Resistor Mystery

[Pilotdave]

I recently installed LED tail lights in our Tudor. I added a 50W 6 ohm resistor to each side to slow down the turn signal flash rate. These were soldered to the lines running back to the lights with the opposing ends grounded, so they are in parallel to the turn signal circuit. Initially this worked fine, but after a couple hours drive today the flash rate was high again.

What might cause the resistors to lose their effect? And what might I do about it?

Thanks!
Dave

[wbedwards]

Do you have an Ohm meter to check them with? My bet is they are burned in two so its though they weren't there. Did you mount them to the body to help absorb the heat when they are working? just a couple of ideas

[BILL WILLIAMSON]

Dave, Dog here,
I "think" the resistors shuld be spliced in series, in each wire. NOT to a GROUND, cuz thet wuld cause a "short" circuit. (Ol' Bill wouldn't write this, cuz IF he wus wrong, he'd look like a FOOL!)
Buster T.

[Big hammer]

A 50 watt draw to ground they should be wired in series :-)

[J Witt]

He has it right, Bill. The resistors should be in parallel circuits, not series. Something has happened to disconnect the resistors from the circuit.

The power is P=I^2R, and I=E/R. I=6 volts/6 ohms = 1 amp, P= 1^2 x 6 ohms = 6 watts,
so a 50 watt resistor should be very safe.

[Pilotdave]

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wbedwards - I just pulled both resistors out and checked them with my digital meter - both read 6.3 ohms. They were both strapped to the steering column which should have been able to absorb some heat. That said, when I turned the car off, both resistors were too hot to touch - but so was any other metal within a few inches of the engine!

Dog - that's an interesting point. I initially thought the same thing, based on my electronics course from long ago that taught me that the total resistance of a circuit consisting of two resistances in parallel was less than the smaller of the two. And that adding resistance in series increased the total resistance of the circuit. But I installed them in parallel as advised by the tech fellow at a well-known parts emporium - and also as I've seen illustrated on the internet. And we all know that the internet is never wrong.

Thanks, both of you, for your ideas!

Now....after I pulled the resistors out of the car for testing, the flash rate on both sides was slower than during the today's tour. Interestingly, the left side is noticeably slower than the right side. (This corresponds to what I saw after installing the turn signal system with the LED tail lights. I had installed the resistors to slow the flash rate down more. This worked initially but then the flash rates became way too fast during the tour.) It's possible that I have a different wattage bulb in the left vs right front units. I will check this tomorrow.

So....should the resistors be installed in series or parallel? Are there any other ideas out there that would explain this odd set of results? Thanks guys!

Dave
p.s. Just saw the replies from Big Hammer and J Witt. I am very confused about the parallel vs series approach. Isn't the formula for resistances in parallel: 1/R(t) = 1/R(1) + 1/R(2) = R(1)xR(2)/(R(1)+R(2))? And doesn't this mean that the combined load if wired in parallel will be smaller than the smaller resistance? And isn't this exactly the opposite of what we are trying to accomplish?

What am I missing? Thanks!

[BILL WILLIAMSON]

Dave,
We usually search & search & search the internet, until we find a statement that AGREES with what we had already decided to do! (DUH?)
Bill W.

[wbedwards]

You may not want to think about this, but my son bought a neat set with supplied resistors and all for his 2009 Mustang. We installed as per factory instructions which were sketchy at best. One side never worked right. He took them off and sent them back for a refund.

[Pilotdave]

That is certainly the truth, Bill! And wbedwards, you are 100% right that I don't want to think about your son's experience!!

[Pete]

Originally Posted by Pilotdave

wbedwards - I just pulled both resistors out and checked them with my digital meter - both read 6.3 ohms. They were both strapped to the steering column which should have been able to absorb some heat. That said, when I turned the car off, both resistors were too hot to touch - but so was any other metal within a few inches of the engine!

