LED - what you don't know makes a difference

jay.pearlman · #1 01-11-2014, 10:26 PM

I have a nice panel built by Aerotronics with a wig-wag unit for the headlights offered by B&C specialty. It was designed for a standard bulb. Seduced by LEDs, I installed a AeroLED microsun rather than the tungsten and the wig-wag wouldn't wig or wag. I called Jason at Aerotronics and he said if I was having a problem, he has seen it tens of times. The solution (not to rewire and use the internal microsun wigwag) is to put a 75 ohm resistor in parallel with the headlight. However this doesn't work every time. Does anyone have experience with this solution using resistors? What value was used?

bullojm1 · #2 01-12-2014, 07:12 AM

Hi Jay,

I had the exact same issue with the B&C SSF-1 flasher. I was able to fix is by using 50ohm 10 watt wire wound resistors, which are available at Radio Shack (part number 271-133) instead of the specified 75 ohm resistor.

rzbill · #3 01-12-2014, 07:26 AM

Mike beat me to it.

The flasher is using current sensing to trigger to flip.
The LED by itself will not pass enough current to trigger the flasher.
Adding a 75 ohm resistor provides a "leak path" to increase the current that the flasher has to pass.

In your case, it appears that the LED plus resistor still is not passing enough current. Reducing the resistor size will increase the "leak". I was going to suggest cutting the resistance in half but Mikes handy reference to a Radio Shaft resistor is a good option.

I am mildly surprised that a solid state flasher still requires this. Maybe it is designed in as a failure indicator. The old style mechanical flashers used a bimetalic spring that was heated by current to make it "snap" over. This mechanism had to have enough current to work. That is why some old cars need the signal lights cleaned or jiggled to make them work.

bullojm1 · #4 01-12-2014, 02:54 PM

Quote:

Originally Posted by rzbill

I am mildly surprised that a solid state flasher still requires this.

The B&C SSF-1 is NOT 100% solid state. It has a mechanical relay in it. Here is B&C's description of it:

Quote:

Features solid-state relay driver electronics

This description is a little misleading. The electronics driving the relay are solid state - but there is still a mechanical relay used to drive the lights. This is the same flasher Amazon sells for $13 - the Tridon EL13A2, shipped free!

rzbill · #5 01-12-2014, 04:14 PM

Right. I was misled. I read it as all solid state.

johngoodman · #6 01-13-2014, 07:34 AM

This brings up a good point - I have a VP-200 and the wig-wag is part of it. I seriously doubt that there is any mechanical part in it for wig-wag, and assume it must be completely digital.
Anyway, I changed out my landing lights from Van's to LEDs last year, and everything is working fine. The only change is that there is very little amp increase with the LED lights - as expected.
John

jay.pearlman · #7 01-14-2014, 05:03 PM

John,
If you are changing from bulbs to LEDs, why is there a very little current increase? or even any increase? I would have expected less current.

rapid_ascent · #8 01-14-2014, 08:33 PM

I'm sure the VP-200 uses a FET as the switching element. These devices are very cheap, last forever and now days have very high current handling ability. Rarely are relays used these days in current designs for DC switching. They will eventually fail. It sounds like your flasher uses a primitive control circuit that makes use of the resistance of the bulb to create an RC time constant for the flashing function. I personally wouldn't just burn power with a "leak" resistor. I would find a new flasher that worked with LEDs. I'm sure many of these flasher designs have been around for a long time and have served their purpose sufficiently well but I wouldn't hack the circuit by adding the resistor. At 14V and P=V*V/R you will be burning 4 watts in that resistor not the end of the world but I'd look for a proper solution to quote my Brit friends at work.

johngoodman · #9 01-15-2014, 07:43 AM

Quote:

Originally Posted by jay.pearlman

John,
If you are changing from bulbs to LEDs, why is there a very little current increase? or even any increase? I would have expected less current.

I guess I wasn't specific enough - As apposed to the Van's bulbs, I see almost no amp increase with the LEDs. The Van's bulbs had a noticeable amp increase. In short, I love the LED landing lights, but I'm still afraid of the dark

John