diodes hot

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=102048
Printed Date: May 04, 2024 at 2:28 PM

Topic: diodes hot

Posted By: seeker1
Subject: diodes hot
Date Posted: February 10, 2008 at 2:43 AM

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

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Only the strong survive.
Eat the weak.

Replies:

Posted By: mad550
Date Posted: February 10, 2008 at 4:26 AM

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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WOW Sight and Sound
Maroochydore
Nothing is impossible!
Do it right the first time or don't do it at all.

Posted By: i am an idiot
Date Posted: February 10, 2008 at 5:04 AM

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

Posted By: seeker1
Date Posted: February 10, 2008 at 9:39 AM

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.

Posted By: dualsport
Date Posted: February 10, 2008 at 11:39 AM

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.

Posted By: cruzsport1
Date Posted: February 10, 2008 at 12:56 PM

i would use a relay in stead of diode

Posted By: seeker1
Date Posted: February 11, 2008 at 11:33 PM

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.