need a "translator" for 12 VDC power supply project

[madbear]

I am building a 12 VDC power supply out of a computer supply.
I got the info off wikihow.com
Here is a list of the parts that I have:

power meter
lm 317 voltage reg.
banana jack posts
5k potentiometer
.1 uF ceramic capacitor
1 uF capacitor
330 ohm resistor (1/4w) for power meter
120 ohm resistor (1/4w)
10 ohm power resistor 10w
LCD voltmeter
PC board ATX power supply

It also lists a 5k potentiometer & banana jack posts which I think is repeat.
Now electronics is about like trying to read Chinese for me. When I went to buy the capacitors, resistors & etc. I ran into a real black hole!
these things come in so many different flavors. some are for audio. some for speed control. they come in glass, metal & who knows what.
can someone tell me "exactly" which ones to use for a power supply or does it make a difference?
thanks for any help;
madbear

 

[(*steve*)]

To make a computer power supply work line a 12V supply, you need to do the following:

1) get a working PC power supply.

2) figure out how to turn it on (typically grounding the power on cable). Google for this information, it's pretty easy to find.

3) Determine if the power supply turns on (if not, you have to figure out why)

4) Using a multimeter, measure the voltages at the main rails (+5, +5sby, +3.3, +12, -12. It is possible your power supply has multiple +12V supplies, so you may want to check each of them. Write down the voltages you measure for all of them

5) Are all the rails within 10%? If so you're OK. Go to step (8)

6) If the rails are out of regulation, try placing a load on the 5V rail and re-measuring. A 12V 12-24W globe is a suitable load for testing (and will be cheap to get hold of. If this brings the rails to within 10% go to step (8)

7) Try heavier loads, try them on other rails (but not the +5sby or -12V rails!) If you find a suitable combination, go to step (8), otherwise you have a problem.

8) If you want 12V, take it directly from the 12V (yellow) and ground (black). For low current (less than 5A) you can probably just take it from a single drive connector. For larger currents you can parallel several of these.

PC power supplies are reasonably well protected against shorts, but less so against long term overloads. Be careful to stay within the manufacturers recommended loads.

Note that many PC power supplies have only a single regulated output (most often 5V) with the others less well regulated. This might mean your 12V rail will vary somewhat with load, especially if the 5V rail is unloaded or very lightly loaded.

You can't easily use an external regulator like a LM317 to make a variable regulator up to 12V, but you can probably do 1.25 to 10V. This is because the max voltage you'll get out of the PC power supply is 12V and the LM317 requires an input voltage higher than its output.

It is true that you could use the -12V and (say) the 5V rail to get 17V, but you would have to be very careful because the -12V rail is usually limited to a significantly lower current, and your power supply will no longer have either rail being ground referenced (the ground lead from the PC power supply is connected to mains earth).

 

[(*steve*)]

It also lists a 5k potentiometer & banana jack posts which I think is repeat.

You only need 1, and probbably 2 terminal posts, although you might want more than 2, 1 for ground, and others for +5V, +12V, and variable?

Now electronics is about like trying to read Chinese for me. When I went to buy the capacitors, resistors & etc. I ran into a real black hole!

Take that list *exactly* as written to the store and tell them you're making a voltage regulator. If they don't immediately know what you want, then you've gone to some place that has staff who don't know what they're selling (which is unfortunately going to be the rule these days)

The only information you don't have is that the 10uF capacitor is a 25V electrolytic, the 0.1uF capacitor has any voltage rating above 20V). In general you can pick a device with a higher voltage rating. It may be larger or more expensive but it will work exactly the same.

these things come in so many different flavors. some are for audio. some for speed control. they come in glass, metal & who knows what.
can someone tell me "exactly" which ones to use for a power supply or does it make a difference?

Pretty much it doesn't matter. You want the cheapest option

The only thing you want is that the devices not be surface mount (you want ones with wire leads). However anyone selling you surface mount components is likely be doing it to be deliberately unhelpful given the list of your requirements.

Point us to a link to the circuit you're going to make and we can advise you more and better.

Oh, the LCD volt meter may be harder to get from a store. These are comparatively cheap on ebay, or you can just use your multimeter.

If you don't have a multimeter, get a $10 cheapie in preference to the LCD voltmeter for your power supply. You'll use it far more often and get far better value from it.

 

[madbear]

Here is the link. It's for an anodizing setup . From what I understand I will need about 12 VDC & 6-12 Amps depending on the size of the part & I need to keep the current steady. I think my power supply is rated at 400 w.
I'll go find it & check in a little while.
thanks

 

[davenn]

you forgot the link

 

[madbear]

Sorry. wish I could say that was the first time I've done that


http://www.wikihow.com/Build-Your-Own-Variable-Bench-Power-Supply-Using-an-ATX-Power-Supply

 

[(*steve*)]

OK, that's not the best set of instructions.

They use +12V and -12V as I mentioned above in a way that's not really recommended. Oh well.

They don't tell you that you need to short 2 wires together on a modern power supply to turn it on.

I would reccomend you get an extension cable for the motherboard connection. That way you can remove the power supply and connect another one if you need to (and you're really not going to reuse those connectors)

I have no idea how the regulator circuit they show is supposed to work. It's certainly not variable.

I also wonder why they think you need hot glue.

I'm trying to come up with something positive to say about it...

The idea is a good one, but the implementation in that wiki-how is far less than perfect.

Perhaps you should tell us what you want the power supply for. You may be able to do with a far simpler circuit.