Dog - that's an interesting point. I initially thought the same thing, based on my electronics course from long ago that taught me that the total resistance of a circuit consisting of two resistances in parallel was less than the smaller of the two. And that adding resistance in series increased the total resistance of the circuit. But I installed them in parallel as advised by the tech fellow at a well-known parts emporium - and also as I've seen illustrated on the internet. And we all know that the internet is never wrong.

Thanks, both of you, for your ideas!

Now....after I pulled the resistors out of the car for testing, the flash rate on both sides was slower than during the today's tour. Interestingly, the left side is noticeably slower than the right side. (This corresponds to what I saw after installing the turn signal system with the LED tail lights. I had installed the resistors to slow the flash rate down more. This worked initially but then the flash rates became way too fast during the tour.) It's possible that I have a different wattage bulb in the left vs right front units. I will check this tomorrow.

So....should the resistors be installed in series or parallel? Are there any other ideas out there that would explain this odd set of results? Thanks guys!

Dave
p.s. Just saw the replies from Big Hammer and J Witt. I am very confused about the parallel vs series approach. Isn't the formula for resistances in parallel: 1/R(t) = 1/R(1) + 1/R(2) = R(1)xR(2)/(R(1)+R(2))? And doesn't this mean that the combined load if wired in parallel will be smaller than the smaller resistance? And isn't this exactly the opposite of what we are trying to accomplish?

What am I missing? Thanks!

It's just a bunch of dumb electronic parts so it CAN be made to work. The resistors should be in series. It is hard to say what value you need without knowing the internal resistance of the circuit under load. I have had similar problems and used a wire wound pot of about 2k ohms. Put it in SERIES in the circuit with it set at maximum and
turn the circuit on. Dial the pot till you get the blink rate you want. Turn off and take the pot out and measure the resistance that was in the circuit. Get a fixed resistor and install it in where the pot was.
Roundabout way but it works.

[Mike V. Florida]

Get an electronic flasher and get rid of the resistors.

6 volt led flasher

[BILL WILLIAMSON]

You're right, Pete,
Adjustable potentiometers are a handy thing, like dialing in '40 Ford gauges to work on 12 Volt. I used them on Old 280Z's, with Old lean injectors, just wire it in series with one of the injection water temp sensor wires & DIAL-ER-IN!---"vrooooom"!
OH, on his LED's, "maybe" on one side, there's a "less than perfect" ground, somewhere??? Eliminate that possibility by by-passing the grounds with a jumper wire.
Bill W.

[bettlesr]

They should be in parallel. You need to increase the load on each side.

[gweilbaker]

What's supplying the led flashers? Old technology? If it's new technology maybe it can't handle the extra load of the resistors.

[stouchton]

If you have a thermal flasher, then the added current flow into the resistors will speed up the flash rate.

Also, you are only pulling another amp, where incandescent turn signal bulbs pull up to 4 amps - 2 amps front and back. So the flasher will be no where near what it "expects".

[Tom Wesenberg]

Dave, you mentioned "BULB WATTAGE", which makes me think of regular bulbs, and not LED's. Regular bulbs shouldn't need an added load to the circuit, but LED's may need the added load if the flasher isn't working correctly.

To add a load to the circuit the resistor is added in parallel as you had it. If you add in the resistor in series you increase the circuit resistence and make the bulbs dimmer.

Now, I'm trying to figure out why the steering column is so hot. or even why the resistors got hot. The resistors would only be passing current while the turn flasher is on, and even then the resistor is only being heated by 6 watts, so it would take a bit to get real hot.

[BILL WILLIAMSON]

Originally Posted by bettlesr

They should be in parallel. You need to increase the load on each side.

2 resistors in parallel, will DIVIDE the load. 2 resistors in SERIES, will INCREASE the load.
Bill W.
Chief taught me like, if you put MORE cars on a 1 lane road, it'll be crowded & SLOW, if you put another lane in PARALLEL to it, it'll be LESS crowded & FASTER!

