0-30V 2mA-3A DC PS Kit - Messed Up! - Page 1
Forum section: electronics / beginners

author: kiwizz
author_rank: Contributor
timestamp: January 23, 2018, 11:19:20 am
content: Hi All,My first post here so be niceplease.I spent an hour or so meticulously putting together this kit:https://www.aliexpress.com/item/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-Diy-Kit-Short-Circuit-Current-Limiting-Protection/32814203124.html?spm=2114.search0204.8.24.77151dbKM88qE&priceBeautifyAB=4after which, I wanted to hook up a voltage meter and an ammeter (https://www.aliexpress.com/item/1pcs-Top-Quality-5-bit-DC-0-0000-3-0000A-Red-LED-Display-Digital-Ammeter-amperimetro/32640299154.html?spm=a2g0s.9042311.0.0.QEKCjh)Once I had connected these, and added a DC motor to the DC out - I powered the unit on and something or multiple somethings started smoking. Now the unit can no longer adjust the voltage - its 'stuck' at 30v DC out. I re-read the installation instructions for the ammeter and it said to connect after the DC load, whereas I connected it before the load. I'm not sure this would have caused the problem.I've attached the circuit diagram for the unit (does not include what I added). Here's how I connected things:24v 'fan' output (+) --> ammeter + (to power the unit, not the current measuring part)24v 'fan' output (-) --> ammeter - (to power the unit, not the current measuring part)PS DC OUT (+) --> ammeter (+) && PS DC OUT (+) --> voltage meterammeter (-) --> DC motor (+)DC motor (-) --> PS DC OUT (-)So essentially the voltage meter is connected in parallel across the (+) and (-) of the DC out, while the ammeter and DC motor are connected to the same output in series.I disconnected everything after it smoked a bit so I can't be 100% this is how it was connected, but I'm pretty sure it was. One thing I noticed is that the ammeter display started flickering and the DC motor didn't start moving when I increased the voltage (just before smoking). Any suggestions would be greatly appreciated. A friend of mine suggested buying a new kit (they are pretty cheap) but I am curious as to what went wrong and would like to repair if possible.Cheers!

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2018, 12:02:30 pm
content: That kit is notoriously buggy.It's a classic, cheap Chinese kit. It won't meet its specifications and the op-amps are powered from too higher voltage. At worst it'll smoke, at best it'll just be unreliable. Here are some threads where this has been discussed previously.https://www.eevblog.com/forum/beginners/bangood-psu-enhancements/msg897523/#msg897523https://www.eevblog.com/forum/beginners/poorly-designed-kits/msg1314404/#msg1314404

author: Microcheap
author_rank: Frequent Contributor
timestamp: January 23, 2018, 01:51:16 pm
content: Looks like that Q2 and/or Q4 are gone, check them and replace it if necessary. Both must be mounted on a good heat sink.I assembled my power supply based on this project more than 8 years ago when I started with electronics, and despite the well know e extensively discussed issues with the design, it has served me well that long. I had to change those transistors 2 or 3 times but apart from that it works well if you are aware of its limitations.

author: zvonex66x
author_rank: Contributor
timestamp: January 23, 2018, 02:32:33 pm
content: Think that U2 is blown... if u want i will upload schematics of my power supply... it's very simple and very good PSU, useing standard TIP3055 tranzistors as output regulation.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2018, 03:40:21 pm
content: Quote from: Microcheap on January 23, 2018, 01:51:16 pmI'm glad you find it useful, but to me and perhaps, most people, replacing two transistors a few times in 8 years, would be unacceptable. What's worse is transistors have a nasty habit of failing short circuit from emitter to collector, which would result in the full voltage on the reservoir capacitors being applied to the load, causing destruction, if it can't handle 40V.Quote from: zvonex66x on January 23, 2018, 02:32:33 pmThat wouldn't be surprising, since the TL081 is only rated to 36V and this circuit can subject it to 40V or more. You could replace it with another op-amp, rated to 44V.Here's another thread, which discusses the shortcomings of this design.https://www.eevblog.com/forum/beginners/im-confused-about-power-supply-for-op-amps/msg932766/#msg932766

