Daytime running lights

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Re: Daytime running lights

Post by RichardW » 02 Feb 2017, 13:57

Original bulbs are 24W, which gives a resistance of 6ohm (R=V²/P). LEDs looks to be 7.5W (you can get them on e-bay), which gives a resistance of 19.2 ohm. Parallel resistances sum by the inverse (ie 1/R1 +1/R2 = 1/Rtot) so applying this for the LED to get the total gives a resistor of 8.7 ohm. On 12V this gives a resistor power of 16.5W

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Re: Daytime running lights

Post by GiveMeABreak » 02 Feb 2017, 14:47

We've moved onto the Angular lighting - these are the HP19W Angular bulbs in the X7 equipped with the Xenon headlamp unit Richard (the non-xenon angular lights take an H7) and these HP19Ws are 19 Watts, not the HP24W DRL which are 24 Watts. I've already done the DRLs and the specific LEDs I used don't need additional load resistors, but the angular lighting replacements indicate otherwise on at least 2 types of LEDs that have been fitted by others - so would appear to need external resistors, otherwise they flash on and off. It is sometimes hard to tell what resistance is already built into some of the CANBUS LEDs as not all suppliers list this information. This example I think clarifies this where no additional resistance is needed with one LED type on the original 24W DRL bulb fitment wiring circuit, yet other LEDs do need additional resistors on the 19W bulb fitment wiring circuit.

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Re: Daytime running lights

Post by Paul-R » 02 Feb 2017, 15:20

RichardW wrote:Original bulbs are 24W, which gives a resistance of 6ohm (R=V²/P). LEDs looks to be 7.5W (you can get them on e-bay), which gives a resistance of 19.2 ohm. Parallel resistances sum by the inverse (ie 1/R1 +1/R2 = 1/Rtot) so applying this for the LED to get the total gives a resistor of 8.7 ohm. On 12V this gives a resistor power of 16.5W
Accepting that the discussion is for a different bulb now, you can easily see what wattage a shunt resistor must dissipate by subtracting one bulb from the other. So any shunt resistor has to have at least that capacity.

My thoughts are that maybe the resistance needed is not as linearly straight forward as you have worked out and that, say, a 24 ohm resistor will provide enough shunt current to fool the BSI. At 12v this will shunt half an Amp and therefore dissipate 6w meaning a 10W resistor would be needed. Experimentation may be the only way to find out for sure but it seems ridiculous to me to have to waste power in this way.

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Re: Daytime running lights

Post by Paul-R » 02 Feb 2017, 15:25

Alternatively, is the flashing of the LEDs a characteristic of the LED itself? Has anyone tried putting capacitors across the LED to shunt any possible oscillation away? These would not consume power in the same way as a resistor and be a much more satisfactory answer if proven to work.

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Re: Daytime running lights

Post by Paul-R » 02 Feb 2017, 16:13

And another thought!

Has anyone run a multimeter across the cables feeding an LED when it's flashing? Does the voltage drop in and out - which would imply that the BSI really is causing the flashing - or not?

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Re: Daytime running lights

Post by myglaren » 02 Feb 2017, 18:11

Paul-R wrote: Experimentation may be the only way to find out for sure but it seems ridiculous to me to have to waste power in this way.
Agreed - it seems ludicrous to use low- consumption LEDs than have to waste power and money with shunt resistors - that probably cost more than the LEDs too.

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Re: Daytime running lights

Post by GiveMeABreak » 02 Feb 2017, 18:45

I'm still deliberating - still not happy with any I have seen so far - but may take the plunge as soon as this flaming rain stops.

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Re: Daytime running lights

Post by GiveMeABreak » 02 Feb 2017, 21:49

So using my calculations for a 19W Original, this would give 7.58 Ohms and 1.58 Amps. Using the same 7.5 LED, this would give a total of 12.52 Ohms and 11.50 Watts.

The problem is, as I think I mentioned earlier somewhere is that there is the power that they give for the LEDs can sometimes vary - as in this example, I managed to track down further specs of these '7.5W' LEDs. The LED Quantity is 5 Pieces (5 x 1.5W = 7.5W), but the power consumption is stated as 2.38W.

So using that as the power figure for the '7.5W LED' would give 60.50 Ohms and a Current of 0.20 Amps, giving a total of 8.66 Ohms and 16.62 Watts .. or have I lost the plot completely now? :shock:

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Re: Daytime running lights

Post by xf1ref » 03 Feb 2017, 23:27

First I tried the LEDs without resistors but was making just one flash and not repetitive flashes. No error found with diagbox :?
The only way is to try different resistor values for same power in order to have consumption as low as possible...for example 10ohm, 15ohm etc until the Led start to flash. The easiest way is to have a variable resistor to do tests.
Also from what I know the resistance of the filament when is glowing is different compared when the bulb is not powered...but I think we don't need to complicate this.

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Re: Daytime running lights

Post by Paul-R » 04 Feb 2017, 12:17

Marc - some simple figures.

The 19w original bulb will use ~1.58A at 12v as you worked out. But there is an easier way.

In order to use the same current with a nominal 7.5w LED you would have to sink 19W - 7.5W = 12.5W of power through a bypass resistor. This is near enough to 1A as to make no difference. Therefore the resistor should have a value of 12/1 Ohms i.e. 12 Ohms and have a power dissipation capacity of at least 12W.

There are a few provisos here though. First of all if the LED actually consumes much less power (2.38W) than stated then the bypass resistor will have to have a lower value and higher power rating. Going through the figures:

19W - 2.38W = 16.62W power must be shunted and this will flow 16.62/12 Amps = 1.39A. This will need a resistance of 12/1.39 Ohms = 8.63 Ohms.