[Mike V. Florida]

The mechanical flasher has a piece of metal that bends when heated. The current in the circuit heats up the windings around the metal, the metal bends, the circuit opens and the metal cools down and makes contact again. The windings heat the metal, the metal bends, and so on.

The LED's have a low current draw, so the windings never get hot and the metal never bends. When this happens one needs to increase the current by lowering the resistance.

Not flashing, slow flashing place resistor in parallel. Fast flashing place resistor in series.

The real easy solution, replace the flasher.

[Patrick L.]

Why not just add higher wattage or CP bulbs to the front signals and forget about resistors or trying to find an electronic flasher that might or might not work.

[wbedwards]

Originally Posted by Mike V. Florida

Get an electronic flasher and get rid of the resistors.

6 volt led flasher

That's the ticket! Cheap too. You don't have all that current heating the resistors.

[BILL WILLIAMSON]

We used to get those long, cigar shaped, variable load flashers, with a pig tail wire on each end. They could be used with almost any amounts of lights, used a LOT by truckers, so when they unhooked their trailers, the lights still flashed the same.
Bill W.

[Kurt in NJ]

When I have had to "fool" bulb warning electronics when aftermarket LED lights are used I like the dual ballast resister from late 70s Chyrsler electronic ignition, it gives you 2 resistors to use, most times the 6 ohm one is emough--

[jmeckel]

The resistors go from the "powered", flashing / pulsing side of the bulb circuit to ground, normal LED lights do not draw enough current to operate a standard flasher properly. If the flash rate is too high you may find that the manufacture already added resistance to the LED assembly so normal flashers will work. On the point of the resistors, depending on what type of resistor you are using they will change value with heat. Some are positive coefficient, meaning when they get hot the resistance goes up, others are negative coefficient, meaning when they get hot the resistance goes down.

When you are trying to increase the current through the flasher circuit you place the resistor from the powered bulb side (this is the side that flashes) to ground, make sure you do not place the resister on the supply side or better known as the battery side as this side NEVER flashes, and is before the flasher. Most turn signals feed the power to the flasher, from the flasher it goes to the turn signal switch then out of the turn signal switch to the bulbs. You place load resistance on the flashing hot wire that goes to the bulbs, no place else.

[Pilotdave]

This is getting interesting! I've been away all morning and just now responding to some of these posts. Several things:

1. I referred to bulb wattage as there incandescent bulbs in the two front turn signal lights. These are the type that are mounted between the rails of the front bumper. I replaced one of the bulbs a while ago but didn't look too carefully at the wattage - so it's possible that the two bulbs now installed are different wattages. I need to check this out.

2. Each light unit in this car has a separate wire providing its ground.

3. Electronic flashers seem readily available for 12v neg ground systems but I've had trouble finding them for 6v pos ground systems. Thanks for the link, Mike V.

4. The resistors I added were soldered to the lines running from the turn signal system to the tail lights and then connected to ground.....so I believe they were installed as described in the last paragraph of jmeckel's post (#23).

5. The turn signal system installed in the car is the Signal Stat 900.

6. Perhaps I should wire an ammeter in series with the turn signals and find out how much current each is drawing when it flashes?

7. Tom, I think that the heat I was feeling at the lower steering column was heat radiating from the engine, not heat generated by current load.

8. It's still a little unclear whether there's agreement on how adding resistance in series vs parallel affects the flash rate and why.....perhaps if we can get THAT clarified the rest will become simple!

Thanks everyone for all your input!!
Dave

[Pilotdave]

From post by Mike V on another (similar) thread that addresses #8 in Post 24:

"The LED's have a low current draw, so the (flasher) windings never get hot and the metal never bends. When this happens one needs to increase the current by lowering the resistance.

Not flashing, slow flashing place resistor in parallel. Fast flashing place resistor in series."

Which tells me that I need to add resistance in series with the wires running to my tail lights. Does this make sense? (I KNOW that The Dog will say "yes"!!)

