(Topic ID: 136771)

Bridge rectifier - explanation needed

By jimy_speedt

8 years ago


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  • 27 posts
  • 8 Pinsiders participating
  • Latest reply 8 years ago by terryb
  • Topic is favorited by 4 Pinsiders

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    #1 8 years ago

    Hi,

    I am wondering about the adequacy of BR for my BAtman Forever. On the power supply board, I have a CM3501 BR which is 35Amp 100V. When I measure the voltages with the DMM I read 21Vac and 29Vdc.

    My question is, would a BR 35Amp 200v do the same job or would the voltages be different ? In simple words, what does these figures (35Amp, 100v) mean when applicable to a BR ?

    Thanks in advance

    #2 8 years ago

    Maximum ratings. The rectifier's diodes can handle a reverse voltage of 200V, 100V, whatever. The circuitry downstream from the rectifier can not draw more than 35A, or whatever.

    So the rectifier's input must not exceed its rated voltage, and the circuitry connected to it must not exceed its rated current.

    The voltages you are measuring at the output are from the input voltage minus diode drops +/- some ripple. The other rated rectifier would work the same at the voltages you're working with.

    #3 8 years ago

    Thanks a lot it is very clear !

    #4 8 years ago

    Just one thing please: "The voltages you are measuring at the output are from the input voltage minus diode drops +/- some ripple.".

    My output voltage is greater than the input ac measure. What does it mean ?

    Thanks again

    #5 8 years ago

    When measuring AC voltage, there are a few ways to indicate the value.

    The most common is RMS which can most simply be described as taking the area under the sinusoidal curve and equating it to a DC voltage.

    AC voltage can also be described in terms of the peak voltage, and this is much closer to what you get out of a rectifier once you smooth it with capacitors. Think of taking the sine wave, flipping the bottom half up, then smoothing the bumps.

    Vrms is roughly Vpeak * 0.707, and you can use that along with the diode drops to figure out what DC voltage you will get from a particular AC voltage.

    #6 8 years ago

    I thought I had understood, but looking a second time at it, I am still not with you

    I thank you very much for the explanation, maybe with graphic the vocabulary Vrms, V peak, etc. would be clearer, but I do not want to bother you. To be honest, my understanding of electricity stops at the usage of a component and I only try to understand the values I read.

    I guess that out of the BR, is the DC voltage which needs to be smoothened with capacitors and this current is still unregulated. You need a regulator IC to have a fixed current. I am right ?

    In your explanation, whatever the input voltage, can I roughly apply a ratio from AC to obtain DC (incl the ripples and diodes losses) ? Or does it depend on other factors ?

    thanks and sorry for my ignorance.

    #7 8 years ago

    got my answer. thanks to both for your help

    #8 8 years ago

    Bridge Rectifier explained:
    http://www.electronics-tutorials.ws/diode/diode_6.html

    and a video explaination:

    #9 8 years ago

    Thanks for your link, actually I went through it this morning.

    I am confused with what is depicted there, compared to the schematic I attached. I perfectly understand the DC side, but the AC side gives me some problems. I see 2 wires 10 and 11 coming from a connector (based on the manual, they both have 9Vac, on each one there is a fuse)

    - Are these wire the "ends" of the AC side ? In other words what is the path of the AC side ? I ask that because there are 2 wires coming from another connector with a diode on each (in reality, these wires are n.c. on the connector). And I am a bit consused with that.

    - Why are there 2 fuses in this context ? One on each wire.

    - I can measure 18Vac on the BR AC lugs, am I measuring correctly ? It is apparently the sum of the Vac of the 2 wires, what is the logic ?

    - In the tutorial, the Vdc is a positive voltage on one end and a 0V on the other end. Here, according to the schematic, one end goes to a +12vdc connector, and the other -12Vdc. So I do not understand.

    thanks a lot for your patience

    IMG_0374.jpgIMG_0374.jpg

    #10 8 years ago
    Quoted from jimy_speedt:

    I can measure 18Vac on the BR AC lugs, am I measuring correctly ?

    Meter on AC voltage, red probe on pin 10, black probe on pin 11.