author: Cliff Matthews
author_rank: Unknown
timestamp: January 23, 2018, 04:31:01 pm
content: Another threadhttps://www.eevblog.com/forum/beginners/bangood-psu-enhancements/

author: abraxa
author_rank: Frequent Contributor
timestamp: January 23, 2018, 04:58:18 pm
content: A linear regulator being fed with 32V? That's gotta smell when using this to supply a 3.3V load - even at 1A, especially at 3A. ~70W of power dissipated in heat.Quote from: kiwizzWhat's that fan output, btw? Was it AC or DC?

author: Calambres
author_rank: Frequent Contributor
timestamp: January 23, 2018, 05:08:26 pm
content: Quote from: Hero999 on January 23, 2018, 03:40:21 pmCan you be a little more specific?... what op-amp?

author: Microcheap
author_rank: Frequent Contributor
timestamp: January 23, 2018, 06:43:51 pm
content: Quote from: Hero999 on January 23, 2018, 03:40:21 pmI totally agree with you, for me nothing is worse than not be able to trust your equipment while working in a project. But for the purpose that I built it, that was to start learning something, it was useful. And to be honest, I got to the conclusion that with the prices of a power supply today, I don´t think that even worth it to build your own. When you add the costs of components, transformer, enclosure, connectors, display and so on, you end up spending the same or more than a off the shelf PSU with better performance.Quote from: Calambres on January 23, 2018, 05:08:26 pmI think he refers to the TLE2141.Improvements to this project had been extensively discussed in this and other forums:http://electronics-lab.com/community/index.php?/topic/26825-0-30-vdc-stabilized-power-supply/http://electronics-lab.com/community/index.php?/topic/40835-0-30v-0-3a-latest-data/Quote from: abraxa on January 23, 2018, 04:58:18 pmI don´t own the Chinese version of this board, but as far as I understand, it has an auxiliary 24V DC output to connect a fan and the OP is using it to feed his meter.

author: David Hess
author_rank: Super Contributor
timestamp: January 23, 2018, 07:00:21 pm
content: Oh, that circuit. I do not understand why it is so popular.Quote from: Calambres on January 23, 2018, 05:08:26 pm741, 741A, or 741M but *not* the 741C unless it is from TI because they like to confuse things. Check the manufacturer's datasheet to verify which suffixes are 44 volts.LF356B, but again check the manufacturer's datasheet to verify which suffixes are 44 volts.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2018, 07:04:29 pm
content: Quote from: Microcheap on January 23, 2018, 06:43:51 pmHave you tried modifying it to make it more reliable? That would be a good learning exercise.Quote from: David Hess on January 23, 2018, 07:00:21 pmHow about the OP07? It should have a low enough offset to eliminate the trimming circuit.As to why it's popular: the PCB is available cheaply from many Chinese suppliers and it was featured on electronics-lab, a very popular site in the early 2000s, until a bad moderator caused all the nice and helpful people to leave.

author: Microcheap
author_rank: Frequent Contributor
timestamp: January 23, 2018, 07:45:20 pm
content: Quote from: Hero999 on January 23, 2018, 07:04:29 pmIn fact I did. I was working on this on the past few weeks and was thinking in make a post about it when I found this thread. I've been away from the electronics for quit some time and I had the opportunity to go back now so I thought that revive this project would be a good exercise to refresh things up.I'm not quite satisfied with the results yet, but if there is interest I would be happy to share it.

