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What type capacitor works best for 100KHz?

Discussion in 'General Electronics Chat' started by gary350, Apr 12, 2018.

  1. gary350

    gary350 Well-Known Member

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  2. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    You don't mention any peak current ratings, ESR/ESL requirements, DF requirement, etc. It's difficult to spec out a cap without general values for these specs.
     
  3. gary350

    gary350 Well-Known Member

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  4. dave miyares

    Dave New Member

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  5. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    ESR = Equivalent Series Resistance
    ESL = Equivalent Series Inductance
    DF = Dissipation Factor = ESR/Xc (Xc is capacitive reactance at the operating frequency)
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Every other version of that circuit has blown up or burned down so what do you think? Personally, I'm putting my money on this one doing the same. Either the switching devices pop or the coil or capacitors melt down just as they have countless times before.

    If you point a loaded gun at your foot and pull the trigger and it shots you in the foot do you think that if you use a slightly different gun and or bullets and try the same experiment it wont too shoot you in the foot like every one before it did? :rolleyes:

    There's an inherent design flaw with that type of circuit that makes it unreliable at higher power operation and there's no ways around it without going to massively over sized and rated parts of which you obviously will not do. :facepalm:

    And what makes it worse is that for the time and money you have spent doing it wrong and for the time how many people have told you how to do it the right way, only to be ignored, you probably could have bought the right parts and built the right circuit and had a functional design done a long time ago. :(

    So what exactly is the point in this anymore beyond proving that you like to come here and ask the same question over and over then ignore the answers every single time? :banghead:

    Is is a stone hard mental block (cognitive capacity limitation) on being able to learn something new or a fear of succeeding with a different properly designed circuit or something else? :confused:
     
  7. gary350

    gary350 Well-Known Member

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    This is what a person does when they are RETIRED I am having FUN. This is more of a learning project than a useful project. So what if I build a different version of the same CRAP circuit LOL. Technology has come a long way since I was in college 50 years ago. There are a lot of different type capacitors these days that had not been invented 50 years ago. I guess I should make a memory note book for myself I can remember things 50 years ago better than 2 days ago. I recall reading certain caps work better for high frequency than others? My caps are rated 1000v if I replace them with 200v or 100v the circuit will be smaller. I was thinking about building this circuit into a plastic flash light body with 2 wires to clip onto a car battery then give it to my son he is a certified auto mechanic he can use it at work. My son was telling me, you should see the stuff people do they try to do their own auto repair with the few tools they have once the bolts are damaged to the point it can not be removed they bring it to the dealership to be fix. My son said, build me a 12v hand held induction heater it will be useful at work.
     
    Last edited: Apr 13, 2018
  8. dave miyares

    Dave New Member

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  9. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Generally speaking for high frequency you'll probably want a metallized polypropylene capacitor (MKP).
     
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  10. alec_t

    alec_t Well-Known Member Most Helpful Member

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    In that case, why don't you buy and try several different types of capacitor and report your findings? Other members here could then benefit from knowing which type works better (or not).
     
  11. Colin

    Colin Active Member

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    8 caps .47u each is not an electronics way to describe the colour of your hair.
    I have absolutely no idea what you are doing. But I am sure your are. You want a crew cut.
    The fist thing you ask is: what is the capacitor doing?
    At 100kHz, a 0.47u represents a reactance (resistance) of 3 ohms. Even though it will charge and store and deliver, it will be like 3 ohms in the circuit at some point in the cycle and an enormous amount of energy will go into charging it.
    Sometimes the capacitor works in harmony with the transformer to produce a tuned circuit and this increases the output enormously.
    The circuit cannot tell you anything as you need to know the features of the transformer and the actual waveform.
    But if the response is negative to the operation of this circuit, you need to find out why and this will be very difficult because the qualities of a transformer can never be related by a simple voltage, wattage, frequency description.
    A simple 1mH inductor can be 4 ohms or 36 ohms and one will work and the other will fail.
    These sorts of circuits are highly technical and if you're asking for advice, the whole project is beyond your grasp.
    I would not even start to copy a circuit like this unless I had the actual transformer in my hand.
     
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  12. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    That sort of makes more sense. I often destroy things in the process of learning as well.


    Sounds like a noble cause but the logistics of your current designs and their realistic implementation are terrible to outright dangerous for a number of reasons.

    1. The coil is uninsulated and unissolated from the power sources so if it being powered off the vehicles battery it's essentially a high current live line with zero isolation which means as soon as it bumps anything it's going to be a major park show.

    2. To do any degree e of fastener heating it going to take a lot of power which at 12 volts will require hundreds of amps just to equate to what a small hand held propane or butane mini torch can do.

    3. Its a high powered HF electromagnetic field generator which means its has the potential to induce a fairly high current in every wire of every wiring harness that it gets near.

