Proper Diode?

Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=142294
Printed Date: May 02, 2025 at 7:34 PM

Topic: Proper Diode?

Posted By: irish charm
Subject: Proper Diode?
Date Posted: December 24, 2016 at 12:00 PM

Hi,

Need help selecting a proper diode. Tapping into preexisting separate 10A and 30A fuses, each operating separately and not at the same time, combining them to power 4 separate side marker bulbs. I'm concerned about the feedback when the constant lights switching between the 10A and 30A fuses. Individually, each bulb has a power draw of 69mA/0.89w. Combined, the four bulbs have a power draw of 276mA/3.56w. Thought about just using a 1N4004 or 1N4003 diode. Thoughts?

Replies:

Posted By: the12volt
Date Posted: December 24, 2016 at 2:22 PM

I would use two SPDT relays instead of diodes.

Relay One
87 to 12V+ (fused at battery, accessory, or ignition depending on your needs)
85 to 12V+ from 10 amp fuse
86 to ground
30 to terminal 87a of relay two

Relay Two
87a to terminal 30 of relay one
87 to 12V+ (fused at battery, accessory, or ignition depending on your needs)
85 to 12V+ from 30 amp fuse
96 to ground
30 to marker lights positive

Anytime you have power from the 10 amp fuse or the 30 amp fuse, the marker lights will have power and both fused circuits will remain isolated.

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Posted By: irish charm
Date Posted: December 24, 2016 at 10:46 PM

Adding two relays would make sense; however, a diode to prevent feedback is also practical in this application as well. Thoughts on the diode?

Posted By: irish charm
Date Posted: December 24, 2016 at 10:51 PM

The bits I'm not really passing along is that I am not adding an accessory, simply substituting the current way the sidemarkers are ran. I'm choosing the spike/feedback suppression only as an overly cautious precaution.

Posted By: the12volt
Date Posted: December 25, 2016 at 9:24 AM

Either of the diodes you listed will work, but you will need two with the cathode ends tied together at the lights and each anode end toward each power source. The reason I suggest the relays versus the diodes is to maintain complete circuit isolation which would be the most "overly cautious precaution."

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