Dave

[DanK]

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If you add resistance in series with the brake/turn signal bulb/led you will decrease the current to the bulb. In series, resistance adds, and more resistance means less current. Less current through the bulb means a dimmer light and a slower flash because of less current through the flasher.

If you put the resistor in parallel with the bulb you will still get full voltage across the bulb and the same amount of current through the bulb so it will be just as bright. The parallel path of current through the resistor means more current through the flasher and a faster flash.

Put the resistor in parallel with the bulb and make sure it is on the bulb side of the flasher.

[DanK]

Originally Posted by Pilotdave

Fast flashing place resistor in series."

While this will slow down the flashing it will also make the light dimmer.

[Pilotdave]

Thanks, Dank. I'm looking for slower flash rate.......but I don't want to reduce brightness. Maybe time for some experimenting.
Dave

[DanK]

Dave,

Led's generally draw much less current than incandescent bulbs so the problem usually encountered with them is slow flashing. I don't understand why yours would be flashing faster if all you did was replace incandescent with led.

[Tom Wesenberg]

My EF-32 is a 2 prong 12 volt electronic flasther, but when I bench tested it on my 6 volt car battery and led bulbs, it worked fine. 6 volts is the lowest it will work, but with the engine running the system voltage should be about 7.2 volts.

[PepeLoco]

Did you try to flush it with Vinegar?
Sorry, I couldn't resist....

[SeaSlugs]

Originally Posted by Mike V. Florida

Get an electronic flasher and get rid of the resistors.

6 volt led flasher

agreed, whole benefit of using LED anythign is to save power while having brighter lights, adding resistors eats more power than light bulbs most of the time...

electronic flashers fix all that as they dont rely on current draw to determine flash rate

[Pilotdave]

DanK - perhaps the mixture of incandescent bulbs in front with LEDs in the back explains the flash rate?

Tom - this system requires a 3-prong flasher; perhaps an EF-33?

PepeLoco - good idea - a vinegar flush cures most everything.

Dave

[Patrick L.]

Originally Posted by DanK

Dave,

Led's generally draw much less current than incandescent bulbs so the problem usually encountered with them is slow flashing. I don't understand why yours would be flashing faster if all you did was replace incandescent with led.

It actually results in fast flashing. Adding higher wattage [ 10W] or CP bulbs in the fronts with a standard 535 flasher resolves the problem.

[DanK]

Originally Posted by Patrick L.

It actually results in fast flashing. Adding higher wattage [ 10W] or CP bulbs in the fronts with a standard 535 flasher resolves the problem.

Then my understanding and experience with thermal flashers is all wrong. When I was going to college I had a job with an RV dealer and wired up a lot of tow vehicles for trailers. The added current of the trailers always made the flashing faster. To slow it down we changed the flasher to a heavy duty one. So, again, if the led's, which draw less current, cause faster flashing I don't understand what's going on. Can you explain it?

[DanK]

My curiosity got to me. I had to figure this out. I found this link with an explanation of the evolution of flashers. The one Dave has is a later one that can detect a burned out bulb and hyper flashes to alert the driver of the bad bulb. Led's draw so little current the flasher thinks a bulb is out. So, the fix in that case is a resistor in parallel. If he had one of the old thermal flashers the flashing would have been slower but the fix would be the same.

http://johnatchley.com/?page_id=196

[Pilotdave]

Thanks for all the ideas and information. I'm going to reinstall one of the load resistors in parallel to the tail light line and see if that cures the problem. Will report back.

Dave

[DanK]

Dave, if adding that one resistor to one light doesn't slow down the flashing it may be that you are not increasing the current enough. To check, add both resistors in parallel to one light. If that works then a single 3 ohm resistor is what you need for each side.

Dan

[Pilotdave]

Thanks, Dan. It'll be easy to test once I get a chance to get back into the shop.

Dave