both sides of the board, with the solder side flipped so that it is easier to visually match with the component side:
    [​IMG]

    I can post additional details as needed which may not be visible in the image.

    I would appreciate any tips on turning this into a USB-powered charger, instead of an AC/mains-powered charger. My current thought is just to remove the transformer and connect USB positive/negative to this board right where the transformer DC output is currently. Maybe I don't even need to remove the transformer.

    I know USB voltage isn't exactly 4.2, but maybe that isn't too big of a deal?

    I don't need it to sill work via AC, because I have another charger.

    The battery is lithium ion, 3.6 V, 910 mAh (3.3 - 3.4 Wh)

    Thanks much
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    rectifier is the diodes D3 and D? near the AC input. Looks like the tall transistor near R6 is the regulator.

    Do you have a voltmeter? THAT is the prefered way to probe this yourself. they are cheap as dirt and as necessary as air.
     
    Last edited: Nov 6, 2010
  3. scootley

    Thread Starter New Member

    Oct 27, 2009
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    Oh. I was confused between rectifier and transformer, I think. That's a transformer in the middle with the big green horizontal part with black above/below, right?

    I have attached a labeled and re-numbered diagram, since I cannot read all of the actual labels printed on the board.

    [​IMG]

    You're saying the rectifier is components #2 and which other one?

    And #6 is the voltage regulator?

    Yes, I have a voltmeter. I will now try to use it to figure out some stuff, but I am not really that familiar with the typical key components in a battery charger.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Damn, the longer I look at the thing the more I'm starting to doubt it is a traditional transformer to regulator circuit. The diodes I had refered to as the rectifiers are D3 and the other one with the black body that looks just like it.

    To probe it further requires you using AC power and reading the dc levels at the transistor devices using AC and DC settings on the meter.

    @Anyone: someone else want to add something, confirming or denying my fear that this is some sort of cheap switching type supply?
     
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  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You are exactly right, that is some very cheap switching power supply, and I doubt it will be regulated enough not to harm the battery. The battery may not last too less than with the original charger, depending on the battery type, but I wouldn´t bet on it.
     
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  6. CDRIVE

    Senior Member

    Jul 1, 2008
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    I don't see the point of trying to save anything from this charger except the connections to the battery. Everything else, from the USB port to the battery connections should be built from scratch. On the other hand, I wouldn't be surprised to find that inexpensive USB chargers are available.
     
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  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    A USB port has a output about 5 volt. The current a USB can source may vary. According to spec the USB port shall limit the current to 100 mA, if not the device are able to "negotiate" more power. However how well this spec is implemented in the USB controller may vary. Have you measured the voltage from your port? On this site you will find the USB pin configuration. http://www.addonics.com/emerging_technologies/usb3_tutorial.asp I guess in your case you could just connect a diode in series with the battery connector cable. This should lover the voltage enough.
    However you seams to be not so experienced. So I suggest you do your experimentation via an USB hub. If you do something wrong you may end up frying your USB hub. But if you connect directly to the PC. You will in worst case render your laptop useless. The cost of a USB hub i peanuts compared to a NEW laptop.
     
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  8. scootley

    Thread Starter New Member

    Oct 27, 2009
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    Well, I am in Asia in a place where I don't have "mail order" and really only have basic electronic components accessible. But even in the US, I have never seen a USB charger for a Sony camera battery, even online.

    So, can someone get me started on how to re-build it from scratch? Where could I read about a similar project?

    I should mention that my intent is not to actually connect the USB connection to a computer's USB port, but to other DC devices that have USB connections, such as a solar charging unit that I have, and an external "universal" USB battery, that I could use to charge/power a number of different USB-accepting batteries/devices.

    My true end goal is to be able to charge my camera battery while in the wilderness where I have only solar or mechanical energy, and do that via a standard USB connector.

    To do testing easily, I can just connect the charger to an existing AC mains-to-USB adapter that I have, instead of to a computer.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    I spiced a Vreg/Current Limiting circuit and I'll post it when I get back from my watering hole.
     
  10. CDRIVE

    Senior Member

    Jul 1, 2008
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    I included the above quote from 't06afre' because the precautions he posted are imperative if you're going to proceed with this.

    Anyway the attached circuit limits the max charge current as shown in the spice simulation and also limits the max charge voltage as shown. You may have to tweak some values depending on the transistors you use. Any PNP with Beta >=100 and max PD >= 500mW should be adequate for Q1 and 2N2222's should be fine for Q2 and Q3. The battery on the left, labeled 'USB Source 5' represents the PC's 5V USB output. The battery on the right, labeled 'Bat 3.6' represents your battery under charge.
     
    Last edited: Nov 7, 2010
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  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You're going to need a starting voltage preferrably 7V DC or higher to make it simple.

    Shame we can often buy all these USB chargers and hubs from Asia for less than $5 including shipping yet you have no access to them. Amazon.com is full of them as are places like mwave.com , newegg.com and especially eBay.
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Yes, it is kind of odd. I can buy a 12V - 5VDC regulated car adapter for $3 or so when on sale. For $3, I can maybe get a USB A connector and a 12V connector, but no regulation, etc.

