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Hi All,
My first post here so be nice
please .
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=4 after 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 meter
ammeter (-) --> 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!
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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/#msg897523
https://www.eevblog.com/forum/beginners/poorly-designed-kits/msg1314404/#msg1314404 -
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. -
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.
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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'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.
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.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.
That 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 -
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: kiwizz
24v 'fan' output
What's that fan output, btw? Was it AC or DC? -
That 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.
Can you be a little more specific?... what op-amp? -
I'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.
I 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.
I think he refers to the TLE2141.That 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.
Can you be a little more specific?... what op-amp?
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/What's that fan output, btw? Was it AC or DC?
I 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. -
Oh, that circuit. I do not understand why it is so popular.
That 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.
Can you be a little more specific?... what op-amp?
741, 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.
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Have you tried modifying it to make it more reliable? That would be a good learning exercise.I'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.
I 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.Oh, that circuit. I do not understand why it is so popular.
How about the OP07? It should have a low enough offset to eliminate the trimming circuit.That 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.
Can you be a little more specific?... what op-amp?
741, 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.
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. -
Have you tried modifying it to make it more reliable? That would be a good learning exercise.
In 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. -
How about the OP07? It should have a low enough offset to eliminate the trimming circuit.
Not 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.QuoteAs 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.
Every time I see its schematic, it prods me to design and release my own version. Then I consider the economics and lose interest.
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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..
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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.
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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. -
U2 or Q2? I've ordered another kit as its cheaper than getting a single component
I 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! -
DC
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Thanks for the reply - I don't see what you are referring to? previous schematic? forgot to add a link? Cheers!
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Thanks for the reply - I don't see what you are referring to? previous schematic? forgot to add a link? Cheers!
Kiwizz, FWIW some users reply to specific messages by prefixing something like @username, but most just use the Quote function on the right side. BTW, welcome to the forum! -
Thanks for the reply - I don't see what you are referring to? previous schematic? forgot to add a link? Cheers!
Ohh, yes, i'm sorry, forgot it hahahah....
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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..
The 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.
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The MC34071 is not a bad choice but it is only available in surface mount..
That's why having a bunch of these is handy: http://www.dipmicro.ca/store/PCB-SOIC-SSOP16
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So, is there a more gooder diy kit available that is similar ?
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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.