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Alternatives to Power Inverters

Discussion in 'General Electronics Discussion' started by Raven Luni, May 20, 2012.

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  1. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    Greetings,

    Having had 2 car power inverters die on me after only a few uses (12V --> 240V, one 300W and the other 150W), I was reading about how fickle these things actually are.

    A couple of things I was wondering: first about the technology itself. I opened the 300W to see if I could find a blown fuse or something. There were 2 but both intact. What I did notice was the amazingly complex circuitry for something with such a simple function: a surface mount board more packed with ICs and other components than my PC's motherboard - in addition to the expected large transformers, capacitors, power transistors etc, also a peripheral board mounted at a right angle as crazy as the main one - just insane. Surely there cant have been any need for all that!

    The other thing: Although I'm tempted to build one myself without all that bloated, easily damaged crap, I still have my rule about not messing with mains power, BUT given the kind of stuff I wanted the inverter for in the first place i.e. phone and laptop chargers and basically devices that operate in the 5-12V region via a transofmer, why not skip that whole step. I assume that all I would need is some basic current protection and a voltage regulator right? (and maybe a voltage doubler for the occasional device needing 24V)
     
  2. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    I came across this while doing my research. It's a really good article explaining wire gagues and fuses and basically how not to set your car on fire: http://www.bcae1.com/fuses.htm
     
  3. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    Right - question: I have available some 7805s, and few assorted high power transistors which can easily be used for passing higher currents. I'm not looking to draw more than 3A, but all my resistors are 1/4W. If I use a divider network to increase the voltage of the 7805 to 9V, would these be suitable? (I read that hardly any current flows through the regulator anyway)
     
  4. duke37

    duke37

    5,273
    733
    Jan 9, 2011
    You are up early!

    The 7805 will probably do the job but remember that it is limited to 1A without using a bypass transitor. Even so dropping from 14V to 5V (9V) will dissipate 9W and will need a heat sink.

    I do not think that you will need resistors of more than 1/4W but each should be checked.
     
  5. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    I've been looking at a few configurations using pass transistors and I favour the ones using a second transistor for short circuit protection. The divider network wont draw much current (probably less than 20mA) but I'm still going to need a couple of heavy duty resistors on the input side so it looks like another order and more accumulation to my out of control component horde.....

    There are quite a few safety considerations for something as seemingly innocuous as taking 9V from a 12V car battery. I'll be sure to make good notes and share :)
     
  6. GreenGiant

    GreenGiant

    830
    6
    Feb 9, 2012
    I think another way to look at this would be to look at the input to the actual device, does the plug go directly into whatever it is that needs 240V?
    or does it have a transformer in between?

    if the device ultimately runs on DC then you may be able to modify just a plug and change the voltage a little

    Just my 2 cents
     
  7. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    That's exactly what I'm doing. Of all my devices, the most demanding runs on 9V @ 2.5A (my 4 track, and all part of my master plan to record the vocals for my song in the car so noone can hear me)

    The issue is in dealing with a car battery capable of delivering very large currents - make a mistake and things start to burn very quickly. I like my car and I need it to get around :p
     
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