How to Choose the Right Diode Size for Your Off-Road Lights | Expert Tips

[Mike1220]

Hey guys, brand new to the forum and have an electrical questions or you guys. I can work my way around wiring but only the basics, I tried to do a search but with my knowledge I came up empty handed
So here's the background

I'm trying to find what diode size my buddy needs for his truck,
He has some off-road light pods that he wants to wire into his OEM fog light feed so they will turn on automatically during the day and when he hits his high beams, but he also wants to run them on a separate switch so they can turn on with another small bar he has upfront.
We are trying to prevent one feed from backfeeding to the other, such as the fog circuit backfeeding to the wire harness and possibly frying something

The lights are very low power since they are LEDs, only draw 1AMP each if that I believe

Can anyone help me to figure out what size diode we need to allow enough power to flow to the lights?
This is on a vehicle so it's all a 12V system

Any help is VERY much appreciated!
Thanks in advance
- Mike

 

[CWatters]

Need to know total current. You said 1 Amp each but not how many light there are.

 

[berkeman]

And once you have the total current, you can use a browser like this one at Digikey to start making your selection. I'd be inclined to use a Schottky rectifier diode for this application, to minimize the forward voltage loss through the diode...

http://www.digikey.com/product-sear...es-rectifiers-single/1376383?k=schottky diode

.

 

[Mike1220]

Need to know total current. You said 1 Amp each but not how many light there are.

My apologizes, didn't realize I forgot to mention that, there will be 4 pods total, 2 per diode. Or would 1 per diode be better?
The lights are rated at 18W each

And once you have the total current, you can use a browser like this one at Digikey to start making your selection. I'd be inclined to use a Schottky rectifier diode for this application, to minimize the forward voltage loss through the diode...

http://www.digikey.com/product-sear...es-rectifiers-single/1376383?k=schottky diode

.

Thanks! I'll check it out [emoji106][emoji106]

 

[berkeman]

there will be 4 pods total, 2 per diode. Or would 1 per diode be better?

If you can use one diode per light, that will let you use lower current diodes, and spread the heat dissipated out more.

The lights are rated at 18W each

That's more than 1A per light. 18W/12V = 1.5A, so in looking through the Digikey selection guide, you should probably be looking at 2A Schottky rectifier diodes...

 

[berkeman]

Here's the selection guide with filters applied for 2A Schottky Rectifier Diodes in through-hole style (instead of surface mount style):

http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

 

[meBigGuy]

I'd double or triple the rating just because. The cost is about the same. Maybe even 10A

This is a car, and things happen. Voltage can go to 15V, owner can buy more powerful bulbs, etc.

 

[Mike1220]

If you can use one diode per light, that will let you use lower current diodes, and spread the heat dissipated out more.

That's more than 1A per light. 18W/12V = 1.5A, so in looking through the Digikey selection guide, you should probably be looking at 2A Schottky rectifier diodes...

The lights are LEDs, not sure if that makes a difference. The specs said they draw less than 1A, but then again, can't always believe everything you hear on the internet I guess haha

Here's the selection guide with filters applied for 2A Schottky Rectifier Diodes in through-hole style (instead of surface mount style):

http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Yes that's the kind id rather forward to him! Whatever will be easiest to put inline with the wiring.
So any of those Diodes would work?
But I guess I should mention the same question I am asking meBigGuy, which is should I go with a bigger diode just to be safe? Such as a 5A or 10A just to make sure that the diode is powerful enough to not have any issues? There are fuses elsewhere in the wiring to protect the battery and any other circuitry that matters like the OEM computers

I'd double or triple the rating just because. The cost is about the same. Maybe even 10A

This is a car, and things happen. Voltage can go to 15V, owner can buy more powerful bulbs, etc.

So might it be best to go with say a 5A or even a 10A diode instead of a 2A just to be safe?