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12V-100AMP Supply for $20.00!!

Discussion in 'Home Brew' started by unit_399, Jul 9, 2012.

  1. dave457

    dave457 Sr. Member

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    I just ordered one, can't go bad at $18 And free shipping


     
    309hellinois likes this.

  2. Onelasttime

    Onelasttime Sr. Member

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    I have not had time to do much. I want to build a new work area, not in my basement. If I get too desperate I will use my old Kitchen table in a pinch. LOL
     
  3. Onelasttime

    Onelasttime Sr. Member

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    In terms of why you use a resistor sometimes, it is normally on the 3.3V or 5V bus. Because these are computer supplies the 3.3V and 5V if they have them on a supply are the big bosses and the 12V is far less important. The unit takes regulation cues from 3.3V or 5V bus. So if you put a nice load that is stable you trick it into increased output.

    Usually, if you go inside and just crank the pot up the unit will shut down long before you hit the current limit it is an either/or situation you can have 13.8V's or you can have 63 Amps at 11.9V's but you can not have both!

    If you can figure out the right spots inside to do a bypass or change the load sensing internally than you can have both but not at the pins or jumpers. So normally the best you can get is 12.5-13.3 volts without tripping the protection circuit with the full current output.

    If someone needs the full monty they are not server supply types and either need to do a linear supply or buy a less robust more expensive supply that is actually designed to go up to 13.8 out of the box. The other option is an unregulated linear supply no crow bar protection just red neck wonderful at it's best.

    The old MFJ ALS-500 I think it was called their solid state mobile that used to use 4 Toshiba 2290's clearly told the user that for every volt bellow 14V's you lost 85 watts off your peak output. No reason that is not still true today. Some people cherish every watt and run their gear hot. Also the higher your voltage the less current you need. THat said server supplies have plenty of current but are low on voltage so you see the irony I am sure! LOL

    MFJ's current mobie with it's DEI or other generic Chi-Com transistors can not stay running and I am guessing much past 14V it will give up the ghost or will let the smoke out!
     
  4. Onelasttime

    Onelasttime Sr. Member

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    You know guys you can use these for any 12V needs. My Mom and Dad just bought a 5th wheel and I plan on adding more 12V for them.

    Also I had spare audio gear but not enough to build an entire system in my bedroom. I want to have 8 hours of ocean waves or thunderstorms. What I was missing was a cheap amp just for this lo-fi non-demanding needs. Now I am going to pick up a fairly cheap car audio amp and use a server power supply to power it. No need for audiophile level of amplifier to play white noise, pink noise and thunder storms and such in the bedroom for sleeping.

    So the sky is the limit.

    Same thing goes for reworking MOT's Microwave Oven Transformers. Nock out the shunt and rewind a custom secondary and the sky is the limit depending on how many you use and what you are using them for.

    Just some more idea's for what these insanely cheap power supplies can be made to do. The 40-52 amp models are insanely cheap especially if you buy them by the lot.Your creativity is the only limit. Even if you had to recap everyone you bought it is still crazy good deal. If you get enough of any one model cheap enough you can have spare parts for a lifetime!

    Kind of like buying cheap transistors though you need spares because the price to buy parts and or put it on someone else's bench is not worth it. When looking at $10-$16 each with free or low cost shipping no reason not to stock up!
     
  5. 309hellinois

    309hellinois Active Member

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    .
    With lower voltage, the load will pull more current. At $16 to $18 per psu, it's worth experimenting with them. The site that I read said 13.3 to 13.5 volts capable without tripping to over voltage protection. Worth a shot. If it works, I'll share it. If it fails I'll update.
     
    #110 309hellinois, Jan 2, 2018
    Last edited: Jan 2, 2018
    wavrider likes this.
  6. Onelasttime

    Onelasttime Sr. Member

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    Depends on the unit. There is no universal constant with Server Supplies. They are all over the place in terms of what each model can or can not do. I have read posts by guys that buy these by the pallet and some guys will only get 11.9V and some can get 13.3 out of identical units with identical mod's!

