Make a housing for the power supply with your own hands. Laboratory power supply from AmpExpert. Laboratory power supply housing
The long-term construction is finally over! And now you can see a full-fledged multi-channel laboratory power supply.
Laboratory power supply housing
The first task was to make the case. The idea of purchasing a plastic case for REA quickly disappeared due to the high cost of it with such dimensions. Well, the toad is strangling to pay more than a thousand for a piece of plastic. Therefore, it was decided to use 6 mm foamed PVC.
We cut PVC to the required dimensions:
Let’s imagine what it will look like and mark it out:
On the front side we mark and make holes for the display elements, voltage regulation and terminals.
We glue the body and try on the transformer.
Transformer TSA-70-6, but rewound to suit your needs
On one part it produces 25 volts 0.6 A, on the other part bipolar power supply +15 volts 0 - 15 volts 0.6 A. I don’t remember the winding data, but it’s not difficult to calculate.
Internals of a laboratory power supply
Maybe someone has already understood what parts the power supply is assembled from; those who don’t understand or don’t know are already assembled boards for single-polar and bipolar power supplies from previous articles:
The source board is based on KR142EN12 and KR142EN18.
Unipolar source board based on KR142EN12
Assembly and configuration of these blocks with circuits and printed circuit boards see separate articles.
We continue the assembly. DSN-DVM-368 was used. I have already written about them. Miniature and fully functional indicators.
First start.
Then we connect everything else. And we get chaos from the wires.
The top view shows that another power supply is installed for the digital indicators of the voltmeters. It was not possible to power it from ready-made power sources because the indicators have the same common minus and minus measurements, which will not allow taking correct readings.
Everything fell into place.
We tidy up a little and cut off the excess.
To make it more convenient to use, I decided to design the front panel. I made it in CDR and laminated it
Now the assembly is complete and you can use it
What we end up with:
2 independent adjustable channels
Possibility of parallel or serial connection of channels
1 channel bipolar:
15 V per polarity
current 0.6 A
Channel 2 unipolar
Indication: 3-digit LCD displays for current and voltage simultaneously
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This article is intended for people who can quickly distinguish a transistor from a diode, know what a soldering iron is for and which side to hold it by, and have finally come to the understanding that without laboratory block nutrition their life no longer makes sense...
This diagram was sent to us by a person under the nickname: Loogin.
All images are reduced in size, to view in full size, left-click on the image
Here I will try to explain in as much detail as possible - step by step how to do this with minimal costs. Surely everyone, after upgrading their home hardware, has at least one power supply lying under their feet. Of course, you will have to buy something in addition, but these sacrifices will be small and most likely justified by the end result - this is usually about 22V and 14A ceiling. Personally, I invested $10. Of course, if you assemble everything from the “zero” position, then you need to be prepared to shell out about another $10-15 to buy the power supply itself, wires, potentiometers, knobs and other loose items. But, usually, everyone has a lot of such rubbish. There is also a nuance - you will have to work a little with your hands, so they should be “without displacement” J and something similar may work out for you:
First, you need to get hold of an unnecessary but serviceable ATX power supply unit with a power >250W by any means necessary. One of the most popular schemes is Power Master FA-5-2:
I will describe the detailed sequence of actions specifically for this scheme, but all of them are valid for other options.
So, at the first stage you need to prepare a donor power supply:
- Remove diode D29 (you can just lift one leg)
- Remove jumper J13, find it in the circuit and on the board (you can use wire cutters)
- The PS ON jumper must be connected to ground.
- We turn on the PB only for a short time, since the voltage at the inputs will be maximum (approximately 20-24V). Actually, this is what we want to see...
Don't forget about the output electrolytes, designed for 16V. They might get a little warm. Considering that they are most likely “swollen”, they will still have to be sent to the swamp, no shame. Remove the wires, they get in the way, and only GND and +12V will be used, then solder them back.
5. Remove the 3.3 volt part: R32, Q5, R35, R34, IC2, C22, C21:
6.
Removing 5V: Schottky assembly HS2, C17, C18, R28, or “choke type” L5
7.
Remove -12V -5V: D13-D16, D17, C20, R30, C19, R29
8.
We change the bad ones: replace C11, C12 (preferably with a larger capacity C11 - 1000uF, C12 - 470uF)
9.
We change the inappropriate components: C16 (preferably 3300uF x 35V like mine, well, at least 2200uF x 35V is a must!) and resistor R27, I advise replacing it with a more powerful one, for example 2W and a resistance of 360-560 Ohms.
We look at my board and repeat:
10.
We remove everything from the legs TL494 1,2,3 to do this we remove the resistors: R49-51 (free the 1st leg), R52-54 (... the 2nd leg), C26, J11 (... the 3rd leg)
11.
I don’t know why, but my R38 was cut by someone and I recommend that you cut it too. He participates in feedback in voltage and is parallel to R37. Actually, R37 can also be cut.
12. we separate the 15th and 16th legs of the microcircuit from “all the rest”: for this we make 3 cuts in the existing tracks and restore the connection to the 14th leg with a black jumper, as shown in my photo.
13.
