red baron

About a month ago I asked if anyone could explain why my 30V 5A (with 3 x TIP3055 output transistors) suddenly failed at 45V and no current. Both Audioguru and Redwire (I think) suggested a short in one of the 3055s. Finally I have isolated the fault to a 'popped' 3055. At the time that the PS failed, I was trying to charge a 'golf cart' battery which was nearly fully charged so no significant current. I set the volts on 14.1V and current limit at 1A. When touching the PS leads to the battery there were a few sparks (possibly back to front polarity), and maybe not, but PS popped the 3055. Has anyone had experience with the PS and 'active' loads like batteries, as opposed to passive loads like resistors?

Earthing matter sorted thanks. Next question: our DIYFAN option shows a 24V Zener and resistor across input +ve and -ve to provide a stable 24V supply voltage to pin 7 of U1. Remove the connection of pin 7 to +ve. Since the +ve input voltage can drop at high loads, what do you think of this idea?

Thank you for the helpful response. I am not sure what you mean by 'electrical outlets that were wired backwards'. In Australia mains outlets have three wires - live, neutral and ground/earth (for earth leakage protection). Would you recommend that I simply do not connect the earth to the chassis. The danger is that if there is a fault (fingers in the wrong place!) on the mains side of the transformer then the full 240V could be fatal.

I have two questions: 1) can the circuitry associated with RV1 be omitted? What would be the consequence? 2) when mounting in a metal box with the chassis earthed to mains earth (green/yellow), should the -ve on the electronics also be connected to mains earth?

Hi liquibyte I have been involved in this project for nearly two years. I built the Picmaster version from March 09 and it worked fine for a while. Recently while charging a 34Ah battery the power supply failed - voltage went to 42V and zero current. What do you suspect has blown?

Hi mate Thanks for the idea, but already changed to 56ohm with no effect. I suspect that there is something wrong somewhere but cannot find it.

Audioguru/Redwire - thank you both for all the input and help. While trying to make further voltage measurements on the pcb I managed to blow up the regulator circuit, and have now had to replace the 10V zener, Q3, and LED. The PS now operates as before, without the 'dimming' of the LED at high currents, but still with the LED illuminated when the current limit (P2) is turned down to nearly off. Regrettably I cannot afford more time to fix this 'bug' and since the PS works fine, I will live with it as it is. Once again, thank you for your interest.

Hi Mendimano It is amazing how closely our projects look in the end. Thanks for the photos. I have invested too much time (and money) to give up now, so hopefully with the help of others it will get finished and work according to expectations. Regards

Great help, guys. I am trying as fast as I can to check your suggestions. Since the last thread has raised the topic of maximum supply voltages, can you help on this? 1) the supply transformer has input 220V and 240V, and output 0-24V or 0-30V. a) When I use 220V (and Australia is 240V off the street) I get 30V output on the 24V tapping (no load). b) When I use 240V input, then I get 34V on the 30V tapping. Which combination is the best for the regulator circuit? Using combination a) so far I can only get 29.7Vdc through the power supply at 5A, but I can live with that - 30V would be nice. 2) I checked on the effect of reducing R7 from 0.33ohms to about 0.25ohm. No noticeable change, and LED behaviour the same. 3) 10V zener is correct. I get 39.3V on the bridge rectifier +ve, and 29.3V at the emitter of Q3. 4) I am busy replacing Q3 5) I will reduce R22 from 3.9k to say 2.8k and see if this changes the LED behaviour at all. 6) The voltage drop across the 2 x 1N4148 is 1.52V (D2 and D3 are not labelled) 7) Some other observations: U3 pin 4 = -1.52V, U3 pin 3 varies 0 to 1.5V depending on P2 setting, U1 pin 6 is correct at 11.2V What other readings can I check?

Hi Redwire My mistake, the power transisters are TIP3055 in TO-218 configuration. Thank you for the input regarding the input offset question. For some reason, I have +1.6v wherever others have +1.41V and I wonder whether this could be causing the problem. I was unable to get R7 at 0.27ohm here, so I have used 0.33ohm which at 5A has a volt drop of 1.65V, but at zero output current, this should not cause the LED to light. I am also concerned that when I turn the current limit P2 to a higher level, say more than 200mA, then when the voltage is increased to trigger the LED, it does not 'switch' on as it should but increases in brightness from 0 to bright over a voltage increase of about 5V eg. if I set the current limit to 2.5A, with a load of 6ohm, then the LED starts to shine at 14V and is bright at 16V - any ideas?

Thanks Audioguru, I will buy some replacement TLE2141s and see whether this fixes the problem, but I have my doubts, since I have tried moving them around with no change in results. I have also discovered that the input offset pot RV1 has no impact on any of the readings - does this tell us something? Redwire, your positive comments are most appreciated. I have many pics, and will include a few more. The housing is RS Components item 223-988 and costs $89.00 here in Sydney.

More pics

Hi AudioGuru Finally the project is near completion - pics attached. Thank you for the help getting to this stage. I have two problems: 1) The current limiting circuit does not function correctly and I need some help with trouble shooting. With P2 turned down to about 1kohm (near minimum) the LED comes on, but turns off one current limit is set higher. Setting the maximums of 5A and 30V, the LED starts to turn on faintly and then gets brighter, but only at the max. In between all works well. Could Q3 have blown? 2) From the pics you will see that I have used Picmaster pcb, but I believe there is one mistake - the polarity of C10 (in your circuit C3) has the +ve on the pcb away from ground and -ve connected to ground. Surely not correct? Regards

Hi Audioguru I have had a lot of trouble sourcing the shunt resistor (0R27 ohm) for the 5A version in Australia, nearest is 0R22, 10W, or 0R33 10W. But in the process I think I have ordered the wrong digital voltmeters (0 - 99V 3 wire) for the current display. Since the volt drop across the shunt will only be just over 1V at 5A it will hardly register, and at 100mA, no chance. Any ideas how I can fix the display problem? And can I use the 0R33 shunt resistor?

Hi guys I have trawled through the 123 pages about this project on the first listed subject, and then the 96 pages in this listed project, and I note some confusion and some frustration, so I have spent time trying to filter out a solution for the newcomers to get started and to have success - it's a great project. Attached is the latest and most commonly used schematic and parts list from Audioguru (a real master!), but it is left up to the enthusiast to design a printed circuit board, and many of us do not have this desire or these skills. Also attached is the circuit diagram and parts list from Picmaster (the circuits are the same but the part numbering is different!), which also includes a successful printed circuit board design for the 3A or 5A version. Since I wanted the easy and quickest way forward I made the pcb using the 'laser print and Mommy's iron' method, and then I created a comparison list of how to progress from the Audioguru version to the Picmaster pcb. I hope that this is helpful to anyone just starting. Audioguru_schematic_and_parts_list.pdf Picmaster_0_-_30V_3_-_5A_Power_Supply.pdf Parts_comparison_0_-_30V_3_or_5A_Power_Supply.pdf