Electronics Question - Use of Diodes

[ajp3jeh]

I am a law enforcement officer that is currently rewiring his patrol car. I need recommendations on which particular diode to use for my application. I am attempting to close a series of relays in a progessive order and need to limit current flow to "one way" at certain points. I am hoping to pick the part up at Radio Shack so any specific names or part numbe should be very useful.

Here is a link to a rough wiring diagram of what I'm trying to accomplish. The voltage is obviously 12 volts and the amperage is relatively low as I'm merely closing relays.

http://albums.photopoint.com/j/ViewPhoto?u=1361878&a=10151678&p=38100417

Thanks,
John

 

[etech]

ajp3jeh, I couldn't get your schematic to load, but a 1N4001 diode should work. It is a 1 Amp @50v Peak inverse voltage. Common and easily found, I have seen them at Radio Shacks in my area.

RS 1N4001

I am assuming that 1 amp is sufficient current for your relays, it should be.

 

[DaLeroy]

Dunno about helping police officers but here goes...

All diodes have a particular voltage rating. They will all have a small voltage drop across them (less than a volt) and 'pass' the rest of the voltage through. If you need ~12 volts, get a 12 volt diode. You can also use zener diodes, which are basically voltage regulators...get a 10v zener diode and it's output will be 10v, with the rest of the voltage dropped across a series resistor. Supply us with a bit more info, and I'll see what I can work out, as it has been a while since I've done this..

 

[etech]

Ok, got the schematic to load.

I'm assuming you are applying the 12v at the bottom of the page, through the switch and then it goes to a relay 1,2, or 3.

Switch 1/ relay 1 will only turn on the rear lightbar strobe,hide away strobes and rear deck strobe.

Switch 2 will turn on the above and also the front lightbar strobe.

Switch 3 will turn on all of the above and the piecer, headlight flasher and siren/horn relay.

What object is to the left of switch 3?

Check the current rating of your relays, note that the diode between switch 2 and 3 will carry the current for two relays(1&2).
With 12v relays the voltage drop will not be a problem, the charging voltage when a car is running can be as high as 13.6v.

If you need a higher current diode.
RS 1N5401

 

[ajp3jeh]

For clarification, the 12v is coming from a 4 position switch at the top of the page and then traveling to the relays - flowing from top to bottom. The device on the right is an On/On relay that controls the Horn/Siren ring. Basically, you can control the siren by using the vehicles horn, allowing you to keep both hands on the steering wheel.

The diode you listed is rated at 3 amps, is there a higher amperage model available? I posted this same question in another forum and a 12 volt Zener Diode was recommended. Whats the difference between the Zener and your recommendation?

Also, what is the best way to secure the diode between the various points. Also, what would you recommend for an enclosure, I was thinking about using one of Radio Shacks "Project Boxes."

Many thanks,
John

 

[etech]

Some bad assumptions on my part.

First the higher current diode.
6 amp

data sheet - pdf format


For what you are trying to do you do not want a zener diode. They are used for voltage regulation. You need a general purpose or blocking diode.

To secure the diodes I would solder each end to a wire and then cover them with heat shrink tubing(also available at radio shack).

Heat shrink tubing is an expanded polyolefin(think rubber). When heat is applied it shrinks and makes a nice neat covering. Make sure there are no sharp projections on your solder joints that can poke through it though. Putting the diodes in a plastic 'project box" (with the switches?) would be a good idea.

edit/
example of heat shrink tubing

a hair dryer or even a cigarette lighter can be used to shrink the tubing.

 

[ajp3jeh]

ETech,

Many thanks for all your help....

John

 

[etech]

John, no problem, glad to be of some assistence, you just have to promise to not use those lights on me.

 

[IBhacknU]

phew....

thought he said dildos

 

[Rastus]

Overclocking your police car?

 

[Mday]

now that should be a banned word.