Book Reader charger?

Discussion in 'The Projects Forum' started by badspell68, May 12, 2008.

  1. badspell68

    Thread Starter Member

    May 10, 2008
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    My Sony Book reader has an AC charger to charge the internal Lipo batt. The chargers output is 5.2v 2000ma.

    I created a portable battery charger with four 1.2v Nicads to charge it when traveling...Could this setup damage the Lipo batteries or cause them to overheat?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The charger output does not say a lot about the internal battery. But since the NiCads are a lower voltage than the charger, they aren't likely to cause harm. They may not really charge the internal battery, but may extend the run time considerably.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    It sort of depends upon whether the electronics to control charging are in the book reader or in the external charging adapter.

    If the electronics are in the book reader, it would safely limit the battery charge current.

    If the electronics are in the external charger, and the book reader's battery was very low, it may cause very high current flow from your external batteries, causing them to have a short life, possibly overheating/exploding. This is because there would be no current limiter between the two different batteries.

    Without knowing what is inside of the book reader besides just a light and a battery, I can't tell you if it would be safe or not.

    Sony products are usually well-engineered. However, the engineers can't plan for every contingency; but it is likely that there are baleful warnings in the manual about connecting other than the proper Sony charging adapter.
     
  4. beenthere

    Retired Moderator

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    Might have been a rash assumption on my part - the adapter's rating for current makes it sound a lot like the regulator/charger is built into the book reader.
     
  5. badspell68

    Thread Starter Member

    May 10, 2008
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    Looks like the electronics are in the charging unit. Is there any way I can make this useful and not a danger to the internal battery?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    After thinking about it for a bit, there's a way you can determine if the charge circuit is inside the book light or inside the external charging adapter.

    Discharge the book light, and plug in the Sony charger using an adapter that you make from a jack and socket, probably available from your local Radio Shack.

    Monitor the voltage across the + and - side, and monitor the current flow.

    As the battery internal to the book light charges, the current will fall off, no matter where the charger circuit is.

    The voltage from the adapter is the key:
    If the voltage from the charger adapter increases as the charge current falls off, the charger electronics are in the book light.
    If the voltage from the charger adapter decreases as the charge current falls off, the charger electronics are in the adapter.
     
  7. SgtWookie

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    The crude-but-somewhat-effective way would be to use a single current limiting resistor. A 20 Ohm 1 Watt resistor would limit the current to 200mA if there were a 4v differential between the batteries. This is more than just a guess. Unfortunately, the power will be dissipated as heat.

    A somewhat more elegant way would be to build a constant current circuit out of a transistor, a couple of resistors and an LED.

    An even more elegant way would be to build a boost or flyback charger. But you probably don't have time for this.
     
  8. badspell68

    Thread Starter Member

    May 10, 2008
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    WOW...your really over my head on this as I am a newbie. The resistor sounds easy, but what about the unit needing 2000ma?
     
  9. badspell68

    Thread Starter Member

    May 10, 2008
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  10. SgtWookie

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    The Sony unit has a 2A charger. (2A=2000mA)

    The NiCD batteries have a relatively low-current output. If you try to get 2A of current from them by recharging a dead Sony Book Reader, they will likely overheat.

    The charging effect won't be efficient with the 20 Ohm 1 Watt resistor, and the resistor will likely get quite warm. However, it greatly lessens the likelyhood that they will explode on you.

    You would likely be much better off if you picked up a "travel adapter" transformer so that you can plug in your genuine Sony adapter for charging.
     
  11. SgtWookie

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    After looking at the internals of the Sony Book Reader, and the rather large size of it's battery, I'm afraid that your four NiCD AA batteries are woefully inadequate to the task of recharging the Book Reader.

    You really need the proper charging adapter. The NiCD's will give you very little additional reading time. You will not be happy with their performance, or percieved lack of it thereof.
     
  12. badspell68

    Thread Starter Member

    May 10, 2008
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    Good advice!

    I hike often and I'm away from power, so was trying to come up with a work around.
     
  13. badspell68

    Thread Starter Member

    May 10, 2008
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    What is a good place to learn all the basics of electronics so I don't blow up batteries in my face?
     
  14. SgtWookie

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    Jul 17, 2007
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    So, if I suggested that you read a book or take a hike, would you be offended? ;)

    There's a great resource for learning right here on this site:
    http://www.allaboutcircuits.com/vol_1/index.html
    I don't know what your level is, so that points to the beginning. Reinforcement of the basics never hurts anyone :)

    Batteries come in a myriad of technologies, capacities and capabilities. What's good for one battery/technology isn't good for others. Very large (and expensive) books have been written on the subject of just battery charging/discharging cycles alone.

    Funny, I just remembered trying to recharge some alkaline batteries using an automotive battery charger when I was around 11 years old. Yes, they exploded. :eek: I hadn't thought about that for quite a while.

    But basically, take a look at a battery's amp-hour rating. It might be listed as Ah (for larger lead-acid types) or mAh (for small rechargeables, etc). Divide that number by 10. That is the maximum charge or discharge rate you should attempt without further knowledge in order to be safe.

    Example: You have a battery that's rated for 600mAh. That is also 0.6Ah. Divide by 10 to get 60mA, or 0.06A. The battery will safely output 60mA for about 10 hours.

    But then, you need to compare that to Watts, as that's how many loads are rated. Let's say your batteries were 1.5v alkaline, still with a rating of 600mAh. We'll put four of them in series for a 6v output. Since we've configured them in series, we've increased our voltage output, but our total current output is still 600mAh; discharge rate is 60mA:
    P(Watts) = E(Voltage) x I(Current)
    P = 6v x 0.06
    P = 0.36 Watts, or 360mW
    So you can power a 360mW load for 10 hours.

    Charging is a bit more complicated, because certain battery types can be damaged if they're given a constant charging rate when they're nearly charged. Leave the charging up to the engineers for the moment.

    You might consider a solar charger. 5.2v x 2 Amperes = 10.4 Watts. You might even be able to hang the solar cell array over your shoulders as you hike to prepare you for an evening's read. But that's after you do some more reading ;)
     
    Last edited: May 13, 2008
  15. badspell68

    Thread Starter Member

    May 10, 2008
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    Got a bit of reading to do now.

    Thanks!
     
  16. badspell68

    Thread Starter Member

    May 10, 2008
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    The Sony book reader also charges off of a USB connection. Would this reveal that the charging hardware is within the book and not the AC adapter?
     
  17. badspell68

    Thread Starter Member

    May 10, 2008
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    I just thought of using a cell phone car chargers electronics attached to the four NiCad 1.2v batteries to charge the 5.2v Sony Lipo batt. Would this work?
     
  18. SgtWookie

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    Yes. A USB connection is capable of supplying up to 500mA @ 5v, except for laptops. They get an exemption, and also don't power things like that very well.
     
  19. SgtWookie

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    No, you would likely cause the four NiCad 1.2v batteries to explode.

    However, if you could convert the cell phone charger's electronics to a USB port 5v supply, that would charge your Reader.

    As long as it's 5v. Doesn't matter what the current is. Your Reader will only take as much current as it can use.
     
  20. badspell68

    Thread Starter Member

    May 10, 2008
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    That seems simple. Just attach a USB pug on the end that that charges the reader and solder the lighter socket end to the batts?

    What leads on a USB head are power?
     
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