Need Help Need some advice - current limiting resistors for directionals?

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
I am cleaning up the wiring on my FZ and I am having trouble figuring out if I need any current limiting on my LED. Attached is a drawing of my directional / pod light wiring. My directionals are Watsens, and are currently wired in with a 10 ohm 1/2w resistor in series with the anode. The resistors came with the Watsens (got them used) and I am trying to see if I need them. Everything works, but a 10 ohm resistor in a 14.4 v circuit will dissipate almost 21 watts, and as you can imagine the 1/2 watt resistor gets HOT. Because it only heats up when the directional is on, there have been no problems to date. I do not have any electrical specs for the Watsens.

So here is a question for the electrical gurus out there. The 10 ohm resistor only consumes 1.44 amps at 14.4 volts, so it is not doing much current limiting. Who is of the opinion that I need to have ANY resistor on the anode?

Bonus question: The oem plugs from Watsen have a regular PN diode forward biased on the cathode of the LED. There may be instances where something like this is needed, but looking ay my schematic I see no need to block any reverse current at the LED. Can anyone think of why they are there?

Thanks
 

Attachments

  • Drawing4.pdf
    49.9 KB · Views: 3

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
Yes, keep the series resistors in line. I've seen another Euro LED company that does the same. It creates a voltage drop to probably keep the LED junction in it's safe operating temperature. You could bump up to a 1 watt which would keep the resistor cooler.

This is obviously different than parallel wire resistors used for load matching for non electronic flashers.
 
Last edited:

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
Yes, keep the series resistors in line. I've seen another Euro LED company that does the same. It creates a voltage drop to probably keep the LED junction in it's safe operating temperature. You could bump up to a 1 watt which would keep the resistor cooler.

This is obviously different than parallel wire resistors used for load matching for non electronic flashers.
Thanks Cliff. I am still thin on my knowledge of electronics, so I was thinking that a 10 ohm resistor does not do much current limiting, and so could be discarded. I ordered some 1 watt resistors to replace the 1/2s in there now.
 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
Thanks Cliff. I am still thin on my knowledge of electronics, so I was thinking that a 10 ohm resistor does not do much current limiting, and so could be discarded. I ordered some 1 watt resistors to replace the 1/2s in there now.
Yes if those are stock that come with those LED's, keep em. I'll see if I can find some data/specs on those....
 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
I agree with that 10 ohm thought. It's hard to know what resistance is already incorporated in the LED assembly. 10 ohms is more like a load matching resistor. I found a handy calculator. https://www.hobby-hour.com/electronics/ledcalc.php
I also looked for some info on the Watsons and was not successful.
 

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
I agree with that 10 ohm thought. It's hard to know what resistance is already incorporated in the LED assembly. 10 ohms is more like a load matching resistor. I found a handy calculator. https://www.hobby-hour.com/electronics/ledcalc.php
I also looked for some info on the Watsons and was not successful.

I guess I will need to grab the multimeter and measure the forward voltage and current draw and reverse engineer the requirements. Thanks....
 

Gary in NJ

Junior Member
Site Supporter
Joined
May 6, 2014
Messages
1,964
Reaction score
1,908
Points
113
Location
Amoungst the Twisty Roads
Visit site
Why not just use a flasher unit that is made to work with LED lights. So much easier.

 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
I guess I will need to grab the multimeter and measure the forward voltage and current draw and reverse engineer the requirements. Thanks....

Except we don't actually know the designed rating for forward current on those devices. We can measure what the forward current is but that doesn't tell us what what it's intended forward current was designed for. The Watsons may not require a dropping resistor but we dont know that yet and so must consider that the 10 ohm are series current limiting.
 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
Why not just use a flasher unit that is made to work with LED lights. So much easier.


The resistors we're discussing are in series for creating a voltage drop and limit forward current in the LED unit.
The load resistors are used to emulate the load of an incandescent lamp to help the flasher keep correct flash rate. Those resistors are wired in parallel and not in series.
I think all flasher relays should be electronic. Most of the electronic relays are well rated and easily carry incandescent loads.
 

fazerkid78

Junior Member
Site Supporter
Joined
Jul 12, 2009
Messages
15
Reaction score
6
Points
3
Location
Panama City Beach, FL
Visit site
When I picked up my FZ6 it had led flush mount blinkers on the front and the stock incandescent signals out back. It flashed really fast so I swapped in an adjustable flasher relay from TST industries. It works with any combo of led/incandescent bulbs. It works great so far and for less than 20 bucks it was easy on the wallet.
 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,137
Points
113
Location
San Diego, Ca.
Visit site
When I picked up my FZ6 it had led flush mount blinkers on the front and the stock incandescent signals out back. It flashed really fast so I swapped in an adjustable flasher relay from TST industries. It works with any combo of led/incandescent bulbs. It works great so far and for less than 20 bucks it was easy on the wallet.
We were basically talking about series resistors. Series resistors are used for voltage drop in the case where a manufacturer does not house the resistor inside the assembly for physical reasons and instead provides them to be in installed inline (series) to create a voltage drop to keep the LED from over voltage/burnout.
This is different from load resistors that are used in parallel as load resistors to keep the flasher unit at the proper rate by emulating an incandescent bulb's load.
Yeah! Electronic flashers rule! The electronic flasher is stable regardless of the load as long as the load is below it's maximum limit. :)
 
Top