rufinus Posted November 30, 2006 Report Posted November 30, 2006 Well, the problem is that the LED is constantly on! Quote
audioguru Posted December 1, 2006 Report Posted December 1, 2006 Hi Rufinus,Check the values of R17, R18, R19, R20, R21 and P2. Check that C8 and Q3 aren't shorted. Swap U3 with another opamp.What is the voltage of the negative supply? Quote
egres Posted December 1, 2006 Report Posted December 1, 2006 one more question.. ive got twenty high-quality potentiometers, but they are 100K.. how can i modify the power supply to use them?thx, egres Quote
audioguru Posted December 1, 2006 Report Posted December 1, 2006 Hi Grs,The opamps have very high resistance FET inputs so yes you can use 100k pots:1) Their wiring should be shielded so it doesn't pickup mains hum radiated from the transformer or the mains cord.2) Multiply the values of R17 and R18 by 10. Quote
hana_moh Posted December 1, 2006 Report Posted December 1, 2006 i have done my Power....[/b]my changes is:R7:1K 10W*2 ON PARALLELQ1 & Q2: TIP31 with heatsinkQ3 *2 on parallel with big heatsink and fan------------------------------------------------------my problem with:R7 >>>> to set minimum voltage to 0v (before change :p1 is down but the voltage to maximum then move little bit start from 2.1v to 1.4v)R11 >>>> to set maximum voltageU2 temp highany one need any help...... ;D Quote
audioguru Posted December 1, 2006 Report Posted December 1, 2006 my changes is:R7:1K 10W*2 ON PARALLELHi Hana,Welcome to our forum. ;DR7 must be about 0.47 ohms. Use two 1 ohm resistors in parallel if you want.Q1 & Q2: TIP31 with heatsinkQ3 *2 on parallel with big heatsink and fanGood. Q4 should be two power transistors in parallel. Q3 is a small transistor.my problem with:R7 Quote
rufinus Posted December 2, 2006 Report Posted December 2, 2006 OK, found the problem, now everything seems to be working. Q3 was bad somehow and had to be replaced.Thanx, audioguru! ;) Quote
egres Posted December 2, 2006 Report Posted December 2, 2006 well... i have just finished mine.. if i wasnt a bit stupid, it could work on a first attempt ::)i have bought two BD241C as Q1 and Q2 and two 7805 stabilizators for voltmeter and ampermeter... i dont know how, but i soldered 7805 in a place of Q1, and i spent 4 hours checking everything ::) i replaced it and it works fine..i must buy a 0,33ohm resistors, because i forgot to buy them yesterday.. with one TIP3055 the heatsink gets quite hot..so thank you, ;)egres Quote
audioguru Posted December 2, 2006 Report Posted December 2, 2006 Hi GRS,I am glad to hear that you fixed your problem. A regulator makes a lousy transistor, doesn't it?With your 24VAC transformer, the positive supply will be about 32VDC when the project has a 3A load. If the output voltage is set low or is shorted, then the output transistors must dissipate 32V x 3A= 96W which is way too high for a single 2N3055 so I recommended using two in parallel. 96W is a lot of power for a single heatsink so maybe a fan should be used.If I make this project then I would use a heatink in each side for the output transistors then maybe a fan won't be needed. Quote
egres Posted December 2, 2006 Report Posted December 2, 2006 well, the transistor was hot when i managed to connect 12V bulb on it.. i set 14V on supply, and the current was 2A.. so (BIG 500VA transformer with 4 primary wires.. output can be 24,27 or 30 Volts.. set on 27Volts) -> after diodes it is cca 34Volts.. 34-14=20 -> "unused" voltage 20*2=40 watts on heatsink.. heatsink is not black, and it is from pentium 4, 1ghz CPU, so it is not the best for this app.. i am going to do a two-stage fan controller tomorrow.. (off-20%-100%), using 1n4148 diode on a heatsink, and tl082.. would you be interested in it? should i post a circuit diagram here?egres Quote
egres Posted December 2, 2006 Report Posted December 2, 2006 and by the way... looking at yours wattage : 32*3=96Wand mine: (34-14)*2=40Wis mine wrong? is the heat going to a heatsink determined by U*I ? or (U(source)-U(load))*I?egres Quote
audioguru Posted December 2, 2006 Report Posted December 2, 2006 Hi Grs,I am not making this power supply project.I think there is a temperature controlled fan project already in our projects section. It uses a lousy low voltage zener diode as its voltage reference that has more temperature sensitivity than its sensing diode.My 96W calculation was with 32VDC at the main filter capacitor, the current at 3A and the output shorted. At 5V/3A output then the transistor will dissipate 81W which is also too high for a single output transistor unless some liquid nitrogen cools it. A fan might be able to cool a single transistor on a huge heatsink until the fan wears out.Can you imagine the original project smoking? A few guys have seen it. ;D ;D Quote
