400v capacitor bank charger from 230ac

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matters_100

Joined Mar 30, 2016
18
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
 

tcmtech

Joined Nov 4, 2013
2,867
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.
 

#12

Joined Nov 30, 2010
18,224
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.
 

ian field

Joined Oct 27, 2012
6,536
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.
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.
 

tcmtech

Joined Nov 4, 2013
2,867
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! ;)
 

tcmtech

Joined Nov 4, 2013
2,867
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.
 

Thread Starter

matters_100

Joined Mar 30, 2016
18
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
 

tcmtech

Joined Nov 4, 2013
2,867
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.
 

Thread Starter

matters_100

Joined Mar 30, 2016
18
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.
 

ScottWang

Joined Aug 23, 2012
7,397
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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