Wiring up flasher relay - Page 1
Forum section: electronics / beginners

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 04:53:05 pm
content: haii :3im trying to wire up a flasher relay to some led trailer lights. i have the lights wired up like in the attached image but i dont have the "pilots". i can hear the relay pull in but it never flashes.i have a hunch the problem might be that my relay might not support led lights but im not sure about that. the relay is linked below.https://www.biltema.fi/en-fi/car---mc/electrical-system/relays/indicator-relay-12-v-2000017800

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 04:54:12 pm
content: ugh the image didnt attach

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 05:04:21 pm
content: Probably not suitable for LED, connect a 21W bulb to test

author: Algoma
author_rank: Frequent Contributor
timestamp: January 03, 2025, 05:04:44 pm
content: Some mechanical based flashers use bi-metallic stips that heat and cool to make the flash, but they require enough load to heat the strip, or will flash with shorter off-time."Pilot" refers to the indicator light on your vehicle's dashboard, showing when the turn lamp is also flashing.B - BatteryL - LoadE - Earth (Chassis Ground) - Typically to operate the flasher output indepenant of the load

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 05:06:17 pm
content: Quote from: inse on January 03, 2025, 05:04:21 pmi couldn't find a 21w bulb but with a 55w halogen bulb nothing different happened

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 05:11:56 pm
content: figured it would be good to know what type of flasher it was so i tried to get it open with as little destruction as possible. this is what the insides look like

author: Algoma
author_rank: Frequent Contributor
timestamp: January 03, 2025, 05:14:56 pm
content: Provided there is no short to ground. Some electronic flasher relays do have short circuit protection on their output to save your fuses.

author: Algoma
author_rank: Frequent Contributor
timestamp: January 03, 2025, 05:40:03 pm
content: Yes, R2 and R3 indicate that IC is definitly monitoring the input and output, at least if the relay is clicking then its overall in a working state.Volt meter and an test lamp and start poking the outputs. At least even bypassing the relay should light up your lamps steady, provided there remains no short on the output (L).The darker oxidization on the shunt could indicate a breif overheat, The contacts inside the relay could have failed if there was an even a breif overload.

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 06:55:57 pm
content: if i run a wire between B and L the lights do infact turn on.assuming the shunt is the metal at the top, its not actually bark, its just reflecting weird.measuring the terminals while no power is connection, there is no connection between any terminals. but when power is connected and the relay pulls in and as expected B and L get connected, but then there's also few megaohm connection from L to E.

author: floobydust
author_rank: Super Contributor
timestamp: January 03, 2025, 07:49:57 pm
content: It's a cheap chinese blinker module. It might not even work in the first place. Is the timing capacitor OK?You can see it has a wire shunt resistor for monitoring lamp current and detecting burnout. So it's not compatible with LED lights. It will flash high rate 2.2xMystery IC and schematic match UAA1041/LD1041.

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 07:57:00 pm
content: The shunt could be adapted for LEDs though

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 08:03:09 pm
content: how hard would be that to do?

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 08:13:24 pm
content: Depends on your stock of resistors and measurement equipment.Rsn=Rso*(Ibulb/Iled) or Rso*(Pbulb/Pled)Rsn resistance shunt newRso … oldOr give it a try with 200mOhm if the component floobydust mentioned matches to your circuit

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 08:20:34 pm
content: sorry, i dont quite understand the calculation or where im supposed put the resistor. as in equipment i have a generic set of resistors and a multimeter

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 08:47:53 pm
content: Maybe it’s easier to get a LED compatible flasher relay

author: Julimiro
author_rank: Contributor
timestamp: January 03, 2025, 09:08:12 pm
content: yes that would be good but for some reason they aren't really sold in finland so i'd prefer to convert this one if possible, otherwise i'll cobble together with an arduino and a relay module

author: Algoma
author_rank: Frequent Contributor
timestamp: January 03, 2025, 09:22:03 pm
content: 2-pin flasher relays exist for low load applications like LEDs. Perhaps look for those.

