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Can I just built a simple battery charge with a setdown transformer and rectifier?

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  • Can I just built a simple battery charge with a setdown transformer and rectifier?

    Hi guys,

    The new charger I just bought seems has not much use to me, and the other charger that I bought few month back to charge my 12 volts setup has stop work recently.

    Can I ask some one to build a step down transformer from 110 volt to 64 volt and use a full bridge rectifier to charge or EQ my battery banks? if I want it to also charge the 12 volts system Can I just ask to wire the transformer the secondary coil to 14.8 volts and 64 volts?

    Do I need to use a smoothing capacitor? what is the size of the wire to use in the transformer if I want to get 20 amps output safely? I just want a simple charger to pump some current to the batteries when is raining.

    Thank you.

  • #2
    Paul what you are asking for is a custom made transformer. It can be built, but very expensive as it would be one of a kind thing. Today no one really uses transformers anymore, at least not in the form you are thinking of. Today just about all chargers are Switch Mode Power Supplies where you take line voltage and convert directly to DC, then convert to high frequency AC, step up of down the voltage via via transformer, then rectify. Sounds crazy bu tvery efficient, cheap, and light weight.

    I think you are talking about an IOTA charger you bought right. I am not certain but there should be a fairly easy way to modify it so you can get the voltage you want. Reason I say that is because of the IQ option is just a jumper plug which I suspect shorts out a internal voltage divider resistor to boost output voltage. Let me chack around and see what I can come up with. Might be as easy as cutting a resistor out, changing a resistor out, or shorting a resistor.
    MSEE, PE

    Comment


    • #3
      What is the voltage of the battery bank?? 64v AC full wave rectified is going to give about 90v DC.. That would not make 12v batteries very happy.

      Comment


      • #4
        Originally posted by paulcheung
        The new charger I just bought seems has not much use to me, and the
        other charger that I bought few month back to charge my 12 volts setup has stop work recently.

        Can I ask some one to build a step down transformer from 110 volt to 64 volt and use a full
        bridge rectifier to charge or EQ my battery banks? if I want it to also charge the 12 volts system
        Can I just ask to wire the transformer the secondary coil to 14.8 volts and 64 volts?

        Do I need to use a smoothing capacitor? what is the size of the wire to use in the transformer
        if I want to get 20 amps output safely? I just want a simple charger to pump some current to
        the batteries when is raining.
        Generally batteries don't need a filter cap; they do their own smoothing.

        The new switching supplies are light weight, but not something a beginner should tackle. The
        clunky old iron core transformer types are usually very simple, and not too hard to repair if
        the transformer hasn't burned out. I have built a few of these; a ferro resonant transformer
        is ideal. If you leave it connected too long, it will over charge your batteries. Fix that with a
        16 hour timer, or use an SCR phase controlled rectifier to limit the output.

        The easy transformer solution is to find an old one plenty big enough. The 120 V is wound
        first, the secondary is always wound on the outside. Check the voltage of the secondary, then
        remove it and note the turns, this gives you volts per turn (maybe 1/2V). Wind a new secondary
        with an appropriate number of turns. Use a bridge rectifier, a center tap takes twice as much
        winding. Since you won't be able to get the wire on as efficiently as the factory, you'll probably
        have to use a smaller than ideal gauge to get on enough turns. The wire being in a tight place,
        won't be able to sustain as much current as if spread out. I usually take the iron core off for
        working on the windings, getting all if it back is another challenge. Bruce Roe

        Comment


        • #5
          I know some one do rewind transformer and compressors for professional job. I used to use him to rewind my compressors when I was running a mini mart. I just want to know if it is simple that I could find a old transformer and pay him to rewind to the voltage I want. I have the two bank of 48 volts Rolls and two bank of Trace 12 volts batteries (4x6volts 225amps batteries) which supply the current for the small fish pond.

          So 64 volt AC from the transformer does not equal to 64 volts DC after it rectify by the full bridge rectifier?

          The gauge of the insulated single wire, what gauge will safely supply 20 amps charge current?

          I bought this Schumacher XC103 SpeedCharge 100 Amp Battery Charger with Engine Start February this year and I use it to charge the 12 volt battery bank about a dozen time and last time I use it to charge a single Rolls 6 volts battery with 22 amps charging current. It died before it finish the two hour charge. It does not smell any burn so I guess something wrong with the electronics which control those fancy automatic voltage selection and charge controls. I am tired of this kind fancy stuff and just want a simple charger can charge few hours at a set voltage.

          Thank you.

          Comment


          • #6
            Originally posted by paulcheung View Post
            I know some one do rewind transformer and compressors for professional job. I used to use him to rewind my compressors when I was running a mini mart. I just want to know if it is simple that I could find a old transformer and pay him to rewind to the voltage I want. I have the two bank of 48 volts Rolls and two bank of Trace 12 volts batteries (4x6volts 225amps batteries) which supply the current for the small fish pond.

            So 64 volt AC from the transformer does not equal to 64 volts DC after it rectify by the full bridge rectifier?

            The gauge of the insulated single wire, what gauge will safely supply 20 amps charge current?

