steev Posted February 11, 2007 Report Share Posted February 11, 2007 Just a short question: What do I have to change, if i want use an 24 VAC 3,3 A transformer for the "0-30 VDC STABILIZED POWER SUPPLY" and the "Voltmeter + Ammeter LCD panel"? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 11, 2007 Report Share Posted February 11, 2007 Hi Steev,The 0V-30V power supply project will produce a max output voltage of about 25VDC at a max current of 2.3A with your 24VAC/3.3A transformer operating continuously at its rated power rating.The LCD meter project is powered by up to 35VDC. The unregulated voltage with your transformer is about 32VDC fully loaded to about 34.6VDC without a load. Quote Link to comment Share on other sites More sharing options...
steev Posted February 12, 2007 Author Report Share Posted February 12, 2007 I ust worry about D1, D2, D3 and D4 because they are specified for only 3.0 A but there will be an possible input current of 3.3 A ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 12, 2007 Report Share Posted February 12, 2007 Your transformer can supply only 24V x 3.3A= 79.2VA. The peak voltage is 33.9V so the max average current from the transformer is only 79.2VA/33.9V= 2.34A at its max power rating. The 79.2VA power from the transformer is divided by the rectifier diodes, the power supply circuit and the load.The rectifier diodes get too hot when they are operating near their max current rating. Use a bridge rectifier module (10A) instead that can be bolted to the metal chassis for cooling. Quote Link to comment Share on other sites More sharing options...
steev Posted February 12, 2007 Author Report Share Posted February 12, 2007 First of all, I want to use this transformer. Yes, I'm from Germany ;)Input Voltage: 230 VOutput Voltage: 2x 12 VACOutput Current: 2x 3,33 APower: 80 VADo you have any partnumber for suitable diodes? I don't really want the 1N5402 to operate on there limit, I would realy like some buffer up to 4 A?! Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 12, 2007 Report Share Posted February 12, 2007 Use a bridge rectifier module that is bolted to the metal chassis for cooling.They look like this. This one can be 10A or 35A. I don't know which ones are available in your country. Quote Link to comment Share on other sites More sharing options...
steev Posted February 13, 2007 Author Report Share Posted February 13, 2007 Thanks for your reply! I decided to use the KBU 4J. Are there any other parts, which would also work on there limit, if I have a max current output of 3.3 A on the transformer? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 13, 2007 Report Share Posted February 13, 2007 Hi Steev,Read the big long thread about improving the 0V-30V power supply project.Q2 will smoke and melt if Q4 has a low current gain, the output voltage is set low and the current is high.I recommend replacing the dinky little 2N2219 transistor with a real TIP31A power transistor that has a real heatsink.The TIP31A costs nearly half and can dissipate nearly 20 times as much heat.C1 is the main filter capacitor and its value is much too small.Here is the parts list with changes that I recommend: Quote Link to comment Share on other sites More sharing options...
steev Posted February 13, 2007 Author Report Share Posted February 13, 2007 Once again a big thanks for your help!!After searching a while on my german shop's site I decided to choose these parts:transformer: RKT 12015R1: 2W METALL 2,2KR2: 2W METALL 82R3: 1W 220R4: 1/4W 1kR5, R6, R13, R20, R21: 1/4W 10kR7: 11W AXIAL 0,51R8, R11: 1/4W 27kR9, R19: 1/4W 2,2kR10: 1/4W 270kR12, R18: 1/4W 56KR14: 1/4W 1,2KR15: 1/4W 100R16: 1/4W 1KR17: 1/4W 33R22: 1W 3,9KR23, R24: 2 x 2W DRAHT 0,33 (the two resistors for Q4)RV1: PIHER 10-S 100KP1, P2: P6M-Lin 10kC1: AX 10.000/63C2, C3: RAD 47/63C4: MKS-4 100NC5: MKS-4 220NC6, C9: NPO-2,5 100PC7: RAD 10/63C8: NPO-2,5 330PD1, D2, D3, D4: KBU8BD5, D6: 1N 4148D7, D8: ZD 5,6D9, D10: 1N 4148D11: 1N 4001D12: LED (LED 5MM 2MA RT)Q1, Q2: TIP 31C MBRQ3: BC557CQ4: 2 x 2N 3055 U1, U2, U3: OPA 445 APand some heatsinks I already bought. Are the 10.000 uF of C1 enough? It's the biggest on I found...BTW: I would really like to make a HowTo of my version of the power supply aviable on my (and another modding-) website with downloadable schematic diagramm and layout (of course selfdesigned and with the fitting parts). Are I'm allowed to do this or is there any problem because of the copyright? I DO NOT want to sell the power supply or its HowTo! Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 13, 2007 Report Share Posted February 13, 2007 Hi Steev,You project will have very good performance.10,000uF is fine for C1.You changed the value of R7 by 8.5%. Then the max current might not be 3A, depending on the actual value of the current-setting pot and other resistors. Some people add a trimpot in series with each pot for calibration of 3A and 30V.Each 2N3055 output transistor must dissipate about 60W if the current is set to 3A and the output voltage is set low or ithe output is shorted. So it would be best to have them on separate large heatsinks, one on each side of the case. Or one lage heatsink for both transistors and a fan. Or two medium heatsinks and a fan. Your choice.I would not use an insulator between the output transistor and its heatsink, just thermal grease for better heat transfer. Then I would insulate the heatsink from the chassis.I don't think there is a copyright problem since you are not selling anything. Quote Link to comment Share on other sites More sharing options...
steev Posted February 13, 2007 Author Report Share Posted February 13, 2007 You changed the value of R7 by 8.5%. Then the max current might not be 3A, depending on the actual value of the current-setting pot and other resistors. Some people add a trimpot in series with each pot for calibration of 3A and 30V.Well, the problem is, that i cannot find exactly the same resistor... I only found 9 Watt resistors from 0,33 to 0,47 Ohm, but it would be too small, wouldn't it?And don't worry about the cooling stuff, I have some old CPU cooler. I wanted to use a fan anyway ::) Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 13, 2007 Report Share Posted February 13, 2007 3A in 0.47 ohms is 4.23W. A 5W resistor would be extremely hot. A 9W or 10W one would be cooler. I have seen many 10W resistors but never a 9W one. A 9W 0.47 ohm resistor would be fine. Quote Link to comment Share on other sites More sharing options...
steev Posted February 16, 2007 Author Report Share Posted February 16, 2007 I just finished the the layout and the schematic diagramm (Eagle files) !!After buying all reqired parts I will post some fotos and a link to the german HowTo ;D Quote Link to comment Share on other sites More sharing options...
steev Posted March 8, 2007 Author Report Share Posted March 8, 2007 It's me again!I nearly have done the powersupply, only the transformer is not available :-\Although here are the first pictures including a modified layout: Quote Link to comment Share on other sites More sharing options...
steev Posted March 29, 2007 Author Report Share Posted March 29, 2007 The powersupply itselves is done so far. I can change the voltage from something about 0 up to 30 Volt and the current LED seems to work fine!Now I have to grill some AVRs to get the multimeter working ;D and build a small case...Want to see some pictures? Here you go: Quote Link to comment Share on other sites More sharing options...
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