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Charging capacitor from rectified mains? Answered

recently my father brought 2 6400uf 400v phillips from his work. i want to charge it with rectiried mains. will be using them in paralell for coilgun 

1) what is the voltage of 220v mains when rectified?(my voltmeter bunt)
2) when i try to charge them directly from a rectifier it melts my wire due to current. unfortunately i donot have a high power resistor to limit the current. How can i solve this without buying a high power resistor?
3) I want an led to light up when the voltage from the rectified mains is attained.
4)what will be the best. a 55 amp relay or a 75amp switch. i know that the switch can handle much more current but will the switching be quick  enough?
thanks in advance.



Best Answer 7 years ago

You want to look-up RMS, 220VAC would peak at 310V.
Your initial problem is too much current, and I don't believe "donot have a high power resistor to limit the current" - are there no filament light-bulbs in Mauritius?

Be careful, I don't think this method advisable.


how about switching to coil. 55amp relay or 75amps switch spsdt

I've written at length, and not long ago, on charging times etc for capacitor banks.

L. is right, using a filament lamp is the classic method of limiting charging current - charging time is now R of filament X capacitance. Resistance of a filament lamp is hard to calculate, since it is a strong function of temperature, but 100W bulb would work just fine.


Think about it. Without the resistor WHAT limits the inrush current ????


Well done.
Exactly, and that has a resistance of milli-ohms. Hence killing your rectifier wire.
You'd be amazed at how many people think that their fuses limit the current.

W/ref how about switching to coil. 55amp relay or 75amps switch spsdt?
Neither will solve your problem with "it melts my wire due to current", but the 75A switch would be better.


no when discarging the energy from the bank to the coil. the switch works well but will the relay get damaged. i've read that relays will switch faster but will it last long. because it will only drive large current for very little time.

I don't think the relay will like it for long if it's only designed for 550mA.


So you've burnt your voltmeter and melted wires trying to do this.
I think you've adequately proven that YOU SHOULD NOT BE PLAYING AROUND WITH MAINS VOLTAGE!
You are trying to do something which could go very bad, very quickly.

On the other hand, if he keeps trying, eventually he won't be trying any more. Does anyone know the mailing address for the Darwin Awards nominating committee?

i know what i am doing and what precaution to take. don't post answers not related to what i am asking.

When posting answers to questions that might be dangerous the responsible answer includes warnings. When we have no knowledge of the asker and what they do or do not know it's better to give no info than give an unsafe start. You are not the only person that will read these suggestions. If you get suggestions or warnings that you don't need then just ignore them. Warnings that are below your knowledge are not an insult to you so don't tell us what to post.

. I have to agree with the rest - stop before you kill yourself. Study up on electrical safety and get some experience working with low voltage before attempting to work with mains power.

i've worked with mots. made plasma launchers.coilguns(400v) and played a lot with high voltages of about 20-200kv.

just telling you i can't measure the voltage of rectified mains cause my voltmeter is damaged from another exsperiment.