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I am looking for advice on replacing my radio adapter

  1. Jun 3, 2015 #1
    Hi there

    I recently lost the adapter for my radio. On the back of my radio, it says "INPUT: DC 5.9V --- 0.8A". So I am guessing I need an adapter that has an OUTPUT of DC 5.9V and 0.8A to match... .

    The only problem is having done a quick search online, the closest adapter I can find has an output of 5.9V and 1000mA (see here: http://www.amazon.co.uk/Danelo-1000mA-Adaptor-Supply-MBP36P/dp/B00IWWI05A). Will this be sufficient or will the mismatch in the current cause damage to my radio?

    Last edited: Jun 3, 2015
  2. jcsd
  3. Jun 3, 2015 #2
    That depends. Does your radio have a rechargeable battery?

    If it doesn't, then there's a good possibility it will work. I would try it realizing there was a small risk of damage to the radio.

    If it has a battery things get more complicated. It is still probably fine, but there's a small chance the battery might overcharge from too much current. What happens then depends on the battery type. It could lead to a toxic fire in extreme (and extremely unlikely) cases.

    If you can identify the battery, that would help in the decision making process.

    Me, I would just buy and plug in the adapter, charging it in the (dry) sink the first few times. But I like to live on the edge. o:)
  4. Jun 3, 2015 #3


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    I'm sorry, Jeff, but unless you are thinking of something way more complicated (an integrated charging/regulating circuit in the adapter), that isn't correct.

    The 1A output of the adapter is its capacity, not what it always sends. The radio will just pull what it needs: 0.8A. It should be fine.

    Remember: the power supply provides the voltage, but the load draws the current.
  5. Jun 3, 2015 #4
    What you say is almost always true.

    I've designed a battery charger that was current limited. Its purpose was to prevent hydrogen out-gassing from lead acid batteries. Such out-gassing can and has led to explosions. (But not in something as small as a radio.) Such things are as rare as hen's teeth, but it is a small risk of which the OP should be aware.

    Still, as I said, I would ignore the risk except to mitigate the risk of harm to people.
  6. Jun 3, 2015 #5
    There's no risk. You're not connecting a battery.

    You're connecting a device that requires a voltage source with a certain current capacity, as russ_watters wrote.
  7. Jun 3, 2015 #6
    Thanks for all comments.

    To clarify the radio can run from either DC mains adapter or it can have batteries... I don't know exactly what happens when for example batteries are inserted and the mains DC adapter is plugged in at the same time.. Would the radio draw power from batteries or the DC adapter in that case (or does it depend on the model of radio)? and also, assuming the batteries are rechargeable and we again put in the batteries and plug in the DC adapter, would the DC adapter begin to recharge the batteries?

    Lastly, after a bit of browsing, I have come across a cheaper adapter on Amazon http://www.amazon.co.uk/STOREINBOX-...id=1433368619&sr=1-1&keywords=5.9v+1a+adapter .

    But this adapter has a less closely matched OUTPUT of 9V 1A. Recall that the radio in question requires input of 5.9V 0.8A. Would it again (probably!) be OK to use this mismatched adapter, now that the voltage as well as the current is not exactly to the requirement of the radio?

  8. Jun 3, 2015 #7
    As long as the voltage matches and the current meets or exceeds the 0.8A, you should be fine.

    My concerns for the battery would only apply to an integral, rechargeable battery. That's not the case with disposable batteries.

    Good luck.
  9. Jun 3, 2015 #8


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    No, there is no almost about it ... it was an accurate statement
    the rest of your statement is irrelevant in regards to the OP

    on a non-rechargeable batteries device, when the DC plug is inserted, the internal batteries are switched out
    with a device designed with chargeable batteries. plugging in the external power will run the device and charge the batteries ... ie, the external power is used for both purposes

  10. Jun 4, 2015 #9


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    I second the view that the current capacity of the supply (it is not really a charger) must be 0.8A or higher, and that there is no way in the real world that a commercial 0.8A plug-in power source will be depended on to provide current limiting for a charger. The plug's label is merely stating that the supply must be capable of supplying 5.9V when the radio draws 0.8A. The fact that the charger you buy can even supply 5.9V when the radio draws 1.0A is a bonus.