Frankly this is all theoretical and as xf1ref says I would just wire a few different values in to see what happens. I would always start off high as these will be cheaper and not have to dissipate so much power. For starters I would match the nominal value of the LED bulb - i.e. a 12 Ohm 7.5W resistor.

In fact there's a handy resistor of just such a value hanging around - the other LED! What happens if you temporarily put two LEDs in parallel? This may not be entirely valid but it would be a starting point.

I still have some questions that need answering first as I posted above.

is the flashing of the LEDs a characteristic of the LED itself?
Has anyone tried putting capacitors across the LED to shunt any possible oscillation away?
Has anyone run a multimeter across the cables feeding an LED when it's flashing?
Does the voltage drop in and out - which would imply that the BSI really is causing the flashing - or not?

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Re: Daytime running lights

Post by GiveMeABreak » 04 Feb 2017, 13:43

Thanks Paul - I'm out in the car now taking out the DRLs at present (not the HP19s) as I need to make a further modification to the LED.

Regarding these flipping resistors:

Lets assume I am going for an LED that is a 50W (that has 10 x 5W Cree LEDS) - the actual power consumption for this bulb is 3.24W. So doing all the calcs, this will need a resistance of 9.14 Ohms - so a 10 Ohm will be the nearest I can probably get. However these are available in 20W (10 Ohm) or 50W (10 Ohm). From what I have picked up it is recommended to get the 50 Watt resistors as these babies are seriously hot after only a few seconds of operation! This was from some guy who fitted the 20 Watt one initially using this specification of LED for his HP19W replacement.

Thankfully, these are only for the angular bend lighting, so won't be on for very long. But as our friend in Romania, xf1ref says in a previous post, these resistors will likely need to be mounted outside of the bulb housing due to the heat involved.

It's tighter than a crab's rear with the Xenon lamp unit housing with all the tubing for the washer jets and cabling, so I'm going to have another look once I've done this DRL Mod to see where I could mount the HP19W Resistors.

This is such fun!

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Re: Daytime running lights

Post by Paul-R » 04 Feb 2017, 14:57

I'm supposed to be working on my own car so I'll look at the bulk of your post later but there's one thing that stands out.
GiveMeABreak wrote:Lets assume I am going for an LED that is a 50W (that has 10 x 5W Cree LEDS) - the actual power consumption for this bulb is 3.24W.
That doesn't actually make sense unless they mean that each LED is equivalent to an ordinary 5W bulb. That would kind of make sense if the actual power consumption is a tenth, or less, than a halogen incandescent bulb. A halogen bulb is already a bit more efficient, about 10%, than an ordinary incandescent bulb of course.

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Re: Daytime running lights

Post by GiveMeABreak » 04 Feb 2017, 15:30

That's what they must mean as most of them state these Wattages for each LED. Anyway - I'm not in a good mood, as the flaming LED popped it's socket after the MOD when trying to replace it into the DRL Lens socket under the headlamp. It is now probably floating somewhere in the bumper bay! After all that work. Back to the web to order some new ones now... :twisted:

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Re: Daytime running lights

Post by GiveMeABreak » 04 Feb 2017, 17:44

Right stress over. I should of followed my own advice and padded out the space under the headlamp with a towel to prevent the bulb dropping into the ether if it comes out the holder :roll:

So now these were the original replacement LEDs that I had. I should of realised when I first installed these that for the X7 DRL, the replacement LED does not need a projection lens as that is effectively focussing the top LED into the sky as these DRLs lean out at an angle of about 20 - 30° when mounted in the housing. It is therefore better to remove the top lens (I used a Dremel with a cutting wheel) and then once the fish eye has been levelled, I carefully ground out the plastic a mm or so using a grinding stone. Then I got a needle type screwdriver bit and picked out the remaining glue and lens material. This will now allow the top LED light to be diffused about the cavity and provide a bit more light as you can see in the second and third pictures. These had a claimed 580 Lumens per bulb.
Old 7_5W DRL Plasma Crees.png
Old 7.5W DRL Plasma Cree
Old 7_5W DRL Plasma Crees.png (180.65 KiB) Viewed 192 times
LED Focussed B.png
LED Dispersal With Top Lens
LED Diffused A.png
LED Dispersal Without Top Lens

Now that I managed to drop one of the LEDs into the Bumper area, I've decided to try a newer LED, picture below:
Old 7.5W DRL Plasma Crees.png
New XB-D Cree
Old 7.5W DRL Plasma Crees.png (119.13 KiB) Viewed 192 times
These new ones have a claimed 850 lumens per bulb. :shock: 8-)

Roll on delivery date and this time I must remember to shove a towel down the headlamp recess!

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Re: Daytime running lights

Post by GiveMeABreak » 08 Feb 2017, 15:07

xf1ref wrote:I think this led's are the brightest version but I don't know how long they will survive. When I tested the resistor I noticed that is becoming very hot after aprox. 1 minute but for cornering light this is ok because the running time is generally small. Just in case, with the resistor glued on cover I do not recommend to stay with the cornering light on more than 1 minute.
OK, I've replaced the HP24Ws again today with the new Cree XBD LEDs that arrived this morning and managed to keep all my skin :-D . I used the dremel to remove the plastic projector lenses - although these were freely rotating so made it a lot more difficult to do.

While I was there I looked again at the Angular HP19W bulbs. Now I can get the cap off ok with a flat bladed screwdriver - but I cannot seem to move / pull / twist the bulb holder at all! How do you get this thing off and out? As usual, Citroen service has all the procedures for every other bulb in the headlamp except this one! No diagram no nothing - not even mentioned. Is this supposed to be twisted off or pulled off as the wire does not seem to have a plug - it looks moulded into one and I cannot move any of it - it looks stuck solid!