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From: Fred McKenzie on 7 May 2010 18:26
In article
<2edb1412-a185-4f08-aa0c-984a0966c179(a)o12g2000vba.googlegroups.com>,
whit3rd <whit3rd(a)gmail.com> wrote:

> On May 7, 9:46�am, Omicron <omicro...(a)yahoo.com> wrote:
> > I need to have a Bridge Rectifier 250V 40a .....
>
> Huh? That's a device that makes 10,000W of DC
> power at relatively high voltage. It's not terribly SAFE
> to do that; normal switches and fuses cannot
> control such DC power. Is this for a flashing
> strobe light to illuminate a stadium?

Whit-

Yes, 250 times 40 is 10,000. That doesn't mean the bridge is being used
to produce 10,000 watts.

Both voltage and current may represent peak values of a low duty-cycle
application. If the bridge feeds a capacitor filter, the voltage peaks
across any one of the diodes would be 2.83 times the AC RMS value. That
would be 88.3 VRMS in this case.

With a 2X margin, actual stress might be 44 VRMS and 20 Amps peak, or
880 Watts peak power. With a low duty cycle, it would be even less.
This wouldn't be unreasonable for many applications such as rapidly
charging the batteries in a hybrid automobile!

Fred
From: Cydrome Leader on 7 May 2010 18:36
whit3rd <whit3rd(a)gmail.com> wrote:
> On May 7, 2:14?pm, David Nebenzahl <nob...(a)but.us.chickens> wrote:
>> On 5/7/2010 1:24 PM GregS spake thus:
>
>> > A bridge only works 1/2 cycle so you would need at least 20 amp
>> > diodes.
>>
>> Huh? Where do you get that?
>>
>> Despite only operating half-cycle, each diode gets the full current
>> flowing through it, so you need *at least* 40A diodes, better yet [50A].
>
> No, GregS is right. The rating of rectifiers is on the AVERAGE
> current they pass (peaks can be much higher). The voltage
> rating, for a bridge, has to be higher than the peak of the AC,
> though, because there's a charged capacitor usually on the output.
> So, a '250V 40A' bridge is made with 500V 20A rated diodes.

what about inrush current?

Here's what hammond manufacturing says

http://www.hammondmfg.com/pdf/5c007.pdf
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