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seeker1

Member - Posts: 24

Joined: December 02, 2007

Location: Washington, United States

Posted: February 10, 2008 at 2:43 AM / IP Logged

I have acouple 3 amp 400piv diode I'm using to isolate part of a fog light circuit I've setup in my Mustang. Put man these thigs get hot. Is this normal?

Seeker

Only the strong survive.

Eat the weak.

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mad550

Copper - Posts: 201

Joined: February 23, 2006

Location: Australia

Posted: February 10, 2008 at 4:26 AM / IP Logged

Simple answer is no. The current rating on the diodes is far to low, you'll need at least 15amp rated diodes.

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Maroochydore

Nothing is impossible!

Do it right the first time or don't do it at all.

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i am an idiot

Platinum - Posts: 13,667

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: February 10, 2008 at 5:04 AM / IP Logged

Try Paralleling 4 of these. http://www.radioshack.com/product/index.jsp?productid=2062591&cp=&sr=1&origkw=diode&kw=diode&parentPage=search

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seeker1

Member - Posts: 24

Joined: December 02, 2007

Location: Washington, United States

Posted: February 10, 2008 at 9:39 AM / IP Logged

Thanks

But can you explain why. The fogs only draw 37.5 watt ea x 2 = 75 watts. 3 amps I thought should be able to handle in the neighborhood of 300 watts.

Seeker

Only the strong survive.

Eat the weak.

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dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: February 10, 2008 at 11:39 AM / IP Logged

3 amps at 13V is only 39 watts, if you have two diodes in parallel that'd be 78W.

Assuming the diodes are optimistically dropping only 0.8V across them when you're running 3 amps through them, that's still 2.4W a piece. That's too much power and heat for the diode to handle on a continuous basis. Doesn't really matter what diode you substitute, because the heat generated is going to be a function of the forward voltage spec of the diode, and there aren't any that are going to be low enough to let it run cool .

You really should use relays to do the isolation instead of diodes; much more efficient and cool running- using diodes for power like that isn't the best way to go.

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cruzsport1

Member - Posts: 1

Joined: February 10, 2008

Location: Connecticut, United States

Posted: February 10, 2008 at 12:56 PM / IP Logged

i would use a relay in stead of diode

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seeker1

Member - Posts: 24

Joined: December 02, 2007

Location: Washington, United States

Posted: February 11, 2008 at 11:33 PM / IP Logged

Thankyou for the help and the explanations. A relay it is. I think I've seen to many episodes of "pump My Ride". This will make the 17th relay I've installed in this rig.

Only the strong survive.

Eat the weak.

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diodes hot

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