Diodes - where to get?

[markkw]

A while back someone suggested a place to buy high amperage diodes for use in battery chargers and other DC circuits ... I seem to have lost errr misplaced it.

Also, any thoughts on using the pre-made full wave bridges over putting your own together? I'm working with two volt/amp ranges, one being <20vdc @ <25a; other being <50vdc @ <50a.

Thanks,
Mark

[tech4]

Mark, I don't remember the source that you are referring to but many of the surplus dealers are out of business. I use Mouser since they do not have a minimum order. I prefer the bridges but usually you will need individual diodes for the 50A because of the heat sinking. Here is a link to Mouser
www.mouser.com/Search/Refine.aspx?Keyword=bridge+rectifer

[markkw]

Mouser is the place, think that's the link you gave me before.

Now I got a question ... can diodes be de-rated for low voltage circuits the same as high voltage fuses? IOW, if a 400V/20A diode is being operated in a circuit where it will see an input ¡Ü16V, would it not be capable of handling current in excess of its A rating since the V-in is considerably lower?

Reason I ask is that P=E*I
thus the potential
P-max @ 400V/20A = 8000W
and
P-max @ 16V/40A = 640W

but ... I'm thinking along the lines of thermal breakdown and can't seem to find any data suggesting that the diodes would be subject to breakdown via the actual amperage only the combined VA. Does this make sense?

[tech4]

Mark, in a simple answer you can not exceed the current rating of a diode any more than you can exceed the current rating of a wire. The voltage is just the limit of the reverse voltage on a diode before breaking down.
Just as a #12 wire is rated for 20 amps at 600 volts (insulation determines the voltage rating) you can not run a #12 wire at 100 amps at 12 volts.

You can always use a high voltage diode in a lower voltage circuit but not vice versa. You have to be careful on the voltage rating because as I said it is the reverse voltage that is a concern. Let’s say you have a 100 volt AC circuit. The rectified DC will be 1.41 X 100 or 141 VDC now when the AC side goes negative you will have a difference of over 240 volts so I would use a diode of at least 400 reverse voltage rating

By the way a silicon diode will have about a .7 volt drop in the forward direction regardless of the input voltage. Most diodes have a high surge current but that is for just an instance - do not use a diode in a higher current circuit unless you are wanting to let the smoke out

[markkw]

That hit me later last night ... can you tell it's been a while since I did this stuff? LOL

I'm going to get the higher amperate rated and double them up anyway plus put them on a heatsink. Just a warning, I'm going to emailing you with one of my off the wall ideas ... still doing a little research before I waste your time.

[garystewart]

I can see it now..............a battery operated muzzleloader

[markkw]

Uhhh, CVA already has them, the Electra ... circuit board is made by a Spanish toy maker and no vent which has caused many problems with projectiles being pushed away from the powder charge by the trapped and compressed air.