Topic: How to build your own power supply? - page 3. (Read 16378 times)

Actually, powering ~20 GPUs off something like this might be quite a good solution for large mining farms: http://www.alibaba.com/product-gs/436983856/_YK_AD10KW_10kw_dc_regulated.html

It compares quite well to a computer PSU, and would cut costs a good bit for large scale miners.
--Efficiency of Whole Body: ≥86%. Source Voltage Regulation:
--Voltage-stabilizing ≤0.2%. Load Regulation: ≤2%; Ripple Voltage: ≤4%

The PCIe bus spec only allows 30watts per slot, thats why most higher end video cards have external power connectors on them.
Sure, you probably could bridge together enough cheap power supplies to power all those cards. Or, come up with one really big 12V power supply capable of handling 100's of amps.

The problem with lower quality power supplies is the power you will get out of it then will have ripple, and inconsistent voltage regulation which will make bridging more then a few cheap supplies together difficult, since they will not supply current evenly across all the supplies.

A single very large supply has the other problem that it requires very thick cables, or copper buss bars to distribute all that power to the cards.  Ciopper buss bars carrying hundreds of amps are dangerous at almost any voltage, and require regular maintenance to maintain good connections to prevent excessive heating of the buss or connectors.

I wouldnt risk thousands of dollars in GPU's connected to a makeshift 12V power supply, it's just not worth it.

The real answer in electrical safety is that it takes a combination of sufficiently high voltage, current, and the proper waveform to kill you. 240V mains is nearly ideal for this.

A van-de-graff generator can produce very high voltages, and high current pulses, but has a very low RMS power and averaged current, and is thus safe.

5V USB or a car battery can produce a lot of current with a steady DC waveform, but lack sufficient voltage to produce much current in the body.

Tesla coils can produce hundreds of thousands of volts at reasonably high currents, but operate well into RF, and are thus a serious burn hazard but leave the heart electrically unaffected.

120V mains will generally not kill you, but has a low enough frequency, high enough voltage, and high enough current that I can if you become entangled with the source and are unable to get free.

I hope this has cleared up some pseudoscience.

Also building your own PSU is not outside the realm of an advanced hobbyist, but you are much better off simply buying them given all the design and build time required. If you want to save some money, look for secondhand PSUs.

Source: electrical engineering student and high voltage enthusiast

I think you have yours backwards.
if we are comparing an engine with rpm and torque, the the rpm is like voltage, and torque is the current.

and this is true, RPM's have almost nothing to do with torque
ie an electric motor that can produce all of it's available torque at .0000001 RPM
or a fan spinning at thousands of RPM that you can stop with a finger.

I'm pretty sure you are too, but ohms law is hard, let's go shopping for more 6990s.  NOT!

I'm pretty sure i'm 100% right, do you mind pointing out what's the 50% wrong part of what i wrote?

ehhhhhhhhhhhhhh your half right

It's like saying that, in a engine, torque has little to do with power, it's the RPM that matters.
You can easly jump from current to ampere knowing the resistance (or better impedance) of the load (human body) and of the generator and vice-versa.
In those 100'000V devices, the output impedance is so hight that even slightly conductive loads can drastically cut the output voltage. Cutting the voltage = cutting the current.

Thanks for the backup!

This is what happens when you mix electricity+unknowledge : http://www.clipaday.com/videos/pen-trick-gone-wrong

the voltage has very little to do with it.  it's the current that matters.

a 20,000 volt static discharge is only a few milliamps, while the 5-10 watts available in a USB plug is 1-2 AMPS.
so why arent people electrocuted by USB plugs ?

the resistance of human skin, at 5 volts, is very high, therefore very little current will flow through the body.

It's basic ohms law.

Have you thought of using multiple smaller PSUs you can get them alot cheaper under 900 watts

Your a fucking idiot, i can take 20,000 Volts and be fine, It'll hurt like FUCK, and theres a small chance it could stop my heart if exposed for too long.
But a fucking 5v USB Imput slot can kill you because of the current.

Depends on which side of the switching circuit you decide to poke your fingers into. The 12V on the business end might be safe, but what you get from an unregulated discharge of the capacitors on the other end is a whole different story. Probably one with a sad ending.

