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Digital panel meter - Voltmeter / Ammeter - made in China.

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  • #32
    bestler
    Admin of DIY, Automation
    Yes, I think it costs $ 7.5
  • #33
    kot mirmur
    Level 33  
    Hello forum members. I chose the most radical solution. After starting the module [it worked], I decided to take it apart - easy. I removed the factory current measurement pins, replaced them with a slightly slimmed 2.5 square cable, and immediately extended it directly to the current shunt in the module. Eight amps lasted for an hour quietly. Nothing gets hot, indications ok.
    Unfortunately, a small one appeared? problem. As I wrote earlier, a rectifier based on a 17V transformer + Reg-Pro4 thyristor regulator. the rectifier works very nice, and good. The problem appeared with current measurements. The ammeter, when loaded with a light bulb or a resistor, has even too accurate indications - indications tolerance of 5%. Miracles begin when the battery is connected. The voltmeter works perfectly, the ammeter up to 2.5A too. After exceeding this threshold, the ammeter begins to lower the indications, and significantly. With the actual current of 8 A, it shows only 3.8 A. Where to find the cause?
  • #34
    kot mirmur
    Level 33  
    Hello colleagues. After reading many posts in the rectifiers section, I decided to insert a smoothing capacitor in front of the ammeter. Well, unfortunately it helped, the ammeter started to show correctly when connecting the battery. Unfortunately, because the 4700microF capacitor is very effective in disrupting the charge voltage disconnection threshold, adding a parallel R doesn't do much either. The only option is to interfere with the measuring system - soldering the capacitor in the appropriate places of the A meter itself. These ammeters are not suitable for work with thyristor systems. However, one thing still puzzles me - why the rectifier is loaded with a resistor [the ammeter indications are good in the full range from 0, to 9 A], and after connecting the battery, the indications up to the 2.5 A threshold are correct, and above this threshold - lime. After Christmas, I'll get an old Soviet oscilloscope from the basement and take measurements.
    For all Forum members - I wish you healthy, happy and cheerful holidays. Wet Dyngus! And do not drive a car after drinking alcohol.
  • #35
    gimak
    Level 39  
    kot mirmur wrote:
    However, one thing still puzzles me - why the rectifier is loaded with a resistor [the ammeter indications are good in the full range from 0, to 9 A], and after connecting the battery, the indications up to the 2.5 A threshold are correct, and above this threshold - lime.

    I suppose it may be related to the current waveform associated with the voltage that forces its flow. When loaded with a resistor, the current waveform is a reflection of the forcing voltage waveform of the rectifier. When connecting the battery to the rectifier, the current flows only when the voltage exceeds the voltage of the rectifier - the current diagram is such mounds protruding above the zero line. On the other hand, why, up to the 2.5 A level, they are only correct, no explanation comes to my mind. I noticed a similar phenomenon in the topic using a similar module when charging the battery, but it was the opposite, that the module showed 2.7A current and the ammeter showed zero, here is the link https://www.elektroda.pl/rtvforum/viewtopic.php p = 17136053 # 17136053
  • #36
    kot mirmur
    Level 33  
    I read it, buddy Gimak, in fact, I probably looked through almost everything possible from these threads. In my life, I would not buy this crap if I knew how much time I would have to spend on getting it to work properly. I suggested earlier work with even much larger rectifiers - even with start-up, repair and modernization functions. They were also based on thyristor drivers. But for them I bought domestic measuring modules. Unfortunately, the price does its job. Anyway - the oscilloscope will be used - after all, that's what it is for. It needs to be warmed up a bit, the year was not fired. I'm not worried about its content - this is a military version, after 15 minutes of warming up it is very stable. Merry buddy!
  • #37
    kot mirmur
    Level 33  
    Unfortunately, the oscilloscope measurements were unsuccessful, no power cord. This is how women do the cleaning themselves. It took a while to act. That unfortunate meter is> dsn-vc288. The current measuring input is on the 5th leg of the lm358 system. After inserting C between it and the ground of the system, the ammeter started to work properly. The capacitor is 10 micro / 50V. Why such? - I had one at hand. The most important thing is that the measurement system works correctly, regardless of the type of load and the current flowing through it [from 0.1 to 8 A].
  • #38
    ElectroTom
    Level 24  
    My copy lowers the ammeter measurements and starts showing from about 0.35 amps (in fact it is 0.70 amps. Accuracy is shocking. Most likely I'll sand the shunt a bit.
  • #39
    Szyszkownik Kilkujadek
    Level 36  
    And I got a pretty good copy. :-) After calibration with potentiometers, it shows quite accurately and practically from scratch. It is wrong with max 0.1V on voltage, and it distorts in the range of +- 10% on current. The greatest deviations are in the lower and upper amperage range.
  • #40
    CMS
    Administrator of HydePark
    Friends ElectroTom and The Szyszkownik Kilkujadek , please take clear photos of your "meters" from the PCB side, maybe you will see some differences.
  • #41
    ElectroTom
    Level 24  
    For now I'm away from home, when I go I will take pictures. Out of curiosity, I will buy three more such devices from different suppliers (unfortunately it will take a while). In my case, the voltmeter is flawless, but I meant mainly an ammeter (exactly a milliammeter).
  • #42
    kot mirmur
    Level 33  
    I forgot my colleagues to write, when trying to repair my V / A module, the original current measurement shunt was completely removed from the PCB, and replaced with a completely different, handmade one. But basically it was a purely cosmetic procedure (no confidence in the manufacturer). There are prints of models on the tiles, let your colleagues praise them.
  • #43
    gimak
    Level 39  
    Although not asked, I am enclosing the reverse of my Chinese.

