Anyone understand diodes?

Jamieg285 · December 12, 2008, 04:06:44 AM

I want to add some didoes to some custom wiring, to act as a check valve to prevent the current going in a specific direction.

The problem is, I know nothing about diodes, or how to select what one I need (there appears to be hundreds to choose from).

I figure I could just use a 12v LED, but I'm not sure if that's the right answer or not.

FYI, the current would be low - these would be installed on the trigger side of a relay circuit.

HardRockCamaro · December 12, 2008, 04:58:07 AM

I can't remember my A-Level electronics very well..

Does this help?
http://www.allaboutcircuits.com/vol_3/chpt_3/1.html\" target=\"_blank\" rel=\"nofollow\">http://www.allaboutcircuits.com/vol_3/chpt_3/1.html

Jamieg285 · December 12, 2008, 05:55:51 AM

It explains what they are and how they work, but not how to work out/choose what one you need for my application.

There's all sorts of types, and then different versions within those types.

Big Mouse · December 12, 2008, 07:06:34 AM

Sorry, wrong thread, I thought it said dildos - damn dyslexia

ianjpage · December 12, 2008, 07:24:19 AM

Incursus · December 12, 2008, 08:44:43 AM

Quoting: Big Mouse

Sorry, wrong thread, I thought it said dildos - damn dyslexia

Jamieg285 · December 12, 2008, 08:50:50 AM

Quoting: Big Mouse

Sorry, wrong thread, I thought it said dildos - damn dyslexia

Were you coming in to post expert advice, or learn something

ianjpage · December 12, 2008, 09:27:03 AM

haha

nick69 · December 12, 2008, 09:54:31 AM

You could use an LED as you said. It could be a check light for correct operation. Just make sure you install it/them reversed biased.

Jamieg285 · December 12, 2008, 11:04:20 AM

Quoting: nick69

it/them reversed biased.

Whatever that is

Gator · December 12, 2008, 11:29:14 AM

i think you are saying you want a diode across a relay to prevent back feed

is the relay normaly open or closed ?

what is the current draw if you know this you could go to maplins and ask for the relevant diode ?

why do you think you need a diode ?

Jamieg285 · December 12, 2008, 11:55:44 AM

I'm setting up a circuit for reverse polarity motors (windows), using 3 relays and 1 mom/off/mom switch.

Up works fine, but he down would earth through the up side, unless there is a diode in place to stop the current going the wrong way.

Please excuse the crudety of the pic:

When switch is set to Up, it activates relays 1 & 2 (which control the polarity) and 3, which activates the main power. All good. When down, I want to activate relay 3, but leave 1 & 2 as is. I figure I need a diode at point X to prevent a reverse circuit activating the relays 1&2?

Gator · December 12, 2008, 12:25:23 PM

not sure what your after here what is it actualy for ?

but i am pretty sure so far a diode wont help but it can be done with relays

FUBAR · December 12, 2008, 12:27:52 PM

Quoting: Gator

not sure what your after here what is it actualy for ?

Electric Windows, so normal current to put the windows up & reverse to run the motor the other way & bring them down

Gator · December 12, 2008, 01:05:05 PM

Jamieg285 · December 12, 2008, 02:09:48 PM

that works if you have the GM switch/or similar, that deals with the reverse polarity internally. Being akward, I want to do it with custom switches.

Gator · December 12, 2008, 02:28:23 PM

a switch is a switch

Titsy · December 12, 2008, 04:53:07 PM

Far to complicated my friend... all you need is a double pole momentry-off-momentry switch and wire as follows...

Titsy · December 12, 2008, 04:54:05 PM

Don't forget the fuse...

Jamieg285 · December 12, 2008, 06:06:37 PM

I have seen a double pole switch, and agree it would be a simpler solution. The problem is I have a very specific switch design requirement, and so far I've only found a single pole. I will keep looking though.

Gator · December 13, 2008, 03:34:52 AM

but you just cant use a single pole it wont work you need to do it as per titsy's diagram with a double pole switch

you could use 2 single poles per window but that would be pants

Titsy · December 13, 2008, 04:33:17 AM

Or how about this version using push switches...

HardRockCamaro · December 13, 2008, 07:05:50 AM

I'm pretty sure that blocking diodes allow *some* current to pass through as well...

Gator · December 13, 2008, 08:47:34 AM

Quoting: HardRockCamaro

I'm pretty sure that blocking diodes allow *some* current to pass through as well..

they do mate

Jamieg285 · December 13, 2008, 08:48:22 AM

The push button circuit still uses 2 switches per window, so that is out.

I can't see why it can't be done with single pole switches. In the design I have done the switch makes 2 operations - activate relay 3 to provide power to the windows, and activate (or not) relays 1 & 2 to control the polarity.

What I need to do is be able to isolate these two actions. I may need to add a 4th relay, so UP does relays 1,2 & 3, whereas down just does 4 (which has the same function as 3 - provide power)