Thursday 7 January 2016

12v LED indicator bulbs for Chrysler grand voyager

A short post this one, but I noticed the orange colour was fading from my rear indicators on my Chrysler Grand Voyager.

This is a common problem on many cars now, as they use clear lenses and an orange bulb to make the indicator orange. This 'solution' to me is flawed and since its the bulbs with an orange paint on them, over time the pain burns off/fades which is what happened with mine and the indicator now looks white rather than orange (This is an MOT fail here in the UK, and as my MOT is due I needed to sort it)

So I found these LEDs on an ebay listing

They are ORANGE 581 BAU15s PY21 replacement LED bulbs in the same package, etc.
One warning that I saw on the Chrysler Grand Voyager forums is that the voyagers electrical wiring is non-standard and actually has positive on the surround and negative on the central pin. On normal bulbs this isn't a problem as they don't care about polarity, but LED's require + and - polarity so this could have been an issue.
I did a test with my multimeter on the pins and verified that this was NOT the case though, the central pin was positive like on all other vehicles as standard, so first issue out of the way.

The bulbs fit into the holders fine, and then into the external bulb/reflectors fine too, so these are the right size and shape.
Testing them with the hazard indicators on, all looks good, swapped them and they were blinking away and brightness looked ok (I did expect a little brighter to be honest, but they were comparable to the existing ones).

So all was well.
Until the next day when I actually drove to work, and realised that when I put the indicators on I got the dreaded 'fast flash' or hyperflash as some people call it. This is where the indicator bulbs flash very quickly. Most cars were designed to have a load from the bulbs and this allowed them to flash at a normal pace. When a short or an open circuit (bulb failure) was detected, the current consumed dropped and this causes the flasher unit to flash faster, the idea being that it was then easy to tell when a bulb had failed and needed replacing.
Unfortunately the LEDs consume a lot less current than the original bulbs and so this was causing the circuit to think the bulb was missing, when in fact all the bulbs and LEDs were lighting up correctly.

Doing a bit of maths I can calculate the difference.
These are 24LED units, and assuming an LED voltage of 2v for orange and estimating at 25mA per LED, adding that up we get 0.05 watts at 2v per LED. Multiple by 24 and we get 1.2 watts in total.
The usual bulb consumes 21 watts, so there is a difference of 19.8 watts, which is quite significant and obviously what the car is detecting and causing the fast flash.

There is a solution, this is to use a load resistor. This is effectively a resistor across the terminals (shunting the voltage/power through the resistor as well as the LED) which causes a higher current to flow and the indicator circuit to think it has a valid bulb installed.
This has several problems for me, firstly it's a waste. We would be wasting current shunting it through a resistor effectively wasting this current through heating the resistor up. Secondly you have to cut into the wiring loom and install this load resistor which is untidy and messy. I'm also not sure if this will stop the bulb sensing for the other bulbs in the indicator circuit (I only swapped the rear to LED, front are still standard). So this to me isn't a good solution.
I still did the maths to calculate what resistor I'd need.
So for 19watts at 12v this is 1.58 amps.
So using Ohms law (V = ir) I could calculate the resistor size. So 12 = 1.58R, and calculating that it comes out at 8.2 Ω (Ohms)
So if I were to install a load resistor it would need to be an 8.2 Ohm 19 (or 20) watt resistor. (Which are the larger ceramic style rectangular units as they are dissipating so much wattage)

Therefore I'm thinking of swapping and going back to the regular bulbs rather than LEDs as don't think this solution is quite right. I'm open to comments though, please let me know your thoughts.

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