I looked at the viability of doing something similar, using 48 volt telecom rectifiers as a PSU (but flipping around the ground reference, because they're all negative voltage).  They deliver substantial current on the cheap (200a at 48v, so 800a at 12v if you run them through a bunch of big ass batteries).  But at the end of the day you will have spent 1k on batteries and regulators, plus cabling, plus capacitors and diodes, yada yada yada.  By the time it's all over, you'll end up with 1.5k worth of crap, and a whole bunch of work, just to power up your "30" video cards, with a single point of failure, and a bunch of electronics that are hard to understand and hard to work on.  I looked at other options, like inexpensive 12 volt battery chargers, no dice.. they're too expensive.  The cheapest option you have is the $1000 worth of PSUs.

By the way, I read your other thread about the smoked components.. I've got a pretty good idea of what happened and why, based on a critical omission on your part while describing your setup.  Of course I'm going to be a troll and not reveal what it is, both because it's already been asked/answered on the forum at least once that I'm aware of, and because I'm not going to help anyone devalue my investment in mining any further by making it any cheaper for you, or anyone else, to do business.  Knowledge is power, and when you don't have it, sometimes you have to pay for someone else's, i.e. in the form of those expensive PSUs.  That smoke should make you less bullish on playing with fire, not more.


He seems pretty determined to do so, doesn't he?

power supply is not something simple.. i have studied electronics for 3 years in high school and computer related electronics is not "simple job". psu is devided in 2 groups in the circuit, 1 side high voltage and 1 side low voltage, and there are lots of chips involved. so don't even bother programming chips, its pain in the head, believe me.

Hey here's some advice; if you're looking to join multiple rails together, some PSUs have an option they like to call turbo that joins together all of its 12V rails.  However, I've heard that running on single rail too long will often cause the PSU to die prematurely on high loads.  I know my Tagan can do it, but it's just 800W.

Here's a multi-rail 1200W system http://www.newegg.com/Product/Product.aspx?Item=N82E16817371043  It'll handle just about anything you throw at it.
Here's a single-rail 1200W system http://www.newegg.com/Product/Product.aspx?Item=N82E16817171055  It'll handle what you want too, but any energy spikes you get will go through the whole system.

I had a HDD cause problems with my DVD burner a while back because they were on the same rail and the DVD burner was having power spikes on writes which was causing failed burns.  Putting them on separate rails allowed for steady current to my burner and my burns came out nearly flawless.  So I recommend multi-rail for high-pull hardware.  Just be sure that the specs allow the wattage it needs per rail.  12V * Wattage per rail = output per connector line.  The above should handle around 3 HD6990 cards unofficially without problem and leaving 300W for the rest of your system.  It's cutting it close, but I don't imagine your CPU using more than 150W on an i7 and newer HDDs will use about 11 watts max so you're good to go.
Don't go thinking that the loss in available power per rail makes it less efficient.  The fact is that you'll probably never need 360W on a single rail anyway so the other rails can more than handle the loads on their own while mitigating power spikes making it more efficient on the PFC side of things.

Seems in line with them miners on these forums that have their motherboard running on the carpet with fans blowing into it and all that.

Bitcoins get more expensive everytime there's a big story somewhere. A bitcoin Death would really help us get out this 25 / 30 USD lameness we're in.

Take one for the team!

actually 25mA of current has to go through your heart to stop it. knowing that the human body has a resistance of couple of Mohms(lets use 1 for the equation although is kinda bigger) the equation I=V/R is I= 12/1000000 = 0.000012 Amps of current in your body. that wont kill you, it will only make you stronger

PSUs take a lot of time and skill to design correctly, and to use quality parts.

I was at a local PC parts retailer recently and saw someone walk in and ask for a SHAW brand 680 watt power supply for $17, while I was buying a Cooler Master GX 750 watt for $115 for my bitcoin set up.  Over six times the price for just a little more power?  You'd think I'm crazy to pay that, right?  Well, the Cooler Master will actually deliver its rated power, with high efficiency, stable voltage and current, into multiple voltage rails and do that for years to come.  The SHAW will do none of that, and likely blow up (not joking) and take the customer's other PC parts with it.

The moral of the story is high quality, high current power supplies cost more because they are so much better than the cheap brands and certainly anything you can build yourself (unless you're en electrical engineer).  

Follow the advice of other forum members and please don't attempt to dismantle or build your own PSU.