    Your biggest problem will be connector compatibility.

    To Jeff Rosenury:

    Nearly ALL battery chargers are current limited. What they are not is dependent on the current capacity of a plug-in wall-wart supply to provide that limit.
    A wall-wart supply rated at 5.9V 0.8A is surely NOT current limited at ANY current other than what is required to not self-destruct when shorted.
    Yes, battery charger circuits require current limits. No, that limit never comes from the wall-wart. The charger system would NEVER pass regulatory standards if that were the case. PERIOD!
  11. Jun 4, 2015 #10
    The possibility of a fire, no matter how remote, needed to be pointed out.

    This is a public forum. We have no idea where the OP is located. We have no idea what, if any, regulatory standards apply there. We have no idea how well the OP reads English.

    If I were sure the OP was a reasonably competent American or European I wouldn't have bothered with the warning. But for all I know he is a Somalian child using Google to translate and fixing surplus industrial equipment. Electricity is dangerous if you don't know what you are doing. Not everyone does.

    My personal opinion is that this forum should be about trading professional knowledge. From that perspective you all are right to object to my paranoia. But that wouldn't make me feel better if someone died by taking my advice.

    As an engineer I am required to hold the public safety paramount.

    In 2012 six scientists were convicted of manslaughter for giving "a falsely reassuring statement" in Italy, where they didn't even live. This was later overturned (on a technicality), but they went through hell first.
  12. Jun 4, 2015 #11
    Thanks for all the posts.

    Just to be clear then, are you saying that the second adapter I was looking at which had OUTPUT 9V -- 1A would not be suitable for my radio which requires INPUT 5.9V 0.8A because in this case there is a mismatch between the two voltages? (ie. is it only OK to have a mismatch between the currents?)
  13. Jun 4, 2015 #12
    Oh wait, looking at this comment as well

    I am getting the impression that the INPUT and OUTPUT voltages must indeed be matched and the only mismatch can be current... but would be grateful for confirmation on this and perhaps a little theoretical discussion that would help me understand why this is the case!
  14. Jun 4, 2015 #13
    Yes, the supply and device voltages must match. The supply current must exceed the device's current draw. There can be a mismatch in current as long as the supply is larger than what the device needs.
  15. Jun 4, 2015 #14
    The radio requires a constant voltage source with a certain current capacity, and if you provide this, then it doesn't make a lick of difference what's actually inside the device.

    Rechargeable batteries, disposable batteries, or no batteries - it makes no difference.

    If there's a battery in the radio, then the radio includes charging circuitry that's tailored to the battery configuration and chemistry, just as is the case for your mobile phone etc., but that's nothing you, as the user, have to worry about.

    Consumer electronics is generally designed such that the user doesn't have to know anything about how a particular device actually implements its function. You just have to provide the supply it specifies, which, in the OP's case, is a constant voltage source. Anything else would be absolutely terrible design.

    Again, there's no risk of a fire if you just provide the supply the radio specifies.
  16. Jun 4, 2015 #15


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    Repeating what's been said that I agree with:

    1. The radio wants a 5.9V DC supply. You need to supply a 5.9V DC supply.
    2. The radio will draw up to 0.8A from that supply. The supply must still suply 5.9V when 0.8A is being drawn.
    3. A 5.9V 1A supply will meet both of the above requirements.

    I'll repeat what I posted previously --- your biggest issue will likely be with regard to connector compatibility. The various plugs used to provide voltage are large in number and widely variable. The outer diameter, inner diameter, inner pin length and diameter, etc can all vary. Technically you should also check the polarity, but that will probably be OK.

    For example:

  17. Jun 23, 2015 #16
  18. Jun 23, 2015 #17


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    It looks like one of the three on the right would be appropriate. Can you measure the power hole? Just select the next size down plug OD. The yellow ones with the bowtie shape are the easier choice as the center size is not as important because there is a clip in the center rather than just a hole. They come in other colors but yellow is quite common.

    I have very carefully drilled out the plastic end on those to fit a larger pin size. That is not possible on the other style.

  19. Jun 23, 2015 #18


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