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Powering a 5V device

Discussion in 'General Electronics Discussion' started by mcf57, Jan 4, 2010.

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  1. mcf57


    Jan 4, 2010
    I have a small portable satellite radio that I would like to power with my universal power adapter in order to be able to use it in the home. The radio came with a 12volt car adapter that is intended to be used with it in a vehicle. Now, this 12 volt adapter states on it that its output is DC 5V 1.5A. I take it this means 5 volts and 1.5amps, correct?

    My universal AC adapter is rated up to 1200milliamps and can be dialed for various volts including 3, 4.5, 6, 7.5, 9 & 12. I didn't think it would work since it was essentially only about 1.2 amps & there was no "5V" setting on the AC adapter. However, I set it to 4.5 volts, tried it & it seems to have worked to power the unit & make it function properly. I haven't left it on for long periods as I'm not totally sure about the settings I have picked & wanted to ask around first since I'm not a total voltage or amp expert in how they work together. I sort of figured that as long as I don't go over 5V or 1500 milliamps, I won't blow it & hopefully be OK. Is this thinking correct? Or can I possibly still damage the radio even with these lower settings on the AC adapter?
    Last edited: Jan 4, 2010
  2. Resqueline


    Jul 31, 2009
    Q1: correct.

    Q2: 5V logic devices usually have a tolerance of +/-10%, so 4.5-5.5V is ok. They will sustain damage at 7V.
    The problem with that kind of universal adaptors is that it's hard to know how well regulated they are.
    I'd want to check it's actual output voltage before I'd dare plug it into anything valuable/critical.
    The rated amperage of 1.2 is a little low, it could be overloaded. It should be at least as high as 1.5A.
  3. mcf57


    Jan 4, 2010
    When you say "it could be overloaded", you are referring to the AC adapter itself being overloaded and not really the radio, correct?
  4. Resqueline


    Jul 31, 2009
    Yes, the universal adapter, but only if the radio makes full use of the original adapter's capacity.
    It's hard to say if the radio itself is at risk - w/o measurements.
  5. mcf57


    Jan 4, 2010
    I sort of forgot about this, but I'm actually running another satellite radio (old STARMATE1) unit in an office with a Jensen universal adapter as well. Its been working great for about 10+ months now. The radio itself requires a 12volt connection so I was able to dial that amount exactly & directly on the AC adapter. This Jensen adapter is rated up to 1700 milliamps too.

    I'm not sure how many milliamps this STARMATE1 radio is drawing, but I'm thinking maybe I should swap the AC adapters and have the Jensen power the 1st radio I talked about (5V, 1500milliamps) since it seems a better fitted. I guess I need to find out how many milliamps the STARMATE1 radio is requiring cause if its like the 1st one (1500milliamps), then no need to really switch.
    Last edited: Jan 5, 2010
  6. davenn

    davenn Moderator

    Sep 5, 2009

    Exactly ..... get a multimeter inline in the cct and see what currnet is being drawn :)
    you may find that its only 1 amp (1000mA). Dont forget it doesnt really matter if the current capability is much larger than the current required by the device.... it will only draw what it needs per Ohms law. so it doesnt matter if the power supply is 1.5 amps or 15 amps it will still only draw the 1amp :D

    I would use a power supply that is rated at least 200-300mA more than what is required
    by your device just so that the powersupply isnt at its limit.


    PS late edit.... additionally to that last comment of mine ..... as the current drain for a given device
    gets higher then have a larger headroom of available current by the power supply

    ie ... a 1 amp load headroom of at least 200-300mA
    a 10 amp load a PSU rated for at least 12-13 amps
    you get the picture :)
    Last edited: Jan 12, 2010
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