hana_moh Posted December 3, 2006 Report Posted December 3, 2006 thanks to the Boss "audioguru" ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;Dall is done thanks veryyyyyyyyyyyyyyyyy matchall is ok U1,2,3 is TL081Transformer 3A 39V Quote
audioguru Posted December 3, 2006 Report Posted December 3, 2006 Hi Hana,Does your project work now? Good.Your opamps shouldn't be TL081. Its absolute max total voltage rating is only 36V. If your transformer is only 24VAC which is too low, then the positive supply would be 35.4V and the negative supply is 5.6V. So the total supply for the opamps is 41V if there is no load.Yor transformer shouldn't be 39VAC. It is much too high. I recommend a 30VAC transformer for this project and high voltage opamps.To make 3.0ADC from the output of this project, the transformer should be rated for 4.2A. A project with a 3A transformer can safely produce only 2.1ADC. Quote
Mordechai Posted December 3, 2006 Report Posted December 3, 2006 Hi,Where i can buy PCB from Power Supply and Ammeter LCD Panel?Thanks Vy 73/55, DG1JB Quote
hana_moh Posted December 3, 2006 Report Posted December 3, 2006 Thanks for interest and amazing continuance "audioguru"transformer 18 v* 2 -------------------------R2 is Heating Quote
audioguru Posted December 3, 2006 Report Posted December 3, 2006 Hi Hana,If you have your 18VAC plus 18VAC transformer wired for 36VAC then the very high DC voltages will damage many parts.The original project spec'd a tiny 1/4W resistor for R2. Many members complained about it overheating so I recommended using 2W. Quote
hana_moh Posted December 3, 2006 Report Posted December 3, 2006 sorry i fault not R2 R1.......... Quote
audioguru Posted December 3, 2006 Report Posted December 3, 2006 Hi Hana,R1 is across the unregulated positive supply. Its power dissipation is easy to calculate:1) If you have the original 24VAC transformer then it will be about 26VAC without a load on the project. Its peak voltage is 36.8V and is reduced to 35.4V by the rectifier bridge. So the power dissipation of the 2.2k resistor is 35.4V squared divided by 2.2k= 570mW so the original 1W resistor is fine.2) If you have the recommended 30VAC transformer then it will be about 31.5VAC without a load on the project. Its peak voltage is 44.5V and is reduced to 43.1V by the rectifier bridge. So the power dissipation of the 2.2k resistor is 43.1V squared divided by 2.2k= 844mW which is hot for a 1W resistor so I recommended a 2W size.3) Your 36VAC transformer will be about 38VAC without a load on the project. Its peak voltage is 53.7V and is reduced to 52.3V by the rectifier bridge. So the power dissipation of the 2.2k resistor is 52.3V squared divided by 2.2k= 1.24W. A 1W resistor might smoke and a 2W resistor will be hot.Your transformer's voltage is much too high. Quote
egres Posted December 5, 2006 Report Posted December 5, 2006 hi everybody.. here are some photos of mine power supply.. no housing yet, but few "tests"list of changes: (partlist by audioguru, the tuned one, but few parts changed)power transistors: -a pair of BD249C (100V, 25A, 40A_peak, 125W at 25 Quote
egres Posted December 5, 2006 Report Posted December 5, 2006 and a video, thats all, thanks for your attention :)egrespc050163.rar Quote
audioguru Posted December 5, 2006 Report Posted December 5, 2006 Hi Egres,My browser displays a square box instead of the "E's" in your name. So I called you Grs before.Your project is very powerful. I think its good voltage regulation will improve with thicker wires.I didn't see the car headlight blowup in your video. Quote
egres Posted December 5, 2006 Report Posted December 5, 2006 AG, thats ok, i thought something with fonts will be wrong :)well.. i am sure you know that those bulbs must be cooled.. atkeast with air.. when i wired it in series, and connected 24 volts for few seconds, it did not blew up, but my table is a little brown in that place :D .. and the bulb started smoking :D .. but i did not wanted to sacrifice it for my experiments :D Quote
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