400v capacitor bank charger from 230ac

Discussion in 'General Electronics Chat' started by matters_100, Mar 30, 2016.

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  1. matters_100

    Thread Starter New Member

    Mar 30, 2016
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    Hi,

    I'll like to design a 400V capacitor bank charger from a 230ac line. Ideally, it would charge the capacitors within seconds, which implies in my case a current rate of about 5A, so the charger should deliver a power around 2kW.

    As it is for charging capacitors, a big ripple voltage isn't a problem.
    Also, outputting a bigger voltage (up to 430V as the capacitors are rated for 450V) is not a problem as I planned to use a voltage comparator to stop the charging when the capacitors reach a desired voltage.

    The use of a transformer would be the easy solution, but the cost of such equipment is out of my budget unless you know where to find a large toroidal transformer core relatively cheaply, so then I could wind it myself :)

    I think the a solution would be to build a SMPS, so use a full-bridge rectifier + a capacitor to rectify the AC to a DC, then a boost converter SMPS DC to DC. I was planning to use an old PC power supply + linear regulator to provide the low voltage needed for the SMPS microcontroller.

    To limit the current, I was thinking of a resistor sensing + mofset.

    What do you think ? Do you have any other solution in mind ?

    Also, as I have no experience building such SMTP, I first wondering at which frequency such SMPS should be operated ? (as the higher the frequency the smaller the components but also the higher the losses in the switch)

    Thanks
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    A simple buck/boost transformer in series with your mains would easily get you the added line voltage with out needing much of a transformer.

    As for current limiting a big resistor is all you need.
     
  3. #12

    Expert

    Nov 30, 2010
    16,298
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    I can "name that circuit" in about 3 parts, but it's not allowed on this site because it's awfully dangerous.
    Do be careful. You're playing with enough power to blow a couple of fingers off.

    Apologies if you're not an amateur.
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    Some of the people who turn up, are so dim - if they were going to hurt themselves, they'd have already done it anyway without any help.

    Once I built a multistage Cockroft and Walton multiplier out of a pile of left over VGA monitor reservoir capacitors - I was too scared to discharge it, so I put it on a high shelf and waited for leakage current to do the rest.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
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    As an avid supporter of the Darwin Awards I am obligated to encourage as many as possible to enter. It is for the good of humanity in the end! ;)
     
    Sensacell likes this.
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
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    On further thought given you only need around 5 amps for a few seconds to charge the capacitor bank you don't need a 2 kilowatt capacity power supply to do it unless this is in an application where it's having to do back to back recharges continuous duty.
    If it's an intermittent use, low average duty cycle, a way smaller transformer capacity would handle it just fine. As would a simple charge pump system , Diode - capacitor - diode, provided you have a voltage cutoff to keep it from overcharging.
     
  7. matters_100

    Thread Starter New Member

    Mar 30, 2016
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    Thanks all of you for reminding me how dangerous it is.
    @#12 no offence taken as even experienced need to be reminded.
    I didn't see in the first that transform-less power supply weren't allowed on this forum, but that's definitely for the better.
    In that case, I'll probably use a transformer, to make things a little less unsafe.

    @tcmtech, yes, this will do back to back recharges but for a relatively short amount of time (approx 5min for the worst case). And after thinking about it, probably a lower current rate would as good. I saw a 1.2kW toroidal transformer which seemed appropriated, for £70 ex-VAT (approx $100). This price doesn't seem to be overpriced. Yet, if anyone know where to find a better priced toroidal transformer or only toroidal core in the UK ?

    Thks
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Why toroid?

    Also using an autotransformer setup to boost your line voltages by 60 - 70 volts would easily get you buy with less than a 300 VA transformer.
     
  9. matters_100

    Thread Starter New Member

    Mar 30, 2016
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    Indeed, you're right, I didn't think of this one. Down side though, an autotransformer won't provide electrical isolation.
    And toroidal transformer because it's usually more compact/efficient than solenoid core-based transformers.
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the 230 volt ac when half wave rectified, will give you 391 volts dc. across the caps.
     
  11. matters_100

    Thread Starter New Member

    Mar 30, 2016
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    @alfacliff I'm not sure to follow, because a 230ac single-phase will give you a sqrt(2)*230=322V peak ...
     
  12. dannyf

    Well-Known Member

    Sep 13, 2015
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    "current rate of about 5A,"

    This is one of those cases where a whimpy power supply may be more desirable.
     
  13. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    Welcome to AAC.
    Transformerless powersupplies are not allowed over here.
    See point 6 of the user agreement:
    http://www.allaboutcircuits.com/user-agreement/

    Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies

    The thread will be locked.
     
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