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Why my capacitor charger melt wires when just plugged from mains? Answered

recently completed a coilgun with a portable 12vdc supply. it works very fine,
but i am not satisfied with it performance it is taking 30 to 40s to charge my capacitor bank of 1350uf at 400vdc. however to boost up the charging i've put a mains supply of 230v. 

but whenever i connect it melts my wire at the rectifier. i don't know why but how is it no working here is a shema



Best Answer 7 years ago

I may be wrong, but I read that you're doing something really stupid here.
You're applying nearly 20x to the thing and you report "melts my wire"? Or is it a different mains-to 12VAC supply to the previous?


it works fine without mains supply but when mains is added, there comes the problem. what should i do to increase its power without the mains added
all the circuit along with the transformer are securely insulated with hotglue(without the rectifier D1 and the 230vac input).
yes it has switches and relays for charging the capacitors and a neon bulb lights up when the voltage becomes dangerous.

besides i always wear rubber gloves when working with these things,

You're upping the voltage 20x.
How about starting with only 24V and taking it up in stages?


yup sounds great i've tried it. works great, however the only drawback now is i don't have any scrs. they are too expensive. where can i salvage one???

thanks a lot

If you're melting wire then you're pulling more current thru the wire than it's meant to carry.

You circuit is incredibly dangerous.  No switch, no fuse (you shouldn't rely on the house breaker to interrupt), no isolation transformer.  Or did you just not show everything.

If your going to be using mains buy the right parts. farnell.com have thyristors and triacs at a cheap price plus you can search for the rating you need, not make do with what you can find. best advice you got here was from jeff-o
"don't plug this in again until you've added some fuses"

It would also be good to display your schematics properly, it makes it easier for everyone else to see what you have done. Going from left to right. eg. Inputs -> Processes -> Output. Labelling all of your outputs etc

By having a quick look at your schematic I dont see the point in having two bridge retifiers. Your design is trying to reverse bias the diodes D2 - 1. with 400V DC. Replace d2 with a voltage regulator.

by SCR do you mean thyristor? I got one out of an old TV.


yes. what was your thyristor rating.
i need one which can atleast withstand 400v at 600a
thanks a lot for your support willing to post a complete instructable after exams

It wasn't that much.
600A is a hell of a lot, but it would only be very brief (maybe 1/1000 of a second?). You'll benefit from more capacitance I think, old TVs are a good source of parts.
I'll hope to see this thing later - best wishes for that, and the exams.



Answer 7 years ago

1st picture
on the left u will see the transformer, my bd243c circuit. on the right the capacitor bank.

2nd picture
on the left there is a 250v 3A on/off switch for the bd243c charger( from computer psu)
on the right the fire switch. 275v 80A from an 16kW old water heater.

3rd pic oops posted same pic.

here is the 4th
there is a voltmeter( from a cable extension found in a river dumbed by a noob)
an on/off switch from old tv 2A 250V
the mains input, sure it is well earthed, and the 12vdc input


Not withstanding Re's comments - this IS a really really dangerous circuit.

There are four wires shown at the rectifier. Which is melting. The capacitor bank presents a dead short to the rectifier when its discharged, your 12V circuit self-limits.

But this is a truly awful idea.


"Uh why does my house burn down every time I build something?"


7 years ago

You're drawing too much current. You need to charge the capacitors through a resistor to avoid the massive in-rush of current when the caps are "empty." It'll have to be one huge resistor too, by the way.

Also, I agree with re-design. Incredibly unsafe. Please don't plug this in again until you've added some fuses or something.