author: David Hess
author_rank: Super Contributor
timestamp: January 23, 2018, 08:02:28 pm
content: Quote from: Hero999 on January 23, 2018, 07:04:29 pmNot all OP07s are 44 volts so check the datasheet for the specific part. Also the original OP07 has a very limited differential input voltage range which will require checking the circuit for proper operation.It looks like the inexpensive OP07s from TI will work but the functional schematic they show looks like a 741 so I am dubious about their claims. Having learned not to trust TI datasheets, I would want to test their part to verify it is what their datasheet says it is.QuoteEvery time I see its schematic, it prods me to design and release my own version. Then I consider the economics and lose interest.

author: Cliff Matthews
author_rank: Unknown
timestamp: January 23, 2018, 08:38:18 pm
content: FWIW, there's a lot of good historical (hysterical? to some here) reading posted by user liquibyte here:http://electronics-lab.com/community/index.php?/topic/40835-0-30v-0-3a-latest-data/On the second page he ends up using mc34071's and gives all files required (unfortunately I don't want to be a user there.. so I can't get them and this forum is enough for me). I pinched this though..

author: zvonex66x
author_rank: Contributor
timestamp: January 23, 2018, 09:27:07 pm
content: This is simple circuit for psu 0-30v, 0-10a, i have made couple of adjustable psu, but tis is simple and best of all.

author: kiwizz
author_rank: Contributor
timestamp: January 23, 2018, 10:40:37 pm
content: Wow, so many replies - cheers!How can I check if Q2/Q4 are damaged (other than visual inspection)? I did stick a pretty big heatsink on Q4 with a fan - it was by far the hottest component on the board, even with the heatsink it was too hot to touch when the unit failed.

author: kiwizz
author_rank: Contributor
timestamp: January 23, 2018, 10:43:42 pm
content: U2 or Q2? I've ordered another kit as its cheaper than getting a single componentI am interested in building a more robust system after reading through the comments here - I don't really want to (at this stage) design and build my own PCB though - I have seen you can get them professionally made for a few bucks - do you have your design in a format where it can be sent to one of these companies to print? Also - is it adjustable etc?Cheers!

author: kiwizz
author_rank: Contributor
timestamp: January 23, 2018, 10:44:54 pm
content: DC

author: kiwizz
author_rank: Contributor
timestamp: January 23, 2018, 10:46:54 pm
content: Thanks for the reply - I don't see what you are referring to? previous schematic? forgot to add a link? Cheers!

author: Cliff Matthews
author_rank: Unknown
timestamp: January 23, 2018, 11:07:54 pm
content: Quote from: kiwizz on January 23, 2018, 10:46:54 pmKiwizz, FWIW some users reply to specific messages by prefixing something like @username, but most just use theQuotefunction on the right side. BTW, welcome to the forum!

author: zvonex66x
author_rank: Contributor
timestamp: January 23, 2018, 11:36:51 pm
content: Quote from: Cliff Matthews on January 23, 2018, 11:07:54 pm

author: David Hess
author_rank: Super Contributor
timestamp: January 24, 2018, 04:38:47 am
content: Quote from: Cliff Matthews on January 23, 2018, 08:38:18 pmThe MC34071 is not a bad choice but it is only available in surface mount. If you consider small outline parts then there are a lot more options.My personally preference would be to fix the design so a 44 volt part is not required. A simple zener shunt regulator for the positive supply to the operational amplifiers would help a lot but not really enough to support a 30 volt output without other changes.

author: Cliff Matthews
author_rank: Unknown
timestamp: January 24, 2018, 11:38:23 am
content: Quote from: David Hess on January 24, 2018, 04:38:47 amThat's why having a bunch of these is handy:http://www.dipmicro.ca/store/PCB-SOIC-SSOP16

author: Hextejas
author_rank: Frequent Contributor
timestamp: January 24, 2018, 04:05:32 pm
content: So, is there a more gooder diy kit available that is similar ?

author: Audioguru
author_rank: Super Contributor
timestamp: January 24, 2018, 05:02:37 pm
content: The Chinese kit for this defective old circuit has "clearance pricing" because it has been replaced by a much simpler power supply with poor spec's but with a V and A display.

