Has any one built this psu pcb ? - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 16, 2013, 07:37:27 pm
content: Has anyone built this power supply unit pcb from ebay?

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 16, 2013, 08:53:36 pm
content: Can't say I'm a fan of the parts it uses. The LM723CN doesn't have the best specs i nthe world (150ppm/oC drift, 0.6% load regulation, etc.) Also, no way you get 10A across the entire range with that heatsink. Maybe in a tornado you would or if you submersed it in LN2 but not under real world conditions. If you are trying to output 1V at 10A you are wasting at minimum 140W in heat. He could have easily reduced this amount using a 0-10-20-30 transformer setup, or similar split transformer to minimize voltage overhead, but even then its a lot of heat to dissipate.

author: david77
author_rank: Frequent Contributor
timestamp: July 16, 2013, 09:04:03 pm
content: That transistor on the board is only the driver for external pass units, it doesn't have to dissipate that much heat. That said, I'd mount it on the heatsink with the external ones.It's hard to judge withou a schematic how good the supply will perform. Why are there two 723 and what's the 741 doing?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 16, 2013, 09:32:59 pm
content: The seller just sent me this information.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 16, 2013, 09:35:14 pm
content: I don't understand page 10 on that pdf

author: mariush
author_rank: Super Contributor
timestamp: July 16, 2013, 10:55:38 pm
content: The capacitors the creator of that pdf chose to use are of the snap-in variety, which have more than two terminals.. one is positive, one is negative, the other two are usually just for physical support.You don't have to use that type of capacitor, you should be able to easily find 4700uF 63v capacitors (or even larger ones, 6800uF or 10000uF won't hurt to use) in simple radial can style (with only two leads).In both pictures the two capacitors are connected in parallel , - to - , + to + , in order to obtain more capacitance.The capacitors are supposed to be used directly after a bridge rectifier to smooth out the output of the rectifier, so in the first picture you see the capacitors connected directly to + and - of the rectifier.In the second picture, they're wired to the board to the + and - terminals and the bridge rectifier is connected in two separate terminals on the pcb.Anyway, while the power supply may be able to do 10A, the heatsinks may not be quite adequate at certain voltages at that current.For example, it says at more than 12v it will connect the two windings, so at 13-14v the pass transistors have about 40v on them... 40v - 13v = 27v .... times 8 amps and you get 150w dissipated on the heatsink.

author: tom66
author_rank: Super Contributor
timestamp: July 16, 2013, 11:08:12 pm
content: I'm not sure what a minimum current limit is supposed to do on a power supply.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 17, 2013, 08:09:12 am
content: Thanks for the info mariush

author: johnboxall
author_rank: Unknown
timestamp: July 17, 2013, 08:10:03 am
content: Quote from: snipersquad100 on July 16, 2013, 07:37:27 pmWhat was the ebay item number?

author: madires
author_rank: Super Contributor
timestamp: July 17, 2013, 10:33:19 am
content: Quote from: mariush on July 16, 2013, 10:55:38 pmThe 6 2N3055 will do the job, but even with a dedicated heatsink for each pass transistor board you would still have to buy aluminium bricks :-) Obviously the PSU needs an overheating protection.

author: digsys
author_rank: Unknown
timestamp: July 17, 2013, 12:29:58 pm
content: Quote from: AcHmed99Totally agree .. even better matched pairs are the - MJL3281A / MJL1302A and 2STC5200 / 2STA1943These were developed for class-A amps and have pretty flat betas of 100+ over a large Ic range. My favourite BJTs :-)

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 17, 2013, 05:27:18 pm
content: Thank you guys, For the dude who wanted the ebay item number it is 200944117797

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 18, 2013, 06:37:58 pm
content: Hello againIm having trouble trying to find the relay for this project, I found this on ebay 181141041715, looking at the relay symbol it looks like it should do for this project. Can anyone verify this? Thank u.Also the current limit trim pots are they presets you solder to the board or shall I put them on the front panel.

author: ciccio
author_rank: Frequent Contributor
timestamp: July 18, 2013, 07:41:33 pm
content: Does anyone know what is the unlabeled component wired in parallel with the transformer (page 9 of the wiring schematic)?It looks like a fused and switched mains socket, with the center (earth?) pin disconnected.Where is the Protective Earth connected? There is a "Europlug" in the components list. Most plugs in Europe are earthed.There is a very common mistake in the above schematic: the fuse must be wired BEFORE the mains switch.This is required by most safety standards.Best regards

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 18, 2013, 07:49:01 pm
content: I think it's a mov, wait to get expert advice first tho.

author: madires
author_rank: Super Contributor
timestamp: July 18, 2013, 08:11:17 pm
content: Quote from: ciccio on July 18, 2013, 07:41:33 pmLooks like a small transformer, maybe for the display board?QuoteThe protective earth is connected to the metal box housing the PSU.

author: ivan747
author_rank: Super Contributor
timestamp: July 19, 2013, 11:38:42 am
content: To me, the mystery component could be an indicator light, but I don't know why would they put a third pin there.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 19, 2013, 02:25:12 pm
content: I think ill just use it for low currents 4 amp max and use a smaller transformer I've got in my junk bin.Could I put two smaller transformers in series?And your right about the expense, its cost me about £50 so far in buying just the board and parts that go on the board, But it does give me something to do.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 26, 2013, 06:53:33 pm
content: Well I was looking for something to put this PSU PCB in I remembers about my busted rework station. This unit released the blue smoke some time ago and the hot air gun was all loose inside so not worth fixing.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 26, 2013, 07:11:51 pm
content: I opened it up and took it apart

