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Constantley blows main beam

 
 
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Mouse
Just got MTs


Joined: 07 Feb 2007
Odometer: 185
Location: Kent



PostPosted: Fri Mar 17, 2017 6:17 pm    Post subject: Constantley blows main beam Reply with quote

Hi there
Just recently I have been having trouble with headlight bulbs blowing on my 1992 discovery 200tdi.
It is only the main beam element that blows and they seem to do it in pairs, i.e. both sides at once.
So far I have done 3 pairs in the past eight weeks or so, I am not using main at night only to flash so do not understand how this is happening, they are not cheap bulbs (osram night breakers and Philips blue extreme).
The other thing that might be connected is that at nights I have noticed that my lights go dim and then brighten up, also sometimes my taco (electronic) bounces between 0 and 4000 rpm although this does not seem to coincide with the dimming/brightening.
I have been to a auto electrician who can only suggest a new alternator but cannot say if this will cure the problem.
Can anyone shed any light on this, (Pardon the pun Wink )

Thank you
Mouse.
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mike328
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Joined: 10 Dec 2014
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PostPosted: Fri Mar 17, 2017 9:12 pm    Post subject: Reply with quote

voltage regulator faulty on alternator could definitely blow bulbs, try sticking a volt meter on it and revving engine to make sure you're not getting more than 14.5(ish)Volts...
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Mouse
Just got MTs


Joined: 07 Feb 2007
Odometer: 185
Location: Kent



PostPosted: Sat Mar 18, 2017 10:00 am    Post subject: Reply with quote

Hi
alternator has been checked and seems to be working o.k., if a bit high, (according to auto electrician).

What is most confusing is the fact that only main element blows on both sides because high beam has only been used to flash recently.

It has been suggested to change alternator but this is a bit expensive and might not cure the problem

Mouse.
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Jim1064
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Joined: 22 Feb 2009
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PostPosted: Sat Mar 18, 2017 11:45 am    Post subject: Reply with quote

mike328 wrote:
voltage regulator faulty on alternator could definitely blow bulbs, try sticking a volt meter on it and revving engine to make sure you're not getting more than 14.5(ish)Volts...


I once had that same problem. Intermittent fault on voltage regulator. It fried the ECU before I got a chance to replace it Mad

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Mouse
Just got MTs


Joined: 07 Feb 2007
Odometer: 185
Location: Kent



PostPosted: Mon Mar 20, 2017 8:35 pm    Post subject: Reply with quote

Mummm thanks for that, looks like a new alternator then Crying or Very sad .

Mouse.
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Xpajun
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Joined: 22 Sep 2008
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1988 Mitsubishi Shogun

PostPosted: Tue Mar 21, 2017 8:06 am    Post subject: Reply with quote

Try a diferent make of bulb before the alternator - strange that it's only the high beam that blows
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Mouse
Just got MTs


Joined: 07 Feb 2007
Odometer: 185
Location: Kent



PostPosted: Tue Mar 21, 2017 9:13 am    Post subject: Reply with quote

Hi
Already been down that route, the bulbs have been osram night breakers Philips blue extreme and some from Halfords, bosch I think.

No one I have spoken to can explain why only the main goes and each side is on a separate relay and fuse, I know that at night I can see low beam get brighter and then dim and also the fog lights and dash lights do the same.

Only thing I can think is that when I flash a lot more current goes through and that is what blows the main element, don't know why though.

Mouse.
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
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1988 Mitsubishi Shogun

PostPosted: Tue Mar 21, 2017 1:21 pm    Post subject: Reply with quote

A light bulb is made up of lots of coils so say 100 coils equal a dipped bulb to get a brighter main (at the same voltage) you have to remove coils - each coil you remove makes the light successively brighter until you get to the premium light output - say 75 coils making that part of the bulb 25% brighter

If you increase the voltage to 15 or 17 volts or more (the sort of voltage that can be expected from an alternator with a bad regulator) that is more than a 25% overload, which will blow a main beam but not the dip because it has 25% more coils - it will burn brighter but not blow.

Does that make sense?

Back to your problem - it looks like it could be the alternator - you really need too check the voltage output especially at high revs just to make sure it is that, but unfortunately it does look like a new alternator
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Mouse
Just got MTs


Joined: 07 Feb 2007
Odometer: 185
Location: Kent



PostPosted: Fri Mar 24, 2017 3:52 pm    Post subject: Reply with quote

Hi

Thanks for the explanation makes perfect sense, I suppose that's how these 20% and 50% brighter bulbs work, less coils ???.

I checked my alternator output and it's 14.5 volts at tickover (about 800 rpm) but at max revs (3000 rpm) it's 19.5 volts so deffo looks like a new alternator Crying or Very sad .

Thanks to all of you for the reply's Very Happy
Mouse
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