924Board.org

chrizzzie · Joined: 04 Feb 2004 Posts: 32

the black diode in my headlightmotor is broken but i can nowhere find a 14v/10amp.I tried a 5 amp but this one inmediatly began to smoke. Can somewhone please tell me if i can also use a different one (bigger or smaller) I life in Holand so i don't have anythings about adresses where I can buy these.

thank you Christiaan

924RACR · Posted: Tue Oct 12, 2004 10:27 pm Post subject:

Yes, I've replaced these myself successfully. It should be no special task to find a replacement over there at a place that sells electronic components, but of course, I'm in the US, can't help with recommendations. I have to say, I'm surprised that the diode would smoke on installation - have you confirmed that the motor and linkage tur and operate freely? It is possible that the motor itself is shorted out. Usually the only reason one of the diodes will burn out is due to the headlight linkage being blocked (possibly by body damage or misalignment), or by the motor being damaged.
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wdb · Joined: 02 Nov 2002 Posts: 2024

I know very little about electronics , but I believe diodes are one way streets , that is they have to beinstalled with the correct end in the correct direction ,or no electricity will flow .

chrizzzie · Joined: 04 Feb 2004 Posts: 32

hello,

yes it is possible that i maybe put the diode the worng way i'm going to check this. I asked a few electronic shops but no one had this diode. When i turned the motor on whitout the diode the motor worked fine except i offcourse needed to put the lights down myself, but this is why i think there is nothing wrong with the cables. There was something else strange, when i losen the diode on one side and I put on the headlights and than closed and after this made contact with the diode than the headlights went down.

chrizzzie · Joined: 04 Feb 2004 Posts: 32

hello,

the diode is installed right and I phoned around but nobody has a diode like this one or more than 10a

Paul · Posted: Wed Oct 13, 2004 10:04 am Post subject:

How about two 5 amp diodes wired in parallel?

chrizzzie · Joined: 04 Feb 2004 Posts: 32

a freind of my told the same but i was thinking if there was enough space and also because there are so much cables running on that spot

chrizzzie · Joined: 04 Feb 2004 Posts: 32

hi,

I thougt about a long time about my problem and i tried to put the diode the other way (the mark on the side where the power comes in) but now the motor kept on turning when i put the switch on but they went down when i switcht them off

Smoothie · Posted: Tue Mar 13, 2007 12:40 pm Post subject:

I just had my headlight motor apart over the weekend and couldn't find any of the "diodes" I've been reading about here and other places. Is this black plastic rectangular piece what we're calling a diode? -

I popped the cover off of it and it looks more like some kind of overheat safety switch to me. It has contacts and pops back and forth with a little bit of pressure applied -

Are we sure that's a diode - or am I looking at the wrong part? There's definitely nothing else in there that could be a diode as I know them. Any electrical engineers here still?
This is a 931 headlight motor - could it be that the 924NA version has diodes, but the 931s' doesn't?
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Ozzie · Posted: Tue Mar 13, 2007 3:08 pm Post subject:

Smoothie- your pic looks like a bi metal switch which would be a safety feature to prevent overheat and meltdown.

As for the diode- I haven't pulled the motor down in a long time and dont remember.
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Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

I think earlier cars were fitted with a diode. Then, they changed the wiring to the headlamp motor and did away with the need for the diode. Sorry, I don't know when the change was made.
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Peter_in_AU · Joined: 29 Jul 2001 Posts: 2745 Location: Sydney, Australia

Pre-1979 cars had two diodes in the headlight motor. Have a look in the current-flow diagrams in Haynes.

Putting a diode in the wrong way around will not damage it. The circuit just won't work or won't work as expected.

Wiring two or more diodes of a lower current rating in parallel will work assuming you have the space.
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Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Generally, speaking as a practitioner in the electronics industry, it is considered bad practice to wire diodes in parallel.

What happens is one diode turns on (starts to conduct) at a slightly lower voltage than another; this diode then prevents the voltage from rising any further (which is what diodes are designed to do) and so prevents the other diode(s) from turning on. I.e. the first diode to conduct tends to take the lion's share (if not all!) the current.

In an application like this, where the diodes are only conducting for a short time (the time it takes to raise the headlamps), you might get away with it, if you use 'matched' diodes, i.e. the same type and preferrabbly from the same batch.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

What you want is a Schottky barrier rectifier (diode).

The 80SQ range is rated at 8 A, but will probably be OK for your needs.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Smoothie · Posted: Tue Mar 13, 2007 10:41 pm Post subject:

Thanks.