 

[madbear]

This power supply isn't for a computer. It's for anodizing aluminum parts. I took out the 250 w. supply from my computer & put a 600 w. supply in for gaming. What I need is a 12 VDC power supply to hookup to an acid bath that the parts will be hung in. It will have to be adjustable for amps so I can keep a steady current. The current will need to be between 6 & 15 amps. I might also use this for etching serial #s on these parts which is done with a low voltage applied to a sponge with salt water.
I hope this explains what I am needing.
madbear

 

[Fish4Fun]

madbear, Welcome to the forum!

You are going to have a difficult time building a 15A current regulator, this is NOT a trivial project. An LM317 is simply not going to work for you. Anodizing aluminum is certainly best done with regulated current, but you aren't going to require "ultra-fine" adjustments so you might consider "cheating". You might consider using 12V light bulbs connected in parallel with "switches" to engage each bulb. For example, if you had 4 * 50W bulbs (readily available @ RV & Marine supply stores) you can calculate the equivalent resistance as roughly ((14V)^2)/50W = ~4ohms. 12V/4ohms = 3A....12V/2Ohms = 6A.....12V/(4/3ohms) = 9A......12V/1ohm = 12A.....This of course presumes that your load has no impedance which is FALSE, but the light bulbs will act as an upper current limit.....You might also consider using a double pole switch or relay to switch between 5Vdc and 12Vdc....

Other methods of achieving current regulation unique to anodizing include using "multiple cathodes". The amount of current that will flow will be limited by the surface area of the Anode (your aluminum part) and/or Cathode at any particular voltage. If you use multiple Cathodes you can gain some control over current regulation with nothing more than some switches. You could potentially replace these switches with mosfets/transistors and achieve a semi-automated current regulation of sorts.

While I have never attempted anodizing, I have read a fair bit about both the theory and the practice. Many DIYers simply connect their power supply and "hope for the best"; supposedly this generally gets pretty good results. The "typical currents" required range from 30 to 300 Amps per M^2 of aluminum. Assuming a 100mm x 100mm x 5mm piece of flat stock, this would be 20,000mm + 2000mm = 22,000mm^2 --> 0.022M^2, so @ 30A/M^2 this would equal 660mA and @ 300A/M^2 it would be 6.6A .... the point being that there is a wide range of "acceptable currents", and unless you are planning to do this professionally you will likely be fine w/o worrying about current regulation except perhaps switching between 12V and 5V.

Fish

 

[madbear]

Fish'
Thanks for the help. I am planning to use 2 AL. plates 1/32"- 1/16" X 1 Sq. Ft. each for cathodes. I could go a little bigger or smaller if need be. The parts will be anywhere from 1/2-1 Sq. Ft. From all the info I can find this can be done with a simple (dumb) battery charger but there is no way to calculate the thickness of the anodized layer which needs to be .001" to get a good dye job. By regulating the current I can calculate the time needed to achieve this. Like you said there is a wide range of currents that can be used but I need to regulate & monitor to get the right thickness. Can this be done with a 250 w. computer supply? I do have a commercial battery charger that doesn't seem to work. If I can fix it would that be a better alternative?

This little experiment is to learn how to anodize AL. without the need for a $200+ power supply. If it works I hope to set up a part time anodizing business with the "right" equipment. I'm retired from the woodworking business & have more time than money right now so I'm going to redneck engineer something I can play with. I just don't want to get zapped or set the shop on fire!

 

[KrisBlueNZ]

Good advice there from Fish. He is suggesting that you can limit the current to the anodising setup by connecting light bulbs in series with the circuit. Probably, headlight bulbs would be appropriate.(Edit: No, Fish has better ideas.) Each bulb needs its own switch, and you measure the current flow using a multimeter or a panel meter (analogue pointer type, or digital). Then you just turn your bulbs on and off until you get roughly the amount of current you want. The current will probably vary gradually during the anodising process. I don't know how much it will vary or whether that will be a problem. But using light bulbs is a nice simple way to regulate (well, regulate is not really right) the high currents that you need.

Re the 250W power supply, look on the label and see what the current rating for the 5V and 12V rails are. Don't try to draw more than those numbers, or parts of the power supply could overheat. On an extreme overload the power supply will start "hiccuping" but it probably won't do that on a moderate overload.

Just re-reading Fish's post, all good suggestions and detail there.

 

[madbear]

Well guys I have already bought some of the stuff I thought I needed for this project like a
“Dc 4.5-30V 0-50A Dual LED Digital Volt meter Ammeter Voltage AMP Power Good ESY1”
a “RV24YN2OS Single Turn Carbon Rotary Taper Potentiometer” 5 pairs “Amplifier Terminal Connector Binding Post. & a 4 mm Banana Plug Test Lead”
What do you think of this video. He makes the same kind of power supply but without the adjustability?
Will this work if I regulate the Voltage & Amps & if so where do I add the adjustment?
won’t the dummy load setup work the same as the lite bulbs? they just seem kind of weird.
Thanks;
madbear



Sent from Windows Mail

 

[KrisBlueNZ]

That's a very good video.

Making the output voltage of a PC power supply adjustable is not simple. It may not necessarily even be possible. It depends very much on the design of the power supply. This is why Fish suggested using external light bulbs to reduce the voltage to suit your requirements for electroplating.

The dummy load is needed so the power supply has something to work into at all times. If you don't have a dummy load, when you disconnect your main load the power supply may shut down, or at least start to "hiccup". The dummy load doesn't need to be inside the power supply enclosure though.

I would get a PC power supply with a +12V output that's rated for at least the maximum current you need (you said 15A), remove the motherboard plug, and solder the +12V and 0V wires into a circuit that includes a dummy load, an ammeter, and a string of series-connected light bulbs with individual switches across them, and a voltmeter across the output, that feeds your electroplating system.

You can monitor the current and voltage going to the electroplating setup, and adjust the amount of resistance between the power supply output and the electroplating system voltage by switching the light bulbs ON and OFF, to get the desired electroplating current.