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 26, 2013, 07:23:20 pm
content: I thought this was ideal unit to use as it had holes for pots, 2 on/off switches which I will use for switching the mains and output, two windows I can put an volt and amp meter and I use the holes where the iron and hot air lines where for the output jacks. There's a mains lead and built in fuse already installed. Just need to think of a way to change the look of the front panel, maybe I go to my local sign writer. Any ideas would be grateful.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 26, 2013, 07:32:02 pm
content: Laying out the components.There are still two other pcb's to put in, Have'nt made them yet but there's plenty of room.I also got the rear panel free in case I need to move the fet and add a lager heat sink as people on here think this will over heat.I just found out that the front cover unscrews, this will make it easy to drill.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: July 26, 2013, 07:40:40 pm
content: That's the pcb and transformer screwed in, tight fit that board.Front panel back on, still woundering how to rewrite the face on the panel.That's it for now, waiting for the rest of the parts to come.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 03:30:22 pm
content: Oh well, I wired it all up on my bench today and surprise surprise it didn't work. I'm only getting 0.27v on the output. spent hours today trying to figger it out but no joy. Help Please.

author: mariush
author_rank: Super Contributor
timestamp: August 30, 2013, 03:46:19 pm
content: Post pictures of the whole board , as detailed as possible, and pictures of how you wired the potentiometers and the buttons etc.measure voltages with a multimeter, where they come into the pcb .. etc

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 04:02:12 pm
content: I've pulled it apart now as I want to follow the traces on the pcb, I was thinking the pots too as it don't tell you how to connect them.

author: Unknown
author_rank: Unknown
timestamp: August 30, 2013, 04:06:33 pm
content: Like mariush says, you need to be way more specific if you want any useful advice. It could be a component or wiring error, so you should post clear pictures showing those. If you spent hours, then I guess you measured a bunch of voltages or tried substituting parts. How about sharing that information?A useful technique is to print out a copy of the schematic (or use your favorite image manipulation program) and write voltages on the schematic. You should measure relative to the negative DC input terminal (indicated as ground in the schematic).

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 04:15:14 pm
content: The schematic is on the pdf on comment 4 on page 1, I will reconnect it back up and post pictures later.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 04:45:20 pm
content: I think I found something, there no trace on the pcb connecting pin 1 to c3 on ic3 as it says on the schematic. I pulled out the chip and done a continuity test to confirm no connection.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 04:58:41 pm
content: scrap that, its pin 4 to c3, miss print on my print out. merphy

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 07:39:08 pm
content: ah ha, got it working, had a pot wired up wrong. I take it I can wire a volt meter across the out put but how would I wire a amp meter?

author: Unknown
author_rank: Unknown
timestamp: August 30, 2013, 08:23:18 pm
content: Put the meter in series with the power supply, i.e. between one of the outputs on the PCB and the output jacks. You could also use R31 as shunt, although that will involve some scaling to get the correct reading on a standard panel meter.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 30, 2013, 08:52:19 pm
content: Thank you Alm, I will have a go tomorrow.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 08, 2013, 05:58:29 pm
content: I have a problem, the constant current pots don't seem to do anything and the over current led is always lit, Ive changed the chips but still the same. Any ideas anyone???

author: kizzap
author_rank: Unknown
timestamp: September 09, 2013, 12:45:10 am
content: Does the output give any power at all?is there a short on the output?alternately:check that you have the potentiometer connected correctly.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 09, 2013, 07:04:42 am
content: I'm getting 18 odd volts on the output, the same as the voltage on pos tap on the bridge rec, I've also noticed that the relay is not clicking in the 2nd tap off the transformer. Looking at the schematic the opp amp drives that and I did'nt change that chip, so I give that a go.

author: madires
author_rank: Super Contributor
timestamp: September 09, 2013, 09:22:05 am
content: Please double check if you got all the components and the wiring right (values, polarity, direction, pin outs and so on).

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 16, 2013, 08:30:07 am
content: Another problem, The over current limit led still wont go out. I've noticed that the current resistors on the drawing on the pdf(on page 1) says 7 ohms at 10 watt witch I used, but on the silkscreen on the pcb (very hard to see) it says 0r1 at 5 Watt. Could this be the problem that the over current limit led stays on? But surely a 0.1 ohm resistor is just a dead short.

author: madires
author_rank: Super Contributor
timestamp: September 16, 2013, 11:19:00 am
content: The pdf states "7/10W" for the current sense resistors. It could mean that the resistors should be 7W or 10W types. 7 Ohms would be an unsual value, but 7W is a usual one. If you have a look at Ohm's law R = V/ I or V = R * I you'll see that a larger resistance causes a larger voltage drop for the same current. That seems to be the cause for your problem. So please try 0.1 Ohms.To get an idea of the voltage drop of a resistor with 0.1 Ohms at 1 A: V = 0.1 Ohms * 1 A = 0.1 V = 100 mV

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 16, 2013, 04:52:55 pm
content: Thanks Madires, This has been a big learning curve for me

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 19, 2013, 07:49:11 am
content: No difference after putting in 0.1 ohm resisters. I cant think what I've done wrong or weather its just a faulty design.Only thing I can think of is I put a ceramic cap where a polyester should be but the value was the same, and a 1w resistor where a 1/4 watt should be again same value. One thing I'm sceptical about is that there is 17volts powering the led.

author: madires
author_rank: Super Contributor
timestamp: September 19, 2013, 11:10:32 am
content: Please post some pictures of your PCBs and the wiring for double-checking.

author: Unknown
author_rank: Unknown
timestamp: September 19, 2013, 05:43:45 pm
content: Quote from: ciccio on July 18, 2013, 07:41:33 pmFan. One is mentioned on page 2.