Spec'ing diodes

[PolarBear]

Can someone help me understand diode specifications? I use Mouser Electronics to order most of what I need but I don't know how to specify a diode. Just looking to prevent backfeeding certain circuits in the car with the alarm wiring. The fields I am not sure about are;

If - Forward Current
Vf - Forward Voltage
Ir - Reverse Current
Mostly not sure what the forward voltage and reverse current mean.

I think this will work for me, but I am not positive http://www.mouser.com/ProductDetail/...52b0cCNtw3U%3d

[//<86TA>\\]

Forward voltage is just the voltage rating of the circuit in question. Reverse current is how much amperage the diode will be able to hold back without failing/shorting open. Not sure how to calculate what kind of reverse amperage your circuits will have however.

I.should have looked at the link first, uA should be miliamps, in this case it would appear the uA rating is what will leak back through the diode

http://www.radio-electronics.com/inf...cteristics.php

[PolarBear]

Originally Posted by //<86TA>\\

Forward voltage is just the voltage rating of the circuit in question. Reverse current is how much amperage the diode will be able to hold back without failing/shorting open. Not sure how to calculate what kind of reverse amperage your circuits will have however.

I.should have looked at the link first, uA should be miliamps, in this case it would appear the uA rating is what will leak back through the diode

http://www.radio-electronics.com/inf...cteristics.php

That link is helpful, thanks.

My circuit currents are not high, probably under 10 amps. I am just connecting the wire from the alarm to the running light circuit in the car. Without the diode the interior lights and the chime goes off when the alarm activates or is disabled since it flashes the lights. Previously I had the alarm connected to the turn signal circuits, there are two circuits in the alarms for lighting so I had one connected to each turn. With the running lights, this also seems to cause the headlight side of the circuit to get voltage and the headlight doors go crazy. I am not entirely sure why the headlight circuit is getting voltage, I have been chasing that for a long time.

The headlight and running lights are supposed to be independent, but something is back feeding voltage from the running light circuit and when I put the running lights on only, the headlight doors pop up. I think it has something to do with my HID setup since I think that is when I started having trouble with the whole headlight door, but I haven't followed up with it lately. I liked to put the running lights on to drive with the fog lights as DRLs but since the pop up doors I just stopped. Now since I have had the car all apart I just ran a new wire for the fog light relay to ignition instead of from the running light circuit so I can drive with the fogs on without the running lights.

[PolarBear]

I looked again at some other diodes, the one I listed was a 1.5V forward drop, which is a bit much IMO for the intended application I am looking for. Found some schottky which are under 500mV and approximately the same current ratings that I am wanting

[//<86TA>\\]

Had the same problem with my angry headlight. The feedback caused my high beams to stick on and the high beam light on the dash to stay partly lit at all times. Iirc something would blow a fuse too. I added a diode to the harness as well as an isolating relay, but the diode failed after a few months, never fixed it.

The headlight switch failing will also cause the doors to go up when only in the running light position.

[PolarBear]

Originally Posted by //<86TA>\\

Had the same problem with my angry headlight. The feedback caused my high beams to stick on and the high beam light on the dash to stay partly lit at all times. Iirc something would blow a fuse too. I added a diode to the harness as well as an isolating relay, but the diode failed after a few months, never fixed it.

The headlight switch failing will also cause the doors to go up when only in the running light position.

I tried a different switch and it still did it, so I don't think it has to do with the switch in my case. I'm pretty sure the headlight and running lights are completely separate, that is what I am having trouble understanding, there is no crossover, they are fed by different circuits. If I iam remembering correctly

[PolarBear]

Originally Posted by //<86TA>\\

The headlight switch failing will also cause the doors to go up when only in the running light position.

So I took the headlight switch apart again, there is no possible way it can actually fail short of the contacts getting carbon-ed up. When I opened mine it looks fine inside, all the contacts were bright after I cleaned the grease off.

I figured out why the headlights come up, it has to be something with the logic inside the headlight module. When I put the running lights on I get voltage at pin C on the module and when I put the headlights on I get voltage on the yellow wire as expected. When I turn everything off the voltage on both pins goes low, so it has to be something inside. I will ask on TGO if someone has figured out the logic inside them and see if they are repairable, I would think they are since almost all the components in there are basic, with only one IC.

I did use one of the diodes I bought to stop the ignition feed to the switch to stop back feeding into the running light circuit so the fogs wouldn't make the headlight doors from coming up. And I pulled the fuse from the alarm system lighting since the HLDs were also coming up.

[PolarBear]

Actually, I think I figured out a way to make them work. I tried pulling the brown wire off pin C, but with the pin floating the headlights came up automatically when I plugged it in, so I think the pin needs to be high or low. If I un-solder the pin or remove the wire and then jump that trace to the main yellow wire (it's either A or F, forget) it wouldn't be floating anymore and it would only see voltage from the yellow wire.

[PolarBear]

I found a few threads on TGO, Lon from TDS says that this can happen when you have headlight motors that need rebuilding. I think this is counter intuitive, but I think it is worth a shot since I know that my motors do need rebuild, one comes up sometimes and not the other.

[deadtrend1]

Originally Posted by PolarBear

I found a few threads on TGO, Lon from TDS says that this can happen when you have headlight motors that need rebuilding. I think this is counter intuitive, but I think it is worth a shot since I know that my motors do need rebuild, one comes up sometimes and not the other.

Yes, i've seen that happen. Like when you lock the car with the key fob and the lights move up and down real quickly and grind.

[PolarBear]

So I got the new headlight motor pucks installed and the headlights re-assembled and it fixed my headlight pop-up with the running lights. I was skeptical, but it fixed it.