author: kiwizz
author_rank: Contributor
timestamp: January 24, 2018, 09:31:41 pm
content: Quote from: zvonex66x on January 23, 2018, 11:36:51 pm

author: zvonex66x
author_rank: Contributor
timestamp: January 25, 2018, 12:05:45 am
content: Quote from: kiwizz on January 24, 2018, 09:31:41 pm

author: kiwizz
author_rank: Contributor
timestamp: January 28, 2018, 03:59:23 am
content: Quote from: zvonex66x on January 25, 2018, 12:05:45 am

author: Cliff Matthews
author_rank: Unknown
timestamp: January 28, 2018, 05:35:05 am
content: @Simon, Why are the last 3 posts empty quoting without saying anything? Perhaps from the same IP?If the last two posters seriously want to gain a bad rap, you're getting successful at it

author: zvonex66x
author_rank: Contributor
timestamp: January 28, 2018, 08:26:20 am
content: You have value of all component at this schematics

author: kiwizz
author_rank: Contributor
timestamp: January 28, 2018, 08:27:51 am
content: Quote from: Cliff Matthews on January 28, 2018, 05:35:05 amHi Cliff - I'm not sure either. I'm replying after the 'quote' code block, so it should show up normally. Odd.

author: zvonex66x
author_rank: Contributor
timestamp: January 28, 2018, 09:19:02 am
content: And I have made this one... it's more complex and it's not cheap, but it's pcb and you only need to buy all of components and solder it... when all is done, you should go up to 100$ so it's not cheap, but is good PSU.. take a look...https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F192415947108

author: kiwizz
author_rank: Contributor
timestamp: January 28, 2018, 11:36:14 am
content: Quote from: zvonex66x on January 28, 2018, 09:19:02 amThat looks pretty cool. What did you use for an enclosure?

author: Cliff Matthews
author_rank: Unknown
timestamp: January 28, 2018, 01:47:17 pm
content: Quote from: zvonex66x on January 28, 2018, 09:19:02 amIf you don't link to, or post the schematic, one could think you are selling these.. please, open a new thread to discuss the merits perhaps.. (the current thread is getting stale)).

author: tooki
author_rank: Super Contributor
timestamp: January 29, 2018, 06:59:53 pm
content: Quote from: Cliff Matthews on January 28, 2018, 05:35:05 amzvonex66x screwed up while quoting several posts ago, leaving an unclosed quote tag, and that ripples through every time it’s quoted.

author: zvonex66x
author_rank: Contributor
timestamp: January 29, 2018, 11:24:26 pm
content: Quote from: tooki on January 29, 2018, 06:59:53 pmThen is better to not ppst anything here, becouse if you want to help someone like i did try it here, "discuss the merits"...

author: Cliff Matthews
author_rank: Unknown
timestamp: January 29, 2018, 11:51:40 pm
content: Quote from: zvonex66x on January 29, 2018, 11:24:26 pmI'm sorry I rushed to conclusions there, but there is a reason why tens of thousands of electronics engineers and hobbyists use this forum ahead of any other on planet earth. Just be careful and stay outside those square brackets.. you'll be fine!

author: mikerj
author_rank: Super Contributor
timestamp: January 30, 2018, 04:03:06 pm
content: Quote from: Cliff Matthews on January 28, 2018, 01:47:17 pmDropbox link.It's the Velleman K7200 PSU, I can remember wanting to build that back in my teens (but not being able to afford it!).

author: tooki
author_rank: Super Contributor
timestamp: January 31, 2018, 12:39:31 pm
content: Quote from: zvonex66x on January 29, 2018, 11:24:26 pmMelodramatic much? LOLWhen people screw up with quoting, it makes it extremely difficult (or even impossible) to see the responses. This isn’t an attack on you, it was just a statement of how the problem happened.