I have fitted LED indicators to an old motorcycle with flasher relay designed for LEDs. They work fine when engine is not running but when engine is running they flash very fast and eratic. I asume this is interference from the single phase alternator. How can I provide supression to indicator circuit. Would a 12v zener provide a fix or a large capacitor? I have limited knowledge of electronics but could fit the necessary componants if I had a diagram of what to fit. Any help would be much appreciated.

 

Before I would worry about alternator noise I would look at the non running verse running system voltage. I have no idea what make or model bike you have but less using a turn signal flasher designed for LED as you have done the common trick when installing LEDs on a bike designed for incandescent lamps was to add a few load balancing resistors turn signal line to ground (common). While I have no idea how the turn signal flashers designed for LEDs actually work I would see how much the system voltage increases during running.

When I went with the LEDs on my bike I just added the load resistors and they worked fine for what I had. My system voltage was about 12.6 VDC not running and about 14 VDC when running. The bike is an older 92 Harley. Anyway, I would look for a voltage change before I worried about noise on the alternator.

Ron

 

If it was me I would probably try adding a diode in series and a capacitor in parallel with the LED load. This is a pretty simple way of smoothing the supply to the load. It may not be enough and you may need something fancier, but it might do the job.

Check the voltage on the capacitor if you try this. As @Reloadron notes, your erratic flashing could be a sign of over voltage.

 

If it was me I would probably try adding a diode in series and a capacitor in parallel with the LED load. This is a pretty simple way of smoothing the supply to the load. It may not be enough and you may need something fancier, but it might do the job.

Check the voltage on the capacitor if you try this. As @Reloadron notes, your erratic flashing could be a sign of over voltage.

Than you Ron & Wayneh for you replies. To check voltage effect on operation I disconnected supply from battery to flasher relay and replaced it with a variable bench power supply. The indicators worked fine from as low as 9 volts up to 14 volts. I did not want to go any higher. What I should have done is started engine while I was making this test to see if problem was there with external supply. I will do that today. I have also ordered a new relay in case that is the problem . Thanks again
Lloyd

 

I would be curious to see how this plays out. Unfortunately my bike uses a module which looks at time, speed and a few other things for automatically shutting off the turn signals. Damn annoying.

Ron

 

I would be curious to see how this plays out. Unfortunately my bike uses a module which looks at time, speed and a few other things for automatically shutting off the turn signals. Damn annoying.

Ron

Hi all, I tried the external power supply again today and started bike up. Indicators worked perfectly with bike running on external supply so problem must be interference from alternator. I reconnected bike supply and tried a 12 volt zener across bike supply to indicators with a small series resistor but this did not cure problem. I will wait until repacement relay arrives and see if that fixes it..
Cheers
Lloyd

 

Hi all, I tried the external power supply again today and started bike up. Indicators worked perfectly with bike running on external supply so problem must be interference from alternator. I reconnected bike supply and tried a 12 volt zener across bike supply to indicators with a small series resistor but this did not cure problem. I will wait until repacement relay arrives and see if that fixes it..
Cheers
Lloyd

By all means keep us up on how this plays out.

Thanks
Ron