# My PSU's keep dying -_-

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I'm very interested in electrochemistry and I believe that I can learn a lot from it, but I can't even get it to work for more than a few hours. So far, I just have been using wall outlet power supplies designed to supply power to phones or what ever. These are rated 9-12 volts and 300 mA. I understand a higher amperage would be more efficient, but the power supplies heat up quickly and eventually die. This is apparently because the power supply is almost shorting out or something. Maybe... Anyhow, I'm ready to invest some money into this hobby as it has become to me, so what can I do about getting something that would stand up to what I am doing? Of course, my Dairy Queen paychecks don't supply me with huge amounts of capital, so something of moderat cost would be nice. I just don't know where to look really. What have you guys done?

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Buy a computer psu from ebay. Look for a high current on the 12V line.

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thing is, I have also been told that 12 volts is waay to much. they recomend 2-3 for most things... I think a higher voltage would sometimes create more O2 production which destroys carbon electrodes.

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Then you don't need to worry about the current either as the current is directly proportional to the voltage and resistance. I personally think the results in a 2V cell are pretty ridicules and really only useful in theoretical chemistry demonstrations. Whatever floats your boat I guess.

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PC power supply is best you can get if you are in low budget and can not wire your own. Best for lab use are old AT ( 286 type PC ) power supplyes that were in wide use 10 ... 12 years ago. Most of these will survive any short circuit (they just switch itself of) and you have choice of 12V and 5V rails (some even have 3.3V rail). ATX power supplies and other modern devices are generally less foolproof and usually require some extra connections to work at all.

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If you are tight on budget, then indeed I would go for a cheap computer power supply. With the 12 Volts output you can do many things. However, you also need to be able to regulate the voltage output (between say 1 volts and 10 volts). Even better would be to make a current source of say 0.5 A to 2 A, which automatically adjusts its output voltage in order to keep current constant. These are really great for electrolysis.

With an LM317 you can make an adjustable voltage source, ranging from 1.2 V and upwards to appr. the raw voltage minus 3 volts. These are perfect in combination with a computer power supply.

If you have a little more budget, then you can buy a lab power supply in an electronics store. I do not know American prices, but over here in The Netherlands I can buy one for $150 to$200 with the following specification:

Adjustable max. output current 0 .. 5 A

Ajustable output voltage 3 .. 30 V

With these you can implement a current source and a voltage source. If the current limiting is set to 3A and your circuit draws less than 3 A then the selected voltage will be output. If you want a current source, then set the voltage to 30 V and adjust the max current at e.g. 1 A. Now, the power supply adjusts its voltage, such that the current drawn is 1 A. The latter works perfectly for more concentrated liquids when they are electrolysed.

When you want a device with a lower adjustable output voltage, then you need to spend more money, but such a shortcoming can easily be adjusted for. Buy a few power diodes and place these in series with the voltage output. Each power diode takes around 0.6 V, so with three of these your Vmin will be 1.2 Volts.

the specs I have given are just indicative. With some searching you might be able to find better devices for that price. Especially the lowest voltage setting is important. Electrolysis can be done at voltages as low as 1.5 Volts.

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Xeluc, in the mean time, if you still have a working mains adaptor like you mentioned, if you use a 9v 3W bulb in line, no matter what, youll not blow the thing, even a dead short, as the bulb wont allow you to draw any more power than the 3 watts (well within the adaptors limits).

Im with Woelen though, I use a homemade PSU with an lm317 and a 2n3055 output driver, they work great and Ive had this thing now for a good 15 years!

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Xeluc' date=' in the mean time, if you still have a working mains adaptor like you mentioned, if you use a 9v 3W bulb in line, no matter what, youll not blow the thing, even a dead short, as the bulb wont allow you to draw any more power than the 3 watts (well within the adaptors limits).

Im with Woelen though, I use a homemade PSU with an lm317 and a 2n3055 output driver, they work great and Ive had this thing now for a good 15 years![/quote']

Goodv idea. I actually already killed mine..v Nexttiem though I really don't mean to sound stupid or like I'm unable to do anything myself, but could you elaborate as to how a home made device like this would be made?

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If you want to make your own power supply you have to get suitable transformer at first. This must be rather powerfull not like those in telephone chargers but much bigger. Output voltage of the transformer must also be suitable. Something form 15 to 25V is good. You need 4 diodes and big electrolyte capacitor to convert voltage from transformer output to DC. When converting to DC voltage will go higher - aproximately 1.4 times compared to AC output. This must still remain less than 40V otherwise you can not use simple circuits with common LM317. If this all is done then connecting LM317 as voltage or as current regulator is very easy.

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there a little bit more specific info here also: http://www.scienceforums.net/forums/showthread.php?t=16469&highlight=lm317

just look around the bits in RED.

as for the transformer, I used an old 13.8v 3-5 amp CB power supply transformer, it was center tapped so I only needed 2 diodes for the bridge, but you could use an old car battery charger and convert that just as easily

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I as thinking of using a battery charger but I think the one I have now has some kind of swithc off or something becasue I quickly threw steel wool on both clamps and put it in salt water whiel plugged in and nothing happened. Shoud lI have it on a specific setting?

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Many battery chargers are not simply voltage sources. They contain quite a lot of intelligent sensing electronics, which determines what voltage the battery to be charged has and how much current has to be emitted.

When no battery is present, then probably no current is applied at all.

