1amp diode can block direct short circuit?

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=2050
Printed Date: July 28, 2025 at 3:48 AM

Topic: 1amp diode can block direct short circuit?

Posted By: 2000vsm
Subject: 1amp diode can block direct short circuit?
Date Posted: July 18, 2002 at 3:16 PM

ok if i place a diode to do this, will it block the current? because i don't want to short out something

(+12V constant)----------------------<|--[diode]-------------------(GROUND)

will it still short circuit or blow up the diode?

Replies:

Posted By: the12volt
Date Posted: July 18, 2002 at 4:43 PM

Hi 2000vsm, I'm not sure where you have the cathode side shown in your diagram, but if you have 12V+ on the cathode side and ground on the anode side, no current will flow (no short).

https://www.the12volt.com/diodes/diodes.asp

the12volt

Posted By: 2000vsm
Date Posted: July 18, 2002 at 7:51 PM

yeah the cathode is 12v... but it's directly.. the 12volt is not going through a load.,.. just right to the diode and to ground...

Posted By: go2pac
Date Posted: July 18, 2002 at 10:42 PM

as long you don't reach the reverse break down voltage, then the diode won't short 12v to ground.

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Karl

Pacific Accessory Corporation
Mobile Audio Interfacing Equipment
Connecting You to Your Music Since 1976

Posted By: 2000vsm
Date Posted: July 19, 2002 at 11:04 AM

so current doesn't matter? of course it won't spike passed 400v right?? which is the reverse break down voltage i think...

it's a 1n4004 diode

Posted By: 2000vsm
Date Posted: July 19, 2002 at 12:13 PM

can i put 2 didoes in series to get a more stronger diode?

Posted By: 2000vsm
Date Posted: July 21, 2002 at 10:21 AM

????????????????????

Posted By: Velocity Motors
Date Posted: July 21, 2002 at 10:25 PM

No, a diode does not get stronger when wired in parallel. Here's something to relate to what you are asking"

What's heavier a ton of feather or a tone of bricks ? " It's all relative and it you have a two 1 amp diodes in parallel, it's still only 1 amp. You must use a larger diode in order to have a greater current restriction.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Posted By: 91blaze
Date Posted: August 05, 2002 at 12:02 AM

what if they were wired in parallel?

Posted By: Velocity Motors
Date Posted: August 05, 2002 at 8:00 AM

You CAN wire diodes in series ( sorry about that in previous post, got ahead of myself ). Just watch out that if the current flow is too high you will probably be able to see the diode glow in the dark from the heat posted_image I put a picture of a circuit for a head light that requires diodes in series to increase amperage. These diodes are 1N4148 diodes that restrict about 100 mA of current.

posted_image

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Posted By: cdaw
Date Posted: August 05, 2002 at 10:17 PM

A 1 AMP diode will only hold back - 1 Amp of current, If for instance - you put that 1 amp diode directly betwen the + and - of a 800CCA deep cycle battery - - I believe you would get instant ashes. posted_image

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JT

Posted By: 2000vsm
Date Posted: August 05, 2002 at 11:14 PM

so for those 30/40amp relays, that means i need 40 amp diode? wtf?

Posted By: Pickle
Date Posted: August 06, 2002 at 1:53 PM

The 30 (or 40, or whatever value) generally means the amount of current you can put through the relay contacts. It does not refer to the amout of current that the relay's coil draws when the relay energises. A one amp diode placed across a relay's coil (terminals 85 and 86, I believe) is usually plenty for most automotive relays, as the diode's only purpose is to allow the coil's magnetic field to collapse (when the coil is de-energised) without sending a spike back through the line . When a relay's coil is energised, the contacts are closed or opened, depending upon the type of relay being used and/or the contacts involved. The "30" (or 40, or whatever) is telling you that the contacts can handle up to that amout of current without being damaged/destroyed.

So, if you've got aircraft landing lights which draw 100 amps, switched by a 30-amp relay, you'll have trouble. If you've got, say fog lights, which draw 7 amps, the 30-amp relay will be fine.

If you're using diodes to block a signal from one switch but allow another switch to energise a relay, a one- or two-amp diode should be fine. Just run a fused line from your battery or accessory line to the relay contacts and out to your device, making sure that the fuse is appropriate for whatever device you're switching and then you don't have to worry about whether the diode will handle the amout of current of the switched device itself.

The Basics section of this site contain very good info on diode and relay use, and may help more than my blather...there are good diagrams to accompany the descriptions, which always is helpful.