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Advice on choosing a transformer

  • 23-07-2003 3:03pm
    #1
    oscarBravo
    Technology & Internet Moderators Posts: 28,830 Mod ✭✭✭✭


    I see that this board tends to be mostly about PC issues, but I don't see an electronics-specific board, so here goes:

    I have a car radio with CD changer that I'm planning to install in a bedroom. Being a car radio, obviously it's 12V, but how do I know what it's power requirements are likely to be?

    As an experiment, I wired it up with a 6VA transformer, therefore supplying 500mA. The display lit up, but when playing a disc it dims substantially, and the sound is distorted - not unlike a portable radio with low batteries.

    Obviously, it needs more than 500mA. The "memory power" lead has an inline 5A fuse, so I guess that's my upper limit. Anyone care to speculate as to what an appropriate transformer rating might be? If it plays (albeit poorly) with half an amp, would 2A be a good bet?


Comments

  • #2
    tonky
    Registered Users, Registered Users 2 Posts: 897 ✭✭✭tonky


    Hi, I did this before a couple of times, using a CB supply 13.8V, one was 5A the other 15A. At a guess it sounds like you'd need at least 1.5 - 2 amps to get the thing to work properly, esp with the CD changer included. Hard to tell without seeing it or more details. btw I still have both of those PSU's here somewhere.


  • #3
    milltown
    Registered Users, Registered Users 2 Posts: 4,618 ✭✭✭milltown


    The dimming LEDs and distorted sound was due more to being 6v short on voltage than any current supply problems.


  • #4
    tonky
    Registered Users, Registered Users 2 Posts: 897 ✭✭✭tonky


    OscarBravo, did you get sorted out ok?
    I still have those 2 x 13.8V PSU's here if you're stuck.

    Milltown: I presume Oscar was using a 12V 6VA(Watt) transformer giving 500mA. Where does the 6 volts short come from?. Just curious...


  • #5
    Gerry
    Registered Users, Registered Users 2 Posts: 4,487 ✭✭✭Gerry


    2A is far too low. But what you should do is google the model number, the power requirement is bound to be in the manufacturers specs. Failing this, try and find out what power output the unit has ( if its any good it could be 4 x 20watts or 4 x 35watts ). ( I don't know if the "memory power" is the only power lead, sounds like something to keep the stored radio stations ) The amp in the head unit will be far from 100% efficient, I'd add on some more watts. Lets say 100 - 150watts, 8 - 13 amps. However, if you don't want to use the built in amp to drive speakers ( say you are using line out to a hifi), I'd say you could get away with 1 or 2 amps. If this is confusing feel free to ask for a better explanation....


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