I am trying to build a circuit to create a load on a turn signal blinker circuit. What I did was used a Bourns 5.6OHM 35 Watt Resistor DPAK2 SMD from positive from blinker to ground. This at 13.7 volts is 2.15 AMPS which is approx 29.455 Watts. The issue is the resistor gets hot way to quickly so how they can rate that as a 35 Watt resistor is beyond me but anyway. Is there a better way to do this? I can use the wire wound style at 25 watt and it actually works okay just large and clunky. I just need a solution that wont run away thermally. Idea's? Suggestions? I would change out the relay with a LED style and be done with it but this particular one is built into the body control unit which is totally retarded but that is a different discussion altogether.
That is what the resistor is taking the place of yes. This needs to be mounted somewhere permanently but a flashing light bulb would not be ideal. There has to be a better way.
If you did an LED upgrade, using a resistor is the way almost everyone 'fixes' the load issue... You can wire and mount the resistor in a location away from the LED if needed, or splice into the wiring harness at a different location away from the LED as well, basically put it somewhere the heat doesn't matter... You might also consider 50w 6Ω resistors as that is a common value used, and will dissipate the heat better...
If you want to avoid the resistors all the way, you need to get rid of the old style thermal blinker relay and use a solidstate one that doesn't require the load to alternate the blinks...
If you want to avoid the resistors all the way, you need to get rid of the old style thermal blinker relay and use a solidstate one that doesn't require the load to alternate the blinks...
Ok good info. The only drawback to the 50W 6OHM is it is fairly large as well. I was experimenting with a 25W 5.6OHM wire wound and hooked it up to a relay that cycled every 500ms to simulate a flasher relay and it got hotter and hotter and would have no doubt burned up. The issue I have is it is very possible for someone to hit their emergency flasher button and have a runaway condition. I was hoping to find some sort of circuit I could use to drain off some of that current but it appears that may be a tougher ordeal. Like I stated in the original thread I am not able to replace the flasher relay in this particular application. I will get a 50W 6OHM and do some thermal testing with that one. I also worry about hot climates. If someone is in say 120F desert then heat is already working against us.
I know there is some sort of flyback deal used in some piggyback Fuel Injection ECU's to load the primary ECU and to make it think that the original injectors are functioning correctly. I am not sure how much current that is simulating but I am wondering if something like that is doable. I guess I am off to do more research.
Thanks for all the great advice and help so far please keep the ideas coming.
you DONT drain off current. The current flowing in the circuit is a function of the voltage and the resistance. if you have a fixed voltage (13.7V) as hinted at in your first post, then increasing the resistance of the load will decrease the current flow
Dave
Drain off current may have been a bad choice of words. I need to somehow get the filament in the flasher relay heated by increasing the current flow so that it operates correctly. The issue is doing this with a resistor is a clunky method just asking for disaster. There are a lot of people out there using 25W 5.6OHM resistors that work just fine for short uses of the turn signals but set the emergency flasher and walk away and see what happens.
The use of a 50W 6OHM resistor might "help" as previously suggested but I bet that too runs away thermally unless cooled some how. Especially at higher ambient temperatures.
The problem here is that changing the resistance value (load) will negatively effect the cycle rate of the thermal blinker
Kinda stuck between a rock and a hard place...
That type of flasher is not a relay. Its operation is more akin to a thermostat. Its made of a bimetallic conductor that heats when current flows through it. The unlike metals cause it to bend and break contact, then cool and make contact, repeatedly.
That said, I'm clueless as to what you're doing or why you're doing it.
Regardless of technicalities they are traditionally called flasher relays...
Example... http://www.amazon.com/Universal-Turn-Signal-Flasher-Relay/dp/B000VTTDYY <~ that is a solid state one that will work with bulbs or LEDs
Because when you upgrade automotive 'bulbs' to LEDs the traditional and still widely used thermal flasher cease to function properly as the LED doesn't not draw enough current to trigger the flip flop... Also bulb idiot lights on the dash board will sometimes also come on when using LEDs in place of bulbs and/or you will get a rapid flash (or solid light) on the dash as indication there is a blown bulb when using the flashers... If you tie the supply going to each LED to the frame (gnd) with a 6Ω resistor the load is equivalent (close) to what the bulb would traditionally put on the flasher and thus it works again, same with the idiot lights and what not... Basically the resistor is spoofing the no longer in circuits bulbs load, and thus restores function to the entire turn signal system...
