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  • #61
    Hi Rodolphe,

    My wife and I are busy packing today for vacation and will be on the road through the weekend. It will be the middle of next week before I'll have the time available to respond to your latest questions.

    Regards,
    Gary Hammond,

    Comment


    • #62
      Hi All,

      I just went ahead and made the timing circuit, see enclosed PDF for the schematic and parts list, with the following notes:

      Note 1:
      The shop where I bought my parts did not have the 0.8uF, 25V capacitor, so I exchanged it for a 1uF, 35V version.


      Note 2:
      Instead of using two 1MOhm potmeter, I used four 0.5Mohm potmeters to be able to tune a bit more accurately. In other words item nr 10 = 2x0.5MOhm in series and nr 11 = 2x0.5MOhm in series.
      Also I added 1kOhm resistors in front of them as Peter optionally mentions/suggests in the Handbook.

      I tested my circuit by putting 12V on the input of the circuit and connected my Fluke 115 to the input of the Opto coupler, measuring frequency. See attachment for a photo.

      What I noticed was
      -When I turn the item nr 10 (potmeters) to the extreme minimum, so they have (almost) no resistance, the 2N4401 Transistor (item nr 2) gets hot and the Opto coupler (item nr 3) gets hot too. Especially the Opto coupler heats up fast to the point that I cannot put my finger on it any more (switched of the power supply when this happened.


      My question are:
      -Is it normal that the above mentioned components get so hot?
      -if not, can anybody tell me where I made a mistake/used a wrong component?
      Update 2020-02-04 -> should I try to increase the resistance of item nr 9? From 5kOhm to e.g. 10kOhm?


      Many Thanks in advance,
      Rodolphe

      Attached Files
      Last edited by pearldragon; 02-04-2020, 01:28 PM.

      Comment


      • #63
        Hi Rodolphe,

        Originally posted by pearldragon View Post
        Hi All,

        I’m in the process of building the 555 cap dump circuit, like Cmor, from page 47 of the Intermediate handbook. And have a couple of questions still.

        Question 1: Removing diodes
        Regarding your (Gary) post #20:


        Do you mean I have to remove the 1n4007 diodes from my circuit board? As indicated in image 2 of the attachment?
        Or was this only applicable for the schematic with the separate output winding as in image 1 of the attachment?
        In the Intermediate handbook I’ve not read anything about removing diodes? (in you post you wrote 2n4007, but I assume you meant 1n4007?)


        Question 2: MOSFETS
        Regarding your (Gary) post #33:


        2a: The IRFP260 MOSFETS I have selected at the moment can handle a max of 50A. So if they are unmatched, the first MOSFET that triggers will burn out pretty quick if the amperage goes over 100A as you write…
        So if the discharge would take place very fast (see calculations in question 2c.), what would be the point of using more MOSFETS if they are not matched, if they first one would get the majority of the amperage (and thus burn out)?


        2b: How can I match MOSFETS / how did you solve this? Did you buy IRFP260 MOSFETS that can candle 100A+?
        Is it possible to make a little device to match the MOSFETS like the one mentioned in the Intermediate Handbook to match the normal transistors?
        The MOSFETs I had selected are these: https://docs.rs-online.com/54ee/0900766b80791211.pdf


        2c: I just did a quick calculation to see in which time frame the capacitors would discharge to get the discharge amperage over a 100A as you mentioned (assuming that they would be charged to the max). I calculation that the discharge would take place in 0.022 seconds, see Calculation 1 in the attachment. Is this the ballpark figure you used to calculate your 100A?
        Now in the Intermediate handbook Peter talks about charging the Capacitors to roughly 2x the voltage of the battery. So if I do the same calculation, but now charging up to 30V (instead of 80V), and use the previous calculated 0.022 seconds for discharge time, I get to an amperage of 41A, see Calculation 2 in the attachment. This is something that even 1 MOSFET with a 50A rating would be able to handle.


