Resistor Mystery

Pilotdave

Pilotdave

Well-known member
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
 
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
 
Dave, Dog:cool: here,
I "think" the resistors shuld be spliced in series, in each wire. NOT to a GROUND, cuz thet wuld cause a "short" circuit.:eek: (Ol' Bill wouldn't write this, cuz IF he wus wrong, he'd look like a FOOL!)
Buster T.:cool:
 
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.
 
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!
 
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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.
 
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.
 
That is certainly the truth, Bill! And wbedwards, you are 100% right that I don't want to think about your son's experience!!
 
Pilotdave said:
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!
Click to expand...

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.
 
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.
 
What's supplying the led flashers? Old technology? If it's new technology maybe it can't handle the extra load of the resistors.
 
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".
 
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.
 
bettlesr said:
They should be in parallel. You need to increase the load on each side.
Click to expand...
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!
 
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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.
 
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.
 
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