This is something that has become very prevalent in automotive circles as people upgrade indicator lights to LEDs... The most common fix by far is using the 6Ω resistor to create the load as it fixes everything in one shot, the other fix is to swap out the flasher relay for a solid state one that doesn't expect or require a load... But swapping the flasher unit will not take care of the idiot light or rapid or constant dash flash issues, so you either need to disable that in the dash, in the CPU's firmware or go back to the original resistor fix to spoof the load...
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I missed that.
To be more precise, this is what I missed. At a time when we're supposed to be efficiency conscious, power dumping seems awfully counter productive and wasteful though.
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It seems that way.
However the major motivation to convert to LED indicator lights (outside of EVs) is the long life, high switching speed, and relative immunity to vibration that should come from a well designed LED module.
For brake lights in particular, it has been calculated that LEDs give the driver behind you a small (but at speed, significant) amount of additional warning. 150 ms to 200 ms may not sound a lot...
edit: Here is what appears to be a fairly sensible discussion of this safety aspects of LED brake lights.
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That was the reason they all go swapped out on my motorcycle...
I had the rear break/driving light on my brand new Buell blow on the first day (while driving at night) due to vibration (darn HD V-Twin
)... I replaced it with a new 'heavy duty' light that lasted all of 2 weeks... I then replaced it with a high quality LED, and it's been 5 years without issue...And I have to say due to the way the LED illuminates it's much more eye catching then a bulb, even with the reflector you still get a lot of the 'directional' type light that catches your eyes...
All in all a win, win for me as I suspect for many others as well, the waste of power via the resistor is certainly illogical but it's one of those negatives that gets outweighed, and at the end of the day is only marginally more (if any) then the bulbs it replaced anyway...
john monks
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Did you solder your DPAK2 to a heatsink?
I agree and if a swap out to a solid state flasher will work in your vehicle I would recommend that in a heart beat, but sadly this isn't the case for many vehicles that have other issues beyond just getting the flashing working...
Simple. We are converting from incandescent bulbs to LED's which draw approx 180mA as apposed to 1157's which draw around 2.1A on the brake/turn side. So the issue is because the LED draws such a low amount of current the flasher relay does not work as expected. The bimetals heat slightly then cool quickly so the rate is extremely quick. By adding a 5.6OHM resistor it simulates a regular bulb and the flasher relay then works as expected.
The real issue becomes cooling that resistor. Using a wirewound cement style resistor even at 35W does not work unless you find a way to cool it. They run away thermally until they open or catch fire.
I know the normal way people do it is by replacing the flasher relay with a solid state flasher specifically for LED that does not care about load. The issue here is the flasher relay is built into the BCM (Body control module) which makes that impossible in this situation.
So... In short I need a better way. I have found a 6OHM aluminum resistor with mounting holes I am going to try. By mounting it to the frame I am hoping there will be enough heat transfer to solve the issue. The next issue is going to be ambient temperatures. Here where I live it gets easily to 105 during the summer. Tucked away under a cowl or hood etc the temperature will even be higher. So the thermal capabilities of the resistor itself coupled with the hotter then normal heat may cause either the resistance to be too far off or it to again run away thermally until melt down.
So again I was hoping someone would have a better way for this. Short of putting a light bulb in a box and venting it!
My next questions/thought is I know that some cars have ECU (Engine control module) that can tell when an injector goes bad. These types of cars that get performance mods like and external ECU have to have some sort of flyback circuit in them to simulate the load to the ECU so it thinks the injectors are working correctly. Would something like this work here? I know nothing about those types of circuits hence why I am asking here. It would be nice to have a solution that does not need serious cooling to implement.
Yes, CC explained all of that and I commented that it's wasteful. However, if you insist on not using an incandescent bulb as a dummy load then use a heat sinked power resistor. They're made with a heavy anodized aluminum jacket with heat fins. They have two mounting tabs to screw it to a chassis plane. Use heat sink compound between the car frame and the flat bottom of the resistor.
Edit: I see that I missed the fact that you already discovered aluminum cased power resistors. You are aware that you can series/parallel them to distribute the power dissipation over each of them?
Edit: I see that I missed the fact that you already discovered aluminum cased power resistors. You are aware that you can series/parallel them to distribute the power dissipation over each of them?
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