    4. You have yet to perfect it to give decent power and stable operation with a power source well above what vehicle battery works at which means anything you have figured out still needs a total redue to make it work at lower voltages and even higher currents that you have been playing with so far.

    That all said, I do think the idea of a hand held induction heater has merit in some applications but for the efforts and costs you have been going to if you really think he needs one there are off the shelf units to be had for fairly reasonable prices.

    https://www.amazon.com/Bolt-Buster-BB2-ACC-Handheld-Induction/dp/B00ATSL7VE 1000 watt ~$378

    That's just one your competition. ;)
     
  13. gary350

    gary350 Well-Known Member

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    Several very good points made. My son said he could use an induction heater & buy a hand held unit but it is more $$$ than he wants to pay. Not likely I will get around to working on this project for a while. I tilled & planted some of the garden today and need to get a few more things planted before we leave for our 2 week RV camping trip on Florida beach next week. I was thinking about a voltage double circuit 12v car battery is really about 13.2v x 2 = 26v.

    [​IMG]
     
    Last edited: Apr 13, 2018
  14. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    The isolation issue is what I see being the biggest problem To get 1000+ watts at 12 or 24 still requires big cables and at the lengths that would be used around a vehicle the current they could pass in a accidental short is very high and well above what is needed to burn a hole in a AC line, fuel manifold hard line, or even a valve cover which the replacement costs on any single one of those items would be as much as a professionally made induction heater is worth.

    To me for a pro mechanic $400 for a specialty tool is nothing. I've worked with guys who had $30,000+ tool sets that didn't do any better work than my $3000 tool sets did. They just cost a lot more for who's name was on the side of everything. If anything they did less because they were so afraid to scratch or break anything whereas with mine I could care less. If modifying or wrecking $10 wrench saved me a $20 part or not having to buy a $30 specialty wrench it was worth it. ;)
     
  15. unclejed613

    unclejed613 Well-Known Member

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    you're still going to draw the same current from the battery, the voltage doubler circuit/DC-DC converter will use up about 10%, so you will get 10% less power. it doesn't matter if the heater is running from 12V or 24V from a converter, the current from a 12V battery is going to remain the same if the heater is a 1000W heater. a round figure of 1000W is going to be 83.3A from the battery. you will need at least #3 wire for the battery cables. the only real advantages of using a converter to 24V are going to be 1) less current draw by the heater itself, and smaller wire required between the converter and the heater 2) lower current requirement for the MOSFETs. the drawbacks of using the converter are 1) the converter needs to be able to convert 12V@83A to 24V@41.5A (actually assuming 90% conversion efficiency, the 24V output current will be 38A) and 2) the converter will likely be more expensive than the heater itself.
     
  16. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    And that brings the concept back to being better off powered by AC line power where a simple higher voltage lower current handelsing H-bridge based circuit with a impedance matching transformer is best off.

    To me no matter how we play things it always comes back to a higher voltage H-bridge with dedicated control circuitry systems make it realistically practical.
     
  17. gary350

    gary350 Well-Known Member

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    I talked to my son he said induction heater does not need to heat bolts red hot. It only needs to melt & release lock tight so bolts will come out about 600 to 700 degrees. The dealership has acetylene torch everyone can use. Induction heater might be handy if someone is already using the torch.

    The induction heaters I see for sale are 120 vac. Looks like I need to build a 120v induction heater.
     
  18. be80be

    be80be Well-Known Member

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    His cap only going to be something like .06u adding 8 just increases the voltage voltage they can handle but it lowers capacitance.
    Looks fun to play with tho
     
  19. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Seems like a weak excuse given a $15 mini propane or butane torch would do the same work without the cords or other possible electrical related hazard issues. I use my small jeweler's butane torch all the time for pinpoint heating work and larger soldering jobs as well.

    I can see the possible uses for a small portable induction heater but for loosening fasteners on vehicles just doesn't fit very well given the limited access and capacity such a device would have compared to any small fuel torch. I've done in depth automotive plus farm and commercial/industrial equipment service work and repair all my life and I have yet to hit a fastener where I thought an induction heater would have been remotely superior to any properly sized torch.

    Now for some of my heavier soldering and light brazing work I am seriously considering building a induction heater being for that stuff there are many situations where induction heating would be as good or better than torch heating simply for the more precise and focused heating ability (far less secondary heating collateral damage) it has when used properly.
     
  20. gary350

    gary350 Well-Known Member

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    Aren't box capacitors better than rolled capacitors because rolled caps are rolled up like a coil and have inductance like a coil and box caps are not rolled?

    [​IMG]
     
  21. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Depends on whether or not that tiny amount of inductance is a problem, and if it is can you counteract its effects enough for it to not be a problem. It's highly application dependent, which is why I said generally speaking.
     
    Last edited: Apr 14, 2018
  22. ChrisP58

    ChrisP58 Well-Known Member

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    Be aware, many box capacitors are the same rolled capacitors inside. You need to look at the specs of the individual capacitor.
     
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