        Question 3: Risk to damage the 7812 chip -> Zener diode?
        The voltage regulator 7812 chips that I looked at have an max input voltage of +/- 32V. So it seems to me that if the 555 timer is not tuned correctly, charging the capacitor higher than 32V, you’ll blow up this 7812 chip immediately. So I thought that replacing the 7812 chip for a resistor and Zener diode might be safer, correct? See image 3 in the attachment.


        Question 4: “Photo flash’ Capacitors
        In the intermediate handbook, it is recommended to use “Photo flash” capacitors for fast discharge, but there is no ESR spec given. So I just selected some capacitors with a random ESR value, hoping that they can discharge fast enough: ESR of 14mOhm (3x Mallory 25000uF, 75V type CGS253U075X4C ). Any idea if this is fast enough? What would be the maximum ESR value for a Capacitor to be suitable for this circuit?


        Many thanks in advance,
        Best regards,
        Rodolphe
        #1
        You only remove the diodes when using an isolated winding as in image 1. And yes I meant to say 1N4007.

        #2a
        The MOSFETS should be matched to evenly split the load between them and not burn out.

        #2b
        I think the device you referenced can be used to match MOSFETS as well as BJT transistors. I used a PEAK DCA75 semi-conductor tester to check mine. https://www.newark.com/peak/72-12840...tor/dp/56Y1287 As best I can recall they all pretty well matched when I received them. They were much better matched than any of the BJT transistors I received. Here is a link to the ones I think I used, can't say for sure without looking at them and I'm about 1,300 miles from home. https://www.newark.com/infineon/irfp260mpbf/transistor-polarity-n-channel/dp/27AC6801?scope=partnumberlookahead&ost=IRFP260MPBF .&searchref=searchlookahead&exaMfpn=true&ddkey=htt ps%3Aen-US%2FElement14_US%2Fw%2Fsearch

        #2c
        I didn't bother trying to calculate the discharge time or current flow. I just used 2 FETS because that's what the schematic showed.
        However, they bid burn out after awhile, so when I later made the
        comparator circuit I used 4 FETS.

        #3
        If you build the circuit like the schematic, the voltage won't get high enough to burn out the 7812 regulator. I think the 7812 gives more consistent voltage output and higher current flow ability than a zener diode and resistor would.

        #4
        I don't remember the suggested ESR value. Just look for the lowest value you can find for the voltage and capacity you choose. I suspect the Mallory caps you chose will work just fine.

        Gary Hammond,

        Comment


        • #64
          Hi Rodolphe,

          Originally posted by pearldragon View Post
          Hi All,

          I just went ahead and made the timing circuit, see enclosed PDF for the schematic and parts list, with the following notes:

          Note 1:
          The shop where I bought my parts did not have the 0.8uF, 25V capacitor, so I exchanged it for a 1uF, 35V version.


          Note 2:
          Instead of using two 1MOhm potmeter, I used four 0.5Mohm potmeters to be able to tune a bit more accurately. In other words item nr 10 = 2x0.5MOhm in series and nr 11 = 2x0.5MOhm in series.
          Also I added 1kOhm resistors in front of them as Peter optionally mentions/suggests in the Handbook.

          I tested my circuit by putting 12V on the input of the circuit and connected my Fluke 115 to the input of the Opto coupler, measuring frequency. See attachment for a photo.

          What I noticed was
          -When I turn the item nr 10 (potmeters) to the extreme minimum, so they have (almost) no resistance, the 2N4401 Transistor (item nr 2) gets hot and the Opto coupler (item nr 3) gets hot too. Especially the Opto coupler heats up fast to the point that I cannot put my finger on it any more (switched of the power supply when this happened.


          My question are:
          -Is it normal that the above mentioned components get so hot?
          -if not, can anybody tell me where I made a mistake/used a wrong component?
          Update 2020-02-04 -> should I try to increase the resistance of item nr 9? From 5kOhm to e.g. 10kOhm?


          Many Thanks in advance,
          Rodolphe
          Nothing in the circuit should get hot. You have too much current flow thru these two components if they're getting hot.

          Gary Hammond,

          Comment


          • #65
            Hi Gary,

            Thanks for all your answers, hope you and your wife had a good holiday!

