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110 to 12v converter?

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  • darryl
    replied
    Regulated power supplies aside, most 'brute force' ones actually deliver from 14 to about 16 volts with no load. If you are going to regulate the output voltage, it makes sense to start with 20 volts, but if you just want to make sure you have at least 12V under full loading conditions, then start with 14-16 volts. None of the motors we're talking about here will care if the voltage is a little high. In a pwm or chopper circuit, the output device when fully on won't waste more than a volt or so, so there's essentially full voltage available to the motor when the output device is on. There may or may not be the need for a higher voltage to begin with, depending on the particular design. I'd suggest a good design of controller won't have this 'extra' voltage requirement.

    That being said, you can then select a transformer with a secondary voltage rating of about 11 vac. That will be under load, so what you end up with is about 15 vdc after rectifier losses. That will drag down to about 12v under load, so it gets you into the right ballpark. If all you can find is a secondary rating of 12vac in a suitable transformer, that's fine.

    If I recall, the power pack that used to come with rv's outputs about 16 volts with no load. It would be perfect for your application. If there's a failure mode in those, for the most part it's going to be in a relay contact or charge controller pc board- usually dirt, heat, or water related damage. I'm suggesting here that even a dead unit (which you could probably get free or cheap) would probably have a working transformer, and probably a good rectifier also. It may need a filter to make 'real' dc out of rectified ac.

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  • DICKEYBIRD
    replied
    Originally posted by Fasttrack View Post
    A 12 volt peak input would result in an output that is 12V - 2*Vf where Vf is the forward voltage drop of the diodes. Typically values range from 0.7V to 1.5 volts per diode. If you measure RMS voltage, than you can convert that to Vp by multiplying by ~1.4 (or the square root of 2).

    So, 12 Vrms = ~ 16.9 Vp. You then subtract the two diode drops. Lets assume a Vf of 1.2 volts. Then the output would be ~14.5 VDC.

    Couple the 14.5V with a PWM controller meant for 12V and you'll never know the difference.
    I knew that.



    (Not)

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  • GEP
    replied
    http://www.instructables.com/id/ATX-...op-Power-Supp/
    Here is a ATX power supply conversion

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  • tricklidz
    replied
    Originally posted by tricklidz View Post
    Updated blog with video
    http://tricklidz.blogspot.com

    Leave a comment:


  • Fasttrack
    replied
    Originally posted by DICKEYBIRD View Post
    12V through a bridge would be about 16V, yes?
    A 12 volt peak input would result in an output that is 12V - 2*Vf where Vf is the forward voltage drop of the diodes. Typically values range from 0.7V to 1.5 volts per diode. If you measure RMS voltage, than you can convert that to Vp by multiplying by ~1.4 (or the square root of 2).

    So, 12 Vrms = ~ 16.9 Vp. You then subtract the two diode drops. Lets assume a Vf of 1.2 volts. Then the output would be ~14.5 VDC.

    Couple the 14.5V with a PWM controller meant for 12V and you'll never know the difference.

    Leave a comment:


  • tricklidz
    replied
    Originally posted by GEP View Post
    You can find a junk desktop computer and remove to ATX power supply and build you a power unit cheap.
    I have some instructions on how to do it but cant attach them here. You can send me your e-mail if you like i will send them to you. Yes you can buy them on e-bay butdon'tt forget to look at the shipping cost
    Can you post a pic of your power feed
    Here's all the info from my blog-
    http://www.blogger.com/blogger.g?blo...0;src=postname
    Last edited by tricklidz; 01-03-2014, 01:26 PM.

    Leave a comment:


  • Fasttrack
    replied
    Originally posted by darryl View Post
    Electrolytic caps will age and lose value, but this happens quicker and will have worse results in a switching power supply vs a 'brute force' transformer/rectifier/filter.
    That depends largely on the design and component choice. A high quality switched mode power supply can last for decades. A cheap Chinese one might last a couple of years if you don't tax it too hard.



    Ripple current and heat are what kills aluminum electrolytic capacitors. In switched mode power supplies, the ripple currents can be very large. With a "brute force" design, the ripple current tends to be much lower.

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  • DICKEYBIRD
    replied
    Originally posted by Stern View Post
    Did the same on my mill, and simply got a 12V transformer, bridge rectifier and some filter caps. Makes a nice 12V power supply with fairly steady DC.
    12V through a bridge would be about 16V, yes?

    Leave a comment:


  • Stern
    replied
    Did the same on my mill, and simply got a 12V transformer, bridge rectifier and some filter caps. Makes a nice 12V power supply with fairly steady DC. Then bought a PWM from China (about $4.00) as a speed control .... works great.

    Leave a comment:


  • dian
    replied
    this is half the price, but they still are expensive, i mean thats only 360 watts.

    http://www.ebay.com/itm/110-220V-to-...ht_9651wt_1187

    Leave a comment:


  • GEP
    replied
    You can find a junk desktop computer and remove to ATX power supply and build you a power unit cheap.
    I have some instructions on how to do it but cant attach them here. You can send me your e-mail if you like i will send them to you. Yes you can buy them on e-bay butdon'tt forget to look at the shipping cost
    Can you post a pic of your power feed
    Last edited by GEP; 01-03-2014, 07:28 AM.

    Leave a comment:


  • C_lazy_F_Guns
    replied
    Most old junk campers have pretty nice converters in them to run the 12v lighting and water pump when on shore power, they can often be had for about nothing. I have one that runs a bunch of stuff in my shop, mine even has a built in battery charger that comes in handy.

    Leave a comment:


  • darryl
    replied
    Electrolytic caps will age and lose value, but this happens quicker and will have worse results in a switching power supply vs a 'brute force' transformer/rectifier/filter. Largely for this reason I stay with the traditional approach when I build a power supply that I want to last. The capacity value needs to be much larger at 60 hz than at some high switching frequency, but the cost isn't really much greater. The transformer based 60 hz power supply will be heavier and larger, but what would that matter- and dc motors don't much care if there's some ripple on the output voltage. As well, they are capable of delivering a higher than normal current for short periods, and don't have any mysterious shut-down characteristics that a switching power supply might have.

    Any controller you find will likely be a pulse width modulator of some sort, and will work fine with this.

    12V power supplies are made for car audio displays, and come in various current ratings. Something capable of 20 amps would be a relative lightweight. The newest ones are likely to be switching power supplies, but you might be able to find an older one for cheap. They are likely to be regulated as well, which might serve you well in some future applications, if not now. I don't think you really need regulation if you're working through a controller anyway.

    You might even find a basic battery charger that would serve, though for the most part these days they have mini-brains which might prevent them from outputting if they don't see a voltage to start with. You can bypass this, but you'll need some electronic knowledge to get the job done. If you find a charger that works, is heavy, and has the current capability, you can use that as the start of your power supply project. For the most part you'd only have to add an electrolytic filter cap.

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  • tricklidz
    replied
    Originally posted by mikeamick View Post
    Hey lidz .. what kind of controller ?
    Cheap Chinese one. Ebay.

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  • Mike Amick
    replied
    Hey lidz .. what kind of controller ?

    Leave a comment:

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