    #11 8 years ago

    Also 18Vac. From where this value based on the 9Vac I have on each?

    #12 8 years ago
    Quoted from jimy_speedt:

    Thanks for your link, actually I went through it this morning.
    I am confused with what is depicted there, compared to the schematic I attached. I perfectly understand the DC side, but the AC side gives me some problems. I see 2 wires 10 and 11 coming from a connector (based on the manual, they both have 9Vac, on each one there is a fuse)
    - Are these wire the "ends" of the AC side ? In other words what is the path of the AC side ? I ask that because there are 2 wires coming from another connector with a diode on each (in reality, these wires are n.c. on the connector). And I am a bit consused with that.
    - Why are there 2 fuses in this context ? One on each wire.
    - I can measure 18Vac on the BR AC lugs, am I measuring correctly ? It is apparently the sum of the Vac of the 2 wires, what is the logic ?
    thanks a lot for your patience
    IMG_0374.jpg

    You must look in the schematics at the transformer first. DE uses here in this section a so called center-tap transformer, where the center-tap is grounded (see CN1-Pin12 - "GREY-WHITE GND 9VAC". With reference to ground (the center-tapping-point), we have a common connection for 2 identical but opposite secondary voltages. With the center-tap grounded, the output of the first secondary winding will be positive with respect to the ground, while output of the second secondary winding is negative and then opposite, because they are 180 degrees out-of-phase against each other.

    See: now the output of EACH secondary winding is 9VAC with reference to the center-tap, the total output of the COMPLETE secondary winding doubles, means 2 x 9 = 18VAC.

    Pretty easy, isn´t it??

    I made I little grafic for you - everything clearer now?

    center-tap-trafo.JPGcenter-tap-trafo.JPG

    EDIT:
    ATTENTION:
    All 3 DMMs are connected wrong. The red plug into the DMM must sit in the red socket "V Ω mA"!!!!! See post #13.
    Sorry for that mistake.

    #13 8 years ago

    small correction )
    DMM fix.gifDMM fix.gif

    #14 8 years ago

    Waow mate, thanks a lot. It is cristal clear .

    Maybe you might have a little explanation also for the the DC outputs. On the tutorial of BRs, one end is a positive voltage, while the other one is 0Vdc. by putting your DMM lead on both DC lugs, you obtain the Vdc voltage.

    I am a bit worried because, on the SEGA schematics, the + (with the help of the capacitors) gives +12Vdc, and the other one is connected to the -12Vdc, i.e. not the ground. I cannot explain that.

    If you know that I would be glad, but anyway thanks for the time you spent.

    #15 8 years ago
    Quoted from zaza:

    small correction )
    DMM fix.gif

    @Zaza:

    You eagle-eye - thanks for the hint. This was done by mistake, always the same, when you are in a hurry.

    By the way: Do you want to have the grafic of the DMM as vector grafic, then you can use it for your own designs - I like all your grafics and you can spare a lot of time in designing it for yourself.

    #16 8 years ago

    @Ingo,

    Thanks for the offer but I'm very comfortable with the basic zaza-tronic DMM in vector format.
    Is yours in .CDR format or a different photoshop version ?

    ZT diode.jpgZT diode.jpg

    #17 8 years ago
    Quoted from zaza:

    @Ingo,
    Thanks for the offer but I'm very comfortable with the basic zaza-tronic DMM in vector format.
    Is yours in .CDR format or a different photoshop version ?
    ZT diode.jpg

    Mine is in SVG-Format. You want to have it for fun??

    #18 8 years ago
    Quoted from jimy_speedt:

    Waow mate, thanks a lot. It is cristal clear .
    Maybe you might have a little explanation also for the the DC outputs. On the tutorial of BRs, one end is a positive voltage, while the other one is 0Vdc. by putting your DMM lead on both DC lugs, you obtain the Vdc voltage.
    I am a bit worried because, on the SEGA schematics, the + (with the help of the capacitors) gives +12Vdc, and the other one is connected to the -12Vdc, i.e. not the ground. I cannot explain that.
    If you know that I would be glad, but anyway thanks for the time you spent.

    I will look into the schematics tomorrow. DE is is sometimes a bit confusing.

