LED Bulb Change - Hazard Issue

[Kodename47]

Today I changed my LED bulbs to a much better variety, however I now have a bit of an odd issue. The indicators run fine, and the hazards flash correctly when the car is running but if I turn them on when the engine is not running I get a single, half flash and that's it. The same thing happens when I lock and unlock the car, so I only get one brief flash. It's almost as if it needs more power than cab be provided when the alternator isn't running. I also noted that if I have just had the car running it might flash twice before it stops.

The bulbs I have fitted are these ones.

I've done the OEM flasher mod as per this thread and this thread. I used a 120mΩ ±5% 3W resistor but I cant find any genuine info on the new bulbs to work out the current draw etc. Paging @Wil and @catsspat

[stevesnj]

Just get this flasher and you'll be good

https://www.amazon.com/81980-50030-0.../dp/B008C9YS0Y

[Kodename47]

Originally Posted by stevesnj

Just get this flasher and you'll be good

https://www.amazon.com/81980-50030-0.../dp/B008C9YS0Y

I've got one sat in the draw, the OEM modded one is better as it doesn't have the delayed 1st blink that I found irritating with the cheaper eBay/Amazon relays. I was surprised that wasn't a link to TapTurn. If I suspect that the relay is the issue then I'll yank it out and get that sorted before I fit the "LED" relay back in. If it wasn't raining hard I'd have tried it to prove it out my theory.

It's hard finding info on the LEDs, the eBay add just states 50W which isn't helpful. I've found info that the 2835 is likely to be ~0.2W per LED and there's 30 on the bulb so I assume that means it's 6W per bulb. If so that means I should really reduce down the resistor that I'm using in the relay to ~70mOhm from the 120mOhm that's currently in there.

I'll also add that when I put the 1st bulb in with my old LEDs in the other 3 corners it worked fine, it was only when I added a 2nd one in that I encountered these symptoms.

[stevesnj]

Just a suggestion, I don't mind the delay. I think ahead . :P

[steve99]

guessing here
car running voltage about 14v
car off about 12.5


the led or flasher electronics may always alter current draw so power output is constant so you will draw more current when car off. Might be right on some limit of flasher.

[Kodename47]

Originally Posted by steve99

guessing here
car running voltage about 14v
car off about 12.5

the led or flasher electronics may always alter current draw so power output is constant so you will draw more current when car off. Might be right on some limit of flasher

This is my thinking, I keep on coming back to this:

Originally Posted by catsspat

Note dead bulb detection logic is disabled when you run hazards because now you're running 4 bulbs, even though the detection logic was calibrated for 2 bulbs. However, even during hazards operation, all power goes through the shunt resistor.

So if my theory is correct (I haven't done electronics in over 10 years)
I=V/R
My resistance is constant but the voltage drops enough that it can't provide enough current to turn on the LEDs. As above, reducing the resistance will sort this problem.

I just wish I knew for certain the power of the bulbs, I've no longer got a multimeter that I can test current draw through.

[steve99]

Brz wiring. https://www.google.com.au/url?sa=t&r...wTIabWl0Jc6WWw


Wont be as simple as v=i\r with semiconductors electronics and leds in circuit, basic equation holds true. But the flasher eldctronics may limit current alter voltage depending on load leds like stock filemnt bilbs dont have constant resistance

Even stock bulbs resistance will change with filiment temp

Who knows whats in the flasher box

As above guy said probably has blown bulb detection possibly over current protection ?? Who knows

https://electronics.stackexchange.co...y-drive-an-led

[Kodename47]

Originally Posted by steve99

But the flasher eldctronics may limit current alter voltage depending on load leds like stock filemnt bilbs dont have constant resistance

Stock bulbs draw more current, they're higher wattage, so it's not going to be a current limiting issue. Also if it was a current limiting, then it wouldn't change when the car is running seeing as LEDs have stated current draw and therefore power consumption.

Originally Posted by steve99

Even stock bulbs resistance will change with filiment temp

Yep, not really relevant here though.

As I said, I've not had this issue until now and I've been running the same setup previously for 2 years. The only thing that's changed is that the new bulbs are undoubtedly higher wattage. The OEM relay has 20mOhm shunt resistor for 21W bulbs, so as the bulb power reduces the resistor should increase. I was obviously within tolerance before, although I never tested the blown bulb feature with it. The modded OEM flasher is better than the cheap aftermarket ones so I would rather fix the issue than just put the other flasher back in.

[Kodename47]

I'd just like to confirm that the LED flasher works as expected. OEM flasher resistor changed to 80mOhm and re-installed and it now works correctly and I've confirmed that you get failed bulb detection as well.

The distributor on eBay said that these were 3W but I reckon that they're closer to 6W based on the light output, which is great. I'm finally 100% happy with the indicators which I wasn't with previous lights.

Old vs New