mechanical turn signal blinker. 4

[StephenVB]

I'm curious about how a (not so) simple electro-mechanical turn signal auto blinker works.

The simple and incorrect answer, given by the how does it work sites, is a heater on a bi-metallic strip. This doesn't explain the blinker properties.

The blinker is in series with the load. A simple bi-metalic strip would have a shorter on time with more load (more current) and once open it would cool at a fixed rate so the off time would not depend on the load.

This would also delay the turn signal lamps while the bi-metal strip first heated up.

In fact the turn lamps are initially on and have shorter on and off times with less current (a single bulb instead of two).

Does anyone know how this actually works?

Thanks

Stephen Van Buskirk

A human being is a computer's way of making another computer. Yes, we are their sex organs.--Solomon Short (aka David Gerrold, US science-fiction author)

 

[Mobius44]

I think the "how it works" explanation is accurate, the one I found shows a picture of a blinker's internals. There isn't any magic going on, it's just a heater and bimetallic strip.

http://auto.howstuffworks.com/turn-signal2.htm

 

[MiketheEngineer]

Take one apart and look at it.

 

[DRWeig]

Yes, it's not just one bimetallic strip - there are two that interact and the resistor is a separate item.

Do like Mike, take one open and watch it work.

Good on ya,

Goober Dave

 

[VEBill]

I'm fairly certain that the quicker blinking feature to indicate a burned out signal light bulb is a later development. The 'original' simple blinker device didn't include this helpful feature. Perhaps that's why things don't match.

If one was really curious, one could probably look up the patent(s) for the feature on the USPTO.gov website.

 

[Skogsgurra]

I noticed that fast blink thing long time ago. I had a Morris 1000 at that time (we are in 1962 now) and when one lamp burned out, I could tell from the higher blinking frequency.

I thought that was the way it should be. But was curious about why it increased frequency and decided to find out - aometime. I still haven't found out. So I am looking forward to someone finding out any year now.

If that fast blink feature is a later development, then later has a new meaning. Must have been more than 50 years ago.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

What Gunnar said!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VEBill]

Well, my recollection differs...

There may be a clue in that the flasher modules, the little can-shaped modules of the sort used in North America, came in several flavours. The general application ones were either 2-terminal or 3-terminal types.

The simple 2-terminal versions of the simple bi-metallic strip design probably don't include the current sensing feature.

Here's an image of a 2-terminal version, with the "MAX6" presumably being the maximum numbers of signal bulbs. So it obviously wouldn't react to one of N being burned out. The DOT probably indicates the flash rate meets requirements.

The next step in this study would be to determine what's different between the 2-terminal and 3-terminal flasher modules.

Maybe that's the explanation, maybe not...

 

[VEBill]

According to:

http://elektroniki.blogspot.com/2010/09/turn-signal-flasher-unit-et-104.html

The 3-terminal versions are for those cars with a single turn-signal indicator light on the dash board.

But this detailed description also explains that a burned-out bulb has a different result than a faster blink rate.

 

[VEBill]

My conclusion is that the simple bi-metallic flasher modules (the simple sort, as described) do not provide the burned-out lamp, rapid flash indicator feature.

 

[Compositepro]

The flash rate is determined by the power input, the heat capacity of the bimetallic strip and heating element, and thermal resistance in the heat flow path. Too little power (burned-out lamp) and it will take longer to heat to the switch-off point, but it will cool quickly, so the lamp will blink-off only for a short time. Too much power (due to a high wattage bulb) will cause a quick flash and a longer off period. The exact effects depend on the specific design.

 

[Skogsgurra]

With you so far. But I am still not satisfied. Remember, I have been wondering around fifty years!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Warpspeed]

I thought that these days the once humble blinker would require at least a fast 32 bit microcontroller to make it go.

 

[StephenVB]

I looked at the web site listed and it didn't have a detailed explanation. It showed one yheater and bi-metal strip and w2ouldn't work as I expect. I'm fairly sure the lamps are on as soon as power is supplied, not after the strip heats up.

My observation is that the blinker on AND off times are faster with less load. I have tried to watch one and still don't understand it, though I'm sure it must involve heat dissipation, different resistors and materials. I was hoping for a specific explanation for no particular reason, just curiosity.

I was looking at the SAE specs. They call for a very narrow range of operating frequencies, +- 5 or 10%, as I remember.
Since blinkers can have more load (4 bulbs instead of 2) and still work, but blink faster with only one this must be quite complex. I did not find any allowance for faster blinking in the SAE specs but it's probably there somewhere.

Stephen Van Buskirk

 

[VEBill]

Mr. Speed: "..32 bit microcontroller..."

My car puts a message on the dash (in any of several languages) telling me that a light bulb is burned out, exactly which one (*), and if it was able to reconfigure a nearby alternate bulb as a temporary replacement.

(* It fails to distinguish between the two rear license plate illumination bulbs.)

 

[Warpspeed]

VE1BLL,
And I bet the CIA can also monitor every single lamp in your car on a big display screen back at Langley.

 

[Skogsgurra]

Good news!

Daughter and son-in-law will visit tomorrow. He builds hot rod and vintage cars and will bring one of those devices.

We will cut it open, make photographs, push currents of different magnitudes through it and record the blinking.

It will be a major scientific undertaking and it will happen on a Sunday. I think it is worth while.

Stay tuned!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

We will!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

"...major scientific undertaking..."

CERN's got nothing on you.

 

[waross]

Wonderful Gunnar. I'm looking forward to the results of your research.
Thank you.

Bill
--------------------
"Why not the best?"
Jimmy Carter