Friday, March 21, 2008

Installing LED Lights and Fixing the LED Flasher

I received a shipment of 3-watt LED lamps and a low-load flasher relay from yesterday. The bulb bases were the same, so replacing the bulbs was easy. I ordered the CF13GL-02 LED flasher relay, which is a plug-in replacement for the Porsche 914 relay and responds to the much lower current pulled by the LED lamps.

After installing everything, I found out that the LED flasher was able to detect such a low bulb current, that it was stuck in the "on" mode (relay clicking) all the time. I measured 3 MegaOhms between the bulb output terminal and ground, even with all the lights turned off. I'm guessing this probably comes from leakage through grease or other leaky paths in the system.

Soooooo, I guess it's time to reverse-engineer yet another component that doesn't work...

Here's my dining room table with the test setup. I drew out the schematic of the LED flasher and got the datasheet for the PNP transistor that was activating the circuit.

Here's the modified flasher relay. Without going into too many details, I replaced one resistor and shunted one terminal to 12V with another resistor so that the input ignores loads with a higher resistance than about 200K ohms.

I'm a bit discouraged that people are selling this relay knowing it doesn't shut off in a real automotive environment.

Addendum: Here is the partial schematic for the LED flasher with suggested hack to fix the flashing problem with a leaky terminal.

Ah well, I'm happy with the results, and the flashing LEDs look great.



pjorg said...

Please post the schematic. Glad you have off on Friday's to help out all the rest of us.



TimK said...

Buggers, I shouldn't have offered to draw the schematic. (Thanks, Paul :)

Joe said...

A) Thanks for trouble shooting another feature. I was also planning on replacing the blubs with LEDs. Mainly because the DC/DC converting blowing, but also the amp draw for the lights seemed a bit high for an electric car.
B) Once you have the new lights in place, do you tink you could post the amp draw before and after?


TimK said...

Hi Joe,

I'm a bit busy this week preparing the car for the Better Living Show in Portland, so please remind me in a week or too if I don't get to it. Adding the series current shunt took awhile, so I'm not too motivated to do it again. :)


Unknown said...

Couldn't you make a flasher out of a 555? I have seen schematics on how to replace a standard relay flasher with a 555 for silent operation.

TimK said...

Hi Carlo,

I actually rather hear the click from the relay because the turn signal indicator on the dash doesn't light and the click lets me know if I accidentally left the flashers on. It also lets me know if I left the parking brake on :).