    BUT you have GND on the board. Measure the negative ouput of the BR against GND and you can measure a negative voltage - measure the positive output against GND and you measure a positive voltage.
    Look here for a first view, all more tomorrow:
    http://www.electronics-lab.com/wp-content/uploads/2015/03/DUAL-VOLTAGE-POWER-SUPPLY.jpg

    #19 8 years ago
    Quoted from german-pinball:

    Mine is in SVG-Format. You want to have it for fun??

    Ok, I sent a PM with my e-mail adress.

    #20 8 years ago

    Hello. first of all thanks for indicating everything is normal and that is called dual voltage PS. I thought I was mad. then my post was originally sent because I do not get a +12v on TP, and more seriously, the fixed+5v. I have only 4.90v. with the wiring, only 4,85v comes to the display processor. This processor need exact 5vdc reg to work fine otherwise the display reboots or simply goes dark.
    My expectation is to obtain a bit more than 5v at TP. maybe it is the Db1, maybe the capacitors. the inputs of Db1 are in fact measured at 10.3v, not 9.
    thank you

    #21 8 years ago
    Quoted from jimy_speedt:

    Hello. first of all thanks for indicating everything is normal and that is called dual voltage PS. I thought I was mad. then my post was originally sent because I do not get a +12v on TP, and more seriously, the fixed+5v. I have only 4.90v. with the wiring, only 4,85v comes to the display processor. This processor need exact 5vdc reg to work fine otherwise the display reboots or simply goes dark.
    My expectation is to obtain a bit more than 5v at TP. maybe it is the Db1, maybe the capacitors. the inputs of Db1 are in fact measured at 10.3v, not 9.
    thank you

    Replace C2 --- 100uF/25V as the very first and check connecter CN1 for corrosion.

    #22 8 years ago

    thanks, I have to order part. keep you updated

    1 week later
    #23 8 years ago

    Hi,

    I purchased all the touchy items, then started by replacing the BR.

    Big mistake !!! I do not know if I put the temperature to high on the iron, but the metallic tracks to which the BR lugs are soldered went away. not more support for soldering and no more contact with the board tracks.

    It is not the first time this problem occurs with desoldering on boards. What is my problem ?

    thanks

    #24 8 years ago
    Quoted from jimy_speedt:

    It is not the first time this problem occurs with desoldering on boards. What is my problem ?

    Temperature too high, didn't clean solder joint before desoldering, didn't use flux (you don't have to, but it makes life a lot easier), kept heat on the joint too long.

    BR's are not always easy since the internal components carry the heat away from the joint and there's typically a large pad area. Best way for less experienced solderers is to use a Dremel with a cutoff wheel and seperate the leads from the BR package. That way you have less heat drawn away from the joint.

    #25 8 years ago

    hi terryb,

    Yes, no flux. I only put a little drop of solder to easy melting. 350°C .

    I do not get your last advice. when you talk about heat drown away, do you mean on the board ? I presume yes as the old BR is anyway for the trash.

    thanks for the feedback

    #26 8 years ago

    350c is too low of temp for a big lug like a bridge rectifier. Try 400c or even 450c is the legs and traces are really fat.

    Try getting one leg loose, bend open the bridge, cut the other 3 legs off and then pull the lugs out. Spade rectifiers take practice and the right tools to remove without damaging the board.

    #27 8 years ago

    I agree with Andrew, 350 is too low. When you go higher though you want to be on and off the joint in a few seconds or you'll have the same result. You also want to use a large chisel tip so you maximize physical contact and heat conduction. The same small tip you use on IC's won't cut it on a bridge--you should always adjust the tip size to the job. Again, flux will always help the process, and adding a little solder will help form a solder bridge which transmits heat more efficiently.

    Quoted from jimy_speedt:

    I do not get your last advice. when you talk about heat drawn away, do you mean on the board ? I presume yes as the old BR is anyway for the trash.

    The components (diodes) inside the BR are conducting heat away from the joint, which means less heat at the joint where you need it. The larger traces on the board also draw away heat, but there's nothing you can do about that. I just cut the leads of with a Dremel tool when I've got a board that looks like it's going to be trouble.

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