    Digital panel meter - Voltmeter / Ammeter - made in China.
  • #45
    gimak
    Level 39  
    Apart from the music (heard), I only saw a dark screen.
  • #46
    Freddy
    Level 43  
    I'm playing with AllPlayer and it's OK.
    Windows Media Player also displays correctly.
  • #47
    CMS
    Administrator of HydePark
    Freddy wrote:
    I will add an interesting video about the meter that is worth watching.


    The video is damaged.
  • #48
    Freddy
    Level 43  
    Nothing is damaged, the movie works.
    Please in another format again.
  • #49
    coperfild
    Level 34  
    VLC media player plays the entire movie normally.
  • #50
    gimak
    Level 39  
    Now I watched, interesting indeed, but in my "No name" modules there is a completely different connection layout and arrangement of elements. Maybe it will be helpful in starting a module in which one module has a 3V zener and I don't know what else, because when I gave the 3V voltage behind it, the display is still dead.
  • #51
    Szyszkownik Kilkujadek
    Level 36  
    And it will not be possible to upload this movie to youtube?
  • #54
    Frredd
    Level 12  
    I bought two such meters ... and they don't want to work at all :( Will connecting the power supply only cause the meter to light up? I connect 12-13V and nothing :(
    Ie. minus to thin black and plus to thin red. Am i doing something wrong?
  • #55
    Zbigniew 400
    Level 38  
    The ammeter measures the DC current correctly and not the distorted battery charging current.
  • #56
    kot mirmur
    Level 33  
    You basically do everything right, buddy Frred. After supplying power to these two cables, the display should work - it will show only zeros. And what did you get the supply voltage from? Check with the meter that there is power on the LM chip - leg 4 and 8. You have the diagram in previous posts.
  • #57
    Frredd
    Level 12  
    Thank you cat mirmur :) It's all right now, it's working. My mistake was to connect the power supply from a simple power supply with a bridge, without any electrolyte. And the meter did not consider it a direct current :) Connecting the capacitor corrected the situation. Everything is fine and buzzing :) (i.e. it lights up in color). Thanks for the hint.
  • #59
    kot mirmur
    Level 33  
    Perhaps there is poor contact somewhere in the measurement circuit I. Check the connectors on the thick cables. If it doesn't help, then improve February on the large socket and on the shunt / this thick wire on the pcb /. There is a schematic attached in post # 53.
  • #60
    damian1115
    Level 29  
    Thank you for the info, I'll take care of these connections, and check February as you were.