{"id":2100,"date":"2019-10-13T08:00:12","date_gmt":"2019-10-13T05:00:12","guid":{"rendered":"http:\/\/racov.ro\/?p=2100"},"modified":"2020-03-31T15:33:11","modified_gmt":"2020-03-31T12:33:11","slug":"modificare-sursa-de-calculator-pentru-mai-mult-de-12v-cu-cm6901","status":"publish","type":"post","link":"https:\/\/racov.ro\/index.php\/2019\/10\/13\/modificare-sursa-de-calculator-pentru-mai-mult-de-12v-cu-cm6901\/","title":{"rendered":"Hacking a computer power supply for more than 12V (with CM6901)"},"content":{"rendered":"

WARNING <\/span>!!<\/strong><\/span>
\nThis work involves danger of electric shock and death !!<\/span>
\nDon’t stick your fingers in it, if you don’t know what it’s all about.<\/span><\/p>\n

Introduction<\/strong>:<\/span>
\nComputer power supplies are very strong. Small, light, all possible protections, high power, ridiculously low price (second hand). This one cost me 10 euros and I wanted as many amps at possible on 12V. 32 amps in my case. The disadvantage is that they <\/span>hold on with the teeth to those t<\/span>wo voltages – 12V and 5V – and <\/span>is hard <\/span>to <\/span>convince them to change.<\/span>
\nI was trying to make even more room on the shelves, so I also reduced the physical dimensions of the radio stations power <\/span>supply <\/span>. I went from LINIAR to SWICTH MODE. I used to listen to the myth that radio stations do not reconcile with switch mode PSU, noise, stuff … Totally wrong. Switching is awesome. Myths from old people, to scare children. The sound is exactly like the one from linear PSU, with a quarter of volume and weight. And 10th<\/sup> of the heat \ud83d\ude00 .<\/span>
\nI just wanted to power 2 radios with 13.8V. So not much more than 12V. There are many tutorials that show how to get up to almost 20V, but with sacrificing all the protections, which destroys the main idea from which we started.
\n<\/span><\/p>\n

Content<\/strong>:<\/span>
\nI only managed to get a <\/span>solid <\/span>13.3V. I went to 13.8V no load, but as soon as I started one radio, the source went into protection and stopped. Curious is that with a purely resistive load it started without problems and went directly to 6A. I did not strive much on this problem, 0.5V less is not too serious.<\/span>
\nThe radios were doing very well with 12V, so who does not want complications can use a PC power supply as it is. Only the actual transmission power decreases. If my HF station consumes almost 20A at maximum power (100W in CW), at a difference of 1.5V, results a loss of transmission power of almost 30W. Enormous!<\/span><\/p>\n

Let’s begin:<\/span>
\n<\/span>
\n<\/span>
\n<\/span>
\n<\/span>
\n<\/span>
\nI added a 220V switch, output terminals and a display, as I had two. The display is not very necessary, as the PSU is stiff, but it adds the cool factor \ud83d\ude0e . It can be seen that at 10A consumption it does not twitch. On the contrary, it slightly increases the output to 12.3V. It went on for a while, until I gathered my knowledge and dared to go through with the changes.
\n<\/span><\/p>\n

Let’s go to the modifications:<\/strong>
\nAt first, the most important is the circuit that makes the regulation \/ stabilization. In my case CM6901. This is not the most popular circuit and is found in the most efficient sources. That’s why I didn’t even find tutorials on modifying it. There are a lot of instructions about other circuits used in PC PSUs.
\nFrom the data sheet I have noted the following:
\n<\/span>On pin 2, is fed the output voltage of 12V\u00a0 – feedback – through a resistive divider.<\/p>\n

\"\"<\/a>I don’t know if these are the actual values of the parts from my PSU, but the 2.5V voltage is measured by me and corresponds to the table above.
\nThe resistive divider that I was talking about and which has to be altered is highlighted in yellow. The idea is to lower the 2.5V value read on pin 2 of CM6901, to, say, 2.3V, so that he thinks the output voltage has decreased and to increase it. So the value of R78 must be lowered. For this you add a resistor in parallel to the 3.3K\u03a9. I put 20K\u03a9 in parallel and got 13.4V at the output. If you can make the change directly on the board is fine, to me it was an impossible mission, because the miserable ones thought to do exactly this circuit <\/span>with SMDs.
\n<\/span>And here’s how I soldered a wire to pin 2.<\/span>
\n<\/span>
\n<\/span>
\n<\/span>And I went to ground with the resistor I was talking about. 20K\u03a9. A lower value leads to an increase in output voltage. From 12V, 13V, 14V …
\nAnd suddenly another circuit intervenes. Overcurrent and overvoltage circuit protection. It switches off the power if it detects values \u200b\u200bout of range (it is still a computer PSU and does not want to cook the motherboard \ud83d\ude09 ). It turns off the PSU if the 12V output goes near 14V or if the consumption exceeds the maximum current written on the label. It can be bypassed, but I do not recommend it at all. As I said, you give up all the advantages of a computer PSU – cheap, small, powerful and protected.
\nIf you eliminate this protection circuit, you no longer have a (semi) professional supply, but a toy, an experimental power supply. It can go like this if you want to.
\nBecause I did not take this step, I could not say how it is done, it depends on what integrated circuit is used for this. Cheaper regulators have the protection circuit inside and are easier to disable. In general, a pin is to be decoupled, there are enough tutorials.<\/p>\n

Here is the new switching PSU near the old linear one.\"\"<\/a><\/span>It is true that the old one looks good too, steam-punk style, just do not try to lift it from the table or you will get a back ache \":mrgreen:\" .<\/p>\n

Conclusion<\/strong>:
\nThis is the second power supply I modify. The first one exploded, I admit. These PSUs do not die slowly, with a hiss, like linear ones do. They tend to explode if something goes wrong.
\nIf I learned anything, you don’t have to be discouraged. If it explodes, you get another one. They are very cheap. I bought two from the beginning.
\nThe technique with the resistive divider is universal.
\n1. See what IC does the regulation (by observing and searching the net)
\n2. Look in the data sheet which is the INPUT ERROR AMPLIFIER pin
\n3. Identify the resistive divider on the board with a little reverse engineering, if you succeed. It’s not mandatory.
\nThen, to increase the output voltage, simply connect the respective pin to the ground with a resistor. 30K\u03a9 for starters, to be safe. If you want to lower the output voltage, you go with 100K\u03a9 at +12V (output). See where you stand and change the value of the resistance until you get what you want.
\n4. If the power supply does not start again, undo what you have soldered and start over. As I said, if the resulting voltage is in the bushes, the supply goes into protection and does not start.
\nIf you make a short on the board somewhere else, blast! Bye. A new one.
\nThe old power supply is described in this<\/a><\/span><\/span> article.
\nIts interior:<\/p>\n

\"\"<\/a><\/span>
\nOld and new.
\n<\/span><\/p>\n

\"\"<\/a><\/span><\/p>\n

<\/p>\n

RO<\/strong>
\nModificare surs\u0103 de calculator pentru mai mult de 12V (cu CM6901)<\/p>\n

ATEN\u021aIE !!<\/strong><\/span>
\nAceast\u0103 lucrare implic\u0103 pericol de electrocutare \u0219i moarte !!<\/strong><\/span>
\nNu-\u021bi b\u0103ga degetele dac\u0103 nu \u0219tii despre ce e vorba.<\/strong><\/span><\/p>\n