            I located the overheating cause of some of the components of the timing circuit: I used a strip board to solder my circuit onto. I forgot to break the connection under the 330-Ohm resistor (Item nr 8), so that resistor was bypassed. After correcting this, the heat issue was gone.

            #2B MOSFETS
            That’s a neat device you got there! I just hooked the three MOSFETS I had bought up to that little matching device of the intermediate manual; looks like I can match them with that, so ordered a bunch more of the MOSFETS, hoping to get some matched. The MOSFETS you used are exactly the same ones as I have.


            #3 Risk to damage the 7812 chip -> Zener diode?
            Please correct me if I’m wrong but I would think the voltage in the in the circuit (capacitor) can get high enough (over 32V) to damage the 7812 chip for the following reason (see attachment for schematic with numbered items/components and screenshot of scope):
            If the potmeter item nr11 is turned to minimum resistance and potmeter item nr 10 is turned to maximum resistance the discharge time is a done in a fraction of a second, I would recon that if the potmeters are positioned in this way, the capacitors charge up to the max (75V) at some point, damaging the 7812 chip as soon as they go over 32V.
            (Only when the capacitors are able to discharge so fast that they discharge faster than those almost vertical lines you see in the graph, the 7812 cannot be damaged. But if that would be true, than there is no adjustability of setting the charge level
            of the capacitors, since they will discharge faster than the minimum setting of the timing circuit).


            Best regards,
            Rodolphe

            2020-02-08 attachment.pdf
            Last edited by pearldragon; 03-01-2020, 03:52 AM. Reason: reason for update: The attachment in the original post had an graph that was made with a damaged opto-coupler.

            Comment


            • #66
              Hi Rodolphe,

              Originally posted by pearldragon View Post
              Hi Gary,

              Thanks for all your answers, hope you and your wife had a good holiday!

              ...............................................
              #3 Risk to damage the 7812 chip -> Zener diode?
              Please correct me if I’m wrong but I would think the voltage in the in the circuit (capacitor) can get high enough (over 32V) to damage the 7812 chip for the following reason (see attachment for schematic with numbered items/components and screenshot of scope):
              If the potmeter item nr11 is turned to minimum resistance and potmeter item nr 10 is turned to maximum resistance, you can see in the graph that the discharge time is a done in a fraction of a second, I would recon that if the potmeters are positioned in this way, the capacitors charge up to the max (75V) at some point, damaging the 7812 chip as soon as they go over 32V.
              (Only when the capacitors are able to discharge so fast that they discharge faster than those almost vertical lines you see in the graph, the 7812 cannot be damaged. But if that would be true, than there is no adjustability of setting the charge level of the capacitors, since they will discharge faster than the minimum setting of the timing circuit).

              Next thing on the list is soldering the rest of the cap dump circuit together.

              Best regards,
              Rodolphe

              2020-02-08 attachment.pdf
              We're still on vacation 1300 miles from home in warm sunny Florida until March 1st. We spend two nights on the road traveling each way.

              If the circuit discharges at least once per second the voltage on the caps shouldn't exceed the rating of the regulator. Here's a link to a photo of the voltage trace across the caps on the old cap dump I made from the book. It only had 2 FETS and they eventually failed. It dumped every 6/10 of a second with the voltage raising to 25.6 and dumping to 21.8.​ http://www.energyscienceforum.com/fi...?photoid=71990

              And here is a link to a picture of the device. http://www.energyscienceforum.com/fi...?photoid=71989


              Later I made a whole new cap dump using the comparator circuit shown in the first couple of pages of this thread. It still works!


              Gary Hammond,
              Last edited by Gary Hammond; 02-08-2020, 08:53 AM.

              Comment


              • #67
                Hi Gary,

                Thanks for your answers!

                I finally bought that second battery, so I can have a battery on the input rather than the variable power supply. Hooked up an amp meter at the input which i could bypass with a switch and did some measurements. Will report back here later next week with my findings and also to reply to your answers.

                Best regards,
                Rodolpe

                Comment

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