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Thread: A little AC/DC conversion help please

  1. #1
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    A little AC/DC conversion help please

    Today, 10:01 PM
    Hi guys. I'm hopeful to get some advice from the electronic sages in these forums.

    First, let me tell you my problem.

    I have a plan to arrange my car's receiver in my home as well as a mini amplifier, which both you know take 12v dc current from the car battery. I am hoping to find a converter/inverter that will do so and to understand the difference between those two words. Its easy enough to find a 12v DC to 120v AC inverter but I have failed to find any 120v AC to 12v DC converters with the amount of wattage I need produced (about 400 if both the receiver and amp is installed, 300 for amp 100 for recievers amp) I am wondering if these common inverters are backwards compatable, so that I can just use any DC to AC inverter in the home by installing it for use as AC to DC. If not then what is my next option?

    thanks.

  2. #2
    Senior Member hasserl's Avatar
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    Mac Tools Online Store - 12V, 40 Amps Battery Charger

    Are you sure of the requirements, seems like a very high demand for an automotive charging system.

  3. #3
    Old Timer Tom Phillips's Avatar
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    I agree that the power requirements seem really high. 100A for the receiver’s amp is 1200Watts at 12 V and 300A for the amp is 3600Watts. Something isn’t right there.

    Inverters are not “backwards compatible” so that option is out even for lower power.

    The output directly from a battery charger is not going to be filtered well enough to properly run your system. What you need is a battery eliminator / 12V to 14V DC power supply with high current capability which is going to be expensive. A car battery hooked to a charger would work but I wouldn’t want it inside my house.

    It may be cheaper & more practical to buy equipment that runs off the AC line.

  4. #4
    ToneOholic! big_teee's Avatar
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    Damn!
    That thing's Thirsty.
    I used to run Ham radios in the shop and different places.
    I liked a big Jell Cell Battery and a 12 Volt Charger.
    Good Luck,
    T
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  5. #5
    don't forget the joker g-one's Avatar
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    Tom: he was talking watts not amps .
    You still need 40 amps or so.
    Here's a cheaper one: pyramid power supplyyramid 40 amp dc power supply PS52KX
    Or you could run off a car battery that is connected to a charger all the time.
    Edit: that would have to be a charger capable of 40 amps continuous.
    "Thank you. Now on this next one , ladies and gentlemen, I'd like you to pay attention to my tone - not so much my singing or the band... " - JP Lepage

  6. #6
    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by g-one View Post
    Tom: he was talking watts not amps ..
    Opps. Gotta read more carefully.
    It's a problem to power this car stuff out of the car.
    Tom

  7. #7
    don't forget the joker g-one's Avatar
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    Just re-read what Hasserl said and he raised a good point. What they are calling 300W may not be what we think. Best bet is to see what kind of fuses they are using in the 12V supply lines. What are the receiver and the amp using for fuses?
    "Thank you. Now on this next one , ladies and gentlemen, I'd like you to pay attention to my tone - not so much my singing or the band... " - JP Lepage

  8. #8
    Senior Member Enzo's Avatar
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    Inverters make low DC voltage into high AC voltage - at least in this application of the word.

    I don;t use the term converter for the "other way around." WHat you are seeking is a 12v power supply. SImple as that. Car systems are nominally 12v but in reality they run on 13.8vDC. SO there are numerous 13.8v power supplies out there for guys who service car stuff.

    And no, they don't work backwards, any more than yelling into the speaker makes sound come out the microphone.


    400 watts is 400 watts, so it would need to be a hefty one. The battery chargers and similar would work as a starting point, but they won;t have much in the way of filtering, which you'd have to add. Batteries don;t care if the DC is smooth as glass.
    Education is what you're left with after you have forgotten what you have learned.

  9. #9
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    Thanks for the suggestions. After checking out all my options I happened to run across a solution to my problem from the fingers of members in another forum. Due to my american styled poorness, I needed a uncostly efficient solution.

    For those curious this the solution: I plan to rewire an old computer PSU to create a 30A unit =) I get to reuse old parts and have something new. Now that's what I call exciting.

  10. #10
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    Well, there are a lot of projects out there about converting a regular PC PSU into a 13.8V "lots of A" PSU, specifically to power Mobile Radio Transceivers , in different bands (VHF, Marine, Amateur Bands, etc.).
    Many are quite clear and very detailed.
    Google a little.
    Such as: https://www.google.com/#hl=en&cp=29&...w=1024&bih=600
    Good luck.

  11. #11
    Noodle of Reality Steve Conner's Avatar
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    Converting a PC power supply is doable, we had several threads about it over on the 4hv.org forum where we converted them to every voltage imaginable, made the output adjustable, and so on. If you're lucky, and get a modern one with lots of capacity on the 12V rail, it may work without modification.

    But why bother when you can get a Mean Well 12V, 29A power supply for $39.99.

    Meanwell DC Universal 12V 29A Regulated Switching Power Supply | eBay

    It looks like the same one I've got, in which case there is a trimpot for the voltage. It may go up to 13.8V, I haven't tried it. The fan is a bit noisy.

    If you still want to do it, here's one of the better practical guides I've seen. Our mods on 4hv generally followed this approach.
    http://www.qrp4u.de/docs/en/powersupply/
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  12. #12
    Old Timer km6xz's Avatar
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    A PC switch mode power supply with a rating of, say 400 watts, will not have enough current available from their 12volt output. That 400 watt rating it total power for all outputs added, most of the power it intended for a 5volt output.
    But switching power supplies made for 12 volts or adjustable to 13.8 volts are low cost and reliable, small and light weight. I have one on my work bench that can supply 13.8vdc regulated at 40 amps that is only 6 lbs. My HP 6269B lab supply is 0-40v at 50 amps is 105lbs and needs a 230volts source and BIG and cost a gazillion $ so it is easy to see why little cheap switching power supplies are so popular. Sure the HP has great specs, low noise/ripple and regulation but in your application you do not need those to a high degree. The gear was intended to work in an environment where regulation is poor, with lots of line noise so a switching supply would be perfect.

  13. #13
    Noodle of Reality Steve Conner's Avatar
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    Correct, if you want the full wattage on the 12V output, you'll need to rewind the transformer, install bigger diodes, rewind the output filter inductor with heavier wire, and so on. A lot of work to save $40. Really only worth it if you want to learn about switchmode power supplies, as we did.

    The latest PC power supplies do give most of their wattage on the 12V rail, because that's what modern motherboards and gaming graphics cards use, they all run off 12V that gets bucked down to something like 1.5V at 100A, right at the processor chip. But they cost more than the Mean Well.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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