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Diode
Lightning - 23/2/10 at 04:08 PM

What diode exactly would i want to put in a line to stop earthing back when off. This is for the fog as when switched on the relay for the headlights is earthing back when the lights are switched off.
I could get one from Maplins but being a bit dense dont know exactly what to get.

[Edited on 23/2/10 by Lightning]

ashg - 23/2/10 at 04:21 PM

3 amp would do it. about 30pence if i remember correctly

Lightning - 23/2/10 at 04:52 PM

I'll have to save up then

craig1410 - 23/2/10 at 07:47 PM

quote:
Originally posted by Lightning
What diode exactly would i want to put in a line to stop earthing back when off. This is for the fog as when switched on the relay for the headlights is earthing back when the lights are switched off.
I could get one from Maplins but being a bit dense dont know exactly what to get.

[Edited on 23/2/10 by Lightning]


What is happening? I don't understand why a diode would be necessary in a lighting circuit. It sounds like something isn't wired up properly. Can you draw or describe the circuit?

If you do decide to use a diode then be aware that you will drop between 0.6 and 0.7V in the diode itself when conducting. So, if you are expecting to flow 3A then you will need to dissipate around 2 watts of heat.

My advice is to review your wiring and try to avoid using a diode.

Cheers,
Craig.

Edit: Have you by any chance connected 12V to the relay and then the other relay terminal goes to earth via the switch? If so then if you were able to turn this the other way around then you probably wouldn't have a problem. Would need to see your wiring schematic though to be sure. Might depend on which stalks or switches you are using.

My setup has 12V going through my headlight switch to a branch. One branch goes to the headlight relay, the other goes to the fog light switch. My foglight switch other terminal connects via the bulb to earth and the headlight relay other terminal connects directly to earth. So it doesn't make any difference if my fog light switch is on or off unless the headlight switch is also on. Hope that makes sense.

[Edited on 23/2/2010 by craig1410]

Rosco - 23/2/10 at 11:35 PM

I share Craig's curiosity. Why would you want to put a diode in an earth circuit? If you have a high potential earth then it's most likely caused by a high resistance joint (bad connection) or under-sized cable. You do sometimes need to put a diode across an inductive load (like a relay coil), but this is a dymanic effect to allow dissipation of stored energy when you switch off the circuit. But your problem sounds more like a static problem.

Someone educate me, please.

Lightning - 24/2/10 at 11:51 AM

Any help would be greatly appreciated. I did this based on other threads. If its b*&%$ks then could you mark what you would suggest. This is one of only a couple of things to do before IVA

MikeRJ - 24/2/10 at 12:40 PM

Are you trying to only allow the fog lamp to be switched on when the headlamps are on, or just the sidelights?

If the latter you should be grounding your fog lamp via the brown ground wire. The Brown/black is grounded by the headlamp switch, or in your case by the fog lamp bulb.

[Edited on 24/2/10 by MikeRJ]

Lightning - 1/3/10 at 08:03 PM

well got my 23p diode today and it now all works fine. No fog light until the dip or main beam on. Possibly not the best solution but what the hell it works.