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 09:43:36 pm
content: Amazon won‘t deliver to Finland?You need to replace that shunt wire mentioned already with a resistor suitable for LED current level.You will not be able to measure the shunt value with a simple multimeter as it’s probably only a couple of mOhms, so all calculation is just guesswork.But only do so if you have verified the relay works at all (with light bulbs).Btw, Arduino would be ridiculously overengineered.

author: Julimiro
author_rank: Contributor
timestamp: January 04, 2025, 12:38:50 pm
content: i found some that claim to work with leds, one had 2 pins and one 3, which one should i get?https://www.ikh.fi/en/flasher-relay-3-pin-12v-st0206d?gQT=1https://www.ikh.fi/en/flasher-relay-2-pin-12v-st0206e

author: Algoma
author_rank: Frequent Contributor
timestamp: January 06, 2025, 04:11:32 pm
content: The 3 pin relays are usually required for automotive applications, as the extra E(Earth/Ground) pin allows the flasher relay to monitor, inidcate and prevent fault conditions on the L(Load) pin.The 2 Pin version is simpler to wire in line, and faults are a problem for either the user or the fuse. Likely the 2-pin is the same as the 3Pin with E and L pins bonded internally.

author: floobydust
author_rank: Super Contributor
timestamp: January 07, 2025, 05:23:18 am
content: The 3-pin one will perform better than the 2-pin which needs parasite power to activate the relay/mosfet. I would use the 3-pin version.Both are rated for LED lamps 0.02-8A it says.Or fix the one you have, and let it blink fast (thinks lamp is burned out).

author: Julimiro
author_rank: Contributor
timestamp: January 07, 2025, 06:38:14 am
content: I'd also like to get the one i have working but nobody is giving me clear instuctions on what i need.

author: SteveThackery
author_rank: Super Contributor
timestamp: January 07, 2025, 07:13:06 am
content: Quote from: Julimiro on January 07, 2025, 06:38:14 amYou need a new flasher relay. The one you gave us the link to says "12V 100W" and it does not say "suitable for for LEDs" anywhere. So it isn't. I think it's silly to try to modify it when flasher units are so cheap.Post #7 onwards gives you guidance on how to proceed if you really want to work on it yourself. But honestly, giving you precise resistor values isn't easy because there would probably be a need to do some experimentation.

author: floobydust
author_rank: Super Contributor
timestamp: January 07, 2025, 07:29:37 am
content: I disagree - if the lamp current is too low, it still flashes but at double rate. The IC also has (lamp) short-circuit detection, and overvoltage (>20V) detection.It seems to be not working if the relay pulls in and stay in.I would suspect the main timing cap C1 - it's that green meaning low-ESR water-based electrolytic which means high leakage current and it's not suitable for timing circuits.So I would check/replace that cap and see what happens. Or the feedback to pin 8 is not working, that resistor R3 3k3 might be open.I don't like the missing cap C2 which lessens voltage spikes from the lamps. It should be around 47-100nF.

author: SteveThackery
author_rank: Super Contributor
timestamp: January 07, 2025, 10:11:53 am
content: Quote from: floobydust on January 07, 2025, 07:29:37 amI'm not disagreeing that the relaymightbe faulty. I'm just saying that repairing it will give the OP a fully functioning relay thatstillisn't suitable for LEDs. So it's about repairing it, and then hacking it to work with LEDs.And that is what I consider to be a silly amount of effort when you can buy one designed for the job for a few bucks.

author: floobydust
author_rank: Super Contributor
timestamp: January 08, 2025, 05:55:01 pm
content: Yeah I think that repairing/modifying this unit could be no joy.Then I realized having OP two flashers - one on the car/truck and another for the trailer, when they are likely different phase and frequency is not allowed in North America. I've never seen it.