Need 10 Amp Diode Suggestion

[Mark Mentovai]

I'm looking for a diode that can handle 10A forward at 12V. None of the
local shops are good for more than a handful of 1N4004s. I need this to
isolate two circuits normally supplied by independent sources when I
must feed them from a single source. The application:

10A 100W
fuse sw1 lamp
+12V -*----^-------/ -------*--(AA)--*- GND
| 10A . | 100W |
| fuse . | lamp |
*----^-------/ ----*--+--(AA)--/
| | |
| diode 1 - - diode 2
| 20A ^ ^
| fuse sw2 | |
\----^-------/ ----*--/

Operation (and slight, although minimal, voltage drop) is less critical
when sw2 is closed, but it is important to keep the circuits behind sw1
isolated. There shouldn't be any voltage drop to the lamps when sw1 is
closed, and the two lamps must remain connected behind independent
fuses. The circuit can't be redesigned to place sw1 and sw2 ahead of
the current protection shown.

Thanks for any suggestions you might have for the diodes.

Mark

 

[Tim Wescott]

Well, the obvious suggestion if you're in the US is to hit the Digi-Key,
Mouser and Newark catalogs, order and wait. The next bet would be to
parallel the 1N4004s that you _can_ get, and ballast them with resistors so
they'll work in concert.

You might consider waltzing into your local auto parts store and seeing if
they have rectifier blocks for automobile alternators -- those things
deliver 100A these days, they're 12V devices and they work by having a
little AC generator and a rectifier. I believe that most of them are
3-phase so each rectifier block should have 3 or 6 diodes if you can figure
out the connections. If they don't -- your girlfriend didn't need to get to
work tomorrow, did she?

If you live close to a big enough city you might see if there are surplus
stores, or any of the small storefront distributors that cater to the
industrial trade -- these folks are often good for that sort of part.

If you go with the 1N4004 idea, you can't just run them in parallel. If you
did the one with the lowest drop would conduct the most, and heat up, and
conduct more, etc., and your diodes would fail one by one. If you series
connect each diode with enough resistor to give you around 0.5V drop, then
parallel said combinations, you'll get the rectification you need --
probably with more time and trouble than you would if you dug up some 10A
diodes, but that's your call.

---------/\/\/\--->|---------
| |
| |
-----/\/\/\--->|----
etc.

-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Mark Mentovai" <www.mentovai.com-slash-contact.html@_._> wrote in message
news:www.mentovai.com-slash-contact.html-91E234.12320909012004@news.isp.nyc.eggn.net...

I'm looking for a diode that can handle 10A forward at 12V. None of the
local shops are good for more than a handful of 1N4004s. I need this to
isolate two circuits normally supplied by independent sources when I
must feed them from a single source. The application:

10A 100W
fuse sw1 lamp
+12V -*----^-------/ -------*--(AA)--*- GND
| 10A . | 100W |
| fuse . | lamp |
*----^-------/ ----*--+--(AA)--/
| | |
| diode 1 - - diode 2
| 20A ^ ^
| fuse sw2 | |
\----^-------/ ----*--/

Operation (and slight, although minimal, voltage drop) is less critical
when sw2 is closed, but it is important to keep the circuits behind sw1
isolated. There shouldn't be any voltage drop to the lamps when sw1 is
closed, and the two lamps must remain connected behind independent
fuses. The circuit can't be redesigned to place sw1 and sw2 ahead of
the current protection shown.

Thanks for any suggestions you might have for the diodes.

Mark