help choosing caps

[Dr_Doggy]

first i have a full bridge rectifier, but it needs a smoothing capacitor, it rectifies ac120, and runs at 15amps max,


the second caps i need i was told;
The local supply capacitors need to be rated for the rms current they will have to carry, to be on the safe side just figure they need to be rated for the same as the dc current flowing into the supply. Their parasitic inductance needs to be kept very low as well.
these are 5 in series,

could someone pick out proper ones for me @ digikey,, this is something i dont trust myself doing....

 

[KeepItSimpleStupid]

Confused:

Cap's in series? Caps in parallel add. Caps in series follow Ct = 1/(1/C1+1/C2+...1/Cn)

Is a transformer involved or are we talking rectifying the mains to get something like 168 VDC at 15 A? That's what you get when you Full wave rectify the mains.

 

[Nigel Goodwin]

As always, you need to give FAR more detail - EXACTLY what is the application?.

But from the little information so far it looks a pretty expensive requirement.

 

[ccurtis]

The local supply capacitors need to be rated for the rms current they will have to carry, to be on the safe side just figure they need to be rated for the same as the dc current flowing into the supply.

The total capacitor RMS ripple current may be several times the average DC load current, depending on the total capacitor value and ESR, the load current, the rectifier type, the line frequency, and other factors; the main concern being the temperature rise (reliability) of the capacitor. The total peak capacitor current may be many times the average DC current; the concern being the peak current rating of the capacitor(s).

 

[ronsimpson]

it rectifies ac120, and runs at 15amps max,

the second caps i need i was told;
Their parasitic inductance needs to be kept very low as well.
these are 5 in series,

.

This sounds like a 60hz project where inductance is not very important.
Five capacitors in series, that will increase the inductance greatly.

How much voltage ripple can you handle on the voltage? We need this to pick a capacitor.

 

[Dr_Doggy]

ok, well here is the schematic the guy gave me for a 1800watt induction heater, the best i can run off my 15 amp surge protected power bar(120volts?)60hz,,

**broken link removed**

he said to rate the series caps for the rms aswell, there will be 5 h-bridges, not like 3 in the schematic, i have labeled the series caps in question as c2, he said to just rate it as the dc current of the supply?!?

the schematic he gave me was only semi, but if we can get those caps down, i should be able figure it out.... the green WAS where my questions lay, but i got a quick tutorial on the coils,

im also not sure about what voltage i should step down to at the work coil or how to limit the current at the supply,


ill admit this circuit is advanced for me, but i am doing this because i am more interested in the fields it produces...

 

[ronsimpson]

This being a heater I see no reason for a large cap to filter the 60hz (120hz) ripple. The ripple voltage could be very large.

I think we need to start a new thread on induction heater. There are many questions here.

 

[Dr_Doggy]

ya large, thats why i dont want to under gusetimate....


btw, are we understanding that circuit, maybe there is a better(cheaper) way to go about this,, i get that i may be drifting with the ??'s but i will stay on topic, i just want to get those capacitors on order soon!


so far i have gotten;
my rectifier GBPC3504A-ND,
tank caps 399-5864-ND x 100
work coil, 1uh, 300amps
....and some toroids

sound ok so far?