    Simply put, its cheaper to distribute power at a higher voltage than a lower voltage. Power loss in wiring is directly related to the Square of current drawn. So if you distribute power at 12V instead of 5V you cut your resistive power losses in a wire by a factor of more than 5x. [122 / 52 = 5.76]

    In addition, most chips these days use significantly less than 5V to run, with typical Intel/AMD processors having internal core voltages of 0.6V - 1.4V in many situations. Other peripherals may need 5V, 3.3V, 2.5V, 1.8V or whatever so the actual distribution rail is rarely ever related to the voltage being used by peripherals. Even typical USB devices don't actually use their 5V rail directly and will drop that 5V from the USB cable to something usable by the actual peripheral.

    You can couple that with the ease of adding inexpensive local Buck switching converters near all the peripherals. These allow your to convert high voltages to low voltages locally at the devices while also being very efficient (90% +).

    If you look near the processor on a motherboard nowadays, you should be able to pick out several inductors. They are part of a polyphase buck converter that's used to drop the voltage down to the level that the core logic needs. The same is true of the graphics processor on the graphics card.

    This is why the 12V regulation is all over the place from one model of power supply to the next. Even the 3.3 and 5 volt buses are over kill. With just things like the DVD/BD drives and hard drives running off of 12V it is not that important to the computer to have more 12V+ and insanely tight regulation. A computer has a lot of wiggle room on the 12V side. That is why it is completely fine for so many of these supplies to be a tad anemic on the 12V side.

    I would suggest that for a computer low ripple clean power that does not fluctuate much is far more important than being able to get a few more volts out. The things powered by 12V nominal in a computer do not really benefit from cranking up the voltage from say 11.9V to 13.8V. So it is not something that is really needed in a computer supply. On the other hand when powering so called 12V devices in many hobbies having 12V-16V can be a huge plus since our radio's and amplifiers like more volts!
     
  7. dave457

    dave457 Sr. Member

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    Ok mine came today, did the simple mod and got 12.4v output
    Under load (2 pill 2879) and radio
    Drops to 12.1v
    Very satisfied with this unit. Thanks 309 for that link
     
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  8. 309hellinois

    309hellinois Active Member

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    I'll be trying for more voltage shortly. I've got everything to do it but I've decided to put it all in a project box with gauges, switches, buss bar and fuse block. I'll try to get some time in the basement tomorrow. Glad it worked out for you.
     
  9. Onelasttime

    Onelasttime Sr. Member

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    My only point was that unlike the crazy stuff we see on youtube with "builders" using cheap switching power supplies or unregulated linear power supplies you are seldom going to get to 13.8V let alone the crazy 15V, 16V, 19V etc.....
     
  10. 309hellinois

    309hellinois Active Member

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    I've never seen the point of voltage that high for anything I've done. I'll be happy to get to 13v.
     
  11. Onelasttime

    Onelasttime Sr. Member

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    I agree with you! That said if someone wants to charge a 12V lead acid battery you need 13.8 minimum in my book to do that and I prefer 14.7 volts. Also I think people should know that unlike a consumer level power-supply you can not just crank them up to 13V or higher on some models.

    I just want people to understand the pro's and con's going in so no one can say they where not told that they might not be able to get more than 12.3V etc......

    Like you said for the money how can you go wrong. Given all the current on tap and the cheap price of the units drawing more amps because you can not crank the voltage up is not a big deal.
     
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  12. dave457

    dave457 Sr. Member

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    The mod seems simple enuff, will try also
     
  13. tba02

    tba02 WOOF

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    I have been able to raise the voltage on these to ~13.2.
     
  14. 309hellinois

    309hellinois Active Member

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    Which method did you use? Resistor across two other pins or did you open the case?
     
  15. tba02

    tba02 WOOF

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    dave457 and 309hellinois like this.

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