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Full bridge rectifiers and PWM controllers

Discussion in 'General Electronics Discussion' started by Ed., Nov 7, 2016.

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  1. Ed.

    Ed.

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    Nov 7, 2016
    Hi everyone, I have just registered as I was searching for help on the web for a project I want to build, and came across this site.

    The project I have in mind is actually a double purpose build, I would like to build a largish electrolysis generator ( brown gas ) to run a welding/heating gas torch and the second function is to do electroplating.

    The stuff I have to work with is so far might give me a few issues, namely I have a largish transformer that I pulled out of an 5Kw UPS. it has a pair of 240V input leads and 2 pairs of output leads. They output 54V AC and 124V AC with no load, I haven't tested the output amp capacity but it should be reasonable, at least enough for my purpose.

    I am intending to buy a PWM controller off eBay which does up to 10-50V DC 60A , it has a potentiometer to control output and can output 3Kw.

    I also have 4 x 18amp UPS AGM batteries which I intend to wire in series to give me the voltage I need to run the PWM controller and I would like to use that transformers' rectified voltage to charge up the batteries as they are being drained.

    So here is where I need advice, when I connect a 50A 1000v full bridge rectifier to that 54V output it should increase the DC voltage and apart from adding a capacitor to smooth out the ripples, is there any simple way to drop the bridges output voltage down so that the PWM controller doesn't get overload by the higher voltage even though it is connected to the 4 batteries, as well as not damaging the batteries.

    The other thing I am not sure about is how to drop the voltage of the PWM controller to say 14-18V so that the electrolytic cells and or electroplating bath don't put out too much heat without dropping too many amps in the process. Now from what I remember about bridge rectifiers is that they should drop the voltage the moment you connect a load to it, such as the batteries or the PWM controller but not sure by how much.

    So that sums it up, am I barking up the wrong tree or is it doable without too much drama and/or am I missing something? Or is there a simpler way to do all of this?

    Cheers
     
    Last edited: Nov 7, 2016
  2. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    If you are charging 4 batteries, just use one at a time.
     
  3. Ed.

    Ed.

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    Nov 7, 2016
    Hi Colin, I thought about that but from what I understand of that PWM controller, doing that will also drop the output amps to about 10-15 which is not enough for the cells to produce enough gas.
     
  4. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    The single battery is used for electroplating.
     
  5. Ed.

    Ed.

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    Nov 7, 2016
    For that it should work but not for producing gas, I was toying around with using my large MIG welder as the power source but I don't know what it would do to anything connected to it, it outputs 10V to 40V DC which I can control to within 0.1V, which would be fine but the minimum amperage is about 60-70A at 10V and max at 40V is over 600A, The problem is that it has a spike of about 80V for a short period when the power is first applied so would most likely blow the PWM to pieces before it had a chance to settle down to a selected voltage.

    If I connected it directly to the electrolysing cell it would be straight DC and not pulsed and with no method of controlling the amperage it could cause the gas in the cell to explode so also not a good outcome. So it would be one extreme to the other with either not enough gas or way too much.
     
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