Now we solder the cable for the regulator board to the points according to the diagram, I used the holes from the soldered resistors, but by the 14th and 15th I had to peel off the varnish and drill holes, in the photo above.
14.
The core of loop No. 7 (the regulator's power supply) can be taken from the +17V power supply of the TL, in the area of the jumper, more precisely from it J10. Drill a hole into the path, clear the varnish and go there! It is better to drill from the print side.
This was all, as they say: “minimal modification” to save time. If time is not critical, then you can simply bring the circuit to the following state:
I would also advise changing the high-voltage condensers at the input (C1, C2). They are of small capacity and are probably already pretty dry. There it will be normal to be 680uF x 200V. Plus, it’s a good idea to redo the group stabilization choke L3 a little, either use 5-volt windings, connecting them in series, or remove everything altogether and wind about 30 turns with new enamel wire general cross section 3-4mm 2.
To power the fan, you need to “prepare” 12V for it. I got out this way: Where there used to be a field-effect transistor to generate 3.3V, you can “settle” a 12-volt KREN (KREN8B or 7812 imported analogue). Of course, you can’t do it without cutting tracks and adding wires. In the end, the result was basically “nothing”:
The photo shows how everything harmoniously coexisted in the new quality, even the fan connector fit well and the rewound inductor turned out to be quite good.
Now the regulator. To simplify the task with different shunts there, we do this: we buy a ready-made ammeter and voltmeter in China, or on the local market (you can probably find them from resellers there). You can buy combined. But we must not forget that their current ceiling is 10A! Therefore, in the regulator circuit it will be necessary to limit the maximum current at this mark. Here I will describe an option for individual devices without current regulation with a maximum limitation of 10A. Regulator circuit:
To adjust the current limit, you need to replace R7 and R8 with a 10 kOhm variable resistor, just like R9. Then it will be possible to use the all-measures. It's also worth paying attention to the R5. In this case, its resistance is 5.6 kOhm, because our ammeter has a 50mΩ shunt. For other options R5=280/R shunt. Since we took one of the cheapest voltmeters, it needs to be modified a little so that it can measure voltages from 0V, and not from 4.5V, as the manufacturer did. The whole alteration consists in separating the power and measurement circuits by removing diode D1. We solder a wire there - this is the +V power supply. The measured part remained unchanged.
The regulator board with the arrangement of elements is shown below. The image for the laser-iron manufacturing method comes as a separate file Regulator.bmp with a resolution of 300dpi. The archive also contains files for editing in EAGLE. Latest off. The version can be downloaded here: www.cadsoftusa.com. There is a lot of information about this editor on the Internet.
Then we screw the finished board to the ceiling of the case through insulating spacers, for example, cut from a used lollipop stick, 5-6 mm high. Well, don’t forget to make all the necessary cutouts for measuring and other instruments first.
We pre-assemble and test under load:
We just look at the correspondence of the readings of various Chinese devices. And below it is already with a “normal” load. This is a car main light lamp. As you can see, there is almost 75W. At the same time, do not forget to put an oscilloscope in there and see the ripple of about 50 mV. If there is more, then we remember about the “large” electrolytes on the high side with a capacity of 220uF and immediately forget after replacing them with normal ones with a capacity of 680uF, for example.
In principle, we can stop here, but in order to give more nice view device, so that it does not look 100% homemade, we do the following: we leave our den, go up to the floor above and remove the useless sign from the first door we come across.
As you can see, someone has already been here before us.
In general, we quietly do this dirty business and begin to work with files of different styles and at the same time master AutoCad.
Then we sharpen a piece of three-quarter pipe using emery and use enough soft rubber We cut them out to the required thickness and use superglue to sculpt the legs.
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As a result, we get a fairly decent device:
There are a few things to note. The most important thing is not to forget that the GND of the power supply and the output circuit should not be connected, so it is necessary to eliminate the connection between the case and the GND of the power supply. For convenience, it is advisable to remove the fuse, as in my photo. Well, try to restore as much as possible the missing elements of the input filter, most likely the source code does not have them at all.
Here are a couple more options for similar devices:
On the left is a 2-story ATX case with all-in-one hardware, and on the right is a heavily converted old AT computer case.
With the circuits of the laboratory power supply - now the case. During the process of assembling the power supply, I came across an old motherboard with a dual USB connector, and I wanted to equip the unit with an output for connecting five-volt gadgets. For now, I connected the connector directly to the power supply output and before connecting the phone, I first set the voltage to 5 Volts. In the future I plan to install a step-down DC-DC converter. The entire inner world of the power supply fits into a box with external size 180*140*90. The power supply board had to be secured at an angle, since the internal height of the box was slightly smaller sizes PSU boards.
First, I mounted the controls on the front panel, the power cord socket and the radiator with cooler on the rear panel. The cooler was turned so that air was blown into the case - now air streams come out of the perforated holes in the case, cooling all components of the power supply unit.
One more distinctive feature This power supply is that a low-capacity electrolytic capacitor is installed at the output of the circuit, which will not allow the connected LEDs to burn out. However, I decided to add a non-electrolytic capacitor at the output, but not for the purpose of suppressing RF interference, but for the purpose of securing the contact lamellas in one position so that they could not turn and short-circuit.
