Relays

Technical MGB discussion
ChargedAutoGT
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Re: Relays

Post by ChargedAutoGT » Sat Aug 01, 2020 11:29 pm

"although they seemed brighter the beam was poor"

I am trying to visualise what you mean by this please? are you saying bright, but the beam does not project as far ahead? or something else?

G

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Peter Cresswell
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Re: Relays

Post by Peter Cresswell » Mon Aug 03, 2020 11:25 am

"although they seemed brighter the beam was poor"
I think to understand this, you have to separate the bulb from the glass of the headlight unit.

As an example, a lighthouse typically these days uses a 250W halogen bulb. The light from this would be scattered 360 degrees from the top of the lighthouse. In order to concentrate the light and direct it into a beam, a lens is used which a rather complex system of prisms. This enables a concentrated beam of light to be seem 20 - 25 miles out at sea.

In the car headlight system, the bulb is obviously similar but much smaller. Again the light would be scattered everywhere and indeed would have difficulty illuminating an average sized living room. The lens in the case headlight units has two parts - the reflector and the glass lens. The reflector is parabolic and concentrates the light into a single beam, which then passes through the glass lens. The pattern on the glass dictates how the road in front of the car is illuminated at night. The design of the pattern is complex and it has to produce a pattern of light which doesn't dazzle oncoming drivers but still illuminates the kerb on the nearside. It also has to 'throw' light further down the road when on main beam, so the driver gets as early warning of hazards ahead.

It is the design of the pattern on the glass that produces the effect of "although they seemed brighter the beam was poor" which means the drivers view of the road ahead is compromised. So not all headlight units are the same and unfortunately it is a case of you get what you pay for, and whilst some manufactures spend a lot of time and effort to produce a headlight unit to provides excellent night vision, others don't!
I also suspect that the quality of the glass and the moulding that forms the pattern also plays a part in this.
The bottom line is that upgrading the bulbs to better modern technology might be disappointing as the beam shape hasn't changed.

Hope this helps as quick explanation of something that is quite complex.
Pete
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965

Allan T
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Re: Relays

Post by Allan T » Tue Aug 04, 2020 1:30 am

Hi Brian,

I think Peter has nailed it beautifully and thoroughly as usual.

But just to repeat what he says in a slightly different way, Duncan Rickards of Classic Car LEDs emphasises the importance of the reflectors and lenses you use with your new LED bulbs.

He sells and recommends Lucas, and I think you'll find he likes Cibie and Hella too.

I've no experience and no knowledge of the Owners' Club hardware - unless they're Wipac, in which case I wouldn't touch them with a bargepole.

Allan

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Peter Cresswell
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Re: Relays

Post by Peter Cresswell » Wed Nov 25, 2020 9:25 pm

Dave Wheatley wrote:
Fri Jul 24, 2020 10:16 am
Peter Cresswell wrote:
Thu Jul 23, 2020 4:28 pm
You need a 30A relay for headlights using 60/55 bulbs, so a relay for LED lighting (probably 5A) won't cope with the current. One 30A relay is ok to power both headlight units. Also if you use a thicker cable to run between the relay and as close as possible to the back of the headlight units, you get much brighter lights as well - and they are even better if you double wire the bulbs so the dipped beam stays on when you go to main beam! When on dipped beam at night try flashing main beam and you will see what I mean. Cibie headlight units should cope with the heat generated by doing this.
I find that led lighting dazzles me at night, so double wiring compounds the felony.

I wonder if double wiring is legal? Not a good suggestion for me anyway Peter.
I have returned to this topic to make a couple of extra observations based on Dave Wheatley's comment above.
I have recently bought an MG HS Exclusive which has automatic LED headlights. Firstly the position of the headlights is almost at roof level to my MGB, so any low car (or car with a low seating position) will get more dazzle from oncoming LED lights even though they are dipped as they have a very broad spread lighting the kerb on both sides of the road. I get this a lot when driving the Mercedes at night and more so when it is raining. Secondly the automatic dip function seems to me to be very slow at reacting to oncoming vehicles. On previous cars without this 'driver aid' I would have dipped my lights as soon as I saw the lights of an oncoming vehicle, but the HS waits much longer and until the oncoming vehicle is straight ahead the lights remain on main beam. If we meet on a left hand bend then often the lights don't dip at all! There is a 'sort of' warning in the drivers handbook about the need to be alert to oncoming vehicles at night, and I suspect this is true in any handbook of a modern car with auto dipping lights, but who reads the handbook???? I now have reverted to overriding the driver aid in the interests of safety.
Just wait until we share the road with autonomous cars!!!!
Pete
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2020 MG HS Exclusive
2007 Mercedes SLK
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Tom Brearley
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Re: Relays

Post by Tom Brearley » Thu Nov 26, 2020 8:27 pm

Pete, that's interesting. I didn't even know auto-dipping headlights were a 'thing'!

BTW, I am fitting relays to my headlight circuit and was wondering where's a good place to get the power feed from. Is the brown wire at the fuse box suitable? Or should I run a new feed up from the starter motor battery terminal?

Thanks :idea:
1973 MGB GT
Mallard Green / Autumn Leaf

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Charles Farran
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Re: Relays

Post by Charles Farran » Thu Nov 26, 2020 8:34 pm

Tom,
It's best to run a new feed up from the back of the starter motor & take the opportunity to fuse the new feed. (Some separately fuse the connection from each relay to the main & low beam bulbs).
Cheers,
Charles
1980 Roadster

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Tom Brearley
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Re: Relays

Post by Tom Brearley » Fri Nov 27, 2020 7:14 pm

Charles, I was afraid you'd say that! I have a starter motor cover fitted and it's a b*gger to get on and off.

Thanks
1973 MGB GT
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Charles Farran
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Re: Relays

Post by Charles Farran » Fri Nov 27, 2020 8:49 pm

Tom,
They aee indeed.
I found it harder to get it back on.
It's easier if you eigher leave the cover in strong sunlight or use something like a hair dryer or fan heater which softens up the cover which enables you to ease it back on!
Cheers,
Charles
1980 Roadster

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Tom Brearley
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Re: Relays

Post by Tom Brearley » Sat Nov 28, 2020 9:02 pm

On another forum I saw that someone had taken their power feed from the starter motor relay. As it's a lot more accessible than the starter motor itself, I've adopted that approach. The brown feed up to the starter relay is presumably doing nothing most of the time, so it seems a reasonable place to tap into without overloading things. But I'll do some precautionary test driving next and see if it gets hot.
1973 MGB GT
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Michael Barclay
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Re: Relays

Post by Michael Barclay » Tue Dec 01, 2020 5:28 pm

Hi Tom
I fitted the relay mod to the Headlights about 4 years ago to reduce the current (≥10A) and volts drop through the switch gear. As i use my horn very rarely, I used the purple 12v wire going to the horns as the live feed for the relays. This is effectively connected via the bottom fuse in the fuse box to the main brown wire that comes from the starter motor. On the horn on the driver’s side where the purple wire connects there was a handy spare double spade terminal so i only need a very short run of wire to the relays if fitted down in the front close to the collection of bullet connectors to the headlight wiring.
I bought relay holders with inbuilt fuse holders so I could separately fuse the main and dip beams circuits.
Hope this is of help.
Best regards
Mike Barclay

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