Fast indicator

One of your right hand indicator bulbs has blown (probably not the repeater)

Pete.

One of the bulbs as blown! Jon

Blown bulb. If you actually bothered to check them once in a while you'd have spotted this.

Your bulb has blown. The indicators (AFAIK) work using a bi-metal strip which when current flows through it heats up, this causes one end of the strip to flip away from the contacts and breaks the circuit. This strip then cools down as no current is flowing through it and flips back, which then makes the circuit and current flows through it which heats it up.....

When a bulb has blown the strip heats up faster due to more current flowing through it (as the bulb isn't using the current to light the filament), and therefore the strip heats up faster, which makes it flip faster and so your indicators flash faster.

At least, they used to do it this way - I assume that they still do as they still exhibit the same symptoms of a blown bulb.

Blimey, not for about 25 years! It's been relays for a long time now, but the bulbs are an integral part of the timing of the circuit - halve the load and double the flash rate. I wonder if it was an intentional idea to keep in line with what had gone before.

No - they're electronic timers with a relay these days, but designed to go fast when a bulb blows because that's what we're used to. Well, some of us, obviously.

LOL... well, I did hear it from my Dad!

I guess, as you say, the principle is the same - with the current flowing being integral to the timing circuit - though the question is - what do they use now to do the same job.

Well, split open a flasher relay and you'll usually find a little circuit board built into it with all the necessary components - a couple of transistors and a few resistors and capacitors.

just as a silly aside, does anyone else remember the fantastic "doioioioioioioioioioioing" noise that Datsun indicators used to make when you first switched 'em on?

The message from Scott M contains these words:

I'm fairly sure it is...certainly would be if I had anything to do with it!

.... and double the load and half the flash rate - which is why, if you t a trailer for example, you need a heavy-duty relay which detects the extra load and kicks-in to keep the flash rate up

As others have pointed out, the bi-metal strip type has not been fitted since Allaggros. However, when a bulb blows on a system using a bi-metal strip type flasher, the remaining bulbs will flash slower because they are not drawing the same current (it's the resistance on the circuit that draws current - less resistance, less current) and the strip takes longer to heat up and 'ping' away from it's contact. Same thing happens when connections go bad (old Fords and Austins come to mind :)). When I was a kid there'd be loadsa Austin 1100s with slow flashers because the old fogeys driving them didn't seem to have the savvy to check and replace bulbs or clean contacts. Now I see plenty of motors with fast flashers.

Oh no they didn't...

How did they manage to flash faster with less current?

V = I * R. V = 12v (approx but constant). R decreases (due to less bulbs), therefore I (current) has to increase. Ohm's law.

Think of it this way, increase R to a infinite amount (ie. open circuit), current flow is 0. Decrease R to a minimal amount (ie. short circuit) and huge current flow.

Remember - current is basically the rate of flow of electrons. If R is high, then these electrons can't flow as easily, so they either require a higher voltage to 'push' them along, or they flow slower (ie. lower current). If R is low, then they flow easily and therefore faster (ie. higher current).

Bwa-ha-ha. What a load of rot. If that was the case I could significantly decrease my electricity bill by plugging in more electric files. The more bulbs you have the less resistance and the more current they draw - resistors in parallel and all that.

If the bulbs are in parallel (they can't be in series, because if one blew, they'd all not work), then surely a bulb blowing will _increase_ R, not decrease.

If the bulbs are 21W (I think), this means that their resistance is nominally 6.8R.

This is all assuming that the bulbs are in parallel, and all of the same power rating.

Pete.

I think you mean in parallel.. ;)

Yup - I forgot about them being in parallel.... they're not Christmas tree lights are they! ;)

I forgot they were in parallel - so yes, the resistance will decrease.

As for V = I * R, if resistance decreases, current MUST increase (assuming constant voltage supply). AFAIK, AC is very different to DC in the maths, plus, can is be classed as a constant voltage supply? I'm not sure.