            I bought this Schumacher XC103 SpeedCharge 100 Amp Battery Charger with Engine Start February this year and I use it to charge the 12 volt battery bank about a dozen time and last time I use it to charge a single Rolls 6 volts battery with 22 amps charging current. It died before it finish the two hour charge. It does not smell any burn so I guess something wrong with the electronics which control those fancy automatic voltage selection and charge controls. I am tired of this kind fancy stuff and just want a simple charger can charge few hours at a set voltage. Thank you.
            64V at 20A is a substantial transformer, weight around 50 lbs. The winding should be at
            least 10 gauge; about 8 gauge transformers start using square wire. You might have to
            experiment a bit to get the right voltage & current out. One way is to get several smaller
            transformers with 20A lower voltage secondaries, and wire the secondaries in series to get
            the needed voltage. A ferro resonant transformer will automatically limit current. Bruce Roe

            Comment


            • #7
              Paul the transformer part is the easy part. For every 12 volts DC requires 18 volts of AC. So armed with that you are looking for a AC voltage roughly 96 to 100 volts. But for a battery charger the voltage has to be tightly regulated and requires more than just a rectifier to do that.
              MSEE, PE

              Comment


              • #8
                Go to YOUTUBE ::: How make a transformer from a old MicroWave Power transformer

                You tube has a good how to on rewinding a old Micro-wave transfor. for what ever voltage you want out .. Hard part is trying to size the wire for current and that well fit on the Pri. core ..

                an other thought is use 120 to 120 trans dimer or motor speed control in front of trans so you can control the voltage , get a controller the work with induction load , like a motor , Fan speed control ..

                good luck


                Sparkskard



                Originally posted by paulcheung View Post
                Hi guys,

                The new charger I just bought seems has not much use to me, and the other charger that I bought few month back to charge my 12 volts setup has stop work recently.

                Can I ask some one to build a step down transformer from 110 volt to 64 volt and use a full bridge rectifier to charge or EQ my battery banks? if I want it to also charge the 12 volts system Can I just ask to wire the transformer the secondary coil to 14.8 volts and 64 volts?

                Do I need to use a smoothing capacitor? what is the size of the wire to use in the transformer if I want to get 20 amps output safely? I just want a simple charger to pump some current to the batteries when is raining.

                Thank you.

                Comment


                • #9
                  You need enough extra voltage to push the current through all the parasitic resistances
                  of the transformer and battery, and the rectifier drop. However rectification occurs near
                  the AC peak of 1.4 times the rms voltage, so you won't need a lot more. A ferro resonant
                  transformer puts out more of a square wave, so more voltage is needed.

                  I think most microwaves now use ferro resonant transformers. The problems I have had
                  with them is they may be welded together, not the most efficient for continuous use. And
                  the resonant winding for the oil cap is combined with the output winding, so you can't just
                  remove it. Old designs were separate. Bruce Roe

                  Comment


                  • #10
                    Originally posted by Sunking View Post
                    Paul the transformer part is the easy part. For every 12 volts DC requires 18 volts of AC. So armed with that you are looking for a AC voltage roughly 96 to 100 volts. But for a battery charger the voltage has to be tightly regulated and requires more than just a rectifier to do that.
                    This information is obviously from someone that has either never built a power supply or has never measured the ACfrom the transformer and the DC from the bridge rectifier.

                    Comment


                    • #11
                      Wow so much things to consider about, I guess I will have to leave it alone as simple is not simple any more. I just afraid of these new chargers, it just died with out any noticeable reasons. not over current, not over heat. I have an old 5 amps 40 amps 100 amps starter charger on two wheels about 30 lbs it weigh, I have it for over twenty years and still going strong. just it is hard to carry on a flight.

                      Thanks.

                      Comment


                      • #12
                        Originally posted by Sunny Solar View Post
                        This information is obviously from someone that has either never built a power supply or has never measured the ACfrom the transformer and the DC from the bridge rectifier.
                        I am sitting here looking at two I have built John. A 60 amp 12 volt, and 30 amp 24 volt. Built my first one at age 14 when I got my ham radio liscense, and have built dozens of them for longer than most have been alive on this forum. You can build a 12. 6 volt supply with as little as 15 VAC RMS. Wanna see a dozen different schematics? I got them ready to go. Just say the word or just butt out and eat your words.

                        For 48 volt you can go even lower than 1.5:1 ratio. If he needs 64 volts can easily just use 70 volt transformer. But for 12 volts fixed regulated, you can get away with 15 volts. At least in the USA you can. Not sure what you do down under. Guess you use different math than we do.
                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by paulcheung View Post
                          I have an old 5 amps 40 amps 100 amps starter charger on two wheels about 30 lbs it weigh, I have it for over twenty years and still going strong. just it is hard to carry on a flight.
                          There has go to be more to this story. Why would you carry it on a plane from Jamaica my friend.
                          MSEE, PE

                          Comment


                          • #14
                            Great stupid reply as it has nothing to do with your ridiculous post ..."""""Paul the transformer part is the easy part. For every 12 volts DC requires 18 volts of AC. So armed with that you are looking for a AC voltage roughly 96 to 100 volts. But for a battery charger the voltage has to be tightly regulated and requires more than just a rectifier to do that."""""

                            If he need a charger for a 48v battery pack he does NOT need 96 to 100v AC.. That is just nutz. he only needs about 42v AC to give about 58v DC,..

                            Having built thousands of audio amplifiers,sound mixers, lighting controllers I have I think a reasonable knowledge of what AC is needed to get a desired DC voltage..

                            Comment


                            • #15
                              You can build a 12. 6 volt supply with as little as 15 VAC RMS.Mabe it takes that much AC for a power supply you would build but the rest of the world could build it with a 12v AC

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