Tuesday, April 21, 2015

Hazard Flasher Unit

One niggling problem I've had for a while is the fact that the hazard lights can be bit erratic. Sometimes they will flash slowly, then speed up, while other times they would just stay lit and not flash at all. Investigating the problem it seems there is a simple fix, so simple in fact I'm not sure why it took me so long to get around to sorting it out.

Under the bonnet, mounted on the bulkhead is a small unassuming round silver 'thingy'. I have seen it many a time, but never really paid any attention to it. It seems that this small mystery object was the source of my problem.

As I could hardly search for 'small silver round thingy' on ebay, I thought I'd better find out what it's really called. Thank goodness for the internet as searching on ebay for 'hazard flasher unit' is a lot more productive.

Once the new flasher unit arrived, it was simply a job of pulling the old one out and pushing the new one in.

Old one out...

New one in.

Once the new hazard flasher unit was in place the hazards were flashing normally once more.

One thing I noticed straight away was that noise, that fantastic ping pong noise it made. I just loved it.

So what makes that ping pong noise, I wonder. The obvious thing to do is to take the old flasher unit apart and see what's inside...

Unpeeling the lip of the aluminium cover with a pair of pliers and lifting it away revealed its inner secrets. Inside there's a switch that seems to be controlled with a bimetallic strip and the way it works is genius in its simplicity.

When the hazards are flicked on, the hazard flasher circuit is energised and because the flasher unit is in the closed position the hazard lights come on.

Critically the bimetallic strip which is part of the same circuit, starts to heat up also and as it does the piece of metal which it's bonded to starts to bend and eventually flips as a result. As the metal flips, it opens the circuit turning the hazard lights off along with the bimetallic strip.

Now the metal strip cools down and flips back to its original position, closing the circuit again starting the whole process again. Lights come on and the bimetalllic strip gets warm, it flips the metal and opens the circuit, the lights go out, metal cools, flips closed, etc etc. 

It's interesting to see how the problem of making the lights flash on and off can be solved with this simple but effective method. 

Anyway, that's it for now, another small niggly job sorted out and a bit of learning thrown in with the deal along with a fantastic 'ping pong' noise! Don't you just love it when something goes wrong!!

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  1. nice one. :)
    particularly like the curiosity taking the old part apart...
    Did it show any signs why it would not work?

  2. I'm guessing that the bimetallic strip was faulty as it did kind of work, just very badly.