Full Bridge with capacitor filter

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Thread Starter

Mohit Aasi

Joined May 21, 2017
3
Hi guys I was wondering when building a full bridge with a capacitor in parallel with a load why is there not a short with the capacitor?

Shouldn't the current in the capacitor be insanely large?

 

dendad

Joined Feb 20, 2016
3,164
The capacitor is like a water tank. It is acting as storage. When it is empty, it will draw a high current but as soon as it starts to charge the current reduced as the voltage building up in the capacitor "opposes" the rectified voltage until they are both the same and there is no current flow. It is like connecting a full water tank to an empty one. The water flow is high at the start but reduces to nothing when both tanks are at equal levels.
A capacitor does not pass DC current. Current will flow through a capacitor, after the initial charge equalizes, when there is a change in the voltage differences across it.
 

Thread Starter

Mohit Aasi

Joined May 21, 2017
3
Makes sense so there will be current surges in the circuit? If I plug into mains and get 170 VDC, I would think to put a D Type circuit breaker in my house for the current spikes and not blow any fuses in the circuits in the house. Would that take care of the current spikes or would putting a D type in the circuit be fine?
 

dendad

Joined Feb 20, 2016
3,164
Makes sense so there will be current surges in the circuit? If I plug into mains and get 170 VDC, I would think to put a D Type circuit breaker in my house for the current spikes and not blow any fuses in the circuits in the house. Would that take care of the current spikes or would putting a D type in the circuit be fine?
It really depends on the size of the rectifier/capacitor combination.
The bridge rectifier circuit is what is used in almost every power supply. Some have a surge limiting resistor in line but some do not.
What is your application? Voltage and current requirements?
I don't know what a "D" type circuit breaker is, sorry. I'm in Australia.
Also, if you are connecting straight onto the mains and do not know what you are doing, you are treading on VERY DANGEROUS grounds.
Please be careful or get someone who knows what is up to help you.
 

Thread Starter

Mohit Aasi

Joined May 21, 2017
3
I was going to charge caps for a coilgun. I will not do anything untill I"m 100% sure and have run countless simulations on PSpice. I take safety very seriously when i ran the PSpice simulation and found a current spike in the filter cap that's when I started to get worried. A D type fuse (Sorry it's not a circuit breaker but a fuse) is for a delay, they are mostly used for anything with a motor or fridges anything that'll draw alot of current for a short period.

The caps have 300 VDC max rating I think only thinking of making a full bridge with a cap filter, inductor in series if need be and then a voltage boost circuit to get it close to 300 VDC. I was going to put a 100 Watt incandescant bulb has a current limiter for now but there maybe a high voltage drop on the bulb. So i don't know yet. I'm just still learning on how to go on with it and making safety my number one priority

I'm going to try the caps at 170 before I make a voltage boost
 

dendad

Joined Feb 20, 2016
3,164
I would recommend you use an isolation transformer.
The lamp in line is a good idea. It will flash brightly at the start then fade out as the current drops. It is an old trick for protecting circuits.
Eventually the caps will charge to full voltage as less volts are dropped across the lamp as the current drops. It will just take longer, that is all.
But please, find an isolation transformer, or 2 of the same transformers and run them back to back so you are not fiddling around with mains directly. Mains will win!
Here in Oz it is worse as we run 240V, not 110V.
Oh, and don't run 300V caps at 300V. Have some headroom.
 

MrChips

Joined Oct 2, 2009
19,747
This thread is locked for discussing two prohibited topics as stated in the User Agreement (transformerless power supplies and railguns).
 
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