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  1.    #1  
    For all you engineers out there -- I have a TomTom Bluetooth GPS receiver (MKII -- the new model). It comes with a car charger 5V 1A ("b" tip), but does not come with nor does TT sell an AC Charger. 5V is apparently an odd charger (Radio Shack does not sell one). Can a charger of less that 5V with 1A be used without ruining the unit. Any advice will me most appreciated. If not doable, I will buy a rechargable 12V battery jumper and use the DC outlet for the charge, but would really like to find a compatible AC charger.

    Thanks
  2. #2  
    The charger for the Treo 650 is 5V, 1A. You could purchase another AC adapter and cut the Treo connector off, find a tip to fit your GPS and solder it onto the AC adapter cable. You can use any adapter as long as you don't go higher in amperage. Lower amperage will take longer to charge the battery. Too low and you burn out the adapter.
  3. eKeith's Avatar
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    #3  
    Actually, you need an adapter rated 5V and any amperage greater than 1A, and of course the correct socket and polarity. The supplied device will only use as much current (amperage) as it requires. A lower amperage power source (adapter) will not provide sufficient power and can damage your device.
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  4. #4  
    Maybe you can order the wall charger for the GlobalSat BT-338 ????

    I checked, and they are compatible.
  5. #5  
    Actually, Radio Shack has one for digital cameras:
    273-1696

    It is multivoltage, 3,5,6,6.5,7, or 7.5 and up to 2000ma (2 Amp). This should work fine. It is $27.99.
  6.    #6  
    Thanks for the feed back. I had a 5v 2a charger from an old Compaq Ipaq -- same tip. Works great. Thanks again for the help
  7. #7  
    Quote Originally Posted by rhare
    For all you engineers out there -- I have a TomTom Bluetooth GPS receiver (MKII -- the new model). It comes with a car charger 5V 1A ("b" tip), but does not come with nor does TT sell an AC Charger. 5V is apparently an odd charger (Radio Shack does not sell one). Can a charger of less that 5V with 1A be used without ruining the unit. Any advice will me most appreciated. If not doable, I will buy a rechargable 12V battery jumper and use the DC outlet for the charge, but would really like to find a compatible AC charger.

    Thanks
    Here you go.

    http://batteryspace.com/index.asp?Pa...OD&ProdID=1406
  8. #8  
    You can use any adapter as long as you don't go higher in amperage. Lower amperage will take longer to charge the battery. Too low and you burn out the adapter.
    Actually, no. That is incorrect. Higher in amperage is ok (within reason). Usually up to double is ok on small electronics with rechargable batteries. It will charge your battery faster, but MAY still shorten your over battery life expectancy. Lower in amperage will take longer to charge, but will still charge the battery as long as it's not too low and you are using the proper voltage. Yes, too low in amperage will burn out the adapter. Up to double the charge cycle time for a charger should not burn it out.


    Actually, you need an adapter rated 5V and any amperage greater than 1A, and of course the correct socket and polarity. The supplied device will only use as much current (amperage) as it requires. A lower amperage power source (adapter) will not provide sufficient power and can damage your device.
    Also not completely correct.
    You can't just go with any amperage greater. If you were to give the battery a charger that could supply 7 amps, the battery is going to pull up to that full 7 amps immediately, until it reaches the charge voltage. Then, it will taper down as it requires less amperage to maintain the charge voltage. So, too large will definitely burn out the device and the battery. A lower amperage will still charge the battery, it will only take longer.

    A lower voltage charger would cause the charger to run at full output as long as you left it on or it timed out and would never fully charge the battery, thus not giving the full run time. Over multiple cycles like this, you will destroy the battery. Batteries need to be fully charged during charge cycles to maintain their life (or cycle) expectancy.
  9. eKeith's Avatar
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    #9  
    True... and well said.

    Note that many modern devices have built-in current-limiting overcharge protection...
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    Current Tablets: Lenovo ThinkPad Tablet 183825U; HP TouchPad 32GB w/ACL
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  10. #10  
    Quote Originally Posted by eKeith
    True... and well said.

    Note that many modern devices have built-in current-limiting overcharge protection...
    Thanks and I didn't realize that some devices have their own current limiting. I'm used to dealing with much bigger chargers and batteries for work.
  11. #11  
    Using a source with lower current rating can also heat the source quite a bit and can be a fire/burn hazard.

    - Sid
    Unlocked 650
  12. Entropy's Avatar
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    #12  
    Quote Originally Posted by CrazyC
    Thanks and I didn't realize that some devices have their own current limiting. I'm used to dealing with much bigger chargers and batteries for work.
    Yup. If the power supply is 5V and the battery is Li-Ion, it's basically GUARANTEED that the device has built-in charging circuitry. Li-Ion battery nominal charging voltage is 4.2v (or 4.1v, depending on the exact cell chemistry), hooking up 5v directly to such a battery is an almost surefire way to kill the cell. The typical Li-Ion charging regime is to use a current-limited constant voltage supply. At the beginning of the charge cycle the charger will reduce its voltage appropriately to keep the current below the maximum, but once the charger voltage reaches 4.1v or 4.2v, it will not increase it any more even though the current will begin dropping. (As opposed to NiCd or NiMh, which are usually charged with a constant current throughout the charging cycle).
  13. #13  
    Quote Originally Posted by Entropy
    Yup. If the power supply is 5V and the battery is Li-Ion, it's basically GUARANTEED that the device has built-in charging circuitry. Li-Ion battery nominal charging voltage is 4.2v (or 4.1v, depending on the exact cell chemistry), hooking up 5v directly to such a battery is an almost surefire way to kill the cell. The typical Li-Ion charging regime is to use a current-limited constant voltage supply. At the beginning of the charge cycle the charger will reduce its voltage appropriately to keep the current below the maximum, but once the charger voltage reaches 4.1v or 4.2v, it will not increase it any more even though the current will begin dropping. (As opposed to NiCd or NiMh, which are usually charged with a constant current throughout the charging cycle).
    So what you're saying is that most small electronic devices with NiCd or NiMh batteries use constant current charging instead of constant voltage??? No wonder most of my rechargable devices weren't able to keep batteries for very long.

    Any rechargable battery should be charge with constant voltage, unless trying to revive a problem battery or making sulfuric acid adjustments on a LARGE flooded battery.

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