Blinker relais

[Peter Douglas Winn]

Has anyone got an idea how many amps should flow through a 2 pole blinker relais? USA car. My car eats blinker relais and I thought I might try and measure the current flowing.

[RobH]

The indicator lamps are rated at 5 Watts so draw about 0.4Amps each at 12.5v  That means for a car with two bulbs each side, the current drawn will be 0.8Amp  plus another 0.2 Amp or so for the dash tell-tale so say around 1Amp total.  

Duff information - see below

Edited August 6, 2020 by RobH

[John L]

I thought that the indicator bulbs front and back are 21W each, + perhaps the side markers at 5w.

John

[RobH]

Apologies for the brain fade - you are right of course John it is the bigger filament. 

So its 47 watts per side or approx 4Amps. 

[Peter Douglas Winn]

How many kilowatts does the indicator bulb use?

[RobH]

The dash-bulb current is negligible if that's what you mean - about 200 milliamps.

[Peter Douglas Winn]

OK off I go to the gartage and start measuring. Your answers match up with my thinking. I seeem to remember from school V x A = W but who knows nowadays?

[Peter Douglas Winn]

New Meter does not work on the amp range. I even read the instructions just in case. No luck. Have found an old relais and it will work, until I get a new one.

[peejay4A]

When measuring amps it’s normal to have to plug the red test lead into a socket marked Amps. Did you?

[tthomson]

10 hours ago, Peter Douglas Winn said:

OK off I go to the gartage and start measuring. Your answers match up with my thinking. I seeem to remember from school V x A = W but who knows nowadays?

Hi Peter,

Provided the voltage is in phase with the current, which is true for this situation, then you remember correctly.

TT

[Peter Douglas Winn]

Have just found an old meter and measured the current. Whow 9.9 Amps for the right hand blinker and exactly the same for the left hand blinker. So I have bought a new fuse for the new Ampere meter and I will go back to the garage see if the readings are the same. If yes, I have got problems.

I wonder where the low resistance could be. If the Amp value was low OK clean up all the connections but in my case I don't see how a short circuit can be the cause. I thought with a short circuit the blinker would not work.

[RobH]

If the meters agree then best check the bulbs Peter to make sure they actually are 21W. It is odd that you get the same reading on both sides if there is some sort of short. Also as you say, the flasher would usually act up  - unless it is an electronic one and not bi-metallic? 

 

One thing does come to mind. Sometimes people who convert to LED bulbs also fit resistors to ensure enough current is drawn to still operate the standard flasher relay. If the car was later converted back to normal bulbs but the resistors were left in circuit, the current would be double.....??

 

 

[Peter Douglas Winn]

Cabel loom is relatively new, from the sparks firm. None of this LED stuff, good basic ON/OFF Lucas engineering.

[Peter Douglas Winn]

Just put a new fuse in the meter unfortunately I could only get a 16A 250 V not a 20A. I hope this has not altered the readings. But I now have about 3.56 A on the RHS and 3,42 A on the LHS. I have contact sprayed everything I could find there was a negligable improvment. So this means the other meter was duff. After 30 years of ownership I have found a discrepency with the front flashers. As it is an American model it has twin filament bulb at the front (Side lights and flasher. Orange/White lens.) and only one of the filaments light up????????? Thinking about it I realised in those days Orange/White lens were not available so everybody at that time, had to use parking lights in the headlights. Now that is why I had to ask the loom manufacturer to give me an extension for the headlight. They had still put the old twin filament system into the loom. As it has worked for 30 years, it never occured to me that there was something wrong. Could this be the reason for the somewhat low Amps?

[RobH]

Ah thats more like it.

Only the bigger 21W filament should light for the flashers - that is the figure the vehicle lighting regulations require. There may be some variation in the bulbs which accounts for the slightly different currents drawn.  An old bulb will have a thinner filament through evaporation and hence will have higher resistance. I guess you are making these measurements with the engine off too - so the voltage will be a bit lower than if it was running. 

So with that normal current, why are your flasher relays short-lived I wonder? 

[Peter Douglas Winn]

I too!

Engine not running.

I accept there will be a drop in the voltage because of the wiring and the bulbs could be 40 years old. I had a habbit of saving bulbs when srapping a car.

Last night at our club meeting came the comment they are just rubish nowadays.