Have a look at this: http://www.hw.cz/data_ic/lm317.pdf

It is the LM317 datasheet, which also contains some circuits you can build around this chip.

If you are not confident enough on building your own electronics, then another fairly inexpensive alternative is the simple PC power supply, with some wiring.

http://web2.murraystate.edu/andy.batts/ps/powersupply.htm

You can adjust voltage by buying a set of power diodes. Each diode takes 0.6 volts. If you put them in series, then you can make many voltages in steps of 0.6 volts. If you also can get two germanium diodes, then you can also adjust voltage in steps of 0.2 volts. That should be perfectly OK and provide you good flexibility in your electrolysis experiments.

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I like the PC Power supply route So jsut using the wires I want with diodes.. will it last or do I need to add a resister or something.

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I like the PC Power supply route So jsut using the wires I want with diodes.. will it last or do I need to add a resister or something.

It will last, provided your diodes are sufficiently large. So, you need to take good power diodes. Suppose your electrolysis takes 5A maximum, then take some headroom, make 10 A of that for headroom, so buy your diodes, such that they can stand 10A of current.

I have been thinking about this and an even better approach would be to buy a bunch of 10 Ohm power resistors and just 2 silicon power diodes. With that setup you have very high flexibility at low cost.

Buy 10 resistors, each 10 Ohm and each allowing between 5 and 10 Watts of power dissipation.

Now you can implement a reasonable approximation of a current source with your resistors. Electrolysis voltages are around 3 volts. Some cells require 4 volts, others less than 3 volts, but 3 volts is a fairly average voltage. Fluctuation around that is small.

Now some theory. Because the voltage of your voltage source is 12 Volts, and the voltage of your cell is around 3 Volts +/- 1 volt, the voltage accross your resistor network is 9 volts +/- 1 volt. So, the current remains constant within let's say 11 to 12% of your selected current.

Selecting currents can be done with resistor networks. Remember: Never put a single 10 Ohm resistor in series with an electrolysis cell. That may destroy your resistor with the rating I have provided you!

The current you select for electrolysis is 9 / Reff.

You select Reff with your resistors by means of series and parrallel circuiting of resistors. I'll try to explain to you how this can be done.

I introduce a mathematical operator // with the property x//y = (x*y)/(x+y). Examples: 2//3 = 6/5 = 1.2; 3//3 = 9/6 = 1.5

Now, I also need to introduce a notation for networks.

I use notation RRR for a series of three resistors (30 Ohm), RRRRR for a series of 5 resistors (50 Ohm).

I use notation RRR//RRRR for a series of three resistors, and a series of four resistors, with both series put in parallel. The resistance of such a network equals 30 // 40, which is appr. 17 Ohms.

You never may have a single R in one branch of your parallel network. That can lead to destruction of that resistor. So don't use networks like R or R//R or RR//R.

Now, some useful Reff values:

RRRRR --> 50 Ohm

RRR --> 30 Ohm

RR --> 20 Ohm

RRR//RRR --> 15 Ohm

RR//RRR --> 12 Ohm

RR//RR --> 10 Ohm

RR//RR//RRRR --> 8 Ohm

RR//RR//RRR --> 7.5 Ohm

RR//RR//RR --> 6.7 Ohm

RR//RR//RR//RR --> 5 Ohm

RR//RR//RR//RR//RR --> 4 Ohm

With electrolysis experiments, you'll most frequently use between 10 Ohm and 20 Ohm networks. For lower resistance you need a good and thick graphite anode, otherwise it will be pulverized in minutes, so going with networks, lower than 10 Ohm should only be done with high quality heavy electrodes.

Now, what can you do with the diodes? These can be used for fine-adjustments. Suppose you want to electrolyse bromide, to make bromate and you see some bubbling at the anode. Then oxygen is formed and you know that the voltage is too high. You can decrease your current in that way by selecting a network with higher resistance, but you can also put a single or even two diodes in series with your resistor network. In fact you make a new network ReffD or ReffDD, with Reff your original resistor network.

Never ever put a diode in parallal to your network, e.g. RR//RR//D or RR//RR//DD WILL destroy your diodes and most likely also your power supply.

What is perfectly safe is a network like this: RRD//RR or RRDD//RR, as long as in a single branch there are at least two resistors, you are safe.

It may seem a little awkward when you start with this, but when you have some experience, then you'll get a quick feeling for this.

When your solutions are very dilute, then the current source approximation does not work anymore, then the voltage accross the electrolysis electrodes will rise to much higher values than 3 Volts and in that case you have a low current and high voltage and you mostly produce oxygen at the anode.

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Wow guys, check this out. I went to a website and they are GIVING me 5 LM317's. I'm not even paying shiping! I requested a free sample and they replied saying they would be more than happy to ship 5 to my... business... :rolleyes: Ha, anyhow, they said that the parts were being shipped from singapore (I hope I'm not benefitting from sweat shops over there ), so it will take "3-15 days to ship". So ha! Anyhow, when I get them, and play with them, I'll tell you guys how everything went.

Using a current source has the advantage' date=' that it automatically adjusts at the halogen to be electrolysed. For an iodide solution a lower voltage is 'chosen' by the current source than for a chloride solution. This eliminates the problem of using too high a voltage, resulting in unwanted formation of oxygen and associated pulverization of the anode.

[/quote']

So, do I have a "current source Woelen? so will my voltage adjust itself or do I need something else in order for this to happen. I wouldn't think it'd do it by itself.. who knows.

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