    Find an obsolete cell phone charger, {they change connectors quite often), and have regulated switching supplies in most of them. Cut off the obsolete charging jack, and add the USB port on the end of the wire. Most I have laying around are about 3" x 1" x 1" wall-warts, rated for 5VDC@500mA - 1A

    Most all useful USB powered devices expect the guaranteed 5V from the jack, and nearly all try for the 500mA limit, the exception being USB Powered Hard Drives, which need two USB ports to get enough power.

    For battery chargers that run from USB ports, they expect the 5V to be there so it can be switched to 1V less with a tad more current.
     
  13. scootley

    Thread Starter New Member

    Oct 27, 2009
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    Thanks a lot. In your diagram, Q1 uses the PNP symbol, but isn't 2N3053 an NPN?

    Would you be able to upload the spice schematic file somewhere so that I can play with it? Or tell me how to model the battery in spice so that I can get the same simulation graphs as you did?

    Huh? You mean like simpler than CDRIVE's design? Because his uses an input of 5V, which is what I have to use anyways.

    Yeah. Not all of Asia is alike, though. And I have searched online a lot and never seen a device that does what I am trying to build (for my exact battery).

    I am not sure I'm getting what you are trying to say. Are you just talking about the ease of buying a similar class of device and how cheap it is? Because I don't want a car adapter, or a 12V connector. To take a cell phone charger and replace the phone connector with a USB connector is not creating what I want. That is an AC mains to USB 5V device. I want a device that takes USB 5V input and charges a very specific battery with that input. But if there is some easy way to turn those devices into what I am looking for as opposed to building the circuit from scratch, maybe I am not seeing it.
     
  14. CDRIVE

    Senior Member

    Jul 1, 2008
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    Oops! Sorry about that. The pit stop to my watering hole didn't make me smarter. :)

    I just edited that post and changed Q1 to a TIP42G sold by Radio Shack but you can use any suitable PNP power transistor.

    Edit: I just read through the specs on the TIP42 and I think I can find something more suitable. Let me look and post what I find. I'd like to see a transistor with higher Beta and a lower Vce(Sat). My sim used a beta of 100 for all the transistors. It was a conceptual simulation where I didn't spec the power requirements of Q1 and R1.
     
    Last edited: Nov 7, 2010
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  15. CDRIVE

    Senior Member

    Jul 1, 2008
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    OK, after doing some calculations, Q1 can be any small PNP that can handle 500mW and has a beta >=100. R1 will dissipate 100mW max if the battery is dead or the output terminals are shorted, so a 1/4W resistor is sufficient.
     
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  16. wayneh

    Expert

    Sep 9, 2010
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    I'm finding this entire thread a bit confusing. The stated goal is to charge a cellphone battery with a solar panel, right?

    I don't think modifying the original AC mains charger is the simplest way to accomplish that.
    [oops update] I just noticed that CDDRIVE made roughly the same point at post #6.

    You need a design that won't ruin your stuff, and the answer could be as simple as a blocking diode to prevent discharge thru the panel.

    The first concern is over-voltage that might fry the cellphone's charging circuitry. If the panel is not capable of producing that high a voltage, problem solved. Admittedly, it might be hard to determine what the "safe" limit is. But if the panel won't make more than 5v, it's probably not a problem. (Of course, it'll be harder to charge a battery.)

    Next concern is over-charge. The cellphone might have smart charging circuitry so you don't have to worry about that at all. I don't think the original charger appears to control state-of-charge, but I'm not sure. Also, depending on the capacity of the panel versus the phone battery, over-charging might be a trivial concern. I mean, if a 50% over-charge would require 2 days of bright sun, it's probably not a problem. If the panel can over-charge the battery in just an hour or two, well that's a concern.

    A final concern is charge rate, if the panel is huge enough to require current limiting to avoid blasting the battery.
     
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  17. iONic

    AAC Fanatic!

    Nov 16, 2007
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    I hope the charge voltage is setup for 4.2V as this generally represents a fully charged LiIon cell.
     
  18. t06afre

    AAC Fanatic!

    May 11, 2009
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    I also find this confusing. From what I can see the charger shown by the OP in the first post. Is a very simple switch-mode constant voltage power supply. It is rated 4.2 volt 0.25. So all the OP has to do is to make a low dropout regulator to transform the 5 volt from the USB port into 4.2 volt.
    At least this will be as safe as the fake mains based charger.
     
  19. CDRIVE

    Senior Member

    Jul 1, 2008
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    No, I made a bad assumption, from the OP's first post, that fully charged = 3.6V. Milking 4.2V from my design will be a hard nut to crack but I'll try.
     
  20. CDRIVE

    Senior Member

    Jul 1, 2008
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    In that case a single 1N4002 would put the charge voltage in range but there would be no over current protection for the USB port. Personally, I hope he decides to used solar cells and not risk PC damage. ;)
     
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