Drive lights - delay to dip
Submitted: Tuesday, Sep 13, 2011 at 21:20
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Member - Allan K (NT)
Just recently my drive lights have developed a delay of 3-4 seconds between dipping the headlights and the drive lights going out. This doesn't win any friends on the road. The drive light relay (12V 100A) is only a couple of weeks old, but all worked OK after it was installed. The in-cabin switch extinguishes the drive lights instantly as it should. Has anyone seen this before? Better still does anyone know how to fix it? Many thanks in advance.
Reply By: Bushranger1 - Tuesday, Sep 13, 2011 at 21:52
Tuesday, Sep 13, 2011 at 21:52
G'day Allan,
I had a sticky relay on my
driving lights some years ago. Played up for a while & then while driving back to
Melbourne on the Princes hwy went to dip the lights & the
driving lights just stayed on!
I was real popular with the oncoming traffic trying to pull over as fast as I could without blinding everyone. I did not have a separate switch to disable them so
disconnected them for the trip
home then changed the relay & never had another problem with them till I sold the car.
For interest sake I pulled apart the failed relay & the contacts had fused together.
Hope this helps
Cheers
Stu
AnswerID:
464933
Follow Up By: Shaker - Wednesday, Sep 14, 2011 at 14:00
Wednesday, Sep 14, 2011 at 14:00
Maybe that is the reason it is mandatory to have an isolating switch?
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738911
Follow Up By: Polaris - Wednesday, Sep 14, 2011 at 20:46
Wednesday, Sep 14, 2011 at 20:46
If the contacts have fused together, an isolator switch wouldn't make any difference. The isolator is usually on the 'trigger' line from the high beam circuit - it only energises the coil in the relay.
The 'contacts' have +12V on one side and feed to the driving light on the other side.
FollowupID:
738968
Reply By: Member Al (Sunshine Coast) - Wednesday, Sep 14, 2011 at 08:39
Wednesday, Sep 14, 2011 at 08:39
Hi Allan, Allan here.
There are a number of possibilities but without knowing your exact wiring arrangement I can only suggest some possibilities.
The fact that the relay drops-out as soon as you operate the cabin switch suggests that it is not a sticky relay. The fact that the system worked OK following installation suggests that the circuit is correctly arranged.
What comes to mind is that the voltage applied to the relay is not falling to zero when the high-beam goes 'off'. In other words, enough voltage to hold the relay energised is still present when switching to low-beam. Some 12v relays only need several volts to 'hold-in'. This voltage could come via the high-beam filaments or the drive light filaments if their earth connection was not 100%. If you have a voltmeter apply it to the coil connections of the relay whilst it is in the faulty state and if it reads even just several volts, then it indicates that problem. If so,
check the quality of any earth points of your headlights and
driving lights.
A diode across the relay will not cure your problem, but it is a good thing to have anyway. Connect the diode directly across the relay coil with the "banded" end of the diode on the positive side of the coil. Get it the wrong way round and you create a short-circuit!
AnswerID:
464952
Follow Up By: Member - Allan K (NT) - Wednesday, Sep 14, 2011 at 19:11
Wednesday, Sep 14, 2011 at 19:11
Thanks for the input Allan. This afternoon I checked the earth wires from the lights and relay, the panel screw securing them to the firewall was not tight. I replaced it with a slightly larger gauge screw that screwed in tight. Still a 1 - 1.5 second delay, but noticeably quicker. The lights are wired with two pre-made looms (one was hella, one a "no-name" that I chopped and crimped connectors onto for the new relay. The relay uses a bolt/nut for the light side circuit and the more usual push on lugs for the trigger circuit. Looks like I might have to find some weekend time to re-wire using soldered connectors. I'm not sure how much latency there should be in a relay. I don't remember previous lights taking noticeably longer than the head lights to dip, but as there is physical switch of circuits so I guess there would be some lag, though it should be too short to be noticeable. I'll post further if I can eliminate all the delay.
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Follow Up By: Member - nick b - Wednesday, Sep 14, 2011 at 21:24
Wednesday, Sep 14, 2011 at 21:24
Allan A1 your quote : A diode across the relay will not cure your problem, but it is a good thing to have anyway. Q what does this do ?
cheers nick
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Follow Up By: Member Al (Sunshine Coast) - Wednesday, Sep 14, 2011 at 23:52
Wednesday, Sep 14, 2011 at 23:52
Nick,
Re diode: When a relay is de-energised, the magnetic energy collapses and in so doing generates an electrical charge. This electrical charge is in the reverse polarity to what was originally in the coil and can be much higher voltage than the original 12 volts. It thus creates a spike on the circuit which can cause problems especially for the electronic items connected in the wiring system. The action of the diode is to shunt this charge, effectively 'short circuit' it, and so prevent the creation of a voltage spike. Usually it is not essential as most of the electronic items now incorporate protection from spikes but can be used if you experience problems. Some relays have the diode built-in and so must be connected with due regard to polarity.
Note that the use of a diode will not solve Allan's lighting relay problem.
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